In order to guarantee that everyone wanting to develop a kids F12 is moving in the same direction, I've put together a prelim set of class rules. This document is intented as a starting point and I would welcome any feedback and be willing to change pretty much everything.

www.ctmd.com.au/F12.pdf

Great start Scarecrow but please re-write Rule 1.3.1.
"Hull panels shall have a weight of not less than 1.2 kg/m2 (equal to 3 mm Gaboon)"

Sounds like something a New York lawyer would dream up....Keep it simple and just state in plain English what the minimum weight is... you can calculate that based upon the general box parameters built out of 3 mm Gaboon ply, just give a minimum finished ready to sail weight and everyone will know where they stand.

Thats fine by me..

My original hulls had approx 20kg (10kg each) of ply in them including bulkheads, longitudinals centre case sides etc. The newer design has much less.

Where do people think the minium weight should be set? 45kg? (100lbs)

Id rather just see a minimum beach weight as its quite hard to get a panel weight without cutting cores from the boat. I think we need to look at least 55-60 kg to make sure we end up with a durable boat, and to also allow the rotomolded crowd an even shot at producing a competitive boat as well.

Also, the sail area measurement needs to differentiate between conventional rigs and pocket luff rigs, not quite fair to add the mast area to their sail area calc. I'll knock out a sail measurement spreadsheet that will take care of this.

In the interest of getting as much racing as possible for the kids, perhaps we might look at the existing designs out there to make sure the rule is as inclusive as possible of what already exists.

Under daggerboards and rudders, skegs should also be allowed as some existing designs have these.

Other than that....great start
RG

I agree, however, do we really want to set a minimum weight heigher than the Paper Tiger (50kg)

Also, based upon my perception of sentiment on the forum I've pulled the length back to 12 ft. Are the majority happy with that?

Take a look at the weight analysis I did last earlier this year :

http://www.xs4all.nl/~whijink/F12/F12_weight_and_cost_push_rod_setup.xls

I can't get it down to less then 63 kg ready to sail when using 4 mm ply.

A rotomoulded version will be heavier by at least 15 kg according to my data.

Even when using 3 mm ply (which is rather weak) you can't get it down to 45 kg overall while limiting yourself to only using simple materials and building methods.

Wouter

The 50kg limit for a Paper Tiger is sans mast, boom mainsheet and sails, so its probably closer to 70-75kg with all the gear on it, so 55-60kg is still pretty agressive for something thats homebuilt or commercially produced. Another thing to think about is that if you set it too low, then a lot of creative people are going to start building carbon hulls which sort of defeats the purpose of trying to make these affordable.

I know that if I got aggressive, I could probably build one under 50kg rigged but it would have no end of expensive stuff on it to get there. These are not A-Class cats, just a better performing Opti that hopefully a bunch of kids will want. Wouters weight estimate is reasonable within the bounds of keeping it reasonably cheap/affordable.

As for the 12 ft, Im happy with that, what about everyone else ?
RG

My design is done at 12 ft 4.5 inches.
It just happened this length allowed me to do what I wanted.

On the other side of the coin the beam , mast length and sail are a little less.

I will build it as light as I can without the use of materials that will increase the cost and based on my own estimates I hope to come in around 50kg.

The rules document is a good idea to provide some clarity and focus.

Regards,
Phill

RG can you please confirm your hull length to date?

mine were done at 3.75m which is what Wouter had for a length (12'-3.67") I presume Wouter wanted a rounded number in metric ?
Phill, would an inch less make a big difference to you ?
Not overly fussed about length and will go with what the majority want.
RG

Yes, and I wanted the maximal hull length that I could get, at these sized everything helps. Also this length turned out to be very nice mathematically, but I won't bore everybody too much with that.

Basically at this length a scaled down F18 or F16 hull will optimally carry 105 kg combined boat + crew weight (at the time I assumed 60 kg for craft and 45 kg for crew). Therefor the F12 was directly comparable to both of these boats and it was easy to make initial conclusions about factors like pitching, overall drag and rig induced loads. As a matter of fact it shared an even more tight relationship to the Prindle 16 catamaran. Basically you can scale that and end up with a very good first try for a boardless F12 using a deep V-ed hull that is very easy to make.

How much difference does going from 3.75mtr to 3.65 mtr (= 12 foot) make ? Well, when using the scaling operations to get a first try at the F12 hull then weight carrying ability would go down from 105 kg to 95 kg, which wasn't (isn't) negligiable.

I'm personally fine with 3.8 mtr if we all wanted a nice rounded number. But, I rather not go to less hull length then 3.75 mtr though. Most of what I've done so far is done on 3.75 mtr. I strongly prefer keeping it there.

Wouter

Scarecrow,

Here my initial suggestions regarding the class rules.


- sail area

Suffice by ruling that a sleeved sail area is determined solely by its total surface area and that the halve the surface area of the mast is to be added when the sail is not fully covering the mast itself (excluding the area below the boom).


- Hull length

I strongly prefer 3.75 mtr overall length or more.


- Panel weight

Remove this rule entirely. For equalizing the performance only the ready to sail weight is needed. Also, ruling on a panel weight assumes you can predict that in the future we will never be able to create cheap and strong panels that weight less than giving in the rule. We simply don't know that. It is also another thing to check when measuring and certifying and it is also as good as impossible to check. Basically, this rule has large drawbacks and hardly any benefits. Give the designers all the freedom they want in this area, no-one wants to design a fragile boat and customers will vote with their feet anyway when one tries.


- Mast

Completely unregulating the construction of the mast may well turn out to be a big factor in losing control over the costs associated with F12's. It also makes international shipping alot harder = more expensive. I have experience in shipping masts internationally now and a significant portion gets damaged in transport. Also shippers really hate long, thin and easily damaged goods. You are alright if you can strap ten or more of those together, but shipping single masts or a pair of them is asking for trouble. Also a 6 mtr. mast is hard to transport legally without using a boat trailer, which will add another 1000-1500 bucks to owning a F12.

I really would like the see a rule that enforces the mast to be collapsable in parts that are no longer then the hulls themselves. Based on my experience so far I'm convinced we'll be thankful for that choice later.

I'm also concerned that leaving the mast unregulated beyond being collapsable is still inviting trouble. Some will want to have tapered carbon masts or specialized shapes. Rotating a mast will immediately add various hardware that will again add costs. I think like that it will proof very hard to control costs. Additionally, potential buyers will became hesitant as they will feel (justified or unjustified) that more expensive parts will always be more performant.

Based on my experience with the landyacht classes I feel we should seriously consider a setup as they have. They rule that the mast must be made up of normal standardized prismatic aluminium round sections. And that if we wanted more performance that we should allow camber inducers rather then fully rotating masts.

I can write a full post on this, but I won't now. Suffice to say that there is both need and room for ample deliberations on this aspect.



As a matter of personal opinion, while I strongly favour a pure formula class rule setup for larger catamarans I'm convinced that that is not the right approach for an simple and inexpensive class like the F12's. Any reductions in complexity and cost we achieve initially will only make adding costs and complexity more interesting to both builders and sailors. At the level of cost and complexity we are looking at to make the class maximally accessible and affordable there will not be much of a selfregulating effect as is found in the F16 and F18 classes. In the case of the F16's customers refuse to pay more the 15.000, no matter how well the craft is fitted out and that keeps the F16's sharp. But at 3000 euro's for the F12 it will be much easier for alot of people to justify spending an additional 1000 Euro's just to get a small advantage over the other sailors.

I really do believe we must look at making the F12 a OD class (but NOT a SMOD class) where the most important aspects of the basic layout is regulated but where smaller factors sail design, rudder design and the way of implementing the basic design are left open. I'm thinking of :

- regulating closely the shape of the hulls (enforce fairness of racing and easy of building)
- regulating the type of rig (stayed / unstayed, sloop, uni-rig etc)
- regulating the major over all dimensions
- regulating the more troublesome components like mast to a medium level (collapsable or not, material)
- regulating to have or not parts like daggerbaords/centreboards, camber inducers, T-foils, etc.

The rest can be left open as their influence on overall performance is too small to really matter and you must use the group of designers and enthousiasts to find the best solutions over time.

Wouter




Wouter

Not sure I agree with Wouter, a simple box rule should suffice and promote choices for the designers and the kids.
Wether we admit it or not, most kids are quite capable of making informed choices and even have "taste's" of their own which I'm not sure we need to regulate with rules.
Ultimately, that which works best on the race course will come out the winner, and I'm not sure that there is enough info or fact available here to determine what that is yet.
Aerynt

Hi All

Stayed out of the conversations for a while to see what would become of the F12 and it looks good.

Well done to those who have taken the time to design the cats, great to see new fresh designs being put out there.

I don't agree with making the F12 a OD, with 4-5 designs already presented, it will only lead to people proceding outside of the arena.

I would also like to say that the mast material be restricted to aluminium, I don't believe there should be any restriction on if the mast is one or more pieces, nor restrictions on stayed/unstayed rigs. There should be a sail area retsriction, but not to restrict things like luff or foot lengths.

Just my thoughts

Regards

Before you write in stone that the mast has to be aluminum…windsurfing masts should be looked into more thoroughly. No performance oriented windsurfing masts that I know of are made of aluminum any more…(that should tell you something) haven’t been for at least a decade…they are all a combination of Glass/Carbon, Glass/Kevlar/Carbon or Carbon alone. Most are two pieces with a very strong furrow joint. I believe they should be strongly considered for the following reasons.
1) Thoroughly tested and refined designs. Already optimized for taper, bend characteristics, weight, and strength.
2) Readily available in two pieces
3) Very Strong “Wave” style mast built to survive wipeouts in huge surf (15’+) allowing it to hold up to the on the water abuse it would see on a “kids” boat.
4) Extremely light weight for easily handling by the kids allowing them to set up their own boats.
5) World wide availability. Many areas have local suppliers. Can be ordered over the internet/phone/mail and delivered to your door for very modest shipping costs.
6) Many available on used market to further reduce cost.

While Aluminum sectioned mast could be an option for sailors which desire to do so, to ignore or outlaw a readily available glass/carbon windsurfing masts would be a great disservice. If it is truly the intent to make building and outfitting this boat easy one of the most logical paths leads straight to the windsurfing masts.

Regards,
Bob

I'm continiously updating the info as provided through the F12 Website :

http://www.xs4all.nl/~whijink/F12/


It has taking a while by I know have a firm quote for a suitable F12 mast made from straight high 0.2% threshold aluminium tubing that will take a F12 sleeved mainsail. The mast can be taken apart into two or three parts.

The same mast is used on the Promo landyacht which are becoming very popular. Its length is 5.5 mtr and the cost is 240 Euro's including 20% European taxes.

The 5.5 sq mtr sail (not suitable to F12 as landyacht sails are too flat for soft water craft) cost 577 Euro's including 20% European taxes. However, the costs shouldn't change much when entlarging the sail and giving it more draft. The total load of a 5.5 sq. mtr landyacht sail in 20-30 knots of wind and a F12 rig in sub 20 knots winds are as good as identical. Please note here that Promo's use 5:1 to 7:1 purchase systems to sheet the sail as flat as a board. That is alot of rig tension ! The promo's are also 2 mtr wide and weight 60kg themselves and carry adults up to 90 kg without a fuss.

Mast, sail, battens and boom will weight a total 14 kg or less. Say under 15 kg. That is certain now. Its centre of weight is below that of a normal prismatic mast as the promo mast is obviously tapered.

I feel confident now that we can have a commericially build and offered F12 unstayed rig for 850 Euro's including 20% European taxes. The amount of EU taxation will be enough to cover shipping to any place in the world.

This result still allows us to achieve the design goals of less the 3000 Euro for a ready to sail F12 and as this can be purchased ready to go it will also go a very long way in achieving the "building under 100 hours" design goal. The Dotan rudders are purchased as well. So that only leaves building the hulls, beams, push rods, trampoline and assembling the components. I think we can get darn close to 100 hours building time.


Anyone out here want to look up dependable pricing for 5.5 to 7.0 sq.mtr surf masts and sails ?

I would be very thankful if I don't have the spend the time to do that. I already invested alot more then I can justify.

Wouter

Well, here we go again. We are again at the point vere one is supposed to buy everything exept the hulls. Please keep the the design open for homebuilders...

A 7m2 mast, sail, boom and mast step will cost from around 600 Euros new. But the big advantage of using windsurfing rigs is that the abundance of cheap second hand ones about, ebay is a good source for this.

Gareth

Gato,
While I think commercial construction has to be a primary objective to get them out there in numbers I agree regarding you rcomments on home building.
I hope to provide plans that detail the construction in ply, foam and cedar strip depending on an individual's preference as well as detailed instructions on making the sail. The only marine fittings will be a couple of blocks. Everything else will be obtainable form a timber yard and hardware type store.

Regards,
Phill

You misunderstand my comments. All the components named can be easily homebuild. The fact that they can ALSO be bought ready to go for the given quotes only serves as proof of the maximal costs and economical viability when a company starts building these commercially. Of course lazy homebuilder can make use of these option if they want to get a craft quickly on the water.

Actually Landyachting (and iceyachting) is far more homebuilder oriented then any other sailing craft. It is a good place to steal tricks from. Actually the commercial landyacht builders often use the same tricks and designs as developped by homebuilders.

From the beginning (that is now several years ago) I tried to design the craft in such a way that both homebuilding and commercial builder would be practical.

We must all learn to think in terms of ".... and ..." instead of "... or ...". We must fight the Pavlovian tendency to equated everything commercial with being hard to copy by homebuilding. That is when looking at my design and proposals. I'm not so sure the same holds for some of the other designs.

Wouter

With regards to rigs I can't see myself supporting any option that limits choices and options where these choices are driven by different priorities. We're trying to create a one size fits all rule and I think we should be trying to be inclusive, not looking for things to outlaw or limit. The fact is that pretty much every spar maker has a suitable extrusion for this vessel if stayed (look for a mast tube used on a two person (one on trap) dinghy. My prefered option is currently the MG14 wing mast (approx AUS$400 for the tube. This mast will be less than 6kg fully rigged, a weight that will enable the young sailor to step it themselves. Having said that, I wouldn't conceive of suggesting everyone should use this rig as it is going to be more expensive than round tube.

We need to focus on keeping the rule open and inclusive. We should also look at drawing a line in the sand (ie 30 Nov) as a deadline for concensis so that designs can progress without being held back or becoming redundant.

Folks,
Something to think about with respect to keeping the rules open and inclusive -
We may find there will be practical limitations on craft depending on circumstances given
particular situations and localities. These limitations may range from the normal
prevailing sailing conditions to something as broad as the general affluence of the Area.

In strong wind areas wide beam and small sails could be the go while the reverse could be
desirable in typically light wind areas. Just like in affluent areas a flash production
boat may be better than a home built boat which may thrive in poorer areas.

It may be wise to just set down a hull length limit and leave everything else open or better
still, allow the other parameters to be set locally.
Afterall the right specs are the ones that get the most kids on the water.

I'm not sure if this would be a good approach or not but thought I'd mention it to see what others thought.


Regards,
Phill

Yes!!! absolutely in favor of this and better yet it gets kids thinking about how best they can improve their boat. The downside to this is out of hand development with $ which could hurt things, so we need a simple rule that reins in the $ spent......only problem with that is who is going to do the accounting and what sort of cap do we want thats in keeping with our goals?
Bottom line is I'm all for anything that keeps things as simple as possible.
RG

A reasonable weight is the easiest way to cap the dollars spent and not hinder the capable homebuilders either.
Aerynt

I wonder as whether the opinion to keep things maximally open is more inspired by not wanting to give up ones own "pets" rather then a serious evaluation of effectively launching a F12 class the world over. And yes, I readily admit to having my own pets.

I do however feel that Phill has made a great point about "the right specs being the ones that get the most kids on the water"

Still, I do not see much succesful precendent in allowing wildly different craft from succesfully launching a serious youth program. Afterall, there are 10's of different 14 foot classes and we still don't have a viable catamaran youth program. I think an very convincing argument can be had where large differences between boats of the same hull length is actually a major obstacle to success.

Remember the F12 project was intended to solve that issue as well. I should remind everybody here that the F12 project didn't start when Phill first mentioned his idea for a 12 foot with an unstayed rig some 5 years ago. His program is actually called the Blade 12. I changed the name a long time ago to seperate both programs. The F12 project here on catsailor started last winter, (dec 2006) because of a youth sailing program discussion on the main forum. I also underscore that this F12 project is not entirely the same as my own efforts in this field prior to dec 2006 either (the craft that I really like to own myself).

I fear we must all seriously consider letting go of some of our own pets in order to arrive at a well balanced F12 concept that actually solves the issue of a viable international youth catamaran program c.q. class that gets to the youth sailors early on and feeds them into the larger cat classes.

Allowing wildly open class rules does not have a particulary great potential of succes at that. Especially not in comparison to highly organised and regulated monohull classes in that age group. We'll look like a ragtag band of eternally disagreeing hippies in comparison.

This is not to say that the F12 class may not use surf rigs and other rig or construction alternatives. It just means that the basic class needs to be well balanced and possibly more strict in it international setup then allowing a wide range of different designs. At a local level the regulations can be relaxed if that improves youth participation as long as serious youths gravitate to a single F12 design when they get into more serious (away of their own club) F12 racing.

Wouter

Gato,

Please take a look at this posting :

http://www.catsailor.com/forums/sho...er=124554&Main=124554#Post124554

To understand how easily the named commercially available rig can be copied by a homebuilder.

I trust this takes away your concern.

Wouter

I Agree with Phill, Prevailing sailing conditions and local influences could play a large roll in design acceptance. For instance, here in East Coast Florida USA our summer season has predominantly light winds 6-8 mph. If you set sail sizes based on conditions in some higher wind areas in Europe or Australia the USA boats will end up being a dog. Vice versa, if they were set to the light wind standards of Florida USA the same boat may be vastly overpowered in the higher wind regions of the world. This has been a problem with other catamaran classes has it not? Where there was a European Rig and a Larger Rig for the USA?

Same might be said of hull design to a lesser extent. An area where a surf launch is necessary might need a different hull design (more freeboard/beam clearance) than some that sail on protected waters.

In the USA the trend seems to be more “Turn Key” as opposed to areas in Australia which seem more inclined to home build. The more options available to optimize for the local conditions, the broader the appeal.

Let the designers bring their a-game to the F-12 table. Let them build and test their prototypes against each other; the cream will rise to the top. The consumer will ultimately determine which designs they will choose to support. Problem solved.

Keep in mind that kids are all about “tricking out” what ever they are involved in… be it their clothes, skate boards, bicycles, school note books, and as they get older their cars…A boat that allows them the freedom to customize and individualize will be more attractive than some vanilla flavored ho-hum one size fits all. If this under taking is really about getting kids on catamarans then its main thrust has to be about the excitement. Forget the optimist class mono slugs…there is an opportunity to reinvent entry level sailing for kids, if done properly this could be huge…it is going to be mostly about PR…but the product has to be exciting enough to give the PR element something to work with.

While safety always has to be a major factor with any children’s event, remember kids this age are doing skateboard “kick flips while jumping over 4 or 5 concrete steps. The design must not be neutered by the “Nervous Nellies” to the point where it is so “safe” that it offers the excitement on par with watching the grass grow.

All that needs to be agreed upon is a maximum length.

With the power of the internet, and the generosity of Rick and Mary offering this web site, the possibilities are nearly limitless.

Regards,
Bob

Sorry Wouter, had mist that one...
Otherwise I think the idea good to keep the F12 close to OD.
And an other important aspect is that the boat must be very easy to build, and in the workshop the V shaped hull is very hard to outrun.

I have been working on that tangent, as you know of course, you helped me there.

Trying to get a deep V-ed hull for the F12 was actually the advice I got from Phill a long time ago and even though I dislike its looks I feel that Phill gave some very solid advice there. It is the reason I'm persuing this tangent.

I also admit that I was always a bit amazed at how well the deep V-ed hull of the Prindle 16 was performing. It outpoints the Hobie 16 upwind and the steering wasn't very sluggish at all.

Interestingly enough the exact Prindle 16 shape can be scaled down to a 3.75 mtr F12. So with your contributions and some smart stealing of other designs we may have a deep V-ed hull F12 design soon.

Wouter

Maybe a design contest is the way to progress things ?

Each team makes their own ideal designs together with full overview of weights and costs (both or parts and the whole lot) as well a sort analysis of building requirements (skill, tooling, etc)

We can then compare these designs to one-another and make the best of them the tue F12 ?

Or possible, combine a best idea's of a few designs into a new single F12 ?

Would that be an approach that the designers will be happy with ?

Wouter

I'm new to this, been following the designs progress. From my limited knowledge I know that what you are suggesting is the exact recepy for a one design class. I don't think the designers will ever accept that the "other one" is better for several reasons, but mainly because the "formula" stands for a more freedom of movement then the one design. BUt I might be wrong....

You might contact Hans Geisler, designer of the GCat family. He has created an incredibly fast deep V hull concept. He is still actively designing and sailing new boat models but I do not think he has gone smaller than 5.0 meters. He might offer great insight toward a tiny boardless design capable of good speed and pointing while perhaps home-buildable. He's a really creative and helpful guy. You can write him at
morningstarfishermen(at)earthlink.net

There is a lot more than competition on my mind. In the south part of Finland there is an archipelago with at least 12.000 islands were it’s possible to beach with a small cat, put up a tent and spend the night. The waters are sheltered but shallow, so for me no fixed part sticking out under the hull, it is a labours way to find stones.
We also travel a lot by ferries, so the whole thing should go on top of a small car. Pulling something behind is rising the price of the ferry ticket about ten times.
There are still very few cats here, so I really would like to get the kids out on the water…

You're gonna send kids out in surf?

ok....we gotta stop all this personal agenda stuff if we are to achieve anything. At this rate we will still be discussing who wants what 100 years from now.
Seeker had a pretty good suggestion in that we set a length and weight and let them evolve on a regional basis.
My personal belief is that if we go down the OD route we will stall the whole thing due to the fact there are too many opinions right here now, let alone all the future people we are trying to attract.
A good example is A-Class, simple rules are delivering more innovation and development than any other class (mono or multi) that I know of on an annual basis <granted its recent>
Whats so wrong with 4 rules, length, beam, weight and a sail area?
moreover, isn't it better to have a bunch of national or even regional designers promoting the class and involving all the people they can muster than a small association group trying to educate the masses ?
Ultimately success will get down to momentum....and that involves passionate people...narrow the parameters and your guaranteed to narrow the passion due mostly to self interest.
RG

Moths, C-class, F18 (spinnaker, selftackers)

Lets just see the A-cats for what they really are ; excellent lightweight singlehander racers that are both very expensive, have a continiously changing design and lay claim to a status that is larger then they really are.

It is also a common mistconception that the A-cat class rules are only length, width, beam and sail area. The only class that still has a simple setup like that are the C-class boats. For example the A-cats rules also rule on ready to sail weight and the forbid the use of any lifting foils. They also break their high-tech masts when they pitchpole in any decent wind.

Surprisingly enough cheaper boats like the F18 are actually outperforming the A's on the race course. To make the picture complete a 11.500 Euro F16 (without a spinnaker or jib setup) is only 5% slower then the newest 18.500 Euro A-cat. That is a whole lot of money (60% more) for a more fragile boat that is only 5% faster around the race course (3 min per hour).

In summery the A-cat is everything that a youth catamaran should not be. Expensive, relatively fragile, outdating older boats relatively quickly and is hardly seriously faster.

I like the A's for what they are but they are simple not a good example of what to do with the F12 youth catamaran. Neither are the F16 or F18 catamarans for that matter.

Wouter

Come on Wouter the A class is back to basics, at a beginner level you can build a fast boat, not world class but really cheap the sails arent dear. With clear decks, low working load, minimum sheets to change its light and super responsive, giving instant feedback on wether youve changed the right thing. Its ideal as a scaled down F12. My 7 year old lad was driving my A class in light wind last weekend, he was tacking, jibing mucking around, we deliberately capsised it and righted it for fun. As for colabsable poles, I reckon they should be an allowable option but not a requirement.
regards

I agree we should keep the rules open and simple. No rules that restrict one type of design, So I am all for length, beam, weight and sail area only.

The main object here is to get as many youngsters sailing cats as possible. Maybe a one design boat might emerge from this in the future but for the time being I want to see what everyone has to offer. So nothing to restrict creativity at this stage please.

Gareth

Gato,
That sounds like a great way to introduce kids to sailing. When they race there is only one winner. Use the boats to go camping and everyone one is a winner. They should love it and associate those memories with the sport for life.
Great idea.
There is no doubt you could build a simple deep V cat quicker than many other types. Just bear in mind that the deep V is not as good at carrying weight if you are moving camping gear on them.
We had deep V 12 ft Surfcats at our club with spade rudders that did not go down below the keel. The kids could sail them in water they could walk in.
However to make the design work the tramp was on a square tube frame and set well above the deck so it would still sail when the hulls were almost submerged. So if you are going for a deep V just be sure it will carry the weight you want to put on it. As you would know a round bilge hull or chined hull will carry weight better and the shallow draft can be achieved with skegs if C/Bs are out.
Which brings us back to building time. They can take a bit more to build although not that much more because you don't have to put much inside them which always seems to be where most of the time goes.
Good luck sounds like a great project.

Regards,
Phill

RG and Gareth,
Weight and length makes good sense but not so sure about beam and sail area.
I just think these would be better decided locally to get what is both safe and
exciting and this may vary depending on the conditions of the local.

My concern about setting a max sail area is people will always go for the
max and it may not be appropriate for that location. I tend to wonder if
this could be agreed locally.
The way I see it is that we don't even have boats on the water yet so
the fewer restrictions the better. Once there are a few boats sailng we
will be in a better position to decide if and what type of restrictions
are required.
Having said all this I'm not that hung up on all this and if everyone
else agrees to the 4 restrictions I'll go along.

Regards,
Phill

If everybody else agrees on only these four limits then I'm out of the project.

Mostly because I think it is going to fail that way and I'm not wasting my time on that. Sorry.

Actually this whole proces does remind me of that time 8 months ago, exactly the same discussions. I made room for somebody else to create this "wide open class" and nobody stepped up. The end result the project fall flat on its face. I revived it, as I have done several times by now, and we just fall in the same trap again.

I hope it fairs alot better this time if the rest decides to keep the rules maximally open. First point on the agenda is to find a new project leader, I'll be watching from the sidelines. If it falls down again then I'm going to step one last time and decided things arbitrarily. Then it will be an OD class along the lines I presented earlier.

So everybody, consider this your last shot to make something of the F12 that you feel is right. I will step aside and allow you all to make your best swing at it.

I will of course keep presenting updates on my design on this forum, there maybe something there worth stealing.

Wouter

Call me when you are serious about doing something like that. For years now I've been saying to friend that I would like to wander about the Swedisch or Finnish Archipelo on a sail boat.

Wouter

I have been serious on that for a while. It's a little bit cold right now, but lets say from May on you name the date.

Wow, thanks, I hope that thought that offer through because I may very well take you up on it.

For may 2008 I'm organising a little wandering-about trip on sail boats here in the Netherlands with 20 people already listed, so I don't expect that I can get away from my normal life during the spring time, but after that ...

I will also send you a private mail concerning this.

Wouter

Wouter, please take this as a friendly observation….

“If everybody else agrees on only these four limits then I'm out of the project.”

That sounds awful lot like “If I can’t make the rules, I am going to take my ball and go home”.

Let the project go forward with just length and weight limits. If your design and approach is superior it will prevail.

While you undoubtedly have the greatest presence here on the forum (7000+ posts), it is obvious that the wheels have been turning behind the scenes on a number of fronts. To be honest, you would have to admit this recent resurgence of interest in the F-12 has a lot to do with RG’s ability to expressed his (and others interested parties) design ideas through high quality 3D Computer Modeling. As they say a picture is worth a thousand words. You can write a text book worth of detailed description on the F-12 and not motivate a single person to act…but put a life like rendering in front of them and the ideas take on new life.

No one is trying to limit your design options, why do you feel the need to limit theirs?


If I remember correctly, you have, on more than one occasion, stated that you had neither the time nor the financial resources to pursue the construction of a proto type based on your ideas any time in the near future…that your time was consumed at work and other things you were involved in…no one faults you for that…Now there seems to be at least two other designers that do have the time and resources to proto type. Work with them, don’t them tie up with rules that may very well put some of the most creative options out of their reach. So you don’t agree with everything that is being proposed… if they are willing to put up their time and money to invest in this promising idea, why would anyone who truly wants the concept to succeed put barriers in their way?

It sounds like the cow that laid in the hay. It didn’t want to eat the hay…but it wouldn’t let any of the other cows to eat it either”

Don’t lay in the hay…LOL…

Best regards,
Bob

Wouter, I seriously hope you don't walk away, and no matter what you end up doing, I'm still going to use your mast and brace ideas as one of the options on what I produce cause they are "Good" ideas.
RG

Aww screw it...I'm building one of these <img src="http://www.catsailor.com/forums/images/graemlins/confused.gif" alt="" />
Puddle Duck Racer <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

Bring your bat and ball back Wouter, behind the scenes things are happening they might not be exactly your boats being built but it may have your ideas. We need every kid out there on a cat and its going to take all shapes and sizes of cats to get them out of dinghys. Advanced heavy kids used to a dinghy with kite need exciting good looking cats that will tip if they get it wrong ( thats the excitement and fear ). New to sailing kids need a stable reassuring platform so the kid and theyre parents dont have too much excitement. Its just my opinion but the time to get super fussy and level the playing field is at F14 etc at the moment we will have 7 yr olds racing 14yr olds they just wanna have fun.

I see this project as serious endeavour and that means achieving results. That also means that sometimes harsh decisions have to be made. This is nothing personal against anyone, just being realistic.

I can honestly say that I'm not the person to pull this project if it is decided by the group that that only 2 to 4 general rules will be layed down for the class. I have indeed no clear idea of how to make that work and as a result I won't be the right guy for the job. And indeed I gladly step aside to allow somebody else who can make this work take the lead.

So indeed this is not a “If I can’t make the rules, I am going to take my ball and go home” as I'm only vacating the team leader role and leaving the ball (and bat) on the court so another guy can take a shot at making it work.

Actually, I'm setting you all free.

The only thing one of you needs to do now is show us all how to swing that ball out of the court.

Wouter

I was so taken by the idea of sailing the archipelo that I want off on a tangent with respect to the F12 design. I used the same basic F12 platform (Deep V-ed hull) and the bottom section of the mast and its supports, as that is both simple, robust and cheap, and just changed the rig to a gaff or lugger sail.

To my surprise the specs work out really well. There is hardly any difference between these extremely simple and cheap sails and the fully battened class 5 sails. Pressure points, sail area's are all as good as the same. Don't even need to modify the bottom section of the mast at all. Just have to make a small insert that slides in its top and holds the halyard blocks. These rigs can then even be fully (de)rigged while on the water (safety), including lowering the mast itself. Put a peddle on board and you can peddle these craft very well too. I'm thinking about each skipper sitting on opposite hulls of the same craft with the second craft behind in tow. I already know that cats are very easy to peddle at decent speeds. Have done it a few times. Once wind picks up one sailor switches back to his own boat and both skippers raise their masts and sails and continue to trip under sail.

I know this will work very well while using a gaff or lugger rig as I've been doing the same on Valk sail boats for years. Just ask Phill Brander, I'm sure he'll still remember how we negociated the low bridges when sailing the Valks. You would sail right up to the bridge and drop the whole rig and mast in 30 seconds, then let the momentum push the boat through under the bridge and then on the other side you would push up the mast and sails in again 30 seconds and continue sailing.

Deck tent over the boom and voila you're camping. Could even do that on the water in a shelted bay when using a small anchor.

Of course we loose some performance with these gaff and lugger rigs but one a travel trip like this that is not much of a problem, I'm happy to sail at 9 knots instead of 11 knots upwind if that saves me a bundle of money and allowing me to make this trip through the archipelo ! Best of these sails is how easy and cheap they are and repaired.

WOW !

I'm still impressed at how easy my basic F12 was adjusted to the different requirements of an archipelo trip.

Gato, what a great idea to use a cat like the F12 for this. I'm sure if you start taking kids along that they will consider it a right adventure. Makes me feel as exited as a kid as well.

Wouter

Gato, I guess you are referring to the islands between Turku and Aland.

Here some maps if anybody is interested to find out what we're talking about :

http://www.visitfinland.com/ima/main/maps/finland_southern_finland_en.pdf

Indeed there are 1000's of them. You can see that more clearly using Google map and then zooming out and zooming in on southern Finland :

http://maps.google.nl/maps?utm_campaign=...p;utm_term=maps

Wouter

I'll give it a week to someone to step forward.

If nobody does then I'll decide to hold a design competition and we'll see then what we can all come up with. I hope to interest RG and others like Grob to produce equally classy 3-D pics and drag simulations of all proposed designs so that all are equal in presentation. We can then move to have the "Battle Royale" and hopefully find the best design out there with which we will run from then onwards.

Would something like that interest the other designers ?

Wouter

Alternatively everyone who is working on a design could get it prototyped. Take some pics of it sailing and come back with a report.

I intend to start my prototype on January 1st even if my other projects are not wound up and will complete it within 8 weeks.
The building process will be documented in detail and both material costs and hours will be logged.
As the craft will have two configurations I will prepare a report on the difference in handling and feel between them.

It would be interesting to hear the plans of others.
I expect everyone will have a different timetable so as each design hits the water it could be given more than adequate exposure this way.
In the end the parents and the kids the boats are designed for will decide.

Regards,
Phill

It is a bit late, but would it be possible to have class rules similar to the 420, with a "club" version (with fixed one design measurements) and "normal" version, with developmet rules similar to the A or C Class rules?

Luiz, part of me likes this idea, will have to think on that.

As for my design, like Phill it will come in 2 versions and hopefully we'll be able to start building the first one in 3-4 weeks.

Right now I'm finishing the structure and will post a cutaway and see-through version here shortly so you can see how it will be built.

Cheers
RG

Wouter, I think that trying to judge any of the designs solely on the basis of computer predictions is not fair. First not everyone has the same quality of software and secondly anyone who says a computer simulation is 100% correct is full of it.
Its an aid, and nothing more.
The correct way to do this is to build and test, and even then it may take us all a few attempts to get everything correct or better yet acceptable to the majority.
Cheers
RG

Luiz,
Not sure if I understand but I see development at club level as each club will set its own rules and develop them in accordance with local requirements.

After boats come together a few times ideas will change in these groups as they swap ideas and experience learnt by the various groups as all the designs move towards converging.

Also we have to be careful to not put too much emphasis on competition. You want to hook all these kids for life. To do that they need all to feel like winners. Not one winner and a fleet of losers.
Building the community feeling will be the key to success.

Just they way I see it.

Regards,
Phill

RG,
I agree 100% which is why I think we should get some boats on the water and compare notes before setting down rules.
I have no problems with rules but hesitate to set them before we do some testing.
This is why I suggested length as the only rule until we have some real life experience.

BTW: - My design will fit well inside the rules mentioned so far except maybe length. I just don't think it wise to tie our hands prematurely.
Also after careful consideration I think the boats should be 12ft6inches or under. A bit more along the lines of what Wouter was saying. It may very well end up many of the rules end up coming back to what he had but I would not agree to it without real life testing.
Just the way I see it.
Regards,
Phill

I'd like to know the rationale of boths parts. The idea, of course, is to please everyone here and also let the market decide what's best.

I believe you all know that the Optimist started with an extremely restricted box rule and nowadays is a strict one design with the goal to keep the price low by narrowing the limits where parents can play "who spends more on the kid's boat". I guess we can start with more freedom if convergence to the wining concept(s) is previously agreed upon.

Really guys, the design isn't the bottleneck; you all know what you are doing and all boats will be wonderful. I worry about obtaining worldwide support from multihull fleets, clubs, organizations and manufacturers, especially the last ones.

I have no firm commitment yet, but I might be able to prototype my design in the coming year as well.

If I do then it will first be a deep V-ed hull with most likely an simplified rig. I too envision a more high tech version with a fully battened mainsail (as the class 5 landyacht) and possibly a more refined hull shape. The latter will still be a multichine hull however.

So I guess that approach will work for us (me and the other guy). The only part we are lacking in are fancy 3-D CAD drawings, so that would be a serious disadvantage to us if the "Battle Royale" comes down to that.

Wouter

I know, but CAD pictures are very effective in mesmorizing others. I actually did not propose to judge the designs fully on the CAD pictures alone, I envisioned having full detailed part listing cost tables and a draft set of class rules to go with them, as well as additional documentation dealing with building effort etc. Basically a full worked out proposal.



Ain't that the truth !

Wouter

Phill says : "but I see development at club level as each club will set its own rules and develop them in accordance with local requirements."

Luiz says : " I worry about obtaining worldwide support from multihull fleets, clubs, organizations and manufacturers, especially the last ones."


I had two immediate reactions to both statements

If everybody and every local club does his own thing (own rules) then we simple don't have a class in the normal sense of the word and organisations like ISAF and local associations will not be impressed at all and steer all kids to lasers and other boats.

The reason all prior efforts folded is because they too concentrated on getting a boat design without planing to whole promotion, launching and growing portion around the design. It is a shame but a good design often doesn't sell itself. If everybody local goes his own route then the resulting fragmentation will make growing the (non-existant) class very difficult. Basically I fear we can't have it both way. Either we all do our own thing, as we cat sailors have done for decades now without any youth succes, or we agree to converge on a single design within a set time frame and that suits the planned promotion, launch and growth game plan the best and have a serious go at creating a succesful cat youth class.

Wouter

Here is my explanation of the 2 variations of the same design.

I don't share the opinion that we should have a full-on development part in the F12 class.

My vision of having two variations of the same boat is this. Both are OD (but not SMOD), but with ample freedom to modify details that don't directly improve performance significantly. The simple version is there to be home-build first time around by an amateur for very little cost. In effect this is the low cost entry for those sailors. The second version can be had by upgrading the simpler version (using the same mast and platform) with a more performant fully battened sail etc. This will be more expensive but won't be expensive. The basic platform remains the same.

The simpler version is not at all expected to be faster then the "real" F12 for competitively oriented youths, but it won't be much slower either. In effect they can always race against eachother as the simpler version will not have any unfair advantage apart from being alot cheaper to build. The simpler version is the craft that many want simply to get kids on the water, the normal version is the design to build the international class upon.

Now I don't really think this makes our life alot easier in getting the class accepted by sailing organisations as a youth boat, but I'm trying to satisfy the diverging desires of the group this way.

Wouter

Phill: the 420 Club version is essentially the same boat, reinforced to take more abuse and with simplified rigging and foils (wood instead of composite, simple blocks instead of ball bearing blocks, etc.) to make it more affordable. The concept is "a school boat" for the 420, 470 and Flying Dutchman (the high performance dinghies of the past).

Wouter: strict one design is my personal preference based on the experience with the Optimist class, but sometimes it is necessary to make concessions to atract more people.

Wouter,

This is ok with me. Especially the last paragraph. Again: I don't expect the design to be critical. The Optimist could be improved in 100 ways.

So let me get this clear, does Phill's boat in any or all configs, fit the F12 box rule, if there is a box rule.

How can it not fit the box rule?
regards

If it doesn't fit, it doesn't fit. What more can I say? Phills' boat is not to be called an F12, just a Blade 12 as I understand it so it may not meet Wouter's F12 specs.

Hey, they are not my specs. Remember, that I wanted the boats to be 3.8 to 3.9 long a year ago. That would have made Phills boat compliant. It was the group here that campaigned heavily for a shorter boat adn I complied.

Some people have really short memories. I also object to people always assuming that I'm the problem especially when I was most vocally of the opposing camp.

Wouter

Berny...Wouter is right about the length issue...he took quite a beating on the forum over wanting the boat to be 3.8 to 3.9m.even when showing that a measurable improvement in performance could be had without any added expense, and a no noticeable increase in weight. Personally I still think it was/is a mistake not to go with Wouter's sugestion on the 3.8 to 3.9m length, but that issue has been argued ad nauseam. Re-ignite that fire at your own risk….

Regards,
Bob

I'll bite on that one. I agreeded with Wouter on the length and I, for one, was disappointed to see the performance depleted to have the boat cover a broader age range. Blade 12 and Phill have the lower age range covered and has stated it (Blade 12) is OD.

I vote to open that length discussion again. Obvious a least a few people involved here haven't gone back to read every post of the last year or so, and from BEFORE there was an F12 forum.

Right, I am one who didn't read it. Maybe cut and paste the best posts?

Here is a copy of one of many posts Wouter made on the topic of length...

"For a while I devellopped 2 designs next to one another a 3.66 and a 3.90 mtr long hulled design and I found the following to be the case.

The difference in hull weight between these two is 0.6 kg per hull and I don't believe you can really get a 3.66 made from less (sheets) ply then you can the 3.90. So from cost and weight point of view there isn't really any significant difference between these two hull lengths.

From the point of weight carrying capacity there is. That much had been explained in the initial posting. My design now both are buildable for 2300 Eur, incl. bought rudders/stocks and luxuries like ratchet block and Ronstan telescopic tiller extension, and the overall weights are 64.1 and 63.5 kg ready to sail. But both of these are conservative summations of the parts in weight and costs meaning that on both points the specs may be lower when actually build or when more attention is paid to weight and cost. The most interesting point is the overall weight. In my initial posting the platform weight was taken at 55 kg (the goal) and that boat could carry max 105 kg with some measure of performance (like a F18 with 180 kg crew). If that platform was really 65 kg in weight then the max crew weight would only be 40 kg. Something I think to be too low to make the boat attractive. Kids do grow and like this the boat would be outgrown with maybe 2 to 3 years. Additionally they couldn't really sail with a friend. The 3.90 mtr is much more forgiving when not build down to min spec. Afterall this boat allows up to 75 kg in crew weight if the platform was 55 kg. As such a 65 kg platform would still allow crews up to 65 kg would still include most teenagers.

From this perspective even 3.95 might even be more attractive, but I'm not sure if that length is wise in the way of storing the hull and transporting them over long distances. Pretty much 3.90 mtr is the max. if looking at those things.

But the most important issue with hull length is sail carrying capability. If I give both designs the same dive tendency then the 4.66 mtr. can only carry 7.0 sq. mtr by 5.3 mtr luff sail giving it a Texel rating of 145. The 3.90 mtr can then carry 8.4 sq.mtr on a 5.80 mtr luff and have a Texel rating of 132. Both sails have the same aspect ratio of 4.0

Simply increasing the length from 3.66 to 3.90 increases speed by no less then 13 points not because of the waterline length of the hull but because of the much increased resistance of the 3.90 mtr against pushing its bows under.

The 3.66 will be about as fast as the Hobie wave (= 3.98 itself) and the 3.90 will be faster then both the Hobie wave and the Hobie 14 (= 4.23 mtr).

My lastest design has a 9 sq.mtr sail on a 6 mtr luff and has a Texel rating of 128. I don't think the design can be pushed any harder than that. But as such it will outperform all other cats of 14 foot and less except the F14 by Darryl Barret. This includes the Wave when fitted with a jib sail and also the Hobie Teddy and Hobie Twixxy when sailed at 65 kg crew weight. And it will beat mono's and skiffs like the 29-er and Tasar. I believe this show cases the catamaran design to new sailors best especially considering the increased stability of the design with respect to mono's.

But more interestingly if the design is sailed with a 7.0x6.0 sail (kids rig) and a 35 kg crew then the rating will still be 127. In effect we can make the kids version and teenager version perform the same by adjusting the sail area. Reducing the sailarea for kids has the extra benefit of reduce the pitching over the bows significantly making the boat less intimidating. As both sails use the same luff length they can both use the same mast and also the same boom. I've read up the laser experiences with different rigs and that shows that using the same luff length is most attractive from a sailing behaviour point of view.

The added benefit of this 7.0x6.0 kiddies rig is that the laser 1 dinghy also has 7 sq. mtr. sail for the above 70 kg sailors. In effect this showcases the cats at their best as well. The kid can sail with the adult laser rig if it were fitted to the F12 AND handle it well. One could even put the laser rig on the F12 if one really wanted to or had one laying around the house.

Another benefit of the taller masts possible on the 3.90 long F12's is that in light airs they keep performance MUCH better as the top of the sail will be pointing into the higher airstreams that have significantly more windspeed. At winds under 5 knots the windspeed increases linearly from groundlevel to 5 knots at 10 mtr up. This means that the top of 6.0 mtr luffed sail (6.4 mtr mast) sees 30% more saildrive in the top then the 5.3 mtr longed luff. As such it will still perform well in the really light winds that will be frustrating to shorter masted dinghy sailors like the laser 1.

As such this longer hulled F12 just works out alot more interesting then one at 3.66 mtr.

I think this to be very important to the teenager and adult part of the F12 as then this boat will really teach them to sail by apparent wind a first feature that needs to be mastered if one wants to sail high performance boats and start gybing downwind instead of running square downwind. We all know that gybing downwind is more interesting then running square.

So both on the mechanical parts as well as psychologically or even marketing wise I think 3.90 mtr works out significantly better then 3.66 mtr.

As 3.90 = 12.8 feet I think we can still call it F12.

Wouter "

From memory the 3.90 mtr long hull was the maximum if you wanted to put three hulls inside a 40 foot container when layed head to tail. At the time I had worked out that 36 boats stored in their rectangular containers (think boxes like sailboxes) could be loaded into a single 40 foot container without any need for internal structures inside the container. This would really facilitate international shipping to customers and international events. It would also place the shipping costs down to some 150 bucks per shipped boat.

At the time I also kept open the possibility of having 2 containers with boats and gear sponsored that would be used as a championship fleet for nationals and international events to which the youths would fly in. Just like the sponsored Hobie events. As such the events could be held in really nice places like the caribian with very dependable wind conditions and veru low entry fees.

Now such a things would still be a long way off but it never harms to take things like this into account when designing the boat. It is just so much better when such a deal is struck when everything fits inside nicely.

Wouter

Quite convincing. I am amazed by the difference 6,2% extra length (24 cm/390 cm) can do to a cat.
What were the reasons to keep it unchanged?

Personally guys I think the horse has bolted on this one. Boats are already and about to be built to the 3.75m Wouter wrote into his rules. I am, however, tempted to stretch the rule to 3.8m (or 3.775) to get Phill's boat into the box.

I would be willing to go to 3.8 mtr as well, next to the other advantages that would also give the F12 design the same waterline length as the laser 1 dinghy when it is already sharing the same size rig with it. I think we can spin this into a darn right promo value for the F12's. Think of it this way : same waterline length (which most people equate to max boat speed), same engine and the cat winds handily on max speed and on speed around the course. That will put the mono's in a position where disgarding the cat by a slight of hand is alot more difficult.

Besides, I prefer to have all class rule related numbers with only a single decimal. Hull length is the only one with two decimals at this time.

3.8 mtr = 12.46 feet and that is rounded off downwards to 12 feet which keeps the class name "legal"

Wouter

Actually, it is not so difficult to understand, I'll try to keep it simple.

Assume the fulcrum of rotation is in the middle of the hull, this results in each small volume of floation to get an increased leverage of 6.5 %. That is your first gain.

But there is more. Giving a 3.90 mtr hull a down sloping angle of say 1 degree puts 6.5% more volume below the waterline then the 3.66 mtr hull. Why because rotating a 6.5% longer lever through the same angle results in its tip reaching 6.5 mtr lower. So at each stage along the hull 6.5% more volume is pressed into action.

This is a magnifying effect. => we now have more volume displaced for a given dive angle, which results in a large restoring force that ALSO acts on a longer leverage. 106.5% * 106.5% = 113.4% gain so far.

Note that this gain already allows us to carry 7.0 * 113.4% = 7.94 sq. mtr. of sail area for the same dive feel. That is a whole square meter more sail area.

I'm not sure if I should proceed with the other magnifying effects, it will get detailed and the general feel for the causes has been established already. Suffice to say that by this increase in power one can widen the hulls a little bit ansd still be faster with the 7.94 sq. mtr. rig. These increases will again improve dive resistance so that we can again allow the sail area to be entlarged (and the mast length with it). This trade-off is so favourable that the increase in sail area is so much larger then the invested increases in drag that the boat becomes faster with each additional increase in hull length not because of waterline length increases but because the max size sail that can be carried increases disproportionally.

This is a commonly accepted principle in sail yacht design. Large yachts can carry disproportionally larger sized rigs. Disproportionally meaning that say a hull length increase of say 6.5 % allows 20% more "sail-area-times-mast-length" when keeping the same dive resistance ratio to be carried (a third power dependency). Of course the opposite effect also applies, meaning when you reduce hull length.

Note how a F18 at 5.52 mtr hull length and 21.15 sq. mtr. sailarea roughly coincides with a 7.00 sq. mtr. sail on a 3.75 mtr F12 when applying this 3rd power law ?

7.00/21.15 = 0.33 = almost = 0.31 = (3.75/5.52)^3

If you do the same to the US I-20 and the F12 you see the numbers match up quite well again. Same if you do the F18 to US I-20 etc. So this law does indeed predict a very large portion of the differences in sail area from one design to another. It is actually strongs dependencies like this one that make the measurement system based handicap systems work, even though none of these rules were used in the creation of these systems ! But that is a whole different topic.

Now a 3rd power relationship is quite strong, it is the same as increases in enclosed volume when you entlarge a fluid container. Scaling up a bottle in every direction by a factor of 2 will increase it contents by a factor of 8.

I hope this clear enough.

It was also one of the laws that allowed me to quite accurately predict the F16 and F14 performances in relation the F18 design before prototypes of both had been sailed alot. In the F16 case it told me what kind of potential the Taipan design truly had. Remember back in early 2001 there was not much Taipan to F18 race data at all to do a statistic race data analysis of the same accuracy.

Just more useless mathematics I guess !

Wouter

ok...if you guys are changing...for sure?....then I can easily do the same...are we changing or not ?
Cheers
RG

RG have any of your guys started building yet? If not I vote to change. Is anyone against, if we're changing I want to update all my drawings on Monday.

I think the only guys needed to weight in are Phill and Luiz at this stage. If they all agree (and why would they object) then I think we can move to accept this change.

So Phill, Luiz ?

And can we also have a raising of hands by everybody else.

The proposal is of course to increase F12 hull length to 3.80 mtr from the current 3.75 mtr. That is a 2 inches increase for our US friends.

Voting ends on sunday.




We here in EU won't start on this before Jan 2008 we are first going to celebrate X-mas and new year overhere. So we got time to fix some other specs as well if that is required. Resizing is not an issue for me as I got my model implementing in excel sheets with scaling factor. I only have to punch in a new numbers to get the new panel offsets.

Wouter

I have delivered one set of plans, but they haven't started yet, so I can still change stuff easily....so I vote to change

I believe the length of Phill's design is clearly his vote. Are you sure it is exactly 3,80? if it is more, I'd go for it to make sure his design is class compliant.
But keep it under 3,88.
3,9 or 3,89 would look like the goal was 4,0 and we decided to give a discount... <img src="http://www.catsailor.com/forums/images/graemlins/laugh.gif" alt="" />

Okay, Phill what is the length of your hulls measured between the verticals excluding the rudders and rudder pintles and with the boat leveled to its waterline ?

Wouter

Given the rapid acceptance of stretching the “rule” to get Phill’s boat into the box do we want to each publish a couple of extra dimensions in order to create a box that fits each of the current designs (shouldn’t be far off Wouter’s original numbers). I figure this will keep the majority happy (although it won’t be one design) by making sure the boats all have similar performance potential. Obviously numbers will be maximums and there is nothing stopping people choosing to go lower (ie Phill’s beam and sail area).

My numbers are:

Length: 3.8m
Beam: 2.0m
Sail area: 7.0sq.m (including mast)
Luff (P): 5.27 m
Mast (above top of beam): 5.8 m

From a previous post Wouter’s dimensions are:

Length: 3.75m (will probably change)
Beam: 2.0m
Sail area: 7.0sq.m (including sleave)
Luff (P): 5.3 m
Mast (above top of beam): 6.0 m

Are there any other dimensions which people believe should be limited?

Note we’ve also been talking about a minimum weight (60kg), however, I believe we should wait and see what the first few boats come out at before fixing this.

Or how about this combination...

Length: 3.80m
Beam: 2.0m
Sail area: 7.0sq.m (and maybe a 4.5 version for the beginners and/or smaller kids?) <img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />
Luff (P): 5.3 m
Mast (above top of beam): 6.0 m

If we have a sail area and mast length restriction, why do we need a luff restriction ? .... you can't stretch it it longer than the mast or lower than the boom.

Cheers
RG

I agree, however, I know Wouter was keen on the luff number and I'm indifferent as to whether its there or not.

Wouter, why exactly do we need a max luff dimension ? to me that seems like just having a rule for the sake of having one and I can't think of a good reason for having it unless you want to rule out boomless rigs?

Cheers
RG

Scarecrow,
Beam is 1800mm
Sail area is 5.7sq m.
Agree as mentioned on weight.

Regards,
Phill

Just finished the weight study for mine with the foam/glass panels and I'm looking at around 53-54 kg.

Cheers
RG

How much weight is saved or added building with the rotomolded honeycomb?

Maybe the intention is to leave reasonable headroom under the sail.

If the luff length is not limited, the highest aspect ratio (best performance) is achieved using the entire mast length for the luff. This reduces the headroom necessary for kids to move on the tramp, making the boat uncomfortable, less fun and potentially unsafe.

[/quote]

How much weight is saved or added building with the rotomolded honeycomb? [/quote]

Luiz,
right now I'm guessing till I get a sample panel made <will have it sometime next week> but I'd guess that if the numbers I've been told are correct, then it will only add somewhere between 3-4 kg to the boat. The weight is not the real issue, its the time to manufacture them that will see the real gains plus the drop in price.

Cheers
RG

[/quote]

Maybe the intention is to leave reasonable headroom under the sail.

If the luff length is not limited, the highest aspect ratio (best performance) is achieved using the entire mast length for the luff. This reduces the headroom necessary for kids to move on the tramp, making the boat uncomfortable, less fun and potentially unsafe. [/quote]

Luiz,
yes there may be a performance gain, so Im all for that but I seriously doubt its unsafe....the opposite in fact because there is no boom to whack them on the head.

Attached pic is of the boomless rig on one of the LR2's which gave a ton of room to to get thru safely.
Cheers
RG

Now thats hot! do those dinky little rudders and centreboards work? Wheres the holes for the centreboards? regards

Okay, can we now official fix the maximum length of the hulls as defined ... to 3.80 mtr ?

Luiz, you are the official leader so you are the one to strike down the hammer and make it official.

Wouter

Setting the max luff length has nothing to do with ruling out boomless rigs. I actually don't even see how those two are linked in any meaning full way. Please explain to me how you think that they are, maybe I'm overlooking something here ?

The true reason for the max luff length is equality in performance, equality in perception, equality to Laser standard rig, good view to the leeward side of the boat, ease of tacking and with respect to my design it is a critical measurement to stiffen up the unstayed mast without increasing mast and boat weight.

Without a luff max limit I strongly expect a run for the lowest Boom/Foot height possible (see A-cats) to gain maximal (perceived) advantage. I think this to be undesireable from several aspects while fixing a max luff length doesn't really have any significant drawbacks.

A more detailed analysis follows now :

-1- Performance

Sails that share the same overall area and luff length will have largely an equal potential for producing sail drive forced on them. Only variables left will be amount of draft, position of draft and overall shape. Our proposed sail area with that luff length will already force a squaretop design as sailshape to such an extend that the variable of sail shape is not a significant discriminator anymore. That leaves draft and position of draft. I would like to get this open in order to have crew suit the sails to their body make-up and sailing style. I think this has been proven to work well other cat classes; in fact this seems to further equalized performance when only one sail per event is allowed to be used. But maybe more importantly the sails will now look very much the same from design to design, with only very small differences that are difficult to spot. I feel this will install alot more confidence in equality of performance in persons who are otherwise not educated technically = youths and most parents.

Basically, the less obvious the differences between rigs are the less cause for parent or crew related "concerns for inequality". And rigs are very important in this respect, even more so then hullshapes.

Drawbacks of a fixed MAX luff length ? The only one I can name are loose some very small amount of performance relative to say a luff the length of the mast. But this is not really a disadvantage as long as everybody is limited to a single luff length (=equality). I just prefer to fix this limit to a measurement smaller then the full mast length and I think the above benefits are sufficiently prefering 5.30 mtr as this will allow sail with aspect ratio of 4 which is already high.
F18/F16 have 4.25 ; hobie 14/hobie wave = 3.2 and 3.5


-2- Equality in perception

This is already partly covered in the paragraph above. Differences in rigs and sails are very easily spotted. Alot more so then any other difference between boats like hulls. Sail that are fixed both in area and luff length will look alot less different, even when fitted to masts of different lengths or when their drafts are significantly different. I also think that to take out this easily spotted difference is good for younger sailors as I expect them to feel more equal to eachother.


-3- Equality to Laser standard rig

I'm intending to have the F12 be very similar to the Laser dinghy in important specs like the waterline length (which is equal now with our max 3.8 mtr hull length limit). Same with respect to masts (5.9 mtr in laser although class allows 6.16 mtr) and sail area (=equal already) and luff length (laser = 5.260 mtr.) The difference in laser mast specs in mostly likely due to some people including the part that is in the pod and below decks. Our 6.00 mtr mast length above "deck" = beam would be highly similar.

Basically I just rounded off the number to these or what I had determined to be very attractive specs. Again, sail aspect ratio of 4 with a 7.00 sq. mtr. rig requires a 5.29 mtr luff length that I rounded off to 5.300 mtr.

I'm after laser equality in these specs for marketing purposes. F12 will definately beat the laser, especially the youth versions of the laser, and by keeping the specs pretty equal we avoid this performance difference being explained away by mono fanatics by refering to some "significant" differs like a "taller sail". I want the F12 to proof the cat design strong points in relation to a mono and partly increase acceptance of all catamarans in the larger fraternaty of sailing.

Again the benefits of fixing the luff length to another limit (like mast mast length) too small to outweight these benefits.


-4- Good view to the leeward side of the boat

I do indeed think this to be a safety issue. I also want to avoid sails with windows in them. The laminate that these windows are made off is sensitive to abuse and rips easily. It is also another thing to do to a sail by a sailmaker and will add cost. I think it is better to be able to look under the boom/foot-of-sail. Mostly I'm unimpressed by the view through these windows anyway, especially in rough weather when lots of water droplets deteriorate the view.

Having a minimal boom/foot height that is sufficiently high (at least shorter then the mast length)is an easy and cheap solution. I know from measurements that 0.5 mtr is pretty much a minimum and the 0.7 mtr boom/foot clearance given by the laser-equality and sail-aspect=4 criteria would therefor be sufficient too.

I also think that having this clearance near the mast is important as boats travelling upwind at equal speeds and equal relative positions (= collision) are to be spotted in this area. Boats that are to be seen further back along the boom will pass behind and boats seen in front of the mast will pass in front.

I don't think this aspect of the design should be discarded without a careful analysis.


-5- Ease of tacking

Low booms are a pain in the neck on a catamaran especially when their hulls are boardless. In order to come close to tacking the F12 much like a laser the F12 crew needs to roll tack. And you'll need to be very quick but smooth in crossing the trampoline as bobbing the boat around slows a lightweight boat down very quickly and being to slow capsizes you. I fear that on the short F12 there is not alot of room to have the boom/foot angle upwards quickly enough.

I want the F12 to be a really well behaved boat, after all it will be compared to modern dinghies which have a few significant strong points here, boom clearance on the laser and Open Bic is one of these. I don't think a very low boom is any benefit that isn't outweighted heavily by its drawbacks.

So for this reason a mas luff length shorter then the max mast length is to be prefered. I know from many measurements and test sailing on a score of boats that 0.50 mtr is very much the minimum.


-6- It is a critical measurement for my own design.

I shall make no secret off it. The push rod setup needs a max luff length shorter then max mast length for ease of raising the mast, stiffening up the mast sufficiently, lowering the stresses on the parts and hulls AND safety !

Safety because I'm counting on my design being able to completely weathervane the rig. When a kid gets surprised by a squal he just unthreads the mainsheet and the rig will completely weathervane itself. If he needs to sail downwind to safety in a blow he can over rotate the rig so the boom is angled forward by 45 degrees and loose all capsize moment (!) and most of the pitchpole moment. For upwind and reaching legs he can of course let out the sail with the same results. As such a kid can always sail to safety on any course with a very calm and easily controlled boat.

On the beach the rig can also weathervane which makes boats tipping over a thing of the past as well as dumb mistakes like slam gybing the boat on the beach by turning it the wrong way.

For the weathervane property the boom/foot needs to be above the push rods. And I'd like to have the push rods as high as I possibly can without compromising looks and performance too much. 5.3 mtr luff length on a 6 mtr mast does the trick for me.

Stiffness of the unstayed rig. The difference in the top of the mast flexing off between my push rod design and Phill pod design, when using the same mast, is 40%.

In effect, the difference is between the top flexing off 0.85 mtr or 1.20 mtr; a difference of 0.35 mtr. and this is alot. (Phill, remember my "feel the need to tell ..." moment ? That was this (and some more I may tell later).

With a max luff length of 5.3 mtr on a 6.0 mtr mast I can have a homebuild mast from basic alu tubing that weights less then 9.00 kg and has sufficient stiffness to not look to bendy and not pump to much. Without it we can probably kiss the unstayed mast principle good-bye.

Seen that way NOT having a max luff length rule (or minimum boom/foot clearance rule) is the same as effectively ruling out unstayed rigs. These already have a performance disadvantage to stayed rigs, with no such limit the disadvantage is getting worse.

Having an unstayed rig is also a critical element in my design; the whole concept of simplicity is designed around it. From the free hanging boom (no fittings) and cheap mast production to the ease of car roof transport and shed storage.


Wouter

Agreed. Headroom will not be a problem if the sail is well designed. Also, I forgot that the Supercat 17 is using this configuration for decades...

Someone recently suggested something along this line for a boat using the push rod mast support system, like the Hobie Bravo.

The idea was to double velcro the lower part of the sail around the mast support tube below the bars (gooseneck) so that the entire mast length could be used for the luff. It seems to makes sense after all... <img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />

(couldn't resist... sorry! <img src="http://www.catsailor.com/forums/images/graemlins/tongue.gif" alt="" /> )

Sorry, none of this make much technical sense. Later more on this.

But also the reasons for having a max luff limit are the same for both boomed and boomless sails.

Booms only "smack over" on slow mono's as the boom only comes over very gently when a cat at normal boat speed is gybed. Remember which direction the apparent wind is coming from on a cat.





That still doesn't allow the rig to weathervane or even to achieve large boom angles as the rods will hook the sail then at 45 degree angle. This max angle could make the boat hard to control on courses between beam reaches and broad reaches in a blow.

In addition this flap makes no aerodynamic sense. Many believe that it does, but it really doesn't.


- first technical reason

All area used up by the flap needs to come out of the total sail area. So low above the watersurface the windspeed is only a fraction of the windspeed higher up the mast. As such the same area is MUCH more effective when used higher up in the sail.


- second technical reason

Because of the relatively low windspeed so low to the watersurface and the fact that the flow here is largely disturbed or even blocked by the hull makes any lift gains here negligiable and any drag looses when not having the flap to small too matter. The loose flap and felcro are more work for the sailmaker (more labour costs) and more stuff to get broken without any measureable benefits in performance or simplicity of design. I've used a similar setup on the 49-er I sailed for a while and I would have gladly removed that whole flap. It was the first part of the sail to crack up and once the velcro is gone it undoes itself and flutters in the wind. By the way, Nothing is as draggy as a fluttering piece of cloth, even if only the leech flutters then that increases airfoil drag by 20-40 % No amount of sail drive of the same piece of cloth can every correct for that.


- third technical reason

For an airfoil to work in unstable flow (as we see all the time while sailing) it needs to have a sufficiently large cord. Wind is basically an unstable airflow that is made more unstable by waves, chop and macro turbulance induced by the wind rubbing against the ground/watersurface or passing buildings, trees, hills, dunes, other sailboats and whatever else was in its way.

Very short cord foils stall very easily and have trouble reattaching the airflow. The flap is basically a very short cord foil unless it reaches back very far along the boom. This can of course not be had for other reasons.

A short cord foil also stalls at significantly lower angle of attacks then a longer cord airfoil. Of course you'll set the boom angle for the lower portion of the sail (= long cord) and the flap (short cord) is set accordingly as well. By any analysis it will be suboptimal. If you are lucky (!) its lift will cancel out its drag and the drag of the mast (but still lower the effective sail drive area of the sail that is above the boom, probably losing some performance)


- forth technical reason

Alot of people think that the flap will smooth out the flow around the mast and thus lower the drag of that part of the mast.

Even if it does that (and it most probably don't) then the drag of that part of the mast must be sufficiently large to matter, which it most definately is not. A 50 mm diameter round tube of 0.750 mtr length (my exposed mast below the mainsail sleeve) produces at max 0.50 kg of drag when sailed at 15 knots on a 45 degree upwind course in 20 knot of winds. It is probably significantly less as the wind so close to the watersurface is travelling significantly slower then the windspeed readings that are officially taken at 10 meters altitude. Additionally you can never remove the total amount of drag of this portion of the mast, even with the flap a portion will remain. So the total drag amount is less then 2% of the total already.

But this assumes that the flap actually smooths out the flow over the mast here. If a round mast with a sleeved flap is used then this won't happen to any significantl extent. Even if the flow was laminair before it reaches the mast (unlikely) then it will become turbulent and detach from the mast+flap BEFORE the side of the mast is reached. When teh flap is properly aligned then the flow will reattach some distance behind the mast. If the flap is too small then flow will not reattach at all and the flow pattern around the mast will be the same as with the flap (foil) completely stalled. In that situation there will be hardly any lift created and the drag of the mast+flap setup will not be less then just the mast alone. In fact, it will mostly likely be more because as a due to the angle of attack (20-25 degrees) a larger portion of the flow will be disturbed.

In effect it is better to have a very small area operate at a bad drag coefficient then a large area operating at a mediocre drag coefficient. A flap is alot larger in area then just the round tube of the mast.


It is interesting to note that flapped mainsails are not found in EU. Any design that had them like the older Nacra's and supercats had these flaps removed because the measurement based rating systems like Texel and SCHRS counted this area with the same weight as area higher up along the mast. It was found that it was better to remove the flap and make the sail above the boom a little larger.

Other area's using yardstick systems still see these flaps as here these systems don't not look at the total amount of sail area just at the performance that is achieved.


For these reasons I see no technical reasons to have flap below the boom to try to maximize luff length. It is either a full sail going down closer to the mainbeam or just cut off the foot along some horinzontal. The jury is still out on the "angled upward booms", but I'm personally skeptical of them as well.

Wouter

Wouter,
all your reasons aside you seem to have forgotten that no one else but you is going for the support tubes and with the exception of Phil's boat the ones starting to build right now are all stayed. I should also point out that the boomless rig was the idea of the people building the boat and they are paying for it, so I guess it's their choice.

BTW, your analysis of the small flap at the bottom is just plane wrong, I have recently done a lot of CFD work on just this subject for the A-Cats in the form of a mini sweeper (about 400mm chord) and it is extremely beneficial even without a seal to the tramp an I for one will be adding them to any design that the owner allows me to.

Cheers
RG

Hi Jeffs
Look on the leeward hull behind the trap wire, you can see the centercase there, and yes the boards and rudders work fine and you can out point most people most of the time.

Cheers
RG

Just to add my 2 pennies worth, I know that RG has 4 boats up north that will all be boomless plus our 2 will also be that way, not sure about the other 3 that are just starting, but I suspect they will go that way so we are all the same down here in NZ and just as a personal observation, I think Wouters arguments while probably meant well just look like rubbish to me.
Aerynt

Wouter, does this description ("angled upward booms") apply to the LR2 photo that RG posted.

I appreciated the effort Wouter went to to explain his thinking about the aerodynamic properties of the flap. Agree or disagree, since this is a community effort (right?) it would be nice if we had some dialog about the substance of his comments, rather than just dismissing them on the basis of some computer modeling that none of the rest of us have seen.

That said, my understanding is that leaving the luff length unrestricted will not actually penalize Wouter's design, since his argument I believe is that aerodynamically a design without the flap is more efficient.

BTW, on the issue of support tubes, I would be careful about making an argument just on the basis that noone else is using them. Don't forget Chris's "McDonald's" story. Eliminating diversity unnecessarily may not be doing the class as a whole a favor.

What makes it official is that all four boats will comply with 3,80 m length limit. A hammer in my hands only serves to open a hole in the head to make room for all that data.

I totally forgot about feathering. Optimists feather their sails when being towed and when rigging. Lasers do it when rigging. This is a usefull feature even for kids who prefer to wait in the capsized boat when things get rough (for quietness).

While we are at it, Optimists around here use a snap shackle (or similar) to fast-release the mainsheet block from the boom to feather. I guess we should copy this feature.

I like Wouter's mast support system. It makes sense from the structural point of view and others. My daughter justified her preference for the chined hull shape because "it is easier to grab in order to climb back to the boat". Those bars certainly help too. Also, the capacity to feather makes it easier to rig and tow. Both are important for kids.

Great ! Lets get into it. How did you model it, how was the flap modelled, what approximation routines did you (or the software) use. How did you model the wind flow. What variances did you use, if any. Does the software allow stochastic modelling at all or just lab style deterministic models.

Can you intepretate the data for us, as in explaining why the flap works when the flow detaches from the round mast section before it reaches the point where the sleeve seperates from the mast tube. This detachment is broadly documented in a score of scientific publications.

I'm really interested in being proven wrong cause that is the way we learn and progress design.

I'm also aware that no single person (including myself) can cover a whole field in engineering like aerodynamics. There is just too much detail there.

If I make a mistake here then I want to know about it.

Wouter

Ohh, I'm perfectly happy to race against any flapped design while sailing a non flapped design myself. It is just the perception thing that worries me and the fact that I do believe the flap obstructs critical visualbility in collision situations.


It is also my believe that without strickter F12 class rules then we have now we'll end up with mini A-cats. Which in my view is the same as the other expensive boats (F16, F14, A-cat) but then with less less performance and robustness. That is in my opinion not the right balance to strick with respect to the entry level cat that the F12 was intended to be.

But I'm happy to have the others decide to go down this route if they really want. I will however keep the orginal F12 concept going on the background just in case.

Wouter