Good. I think trying to design a boat with public input has to be almost impossible, whether for children or for adults, because 20 different people are going to have 20 different ideas and opinions. It's sort of like trying to write a song by committee.

<**** argument there.

Grob, maybe I missed it somewhere, but how long is your design?

12ft

Gareth

Okay now we are getting back into the science of things. Great !





My hulls are

3.66 (12 feet)

250 mm wide
458 mm tall
265 liters volume per hull.

Surface area of hull including bulkheads is 5.038 dsq. mtr. (this includes only 2 ply bulkheads under the beams with a combined area of 0.128 sq. mtr.

Freeboard when sailed by 65 kg crew (65 kg platform) is 458-(188 + 58) mm = 212 mm and I don't want to have less then this as freeboard. I know this from experience on my Taipan that also has its hulls at 450 mm height at max point.


So the question is where do you "loose" 5.038 - 0.128 - 4.15 = 0.76 sq. mtr. surface area per hull ?

From the picture it appears you can only win this by having the keel panel angled upwards at a relatively great angle, but this till really decrease the freeboard when sailing on one hull.



My 3.90 mtr hull (12'10")

236 mm wide
455 mm tall
265 liters volume per hull.

Surface area of hull including bulkheads is 5.214 dsq. mtr. (this includes only 2 ply bulkheads under the beams with a combined area of 0.133 sq. mtr.

Freeboard when sailed by 65 kg crew (65 kg platform) is 455-(189+55) mm = 211 mm and again I don't want to have less then this as freeboard.



As you can see the difference is surface area PER HULL between the two boats is 5.214-5.038 = 0.176 = 3.5 % When done in 4 mm ply this causes a weight difference of 0.45 kg per hull.


The two hull design are so close in length that no additional reinforcements will be necessary to the 3.90 hull in comparison to the 3.66 hull

Additionally my designs now have a 3rd ply bulkhead in the bow, but as the hull is rather narrow they will have a very small surface area of 0.093 sq. mtr.


The picture showing the waterlines is of the 3.66 (12 foot) hull but the 3.90 hull looks exactly the same, including where the waterlines are. As I said earlier I developped both simultaniously.




As can be seen my design has a relatively flat keel. I'm trying to approximate the fat keels of the modern "wave-piercers" as to maximize pitch resistance and hopefully allow some planing at the higher speeds. Also a fat keel line helps keep the freeboard up.

The upper waterline is with a single hull carrying all the weight (flying the other hull) and the lower waterline is when both hulls are flat in the water.

Wouter

Wouter

Thanks for the info, do you have any pictures you could post as well.


Gareth

Although I have stated on a number of occasions that I think a 12ft boat will be fast enough for children and there is no need to go to 3.9m perhaps I should clarify where this thinking comes from.

The Centre of effort (CofE) of the sail is say 2.5m high, The centre of buoyancy (CofB) of the boat is say 1.8m from the stern.

The drag calculations that I have published on earlier posting show that there is around 200N of drag at 15knots. (I think 15knots is a good speed for a childrens boat)

So in order to balance out the forces, the crew could move his weight (60kg) back to the rear beam a total distance of 1.6m from the resting CofB, and wouldn’t be generating any pitching (i.e. still keep the boat sailing flat). At this distance he can exert a moment of 1.6m x 600N = 960Nm, so the force in the sail he can balance out is 960Nm/2.5m= 384N. Twice what is needed to propel the boat at 15knots. I know that there are other factors involved here but it’s a good starting point.

Of course the extra pitching moment of a longer hull is a good safety device, but with such a lightweight low drag, low CofE boat which will tank along at 15 knots without any danger of pitchpolling is it really required?

Gareth

My reasoning goes like this :



Mine is ALOT higher.

Your centre of effort of the sail is consistant with a 3.90 mtr luffed sail on the F12. That would give the boat a 5 sq. mtr. sailarea if the minimal required aspect ratio is 3

This last measurement is important as below aspect ratio's of 3 you loose alot of sail efficiency, almost to the extend that more sail area is almost offset by the loss of efficiecy.

For comparison a laser 1 rig has aspect ratio of 4 and the wave has 3.6

With a 5 sq. mtr. rig the boat will never sail at 15 knots speeds. It will be much slower, thus in turn reducing sailforces. In one way this is a good thing as the pitching is reduced to such an extend that it will be of no consideration. The performance is what is being hurt here. Texel rating of 172. This is about the same speed as the laser 1 with a 4.7 sq. mtr. rig that is the kiddies boat for 50 kg and less.

In summary I think 2.5 mtr leverage of the sail power is far to small.




If the boat is level on its intended waterline, yes. There abouts anyways.





Yes, I've done those calcs as well. Still you assume a static balance while I focussed more on dynamics involved with wind gusts and the courses I'm interested in are the downwind course where accellerating the boat during a gust will increase the force far beyond the 200 N of the static balance.

Just assume a 10 m/s gust hits your boomed out 5.0 sq. mtr. sail directly from the rear when running square downwind and making a low speed gybe. The sail force generated by that LITTLE sail alone will be 250 N already. If the crew isn't at the back of the boat when the gust hits then the boat is about to tip over, especially if the deck dig in and pin the boat down.

In summary I think static calculations aren't dependable enough to concluded that worse case scenarios are well covered.

And of course any boat can be made controllable by just slapping a smaller rig on it. I admit that I had the design goal that the boat HAD to beat all laser dinghies and the Hobie 14 and Wave in performance, as such my designs NEED to have more sailarea then 5.0 sq. mtr. and also have higher sail aspect ratio's then 3. Indeed if this performance design goal is dropped then there is no reason why even a 10 foot design can be made that won't tip over.





And that is where the argument goes awry. This boat WILL NOT tank along at 15 knots as your sail area will be far to small to produce sufficient sailforce WHILE SAILING at 15 knots. It can produce that sail force during a gust when the boat is almost motionless but it can't when the boat itself moves at 15 knots.

In arguments like these I advice somebody like yourself to develop you mathematical models further, they still allow conclusions that are in direct conflict with eachother and as such lead to errornous conclusions. Your models are not yet well defined.

I have a model that takes into accounts all influences like changes in angle of attacts etc and the one clear conclusion was that with each reduction in sailarea the boat because disproportionally slower. Even at 9.00 sq. mtr. (my 3.90 mtr design) I could achieve 10-11 knots at maximum. Which is fast but a 5.00 sq. mtr. sail area at a significant lower aspect ratio will be well below 10 knots (around 6 knots or so).

This is actually why apparent wind sailing is a different form from just yachting about. With each increase in boatspeed your sails produce MORE drive despite having a smaller angle of attack allowing you to go just a little faster again. Just as with pointing ability, each and any speed increase that you can achieve is advantagious as you disproportionally improve pointing and speed that way.

The adagio indeed is "speed is everything !"



Now having said all this. We can still build this 12 foot version, as I wrote I developped both simultaniously, and just see how much sail area it can really carry before becoming scary. The numbers and models are just here to base our decision upon but we may go against them if we decide to do that.

My only real question to the 12 foot supporters is what they expect to win by going to 12 foot instead of 12'10" ?

It isn't weight savings, it isn't cost savings, at least not in significant quantities. It sure as hell isn't performance improvements or even optimal crew weight capacity. Apart from the name being F12 instead of F12'10" what are the arguments for a 12 foot hull ?

Wouter

Gosh, Wouter, now you are asking to start going round and round again. <img src="http://www.catsailor.com/forums/images/graemlins/shocked.gif" alt="" />

Again Wouter you are talking about your design not mine, as I have said all along I would use a 7m2 windsurfing rig on a 460 mast. The gust response of these sails is very good I would not expect to see the situation you describe.

This is a similar rig to that used on the international moth that won the world championship a few years back so perfromance is not as bad as you are trying so hard to make out.

Gareth

My experience of using windsurfing rigs on a multihull does not match your mathematical models, from your comments it appears you have developed your own VPP. It does not seem to be giving realistic results. Perhaps it does not scale well.

Look at the international Moth Length=3.4 beam=2.2 SA=8m2 similar total displacement to an F12, with a windsuring sail it goes significantly faster than your models would predict.

Gareth

I'm not, my mathematical models don't use specific design limits of my F12 design. They assume "perfect" sails meaning that the results of these models act as upper boundery to speed potentials.

As such you windsurfer rigs are also limited to this upper speed boundery.

They may react differenty to gust onslaughts however. But I've seen enough windsurfers being launched by their rigs to know that there is a limit to gust response.




You are not thinking through your counterarguments. On a dead downwind run any gust response based on mast flexing or squaretop sail design is useless. You will only be bending in the same direction as the gust is blowing without the sail area being weathervaned out. As such there is no reduction in sail force. When the apparent wind is coming from the front then pitching is not a problem anyway because the craft will capsize before it will pitch. In effect the improved gust response of a windsurfer rig will only help you on the reaches.





Sorry, but this is one of those bullshits argument.

It sounds nice and convincing but it is actually only succesful in making people believe errornous claims/conclusions.

The NON-FOILING moths are speed wise somewhere between the Hobie 14 and the Hobie wave. It is the FOILING moths that are achieving the impressive speeds. And this not because of the sail design but because of the much lower drag while foiling. The difference between a foiling and non-foiling moth is no less then 25 % that is a BIG performance gap. (Source Empirical Australian VYC yardstick handicaps)

F12 will not be foiling and as such we should not look at the foiling moths to get a feel for the F12 performance. Additionally the moths use 8 sq. mtr. sails on a longer luff, their masts are 6250 mm tall ans as such 35 % taller then 4600 mm the windsurfer rig. Your sail has an aspect ratio of 3 (at max) while the moths use sails with an aspect ratio of 4 and higher. Because of this your sail will provide 25 % less drive then the moth rig.

Additionally the F12 will be between 55-65 kg ready to sail while the moths are 35 kg ready to sail. This all adds up.

The NON-foiling moth is rated 10 % slower then the Hobie 14 (VYC 94.5 ;Texel 135) and as such is rated the same as the Hobie wave (Texel 146). With your smaller sailarea your craft will be slower still. Texel provides a crude estimate of 149 with your 7 sq. mtr. windsurfer rig.

Here it should be noted that punching in the Moth specs in the Texel rating system produces a rating of 133 which is very close to the Hobie 14. Note how the NON-FOILING moth is rated 9 % slower with the FOILING moth being rated 12 % faster.

Despite its crudeness it never fails to surprise me how close the Texel rating system always seems to predict actual performance of a given craft.


Wouter

Well, up till now my models have accurately predicted the F16 and (Darryls) F14 performance (using the F18 reference model) despite strong initial disagreements in both camps. There may still be errors in the models I use (I'm not perfect) but as of yet I have not encountered one and I'm 2 validations ahead of the other guys.

And obviously going from F18 to F16 and F14 is a scaling operation. Now that it is validated on those two designs I really don't expect it to crap out on me for the F12. Certainly not by any great amount, such a thing would be illogical considering earliers hits.






Yes, how is your twin rigged four-hulls doing. I must admit that I'm very interested in that design. It is sufficiently awkward to provide good validation data or show where the models can be further perfected.





I'm not using hulldrag predictions if that is what you means. I found this approach to be far too sensitive to designer induces modelling errors (= oversights). Over the years I've found much better accuracy in scaling performances. Granted, the further you move away from the reference that ties the model to reality the less accurate the predictions become, but it still smashes the accuracy of "hull drag and sail power guesses".

Like I said performance scaling as hit bullseye two times already with the F16's and F14's. So I has some credit to claim here.

I'm an old school engineer.

Wouter

As a side note.

Even if I write in a agressive manner, nothing is personal !

That is just the way I write and it is hardwired in my system, tried to be more diplomatic in the past but that just wasn't me.

Please take it from me that I always keep my eye on the ball. I do respect different opinions.

Wouter

Sorry I still don’t quite understand what is the big deal with it not being exactly 12 foot? <img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />

How about we take the Taipan 4.9 (simplified and minus the wing mast/ use plywood for boards etc..) and reduce everything by 25% keeping aspect ratio that's 12ft at 76kg platform weight? Max. load of 112kg....? <img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />

There is no big deal at all about the size of the boat. I think the only difference of opinion was about what size boats should be included in a hypothetical Formula 12 class. Forget creating a Formula 12 class, and there is no issue at all.

Wouter,
Forgive me if I have missed things in the plethora of posts, but is your design going to include trapeze and spinnaker? I'm thinking NOT, based on the unstayed mast-sail rig being proposed.

I have been trying to think where your design fits into the big picture of youth sailing. When we are talking about youth sailors from 13-18 years of age, most of those with any sailing experience are able to handle the Hobie 16 and the SL 16, which are the boats being used for ISAF World Championships (both using spinnakers).

Seems like your boat, being smaller, lighter, home-buildable and therefore less expensive than the bigger cats the kids are using for the major sailing events, would be a great trainer boat for those who cannot afford to buy an SL 16.

Maybe what we ALL need is just a good, small, light, easy-to-build PLATFORM that can be used with a bunch of different types/combinations of sails and standing rigging, depending upon how any given sailor wants to USE the platform -- ages, weights, goals of entry level or racing level, etc.

The options and combinations for rigs are endless -- sprit sail, lateen rig, Laser-type rig, windsurfer/landsailor rig, traditional stayed unirig, sloop rig, spinnaker, reacher, boom or boomless, fully battened or no battens, traveler systems of all different kinds or boom vang if there is a boom...

It would be so interesting to have a platform that everybody can build and that everybody can decide what they want to do as far as what they put ABOVE that platform in terms of sails.

I know you don't like all the "round and round" discussions, but I think of it is sort of like panning for gold. If you pan long enough, you might get a nugget of wisdom, a flash of gold, out of the stream.

I can have a trapeze, nothing technical is preventing it, but it won't. Reasons, it is neither simple not inexpensive. Additionally the sailarea will be relatively small, so it won't be used very often. In short the return against the investment is not interesting enough.

An additional reason is that singlehanded trapezing is considered a skill. My idea for the F12 was to have a boat that was regarded unintimidating and easy to sail/setup so that it would be a good entry into cat sailing and apparent wind sailing for absolutely novices (both kids, youths, teenagers and adults)






You yourself said many times that racing is not everything. Now I've been earlier involved in a class of cats that certainly qualify are race oriented. They are lean and fast but can be mean at times. This time I wanted to offset that by having a well performing boat that was easy and very well behaved, plus very economical to purchase and operate. For the group of sailors who are not interested in racing , but far more in an enjoyable hobby.

Of course the boat doesn't have to be low performant or against racing, it only needs to avoid making compromises if racing would demand those, against simplicity and easy of sailing/rigging. The trapeze is such a thing I believe.





I think it would be a great trainer for everybody, including owners of real racers like myself. Time-on-the-water is the must important ingredient for succes. I would like to have a boat myself that I can rig and derig under 5 minutes, so I can go sailing in those little hours were rigging up to big one is too must effort or too time consuming.

For the same reason my design won't have a spinnaker, it can but it won't as a class.

Additionally, because of its simplicity it will be very easy to learn "the ropes" on. What I'm trying to so is design a go-cart for sailing. Yes a go-cart is not a nascar or F1 race car but quite a few drivers started out in these things when they were young and moved up later on. Go-carts are relatively inexpensive (compared to the larger bolides) and easy to operate as they have no clutch and no gear box. And a go-cart race course can be setup on a very small piece of land. Overhere we have race tracks inside inner city former warehouses and storage buildings. Hugely popular.





Not trying to overpromote my design but that is actually what my design allows. At this time the exact same platform with mast foot design will take :

-1- The class 5 landyacht rig
-2- The laser 1 rig
-3- The windsurfer rig
-4- The gaff rig
-5- The lugger rig (= very interesting for extreme simplicity and low cost)

and it will even take the sprit and lateen sail setups but both or these are not as efficient as the ones named earlier.

All these rigs can be used because the platform allows the use of an unstayed mast.

A lateen sail will be rather difficlt to fit to this F12.





Well , my idea was to base the class rules upon the most performant setup that can be had. Then all the simpler and less performant versions can be part of the class as they will never have any speed advantage not matter how well they are build.




I don't think this particular posting was a "round and round" type of posting.

Wouter

Been busy but wanted to reply to the Wave Pooh-Pooh Poster. Wow, whoever quoted the prices on that makes it sound like it should be racing with the A-Class Boys -- don't know how you could get the price up that high, but you did.

First of all, there are already a zillion Waves around and used Waves can be acquired at very reasonable prices. To add the Hooter does require spending some money to nearly double the sail power. Granted! But, it would still be as inexpensive as any other proposed boat here in the long run.

Add the fact that for kids this boat would be indestructible. They could hit sea walls and pilings and still keep on ticking like the Energizer Bunny.

And only 2 inches longer than the proposed F12 box rule proposed herein. <img src="http://www.catsailor.com/forums/images/graemlins/smirk.gif" alt="" />

Rick