Foam strip construction

I think Gato is on to something here :

http://www.gust.ax/gallery/f12/2/

See the galleries of

- A new cat
- The start of a new cat
- The beam landing
- Cats everywhere
- I'm sailing
- Sailing faster

The simple foam strip construction he uses appears viable for nice compounded curved hull shapes and seems reasonably simple to contruct by amateurs.

Have you measured the weight of the completed hulls Gato ? And how much is each ?

How many hours were involved in making up a single hull excluding building the jib ?

Wouter

It is definitely a good method to be used by armature home builders. Don’t know if you have been checking the sshhh thread there is a little bit more on the building there.
My hulls are a little overweight as I used a heavier cloth than needed, because I had it laying around in my workshop. If I remember right I ended up at something between 13-13,5 kg, it should be possible to make them around 12 kg.
When the jig is setup you can rip the strips, lay them, glass the inside, install transom and frames make the beambox and the fittings for forestay and shrouds in one day about 6-8 hours for one hull half.
The two halves made its not a big deal to join them and glass. In total I made Had the Tabby on the water in five weekends guess 50 hours (not painted).

Thanks for the quick reply Gato.

I appreciate that.

I have read up on the sshhh thread and have gotten some more info I was interested in. Part of it I has already guessed from the pics in your galleries.

A note. In the F16 class they use seperate decks that are glued on later to properly tape in the keel line from the inside. Some are quite adament that this is needed when the craft sees hard use. Tp prevent the hull from splitting open. Apparently only taping from the outside is not enough in the long run. Just something I wanted you to know.

I'm very interested in your Tabby cat and how its construction holds up. Mostly because I personally have a double edged problem. I don't have access to a dedicated workshop and typically I do all the boat and landyacht building out in the carpark in front of the flat I live in. Individual stages must be finishable in a single day. Additionally, I can't occupied the space for more then a week or so before I get complaints. The second problem is the area I sail. I have strong doubts about the freeboard on some of the F12 designs so far. The north sea is one of the reasons why all the F18 designs have increased freeboard significantly over the last years. It is also what makes the AHPC Viper F16 such a good boat. Greg Goodall of AHPC specifically commented that they learned over time that freeboard is more important in dive resistance and recovery then bow volume. The Aussie Blade F16 is following this trent together with the Viper F16 and the new F18 designs.

I feel that the foam stip plank method you tried is viable for me personally and allows me to get a platform more suitable to true beach cat sailing where there is a surf to traverse.

And you are an inspiration to us all Gato, I'm certainly no exception to that rule.

many thanks and I'll be keeping an eye on your blog page

Wouter

Thanks for the kind words. As for the joining of the two hull halves ncik has a good flanged setup in his drawings. As my intention was to build fast I made some compromises.
For the freeboard I understand your concern, but this is a cat for kids and with the quite choppy sea condition we have here there is no real problem in the conditions you send out your kids on the water.
As for adult sailing for fun I think a 14 feet version with a moderate sailarea and a spar not exuding what you can cartop would be the solution, and there I think that such a cat would benefit from a higher freeboard.
I’m thinking of building one for myself, it would perfectly meet up to my needs.

Gato,

As far as I'm concerned you deserve every praise that is coming to you. A great deal of designing is just giving something a try and see how it comes out. You are almost singlehandedly doing that portion for the F12 class.

Ohh, I forget to ask last time. What is your body mass and length.

I ask as it appears the Tabby lifts just fine with you on board. Now I don't expect you to be of my stature but nevertheless ...





Now, what I'm personally lacking in the "just build it and see" department I make up for in analysis. That is what I did in the F16 class and what I also did in the F12 class.

I actually believe that the F12 can work well for adults. Meaning 85% of the adult women and about 50% of adult males (when keeping the 2.00 mtr width). You may well fall in the last category.

The 7.00 sq. mtr sail area on a 6.00 mtr stick is not really limited to youths. Afterall the laser dinghy has the same size rig with a very oudated sail design and is only 60% slower then a fully charged F18 racing catamaran. This Laser dinghy is actually sailed best by a 80 kg skipper and can be very fast downwind (where it is much less limited by righting moment of the crew).

Additionally, the loading of the F12 hulls and rig is on a par with a 135 kg crew on a F16 when you are around 60 kg - 75 kg. They specificantion that may need to be adjusted is the overall width of the F12. For skippers over 70 kg it is best to make the craft only 1.80 or 1.75 mtr wide instead of 2.00 mtr (and just keep the same rig).

The following combo's of boat weight x mast height x sail area x crew weight x width are very entlightening :

The named ratio is the righting moment of the crew on the luff hull devided by the heeling force of the rig when sheeted tight. A smaller ratio indicates a more overpowered boat.

50 x 6 x 7.0 x 60.0 x 2.00 => ratio 4.05
50 x 6 x 7.0 x 65.0 x 2.00 => ratio 4.28
50 x 6 x 7.0 x 70.0 x 2.00 => ratio 4.52
50 x 6 x 7.0 x 75.0 x 2.00 => ratio 4.76

50 x 6 x 7.0 x 70.0 x 1.75 => ratio 3.96
50 x 6 x 7.0 x 75.0 x 1.75 => ratio 4.17
50 x 6 x 7.0 x 77.5 x 1.75 => ratio 4.27
50 x 6 x 7.0 x 80.0 x 1.75 => ratio 4.38
50 x 6 x 7.0 x 85.0 x 1.75 => ratio 4.58

50 x 6 x 7.0 x 70.0 x 1.80 => ratio 4.07
50 x 6 x 7.0 x 75.0 x 1.80 => ratio 4.29
50 x 6 x 7.0 x 80.0 x 1.80 => ratio 4.50
50 x 6 x 7.0 x 85.0 x 1.80 => ratio 4.71


Other boats in the cat scene have :

109 x 6.78 x 11.12 x 2.35 => ratio 4.04 (Hobie 14 when not trapping; ratio is even higher when trapping ; 5.03)
104 x 6.40 x 8.64 x 2.15 => ratio 4.92 (Hobie Dragoon, 3.91 mtr length)
100 x 6.50 x 9.30 x 2.13 => ratio 4.40 (Paper Tiger, 14 footer no trapeze allowed by class)
118 x 6.10 x 9.20 x 2.13 => ratio 5.08 (Hobie wave, 3.98 mtr length no trapeze allowed by class)

An F16 sloop sailed 2-up and double trapped at 135 kg crew weight has a ratio of 4.13
An F18 sloop sailed 2-up and double trapped at 150 kg crew weight has a ratio of 4.33

Most other modern performance boats are in the range of 4.00 to 4.75 with respect to these ratio's, that is excluding the specialized singlehanders like the A-cats (2.65) and the single handed F16 (3.13) when either is sailed by a 75 kg crew. Note that both the A-cat and F16 1-up are beyond any doubt overpowered boats requiring skills to control. A 40 kg kid (average 12 year old) singlehanding on a F12 will have a ratio of 3.09 ! And he will share the same power-to-drag ratio of a 95 kg singlehanding skipper on a F16. Do we really want to see these toodlers doing 15+ knots while being all on their own and on the edge of control ?

The basic conclusion is that the heeling power (and power-to-drag ratio) of the F12 rig (when placed on a 50 kg platform) is pretty high compared to other designs. That is when sailed by an light to medium sized adult. And sailors seem perfectly happy to sail the Hobie 14, the Hobie wave, Hobie Dragoon or the Paper Tiger. In fact the dragoon is the true youth class < 14 years at the moment. I've sailed both the Hobie 14 and Dragoons as an adult and these are undoubtably fun boats. In fact, the loading per meter waterline length of the F12 with an adult on it is still south of the same ratio's for the other boats.

In fact, the Paper Tiger has the lowest value for this ratio of the alternatives and you'd have to load up the F12 to 156 kg to achieve parity. Achieving a total of 117.5 kg on the F12 (50 + 67.5 crew) achieves drag-to-sail power equality to the Paper Tiger when that boat is sailed by a 75 kg skipper.

The Texel rating system predicts very similar performance for either boat; both Hobie 14 and paper tiger are at rating 135 and the F12 with an adult is at 136. That is under 1 % speed difference around a race course.

In all honesty, I have never understood the large focus on kids when it comes down to the F12. It is far more suited to the crew weight range of 55 kg - 75 kg then for kids of 12 years of age (or younger) who have their mean at 40 kg and of which 85% is in the range 30 kg - 55 kg. Below 10.5 years of age and 95% is below 55 kg (their mean at 35 kg). Although, this also means that two kids crewing together on a F12 will be right back at the ideal weight range.

I hope I don't hurt anybodies feelings but there seems to be a persistant myth that hull length has a direct relation to the age of the crew. As for example that a F12 is for 12 year olds or younger, F14 and F16 for teenagers and F18 for adults. While in reality, the F12 (as it stands) is for best suited for teenagers, females and light males, F14 and F16 are for light to medium mixed crews or medium to heavy 1-ups and the F18 are for medium to heavy doublehanded crews including all male teams.

In fact, Phill Brander was right with his Blade F12, fitted with a 5.5 sq. mtr sail, as intended for 12 years old kids etc. This setup has a ratio of about 4.0 (for a 40 kg skipper and 6.0 mtr mast) and that is what I would put these kids through at maximum if they are to be solo sailing the craft.

To summarize a long explanation. I think the F12 could be a perfect adult (light to medium weigth) solo craft as long as the hulls are designed for the associated weight range and have sufficient freeboard for chop. The rig dimensions are fine as it stands and by making the rig light enough the diving of the platform shouldn't be a problem either. Of course, a rating of 136 (or only 20 minutes slower then a F18 or A-cat (rated at 101) that both completed a windward-leeward race in one an hour is really nothing to be ashamed off either. You will still be doing 11+ knots and beat the laser dinghy in the race by 15 minutes. The current 14 foot alternatives aren't going much faster at all. Ergo, The F12 power-to-drag ratio under an adult skipper is fine too.

Wouter

An interesting detail is that beyond 10 km you can't see the overturned F12 anymore even when standing straight up and the water surface is flat with a cristal clear sky. That is due to the round shape of the earth. The overturned craft will then be hidden by the horizon.

So any boat that can get away from you by that distance in a short time (15 knots => 21 minutes) is dangerous.

Wouter

Wouter

I hope I didn't scare everybody off with the long post.

I just wanted to elaborate that reconsidering the F12 as an adult boat might well be worth while. At least it appears that some redesigning of the hulls may lead to a very enjoyable craft for this target group. And that I suspect Gato is right in the middle of the weight band for that group.

Not saying that 14 footers are worse or anything.

Wouter

Wouter,

If the current F12 does not result in a proper startup boat for kids, the "kids cat" market niche will remain open for designs like Phil's while still F12 compliant. The development of the F12 class will give us the answer. It is perfectly possible that we see two trends develop within the class: one for performance (teens and adults) and one for simplicity (kids). The door should be opened for both ones.

I’m not scared away, and the figures fit and if I had children at the right age I agree completely, an adult can have a lot of fun with a F12 cat. The thing is, if you don’t have kids it is in my opinion better to extend the cat 2 feet to get a little bit bigger displacement to not be at the limit of what the boat can take (on the pics of the Tabby I’m at 75 kg, displacement of the Tabby 120kg, the highest of the three).
The DS12 has been sailing for one season, and it has not showed any signs of being dangerous even with crews with no experience from catsailing.
To make use of the potentials of this craft it takes quite a lot of skill. For a beginner its jus fun because its faster than the opti, but there is no chance you get close to the max without knowing what you are doing, and by then you also knows the risks.
To my experience the kids don’t like to go out alone as long as they don’t feel safe, and this cat looks more impressive than it is in the reality.

Adults can also fit into and sail optis and sabots, but that doesn't make it a good idea.

When the tornado was dropped from the Olympics one of the major discussion topics was development of a pathway into performance catamaran sailing starting with the kids. While there are a number of small cat classes around (arrows, arafuras, paper tigers), few were deemed suitable for kids only as a development class; too heavy, too much sail area, too complicated, too many adults already sailing them, too ugly.

The F12 can fit this niche very well, if the market desires.

Ahhh, come on !

That is a nice sound bite, but not really applicable to our situation is it ?

A F12 is a far cry from either an opti or sabot. The F12 is on a level with the Laser dinghy; same boat length, same mast height, same sail area and comparable or better performance. The F12's simply dwarf the opti and sabot in all these specs. Point in case, the F12 has over twice the sail area of the opti and almost three times the mast height. Not to forget its rig is light years head of the opti sprit sail. With respect to the hull/platform, well, the opti is halve the width and is also missing 5 feet of hull length.

Why would anybody compare the F12 to an optimist or a sabot ?

Hell, the non-foiling moths are significantly closer to the F12's in specs, so why not turn your sound bite around ?





Honestly, no personal disrespect intended to you Ncik, but your statement is a bit unhinged.

Wouter

I like this: a platform that is fast in skilled hands but slow (thus safe) in inexperienced ones. It spreads racing times according to skill, not luck, thus providing immediate response to learned skills.

Your spot on ncik
The F12 gathered so much momentum because it filled a gap in good promoted childrens catamaran. There are no end of small cats out there an adult can carry and rig. This is one of the very few that a 10 year old can rig and manoeuver to the water. If an adult came to my club looking for a relatively light, easy, safe cat to learn on I would recommend a Mozzie, F14 or an Arrow depending on their weight.
regards

Hey Jeff, If you'd ever seen me sail I doubt you'd be counting a Mozzie as easy and safe

Cheers

It was a good sound bite. hehe

But you haven't commented on the major point of my argument, that is filling a niche for a kids cat.

I thought I had but I'll just do it again.

I understand there is a desire to have a true youth catamaran. And in this case I seperate youth ( < 12 years) from the teenagers ( > 12 years). I actually agree with that part of the claim.

I'm not too sure, however, if the F12 is best suited to that role or whether it is simply pushed into that role because it is the best alternative available.

I do believe there is a significant push from a certain geographical area towards the latter part.

And I'm convinced the demographic data and ratios of the F12 design favor usage by the 55-75 kg crews alot more; especially when the F12 is a hiking boat rather then a singlehanded trapeze craft. This weight band is typically associated to 12-18 years olds and adult females c.q. bottom 60% of adult males.

I am really happy to hear from Gato that the expereinces so far have been promising, but I would love to know exactly the ages, weights and length of the people who have sailed her so far and see what percentage is truly a youth (kid). Not too mention the wind and water conditions. The age alone is not enough as some 10% of the worlds 12 year olds are above 55 kg and we all known Scandinavian people are the tallest in the world.


Now having said all this. I don't really care whether the F12 is used and promoted for youths (< 12 years) or not. Anything to keep them of the Laser dinghy and grow the ranks of cat sailors is a good thing.

I do however object strongly to promoting the F12 as exclusively youth oriented. I think Gato's experience that the parents were also after him for a F12 for themselvees as indicative. A F12 is a rather big toy and we all know how feeble the attention span of a youth can be. It is the parent that must justify the expenses and hassle of owning a F12. Being marketing savy means that it is alot smarter to include the parents in the F12 concept. Also for the youths as what youngster doesn't want to play being a grown up ?

I think the biggest mistake ever is to make a design exclusively for kids. It spells "training wheels" to them like nothing else. I remember that back in the day I was overjoyed when I got my first adult sized bicycle. It is a little too big for me but I soone grew into that. Which is another point with respect to F12's. Kids don't stay small for very long. If a design is optimized for < 12 years of age then most of them will outgrow the design in 2 to 4 years. For I really don't see many 8 year olds justify the purchase of a 3000 bucks F12. Note how 95% of the 8 year old kids (or younger) are shorter then 1 mtr and weight less then 35 kg. How would they right the craft ? How would they handle the rig even when on the trapeze they would match the power-to-weight and heeling-to-weight ratio of the 1-up F16 ?

I think it to be alot smarter to design the F12's in such a way that they are truly accessible to youths (if you lean that way) but don't spit them out as soon as they hit their teenage years because the hulls are under volumed.

The succes stories in both the Laser and splash/flash dinghy classes is that the youths get pulled into them at a young age but can stay there till way in their teens (possibly by exchanging the rigs for a smaller one). And Mom or Dad can take out the same boats for a ride using the some rig or the normal sized rig. This goes a long way in convincing Mom and Pop to lay down the money in purchasing the craft.

In short, "filling a niche" does not necessarily imply "being marketable" even when the reverse is true. Design for a niche that is too small or doesn't yet have their own purse is a design flaw. I think the Hobie product range for youths has proven that. Go anf take a look at their product range and see it you know any of these designs. http://www.hobie-cat.net/site_gb/?produits,produits It is the line-up on the lefts in red lettering. The only exception is the Hobie Wave but that boat is mostly sailed/raced by adults. Which give further weight to my proposal to at least ALSO cater for adults.

I also think there is another issue in the F12 class. If indeed we wanted a catamaran truly for youths then why are we fiddling about with single piece carbon rotating wing masts with spreaders, diamond wires, downhaul systems etc ? And not fully focussed on simple sleeved sails using glassfibre tubing for a mast and have only a kicking strap and mainsheet. The latter is heaps less expensive and 10 times more easy to ship. Right now the F12 is going the way of becoming the "A-cat for kids" ? An oxymoron if their ever is one.

I mean it the F12 is to be complete focussed on youths then marketability demands that it is dirt cheap to produce and even easier to transport. Right now the 6 mtr long mast that can not be broken down in smaller pieces is a serious road law infriction when it is car topped. At least in 80% of the developped world where there is enough money to buy a F12. How do I know ? Because I'm avoiding the police at all times when I car-top my non-collapsible 4.70 mtr tall landyachting / windsurfing masts. Most cars are only 3.50 mtr long overall. Having the mast stick out 1.25 mtr at the back and 1.25 mtr at the front will attract police attention for sure.

The "A-cat for kids" promises neither to be dirt cheap or easy (legally) transportable. Of course, if it is the same boat that Dad is using then the justification for getting the additional car trailer will be less of an obstacle. We all know that the difference between men and boys is the price of their toys.


Now summarizing the comments above. I say, lets get away from our focus of making the F12 "kids-only". It is neither a reasonable goal design wise nor smart market wise. Of course, doing a double "humm maybe" on these two points is a serious impediment to growing the F12's into a succesful class.

Lets expand the F12 concept to include all teenagers and small to medium adults. Seperate the class in a racing fleet below 12 years and above 12 year olds if we have too. Market the class to both fleets hard. If we are not getting the youths then at least we are attracting new adults to the cat racing scene and visa versa. Lets expand our market base that way and achieve larger turn-overs. The latter will reduce cost and grow fleets quicker which in turn means the F12 become progressively more attractive to new customers. INCLUDING YOUTHS.

Also there seems to be an adult based niche for these boats, many in this forum have said so themselves and also look at the Hobie wave class. These people y will provide " F12 beach heads" in various nations and regions from which the F12 class may grow internationally. Getting off the ground is the hardest part in any class. Being chavalier on that aspect is more then being "unwise". It may proof to be killing in the long run (ask Hobie corp with their youth boats) if we don't do that.

So get the marketabilty right for the F12 and then adjust the design so it does fill the desired niche for <12 year olds as well. The difference right now is just putting enough volume in the hulls. What is the penality in that ? From the F18 and F16 classes we already known that you can't really over do it with respect to hull volume. Too much volume is nowhere near as bad as too little hull volume. Now the < 12 kids won't notice some 3 % performance loss due to designing the hulls to max 150 kg displacement. They got more then enough power in that 7.00 sq. mtr. by 6 mtr rig to overcome it.

Wouter

150 kg displacement! At 120 kg it starts already to look a little bit poofy.

The difference is just 12% more width and 12% more height in the hulls below the water line.

And the Tabby isn't very poofy if you have seen the newest F18's like the Infusion and Hobie Wildcat.

Poofy is the new fashion !

Wouter


WOW ! I made a post under 4 phrases, did you see that !

Can't...read...whole...post, however I did skim over it.

My definition of a kid is under 16, so we have an overlap in our opinions there. Under 12's I would suggest sail the F12 2-up, it is too big a rig for a 40kg skipper on their own.

An interesting read...
http://www.optiworld.org/ioda-faq.html

Spot on again Ncik
Your right about the regional use's for the F12 Wouter and I would encourage you to keep promoting to the adults. For me the F12 is perfect for our club to get kids into cat sailing.
My 8yo can and doe’s sail an 11ft cat no worries when there’s not much wind, no waves and he’s closely supervised by adults at all times. He doesn’t go far but has a great time. My F12 is for my experienced 12yo girl to sail 1 or 2 up so will have the added benefit of a jib and traps. My 13yo already sails the Arrow 1 up with the jib. Don’t underestimate the ability of the normal kids out there sailing nor they’re apparent average weight (by definition there are hardly any on the average). Most of the youth attracted to this cat will have been sailing dinghy’s for a while and will feel quite safe to see how hard they can push it.
You can make a bigger and puffier with higher buoyancy version for the adults and I would encourage you to do it but you shouldn’t plan to tinker with the minimum class weight’s exc to make your version more viable to adults at the expense of the younger users. There is no better youth friendly cat available in the world at the moment because its super light, has the safety of a short light boom with high aspect rig, minimum controls, easy to make and repair, modern looking and can be adapted to suit different regions.
Well done to the designers that have put these kid cats together
I’ve started to assemble the DS12 with the kids and I think you can say its child play

Okay. So basically we have to decide what portion of the 16 year olds we still want to include in the F12's.

Here some demographic specs taken from the US center for Health statistics. US populace should be somewhere around the middle of the world. In general not very tall (like scandinavia) or vry short (like asia). This to provide some more scientific data to the discussion.

Boys 16 years
5% at or below 47.5 kg
50% at or below 62.5 kg
75% at or below 70.0 kg
90% at or below 77.5 kg
95% at or below 84.0 kg

Girls 16 years of age
5% at or below 42.5 kg
50% at or below 55.0 kg
75% at or below 62.5 kg
90% at or below 70.0 kg
95% at or below 77.5 kg

I restate (form earlier posts) that

Boys AND girls 12 years
5% at or below 30.0 kg
50% at or below 40.0 kg
75% at or below 47.5 kg
95% at or below 60.0 kg


So basically we have to decide what portion of the 16 year olds we still want to include in the F12's.


A few examples

If we want 82% of the 16 years olds to be in the competitive range then the F12 weight carrying ability needs to go up to at least 70 kg

If we want 63% (under 2/3rds) of the 16 years olds to be competitive then the F12 weight carrying ability needs to go up to at least 62.5 kg

If we want 50% of the doublehanded 12 year olds to be competitive (with careful combining of different crew weights) then the F12 carrying ability needs to go up to at least 80 kg. That while we "force" thje top 20% of this group to sail solo (they are above 50 kg and just entering the bottom weight range of the F12 when singlehanding)

Designing the F12 COMPETITIVE weight carrying ability up to 75 kg would allow us to include 94% of all 16 year olds but also 90% of of adult women and 67% of adult males (20 years).

If we copy the competitive range of the optimists, see link provide by Ncik, which is about 40-50 kg then less then boys=max10% + girls=max25% of the 16 year olds will be competitive. Resulting in just under 20% of this combined group being competitive. All others will have outgrown the 50 kg upper limit.



I have attached the demographics graphs for both boys and girls from 2-to-20 years of age. Women havse stopped growing by 20, while male may add some weight (but not length) up to 23 years of age. I propose using this data to fine tune the F12's.

Wouter

Looking over the data provided in the above post.

I think we see a situation developping where designing for the weight range of 50-75 kg is most smart.

We need the upper limit to be as high as at least 75kg to be able to carry 2 normal sized 12 year olds (80 kg would be better still). The same limit guarantees that 94% of the 16 year olds can still race the F12. Side advantage (marketing) is that the majority of parents can then also sail the F12.

The lower limit needs to be at least at 50kg to be able to start moving the top 20% of the 12 year olds into solo sailing the F12.

This 50-75 kg weight range will see the youths singlehanding from 20% at 12 to 94% at 16, the age range Ncik specifies as youths and as the target group for the F12.

If we drop the max weight to 65kg then 1/3rd of the 16 year olds will not be competitive anymore (compared to only 6% when the limit was at 75kg). The competitive participation level at 16 is dropping fast with each kg that is removed from the upper limit.

Personally, I see much reason to follow Luiz suggestion to split the fleet into two racing fleets. As in "below 60 kg" weight and "above 60 kg" weight. That should take care of the bulk od the performance inequality.

Wouter

I've read your post Jeff and I got a question about the following point.





How do you think that adding bouyancy to the hulls will bring the F12 out of reach of youths ?

I would agree with you, refering to "at the expensive of younger users", if I were proposing to increase sail area or something. But I'm not doing that.

I'm just proposing to increase the weight carrying ability of the F12 platform by adding a little more volume and freeboard to the hulls. And this will not have to add much weight at all to the craft. To put things in perspective; increasing the width and the depth (freeboard) of the hulls by 10% (keeping the length the same) should already upgrade the hulls from 120 max displacement to 145 kg max displacement. The difference between max 70 kg crew to max 95 kg crew. At the expensive of what ? 2.5 kg combined for both hulls. Adding only 1.25 kg combined leads to max 82.5 kg crews. The associated cost is pretty negligiable.

Gato is suggesting that he can make the current F12 hulls at 12.0-13.5 kg where the latter number is an actually measurement of his prototype hulls. That leaves 25 kg for everything else on the F12. If we are using carbon masts anyway then we don't need all those 25 kg to complete the craft at minimum class weight of 50 kg. In that case I say, use the difference to increase the volume of the hulls so we extent the weight range for the F12's (in chop etc). I mean it is better than adding pieces of lead right? It would surely improve the marketability of the F12 to the adults/parents.

Wouter

JeffS, It's relly nice to see somebody building instead of talking

If anybody wants to make performance comparisons; here some basic data concerning drag of a catamaran. Source ; MissNylex C-class catamaran research

Platform
Form resistance hulls : 15 % (sailing on one hull)
Skin friction hulls : 22 % (sailing on one hull)
rigging/fittings/beams/hulls : 11 % (parasitic drag / air drag)
Crew : 6 %

Sail related forces.
Centre boards : 21 %
Sails : 25 % (parasitic - form - induced = 1% - 8% - 16%)


By making the hull more volumous we would incur a small increase in skin friction drag for light sailors (youth). Form drag should see only a smaller penalty as the wider hull will also float higher in the water. Note how close to 50% of the total drag is totally related to sail forces that are unrelated to the volume enclosed in the hulls.

Roughly speaking increasing the width and height of the F12 underwater body by 5% (Upgrading max skipper weight from 70 kg to 82.5 kg) would increase hull related drag for the 70 kg skipper by a mere 1.5%.

A 10% increase in both dimensions would upgrade the max skipper weight from 60 kg to 82.5 kg (110 kg displacement versus 132.5 kg) and leads to only 2.5% more overall hull related drag for the 60 kg skipper.


That is the lesson that was learned in both the F18 and F16 classes; increasing hull volume is pretty costless as long as it does't push the ready-to-sail weight over the minimum class weight. Although the Viper F16 is proving that in the way of overall performance the latter is not much of a consideration as well. More a marketing disadvantage. However I feel we still have some leeway with respect to the ready-to-sail F12 weight and the F12 class minimum.

Wouter

Okay, I understand that this is solely intended as a funny remark.

However I still want to respond.

Too many times it appears that talking is considered a "dirty" endeavour. Now okay, I talk (write) too much. It is my job shall we say. As an academic I need to investigate the situation and formulate it correctly as to avoid the organisation from wasting resources on a wild goose chase. Especially one that could have been avoided with some analysis and talk before shooting off in all directions.

That is what I'm trying to do here.

Showing that we are needlessly limiting ourselves to a too narrowly defined F12 setup.

I hate to use the following example, but what would have happened if the F16 group only focussed on getting the singlehanded setup working properly instead of working hard to combining it with a viable 2-up setup ? I can guarantee everybody here that the "1-up + 2-up" capabilities is the biggest selling argument for the F16's. It is one of the big reasons the class has become a succes and grows everywhere.

I'm just trying to draw the attention to a similar potential with respect to the F12's. It could mean the difference between becoming succesful or fail. I kid you not !

Wouter

Spot on. If you trace the complete history of this "debate", back to youth development on the main forum, you'll find a repeating sentement amongst US sailors of...Why do we need another youth boat?

There was interest when this boat was heading in the direction of a platform capable of suporting a "light" adult. I have PM's from more than one American interested in building a prototype boat (at that time). I won a set of plans for a DS12 and have done nothing with them primarily because of the reduced weight carrying capacity. My target sailor was/is a 12yo girl who currently weighs 140 lbs. (63.3kg).

How much interest was shown when this was posted? I beleive the (or an) underlying concern is, what if my kid doesn't like sailing? Then what? I now have a "niche" boat that may be hard to get rid of.

I'm with Wouter on this one (no surprise). Open the range of usage up for the basic formula and it may be more a viable/marketable boat. Think more in lines of skegs vs. daggerboards, i.e. ease of use. Think more development of the unstayed rig, i.e. less time from cartop to water.

The Tabby looks nice BTW, and congratulations to those taking the initiative of actual building, continued design and development. Just thought I'd throw out why I've relegated myself to the sidelines on the F12.

(hijack off)

For me it's simple, there is nothing in the rules to forbit a fat cat, just get one designed and built. It would be a lot easier than to try to convince the existing designers and bulilders to do it for you.

and



How about this side view.

It was designed for 125 kg optimal displacement; this is not the same as MAX displacement. So the 50kg craft with a 75 kg skipper will have the optimal attitude in the water and have the optimal beam clearance. One that is the equal of the 5.00 mtr boats like the Nacra 500, Hobie Max and just a tad less then the F16's when all of these are sailed at 135kg crew weights. Its decks are only 250 mm wide for the 125 kg displacement. A 85 kg skipper will be equal to a 150 kg crew on any of these 5 mtr long boats. That is probably enough. I sailed the nacra 500 at 160 kg and it was fine.

I like this particular hull shape when opting for a skeg. The added benefit of the skeg is thatit takes only about 9 kg at the bow to lift the hulls up to roll the cat tracks under them. That is instead of 21 kg ! A huge difference for a youth boat I say. The skeg brings the fulcrum way forward and you'll notice that. The first mtr in front of the skeg will have an aluminum strip fixed to it. To cut down on keel wear. Of course the true hull will run its keel line in a curve from bow to stern just below the 2.70 measurement line. The skeg itself is just a 20 mm wide plate and protrudes further down.

What I need is a good method of producing such hulls but Gato is developing such a method with his foam plancking idea. That may just do the trick !

How about it John, too poofy ?

Wouter

And here an example of a similar type of hull with a skeg

This is a Nacra 500

The skeg is here smoothed into the hull shape but I suspect we can do the F12 hull shape as a daggerboard design and just omit the daggerboard trunks and inject a flat plate at the keel line. Make slots in the bulkheads and just laminate it in.

We may even do it in one go. Use the skeg to align the bulkheads.

Wouter

The market will decide what the class becomes.

My opinion is that it will not be everything to everyone, it will not be a small performance cat for small adults and a performance kids cat.

The small performance cat for small adults is a bloody tiny niche market if you ask me, and already has the hobie wave vying for those dollars and sailors. The performance kids cat is a currently untapped and potentially significant market, not only for business but also for introducing kids to sailing in general and cat sailing specifically.

You should build the DS12 and let your kid decide if she likes sailing. It is a worthwhile experience building a boat. Plus I see some strong movement in the class so I doubt you'll have a worthless boat at the end of it. Heck, build a Tabby if you want a boat that'll carry a bit more weight.

Regarding design issues, design it, promote it, put something specific on paper/on computer. There is a lot of leeway in the F12 concept, even for a small performance cat for small adults. The Tabby was designed on the cusp of the two weight ranges, not for this reason though, I just like the idea of a very full hullshape on cats.

Ncik, I will soon try to get you some better pics of the Tabby painted and all...

That is like two disagreeing generals saying to eachother, on the eve of a major battle, that each will do their own thing and let the end result determine who was right.

The typical end result of that analogy is of course that they will both loose and they will both have been wrong.

When you are not cooperating with eachother then you'll be much weaker then when you are.

Needless to say that after the battle there won't be enough survivors on the loosing side to regain the former combined strength.





The Hobie Wave has failed in area's outside of the USA. F12 still got a good shot at really becoming an international class.




That is wishful thinking in my opinion. The kids don't hold sufficiently large wallets or drivers license and I don't see any reason why we could expect major sales coming down the road with the way things are going now. That offer by a US producer has died for lack of interest and I don't think the rotomolded Vudu has met its threshold of committed sales yet. Even the concept of kit-building hasn't lifted off yet; although this is just another way of homebuilding anyway.

Lets not forget guys that we are already a few years down the road and Gato is the only at this time who is actually sailing an F12. And he is thinking about making a 14 footer for himself next.

Lots of potential ? Yeah, probably, but not much of that has been realized yet. At some time we have to put some rubber on the road and that means attracting COMMERCIAL BUILDERS. That is not happening yet.Lots of promises but no real breakthrough yet. We are going the way of the F14's rather then the F18's and F16's (who both had more then one commerical builder with boats sold within the year).




That is a mighty big gamble for most parents, if you ask me.

I will personally test the waters first on some second hand Optis or Laser 4.7's if it comes to that. And that is just what we wanted to prevent with the F12.




Yeah, well "a bit" is just not enough.

When I'm a dollar short it won't help much if you thrown me a dime.




This is the same "two generals" theme but with different wording.

I 'm not going to invest resources on a "maybe", that is if I would have them at this time (note I already did a thing like that with the F16's; the money runs out sometime).

This is a thing we have to do all together or we can just forget about it.

But what I don't understand really is why you would the following in a single post.





Either there is potential for it (light to medium adults) or there isn't.

The real issue is whether we ALL TOGETHER build and promote the F12 class as a versatile concept or completely gamble everything on the youths.

I'm out if it is the last and thus leaving only the downunder guys and Gato still in the mix. The Taipan was killed internationally by the same playbook.

With the current downturn in economy I choose versatility overf specialization any day. I think Darwin agrees with me here. Or in sailor terms; there is a reason why we see seagulls everywhere around the globe but not many kolibri's. It may not be the prettiest bird but it sure as hell is succesful.

Or if you will, that Marstom M18 (A-cat+spi) at 80 kg was a bloody nice concept, but marketing wise it failed disasterously when compared to the F16's. That is what I'm getting it. We took the 25 kg hit but gained a pathway to attracting commercial builders and to success. And lets not get started on the 180 kg F18's vs 120 kg M20's as an example to illustrate the same point.

Wouter

I'm deffenetly not abandoning the F12. I will build a 14 feet cat and maybe a 25 feet tri, but that has nothing to do with the F12:s,
The case is that Wouter wants somebody to design (and almost build) a F12 cat that he can sit on himself.

Yes, that is the standard accusation that is thrown at me regulary.

Still, it doesn't adress the points I made in my earlier postings about marketability and dare I say viability.

It is also a bit weird as an accusation, as I think I'm the only one here who has actually founded, build and grown a viable international sailing class once before. Not to mention building a class complient prototype craft that I can actually "sit on myself".

I'm not making these comments because I'm somehow lazy or whatever. Truly, I'm making them because in my opinion the F12 class appears to be failing and there is still time to do something about it.


But I think that I've said my piece and not much more is to be expected from repeating points made earlier.

So I think I'll leave it at that.

Thanks for answer my questions Gato and I look forward to looking at the building pics of your future building plans.

Wouter

Sweet! Thanks Gato.

The class will be whatever it decides it wants to be, but I do suspect it will become the kids cat.

[quote=_flatlander
There was interest when this boat was heading in the direction of a platform capable of suporting a "light" adult. I have PM's from more than one American interested in building a prototype boat (at that time). I won a set of plans for a DS12 and have done nothing with them primarily because of the reduced weight carrying capacity. My target sailor was/is a 12yo girl who currently weighs 140 lbs. (63.3kg).
How much interest was shown when this was posted? I beleive the (or an) underlying concern is, what if my kid doesn't like sailing? Then what? I now have a "niche" boat that may be hard to get rid of.
[/quote]
John it'd be great to build a higher volume F12 if you want to, it would just be another version that can compete under the same rules. The F12 can be altered to suit any use in any region of the world within the very loose rules.
The F12 will easily carry your daughter and a crew or you and your daughter for fun, don't look too much at the figures trotted out but try a small cat yourself if you can. I sail on my lads 11ft Arafura with him and posted a video on this forum of us sailing you can clearly see me jump on it with both of us weighing 140kg on the same side and it not looking unstable or risky. The Arafura doesn't have the bouyancy of any of the F12's. My daughter that sails the F12 is 59kg and she will have a crew taking it to 100+ kg. The technical figures for optimising the F12's is all fine but does it really matter that your 1 inch lower in the water and by using that weight correctly very safe in nearly any weather.
Any adult can jump on this cat and have fun let alone your daughter and a friend.
Wouter you did well to adapt the Taipan 4.9 design into a class thats world wide and if your success with the formula continues you will probably have as many F16's sailing in 5 years as there were Taipan 4.9's sailing 5 years ago. Your input is valuable but its not the same as building a completely new class of cat for kids, now that we have the kids covered It'd be great if you can adapt one of the designs or come up with a new one to suit your regions needs or heavier adults that want to sail it.
regards

I hate to say it but yes being 1 inch lower in the water can be very significant. Of course the boat will never sink when you pile the weight on but it will start to display other undesireable behavior. Examples are ; wave slapping with the back beam (BIM A-cats, older F18HT's, Nacra 500 with lots of weight) or taking the chop on the mainbeam (Taipan 4.9 when 2-up and heavy). The boat can also get very weight sensitive and allow backward flipping when tacking (Hobie 16). Or bad dive resistance.

Interestingly enough all these issue are associated with too little volume in the hulls, never with too much volume. That is one of the reason for my earlier statement that it is relative hard to overdo it with respect to volume.

Wouter

Yes, I understand that the situation is like that.

Will leave it at that or further explore actually building something like this


Regards,

Wouter

The Tabby as The DS12 can take weight up to 70-75 kg depending on how much weigth you build into the boat (displacement 110-120kg)
The funny thing is that some of the people arguing for bigger min weight for the cat (60kg) also wants the boat to be able to carry more weight.

Yes, I admit to that being true !

And I thank you as you have still been to kind to me as I also argued for using aluminium components for dolphin strikerless beamsa and an unstayed mast using commerical alu tubing, Not too forget argueing for rotomolded hulls (possibly using twinex). All things that add weight to the design.

So yes, I do think it to be fair that I'm placed in the low-tech and heavier corner. Not argueing about that I'm afraid.



But on a different topic.

Have you weighted the new DS mast section already ?

I know the Pixie mast (timber/glass) you made came out at 8.9 kg. ; for I guess 6.5 mtr length.

The (strongest and stiffest) aluminium unstayed mast from tubing that I'm looking at (if it were to be extended to 6.5 mtr length) would come out at 9.85 kg with about 20% less moment of enertia with respect to forward swing during diving of the platform; so it is not too far off the Pixie mast (timber/glass) at all.

Wouter

The ready mast for the DS12 (Ply/carbon) all fittings(carbon)forestay and shrouds (dyneema) has a total weight of 6kg (not weighted on a precision instrument)for 5.8 m spar.
Total cost under 300€.
Work about 8 hours
I am about to start one in Foam/carbon just for fun.

I have nothing against alumasts or unstayed rigs, what I did was the cheapest solution I could find where I live.

Ohh please, don't think I have any objections. I think it is very entlightening what you are doing with the masts and hull construction. No need to develop the unstayed rigs, we already know the data related to those.

You are doing new stuff which is many times more valuable.

And thanks for the new data.

Again, for the other designers out there. The 5.8 mtr equivalent (unstayed alu from plain tubing) would come out at 8.5 kg. So a 2.5 kg loss to the unstayed alu mast in that situation. And it will feel the same when accelerating or decelerating. The unstayed rig just has its weight lower in the mast, thus resulting in equality between the two masts. That is good to know as you already state that the dive recovery of the DS12 and Tabby were acceptable.





Now THAT is very interesting.

Also for the F16's. I'm not expecting the foam to add more then about 1.5 kg to the mast weight (using 5 mm thick strips). And we already know that a viable carbon mast without foam comes in at 10 kg when bare. So 12 kg for the bare F16 mast section should be viable; arriving at sub 15kg for the fully fitted mast. With a tip weight a tad above the class minimum of 6kg (alu F16 mast have about 7.5 kg, that is when the supplier ships the right one). And it is homebuildable !

If you can perfect this building method then you really have something very interesting.

So yes, I'll be keeping a close eye on your webpage.

Wouter

That looks good Wouter, and I don't mind the freestanding rig support concept. Not sure about skegs, but appendages are a very personal matter if not one design.

Thanks Ncik,

I'm also a bit conflicted about the skegs.

I know about the various advantages of them especially in the ease of use, low cost and ease of production. Also they are a great feature when gettin in and out through the surf; a thing that is very difficult with a dinghy like the laser and still difficult with a boarded cat. However, I personally would love to squeeze every bit of performance out of the basic concept that I can and of course the kids don't seem to mind having them in the various dinghy classes.

If it is any concellation; the design still allows for both although it will be best for either to have different hull shapes.

Other features of the design are of course that it has not martingale (dolphinstriker) as it simple doesn't need one in the slightest. This is the beauty of the presented mast support arrangement the trampoline (tension) induced forces largely cancel the rig forces when it comes to the beams. This will allow even very low grade alu alloys to be used like the T4 tempers. Only exception is of course the bottom section of the mast.

The bows take no rig loads so it should be possible to build these light.

The basic design is ready although I need some way of perfecting the hullshape. I fear only building it will do that. Anyway we'll see about that.

Wouter

That's a tough decision to make. A few cruising cats use only one daggerboard and John Shuttleworth says that the loss is 1% upwind.
I can think of other alternatives as well: one board in the middle (under the mast base), external pivoting boards (like old Dutch boats), external daggerboards, pivoting daggerboards...

Well that is true but I believe that it is better to go all the way into one direction in stead of doing something half. So for me it is either 2 daggerboards or a pair of skegs. pivoting centre boards have no advantage what so ever, so they are out anyway.

In my design their are two options that I serious consider

-1- Two skegs and a hull shape that is much like the Taipan 4.9 or the Nacra F18 (not inter 18 or infusion or newer F16's / F18's)

-2- Two daggerboards with aspect ratio of 3 (no need to go overboard here, this is efficient enough).


Option 2 basically means a wetted length of 0.45 mtr and board width of 0.15 meter. This should give the craft a draft of at max 0.60 mtr with the boards fully down. The rudders will stick almost as deep so there is not much to be gained in shallow water ability anyway. 0.6 mtr deep water is just above the knee and that is something whole different from a F18 doing a draft of 1.20 mtr (ribcage height) Or even the Laser dinghy at 0.75+ mtr draft with the board down. Note that the Laser dinghy (in my view the main competition) has a board with aspect ratio of only 2.

The overall length of the daggerboards will then be 0.95 mtr and it will have of course a 10% board thickness.

The difference in performance around the course between a good skeg design and a normal daggerboard design is about 2 to 3%. This may be a bit more when comparing the newest high aspect board that also gybe to the skegs, but nevertheless the difference is small. I'm more concerned about the image the design will present. And if the dinghies have boards then I don't want the catamaran alternative to have "training wheels"

Wouter

Makes sense to me.
Note that a pivoting daggerboard should not be confused with a centreboard. It is a hybrid between a daggerboard and centreboard that has been used in fun boards (windsurfers) for years.

The Arrow's and Arafura cadets have pivoting centreboards, the big advantage is that its easy to pull down or up and cleat, with a bit of shockcord in the system its fool proof for breakage. The downside is the frame thats needed to handle the board, it makes it awkward to move around within 2ft of the mast.
regards

One centreboard in the middle or one in each hull?

Just playing a bit here; was thinking of Gato's pictures during the trip when he was sailing downwind. Seemed like things went a bit too slow.

The size of the depicted asymmetric is 8.9 sq. mtr. but I think 8.5 sq.mtr will be a more realistic size. The depicted pole length is 2.0 mtr and quite short for the given hull length.

Wouter

How big will the mast need to be?

The Arrow (14ft) and Arafura (11ft) have a single central centreboard. It works quite well but it is a pain in light winds when you want to sit in and forward near the mast, the frames for the board get in the way.

Do you think the stayless mast will be able to handle the kite? What about trapeze? That would be cool if it could.

Think you said the kids would already go too fast and get too far from the beach with 15knots, and you are still thinking of more power?

Weren't you also they guy that said that I wanted a boat for myself that I could sit on ? I thought that if I get plastered with that accusation anyway, that I might as well go all the way ! (A little joke here)

But seriously, I never intended the boat to be for kids (<12 years) as you remember, but rather for teenagers (>12). And, if the young on the Hobie Dragoon can handle spi then the teenagers on F12 can surely do so too. Although, it must be said that these Dragoon youth are doublehanding. Ohh, it just occured to me that they can double hand on my F12 as well with the weight specs I have on paper. Additionally, the reach will remain the fastest leg, so if any kid can do 15 knots there (and the others are okay with that) then why put on the breaks for the (slower) downwind legs ?


Anyway, I'm looking at the spi only as an option (again for the parents etc), I'm not intending it as a a racing component for youths (10-14 years) if the class picks up in that target group.

I have been thinking about the Water Tribe type events and your own trip in the archipelago. In those situations a spinnaker will surely be a welcome addition. It also acts to keep the design interesting when the owners get older and allows for more market for the builders. The latter is important to improve on their economic viability.

That is basically the idea behind it.

Wouter

The same size it is now.





Yes and yes.


Uhhmm, may I point out something here ?

I have a feeling that many of us here are evaluating the different design features with their gut rather the contents of their sculls. I mean that if the sheeting system can put the leech under 150 kg of tension and do so on a 2 mtr long boom then why does anyone think that a spinnaker luff tension or a trapeze wire are a problem for the same mast design ?

To give everybody an idea of what a commericially bought 250 Euro unstayed aluminium mast can handle I present the following example. On a class 5 landyacht (5.5 sq. mtr. sail on a 5.5 mtr mast), the lower mast section is 50 mm in outer diameter and it handles a 5:1 sheet system fitted to boom about 1 mtr away from the mast. When combined with the heeling loads this means the unstayed mast can handle about 250 kgm bending loads. The sleeved sail design handles in this case a max luff tension of 110 kg and a max leach tension of about 140 kg and is as flat as a board.

My F12, even with a 3:1 sheet system at the leech and a 75 kg skipper, will only put the mast under 294 kgm bending loads. An increase of only 18% and still well within the safety margin for the mast.


The luff tension on a 8.5 sq. mtr spi will not get anyway near 150 kg and neither will a man on the wire. But more importantly the spi luff tension and mainsail leech tension will largely cancel on another and the sideways loading that the spi+mainsail can put on the mast on the downwind is always less then the load the mainsail can generate when sailing close hauled. That is why we don't double trapeze downwind on normal cats. This means that a mast design that works upwind can always handle a spinnaker. The same cancellation principle applies to a trapeze (here the trapeze load and sail force load largely cancel one another)

One reason I opposed trapeze wires is that the proposed platform and rig don't really need it. It is already a wide boat for the rig. It compares to a 2.90 mtr wide F18 (which are now only 2.60 mtr wide). When taking the lower heeling moments of the smaller rig into account then 185 kgm (or a 67 kg skipper on a 50 kg F12) will already achieve parity with that design when hiking. A skipper of 45 kg would do so when on the trapeze, but I personally focus more an having such light crews team up for the F12 rather then solo sailing them. The other reason is that I want to avoid the cost of the trapeze gear (like harnasses that kids quickly grow out of) as well as the hassle associated with it, like puncturing the hulls with the hook. The reasons for not supporting a trapeze were however never technical in nature, the unstayed mast can take the loads associated with it. More of problem will be how the sail will respond under mast flexing. It may become hard to control properly, but only just giving it a try may give the answer there. The estimates however, suggest it may still be acceptable.

Personally, I like the unstayed mast setup idea with a spinnaker. Note that there are no side stays or forestay and the spi can gybe very easily in front of the mast. It can be a very clean set up altogether. The very small spi area may also allow using cheap non-ratcheting blocks. The spi pole is just the same section as the boom (same length etc) with three lines to support it. That leaves only the spi sail itself as the major cost, but with what a performance gain !

Wouter

Wouter,

If you want a spinaker halyard and two trapeze lines to work with a sleeved main, it will be necessary to attach the three of them to the mast after it is already inside the mainsail sleeve. It can be done if the main is like the Laser, without halyard.

In this case one alternative would be a furled spi or screacher without halyard, with its top swivel attached directly to the mast. The spi/screacher would be furled for upwind sailing. Maybe its foot could be attached to a forward bridle instead of more complex pole?

Considering the tensions the leech of an unstayed rig will see anyway I think we can simply attach the turning block for the spi halyard directly the sleeve itself. It will need to have a local reinforcement there and probably a strap inside the sleeve.

An alternative is to just have an opening in the front part of the sleeve and have an eye strap protrude through it on which the turning block is mounted.

A third alternative is to go for a mast top spinnaker and that is not a problem for a mast that is unstayed already. If we do that then this F12 will be monster downwind boat because that will increase the sail area by 2.5 sq. mtr. to a total of 11 sq. mtr. You'll be beating F18's on the downwind legs !

Personally, I like the block-stitched-sleeve and internal trap the best. Simple, cheap and doesn't affect the capabilities of the unstayed rig in any when the spin is not fitted (as in complete 360 weather vaning)

Wouter

I'm personally not thinking about any trapeze lines on this design. If we need more righting moment then I rather choose to make the boat wider. However, I don't think we need to go beyond 2.0 mtr width anyway.





While it is possible to make the sleeved sail "hoistable" by giving it a zippered sleeve, I don't favor that solution. I don't think it is needed as the sail can weathervane 360 around the mast as it is anyway. So there is no safety issue involved. Additionally, zippers are expensive and wear down quicker over time then the sail itself.

If ever the rig needs to come off during a waterborn rescue then one can simply pull the sail off from the top. Hell, demasting the unstayed rig in the same manner will be viable as well. Unhook the support tubes and have the sail fall forward in the water between the bows. Unhook the mast foot and then slide the bottom section out of the sleeve and work your way up the mast that way while pulling it more and more on the boat and rolling the sail around the boom. The top mast section will then be slid out from the top. Rigging the boat up on the water will be the same procedure in reverse. I don't think any of the stayed rigs can mimic something like this. And ohh, the support tubes slide up and down when the mast moves forward or backwards and thus guide the mast in the sideways direction during any of this. It will also be possible to have the mast fall back onto the boat after unhooking the boom. Again the support tubes will double act as a back rest to the mast (while rotating around their supports on the hull. Hell the sleeved rig can even be folded up like that. Just slide the upper section out of the bottom section and fold it along side the lower section. This package will then only protrude some 0.75 mtr past the sterns and about 0.5 mtr in front of the mainbeam while the lower section stays attached to the mainbeam.

We can even use the spi halyard as a support line during lowering or raising of the rig. The option is many and I'm really beginning to appreciated this unstayed rig solution.


We don't use halyards on the unstayed rig on landyachts and I don't see any reason to do so on the F12 when using the same setup.

Wouter

A screacher puts alot higher loads on the components like mast and bows. It is basically an oversized jib and needs comparable luff tension to work well. A furling asymmetric spinnaker could be possible though.

Personally I think the bridle+pole is the simpler solution then any pole-less bridle arrangement as seen on for example the Swell Shadow. Also choosing either makes a HUGE difference in the max attainable spi area. It can easily make the difference between a 8.5 sq. mtr spi and a 5.0 sq. mtr spi.

The simplest solution will however be a symmetic spinnaker (no pole or bridles) and that one can easily be a mast top spinnaker as well due to the very low loads associated with it.

Wouter

Trapeze and spi halyard at the mast top would work, especially with a ram vang instead of a traveller.
A topmast asymetric would be big, but a bridle or shorter pole would bring the area back to normal.
The pole takes only longitudinal (compression) loads, while the bridles take the lateral ones. If the pole isn't longer than the bow, the effort in the bridles should be the same with or without pole.

While I'm not designing to include a trapeze, I'm sure one can be fitted nevertheless. No components will fail but I also make no guarantees that the sail shape or sailing behavior will be optimal. I feel that I can about guarentee that with the asymmetric spinnaker.



About 12.5 sq. mtr. I think ; if we maximize it.





You overlook the sheet and tack halyard loads here; the ones that pull the tack the spi sail and therefore any bridles backward. Ergo one can not simply remove the pole (even if it did not go past the bows) and assume the bridles will see the same laods or even stay in the same place.

The Swell Shadow catamaran has a pole less design but needs an additional line coming of the forestay (which are fitted to the bows in this case) to stabilize the spi bridle. See the attached picture. My design doesn't have a fore stay and adding one is more complex then simply adding a spi pole, which in my design is incidently the same as the mainsail boom. Not having a forestay reduces the stresses placed on the bows and allows for lighter and simpler construction of the hulls. It is also one thing less to pay for or worry about.

This pole-less setup will pull the spi bridle well back from the bow, closing off the opening between the spi sail luff and the mainsail luff. The end result is a much reduced overall sail area for the spi; more like at max 5 sq. mtr. And lets not to forget the web of lines on the front of the boat. Neither looks nice or is it easy to rig. The pole setup is better in the achievable area, in the spi-to-mainsail slot and in construction.

Wouter

Understood.
Your are probably going for a poled narrow furling asymetrical hoisted to the mast top. A tall spi requires more time to douse and a narrow spi furls really fast. The narrow spi is less bulky when furled than a wide spi, so it has less windage when the spi is not lowered.

Actually, I'm currently "investicating" teh setup as depicted earlier. That means a non-mast-top asymmetric spinnaker on a shortened pole. I have not decided towards either the furling option or "retrieved" option, but I do know this. A spinnaker of 8.5 sq. mtr. size is easily set and retrieved by hand even without a snuffer system. The sail is so small that only two swings with the arms is enough to pack it into a bundle before you. Windward retrievals by hand are easy that way as well. There is just so little load involved that a teenager can simply overpower it even in strong breezes. With the windward douce the spi sail slides down the mast and mainsail when the halyard is released.

I'm actually thinking about going the old fashion way with this spi meaning no suffer system at all. Cheaper and simpler, while noting this is viable for a spinnaker this small. I know that by experience. And of course, the spi is an option as this moment not intended for any youth class racing. More for recreational sailing like the coastal trips as Gato has done or for mum / dad to have some fun in a light wind day.

The none mast-top aspect of the current situation has a side benefit that I haven't disclosed at this time yet. But let me put it this way. It interacts nicely with another design feature of the mast avoiding the need for any additional hardware while still being able to transmit a good portion of the load to the mast directly (and not via the sail).

This makes the spinnaker as an aftermarket option/upgrade more marketable.

I'm actually designing this craft more and more along the lines of "Bloody simple, but effective". Sort of like using the boom as the spi pole as well.

But other then that, the depicted spi is very similar to the ones used already on spi boats and that means that we can lock in directly into to the experience about what makes a good spi design. Make it work first time around, that sort of thing.

Wouter

Hi Wouter,

I like the direction this is heading, ie. simple and effective. I like the idea of the additional volume to give better load carrying capacity, cos at the end of the day I want something my kids can flog around a race course on, but also like the idea I can jump on, and have some fun. Very much like the self supporting rig with option for kite turning block sewn into the front of the sock.

My only comment (very much personal preference) stick with center boards, and not skegs. I think you hit the nail on the head, it will be more appealling to the teens.

Look forward to seeing your design progress. I'll be moving country soon, but will be going to a place where beaches and sailing are both plentyful, so look forward to potentially putting something like this on the water.

Cheers.

Thanks Ross,

Thanks for your support.




I understand this line of reasoning very well. It is actually not a big issue to do both (leaving the choice to the owner), the only worry there is that it may fraction the organisation or class formed around this boat. Mostly, because a good skeg hull is really not that similar to a good hull shape when fitted with daggers.

All the other bits will be the same however.

Anyway keep an eye on this forum and you'll be kept updated.

If anybody else wants to weight in on the skeg vs daggerboard choice then please do so now.

Wouter

All other F12s have boards, so...

- A boat to win races against them requires boards. In this case go all the way and use bruce foils and rudder foils like the new Hydroptere. Note that their foils are not dagger style, they are external and the board pivots up and down.

- A boat to be the simplest option should not have the added complexity of daggerboards.

- A boat to be both faster and simpler will require a new approach/solution. I wonder if Hydroptere's external pivoting foils are simpler to use than a simple daggerboard in the F12 scale? They could be. Also, they could be made to work also in the vertical position, rendering the central daggerboard unnecessary.

Yes, but all the other F12's have fully stayed rigs that can't be broken down in smaller sections either. And of course smaller hull volumes.

I'm not sure whether my F12 with compare closely to the others even when fitted with daggerboards.

So this is not a convincing reason in my personal opinion.




Yeah, this consideration is weighting very heavily in my judgement as well.


Actually, on the reach and downwind legs the skegs often proof to be the better option when compared to daggerboards. The disadvantage is too be found on the upwind leg but only when there is sufficient boat speed. In light winds, you'll be surprised how well skegs perform, even upwind.

So is the hit on the upwind legs in winds over say 8 knots worth the additional complexity and expenses ?

I personally dare not give a straight answer to that question, but for the F12 design I'm leaning towards the skegs.

It is just so much simpler (probably lighter), cheaper and the difference is very small or the region where you'll notice any performance hit the most, in light airs.

I also think that skegs really make the design attractive to resorts, novices and owners looking to do day trips along a rugged shore line. They sure as hell make sailing in the surf alot easier and practical.

Wouter

Hi Wouter,

As I have said previously, I very much like the direction your design is taking, with exception of the skegs. Maybe you would consider an option of either.

Cheers

Well, this is basically the last outstanding issue.

All others are at best further refinement after having gained experience with a prototype.

The big issue is of course that an optimal skeg hull is significantly different from a daggerboard hull design. Now it is very much possible to take the skeg hull design, remove the skeg and install a daggerboard well. THAT is not the issue, it is just that that particular hull is not expected to show a significant performance increase. Such a things would require a whole reshaping of the hull. It is the same the other way around although the performance loss when fitting a modern round keel hull shape with a skeg is a pretty bad choice performance wise. You'll need to fit a very large skeg then as the hulls don't do much in the side ways resistance on these boat. This is evidenced by how much sideways these sail when no boards are set.

So "switching over" does not hold much promise; it is better to make a decision to go one way and fully optimized that. This will also be less confusing to the intended customer base. So marketing wise one really doesn't want to come out with two versions.


Ross, may I pester you with one more question ?

What is it that you personally expect from fitting daggerboards ? Or what it is that you specifically do not like about the skegs.

I ask this as I want to fully understand the situation. It is not intended in anyway as an argument. I just what to be further entlightend before a decision is made either way.

Many thanks in advance.

Wouter

Hi Wouter,

Happy to answer your question. It is actually for one of the reasons you favour the skeg - I do not want to build a surf/resort beach cat. I want to build a sexy looking (contemporty design), reasonably well performing 12 foot cat. Not suggesting for a moment that a skegged cat does not perform well, but for me it is really more about what the boat represents. Do kids want to jump on a boat that has skegs, or do they want to jump on a boat, and keep sailing it season on season, that is similar in concept and style to their parents A, F18, F16, etc.

Once again only my humble opinion, and maybe I'm contradicting myself by being concerned by this when the rig is completely different, however for me, the rig seems to be a logical step forward, while fitting skegs feels like to step towards a surf cat.

I have one other question for you. On this forum there has been a bit of talk about possibly fitting a jib to some of the designs to promote two up kids sailing. I assume the inherent flex in an unstayed mast would mean that it would be difficult to maintain jib luff tension, making a jib pointless in this situation. Is this how you see it?

Cheers.

Indeed, the is the exact same worry I have as well. Skegs can be made to work well technically, no real issues there, but aestetically or from a marketing point of view they have the close association to "training wheels".

Thanks for your answer.






Well, as long as there is leech tension, there will also be forestay tension. An unstayed mast will be less "stable" with respect to this but it probably can be made to work well enough on a boat of this size (sails of this size).

However, despite the fact that I'm a believer in the sloop rig for boats like the Nacra 500, F16's and F18's I'm not a supporter of sloop rigs on the F12's. I think these have unacceptable disadvantages for the F12's such as :

-1- They load up the bows requiring heavier construction
-2- Require bridles that need local reinforcements in the bow
-3- Require at least a forestay and a hound fitting on the mast.
-4- Dumping the mainsheet on the unstayed rig will see the forestay go slack and have the jib pump (possibly violantly)
-5- Add significantly more cost to the boat then sail area.
-6- Jibs flap about in strong winds making them harder to rig and scaring novice sailors.
-7- A spinnaker will do more for overall performance and similar costs

So I think rigging a jib on an unstayed mast can be made to work reasonably (although not really well) I think this so-so characteristic combined with the above points make F12 jibs unattractive. It is also just not the natural thing to do with an unstayed rig either. Additionally, adding a jib typically increases heeling and pitching force by some 15% while adding 25% is overal area and drive (roughly speaking). For the F12's I think adding 15% area to the mainsail is a better choice especially when the craft is also fitted with an asymmetric spi. It will feel as the same craft in the way of pitching and heeling and only lack 10% drive upwind while more then just compensating for that loss by increased downwind performance.

I also think the the spi to be more in line with the F16's and F18, and I think it will be more enjoyed by the owners c.q. their kids. More in line with the hot dinghies like the 29er as well. I do believe that far more 2-up 12 year old crews will sail the F12 then 1-up 12 year olds. I envision the crew working the mainsail upwind and the spinnaker on the downwind with the skipper steering and trimming. I see no particular advantage in adding a jib to that mix. And IF a trapeze is added for these 2-up crews then adding more heeling moment (as required then) is best done by adding mainsail area / mast length.

I trust this answers your question.

Wouter

Thank Wouter.

Clear for me. Look forward to following your design as it progresses, and with additional volume, would be my pick to build so far.

Cheers

Just a note in support of Wouter's design direction. I like the "Keep It Simple, Stupid" approach combined with the target audience adaptability (think Laser). The boat with its sleeved mainsail is something of a paradigm shift, which may be harder for us "Insiders" to accept than it would ever be for the potential audience that is "out there". Skegs could be marketed as a major safety / durability / ease of use benefit(esp. to outsiders, that is new entrants to cat sailing), not as training wheels (insider thinking). I see this concept as having the potential to do what the windsurfer did in the early '80s.
I sure wish I had the time and money to invest in this... I'll at least be keeping a close eye on these developments.
Dennis

Wouter... Can you give us an indication of what the theoretical top speed ( or time around the race course) difference would be between a 1.9 m X 3.8 m cat VS a 2.14 X 4.3 meter cat?

Assuming the weight is the same (or within a few percent) and the rig style is the same with a proportionately larger sale for the 4.3m cat...and also would be nice to know with the exact same size rig.

There are a lot of variables that could color this scenario that I don’t want to muddy the water with. You have been suggesting an adult F-12, which makes perfect sense to me as well….others here are saying they would want to go up to a 14’ hull length for an adult “spur of the moment” cat. In general term, what kind of performance increase (percentage) would be gained by adding .5 meters in length?

I know there is a world of difference between Darrel’s A&O F-14 and the F-12 that has been under discussion for adult after work sailing …that’s given…what I am asking for….apples to apples how much is .5 meters going to help? I have a Styrofoam hull/plug shaped out right now at 4.3 m and just looking at it full size it doesn’t look like shorting it .5 meters would make much difference at all. What is your take on it from an engineering stand point? As numbers seldom, if ever lie.

Thanks for the info.

If you want a god example of the foam construction method John & Ian Lindahl have used on his last 3 boats click here

In an update on other stuff, not sure that the original round bilge design is going to make it to production anymore....as with most of the planet, the builder has money issues.
That said, I have been working (very very sporadically) on another F12 design, no builder or customer in mind, more or less for my own pleasure. This is not being offered, nor will it be available to anyone anytime soon....the attached pics are just eye candy.
Cheers
RG

A few more pics, this time wave modelling...this is at about 9 knots with a little leeway

This lot are pressures and wave heights.

Thank you suggest, but good things to come.

Forgot to mention that all hydro's pics are at 100kg displacement, but the hull is capable of carrying 135kg
cheers
RG

Two quickies

1:
What is your philosophy on how to design the hullform for wave handling (if that is something you feel like sharing). I noticed that your modelling is all done in flat water which I assume is a good starting point for optimization. But wave action changes "everything", or??

2:
What software are you using (I assume something really expensive, and I ask not becouse I want to design a boat becouse I am curious).



The Lindahl build looks really good! Much easier than our strip-plank project. Only thing I dont get is how they fit the trampoline to the hulls.

On the LR3 John used the little tool in the first pic to create the indentation, the final attach looked like what you see in the 2nd pic.

Whether the hull is in flat water or in waves, shapes are driven by drag. Software that can handle waves like Fine Marine / Numeca is hugely expensive and requires an expensive computer to run it also, so we had to come up with another solution. The previous pic's can be generated on a case by case basis in about 10-15 minutes on a laptop, and enough data points for a VPP can be generated overnight, so this capability allows you to look at a lot hull shape variations very quickly which ultimately means you spend 3-5 times the amount of time designing a shape because you can play with so many variables and have an idea of what the consequences of any particular change is. This software is not available commercially at this time, but maybe in the future.

So the steel pin stay in there and he sands + adds some cloth on top of it. Neat! But looks a bit work intensive. Will unfortunately not work as well for us on our strip plank hulls + ply decks.


Spending time on the computer is OK, if some surprises can be avoided. And you dont have to do all that sanding

Thanks for a good reply.

Sorry to hear that.
Meanwhile I just sold the big tri (see avatar) and will probably look for a new project in a few months. Keep in touch.

Do you have closer view of the finished product...bit hard for me to tell what kind of impression the "tool" formed from that far away....while you are at it do you have another picture of the "tool" before it is embedded? Interesting method, just trying to get a better perspective on what I am looking at... thank you...

sorry,don't have other pic's, but its essentially a round peg with a stainless cross piece that leaves an indentation. After it sets you insert a stainless pin and carbon over it all, fill, sand and fair....quite a lot of work. It would be easier to insert a wooden block inside and epoxy and screw in some padeyes.

What have you really