If you put the T-shape shoe keel far enough back you may get some of the stability benefits of a T-toil rudder system.

Gareth

Is that from the Teddy ? - because the impression I had was that the T bit was much bigger, heavier, looked like a railway track and definitely "Agricultural" <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" /> And the boat was very slow. The other kids were sailing Dart 16s and loving it <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

I vote for increased length as long as it is less than 13 ft. So, 3.9m. The reasons are both selfish and practical. I am 5’11” 175lb (~ 1.8m 80kg) low body fat. If your calculations are correct, I defiantly would not build one to use for weeknight sails. Through design, we should be able to minimize the penalty incurred by smaller sailors. We can always make the smaller sailors’ boat smaller than the box. It would be nice to have the boat perform while we are taking are children out to learn.

If it is more than 13ft, then it should be called the F13. I would be fine with that. I do see the point of saving on wood, but if you have any curves it will be longer than 1.5 sheets of ply (at least in the usa, I am not sure of metric sheet sizes). Plus the scarf takes a good 6-8 inches out, so it does not seem to me we will save much wood.

Upon review of www.cdc.gov/growthcharts and conversations over the last five days, here's my two cents.

From talking to a small group of cat sailors a general consensus is that there are some expression of desire amongst kids to skipper their own boat, or a parent's desire to show them that they can (case of timid child) skipper a boat around the age of 10 or 11. One person questioned stated she was "forced to skipper" by her father. From year's of coaching, and involved in, youth sports this is a concern, at least in the US, where parents (esp. fathers) want to relive their childhood through there children. This is of note regarding existing sailors, but probably of no relevance to a new sailing parent and child. The general opinion was the Wave is a bit too much to handle at this age.

Reviewing the charts reveal these weights at 50 percentile (average)
Girls at age 10, 32kg
Girls at age 19, 57kg

Boys at age 10, 32kg
Boys at age 19, 69kg

Of note boys weight is still heading up rather sharply at 19 while girls start to level off (by comparison) at 16. Girls also attain a plateau in height at 15, whereas in boys this occurs closer to 17.5 years. Interesting also at 13 years old girls and boys are about the same weight 45 and 46kg.

Wouter based on capacity vs. hull length it looks as though something towards 3.90 mtr looks inviting. I can easily envision a pair of kids up to 90kg (13 yo) wanting to sail (play, not race) together.

Of course this does not preclude a 12 foot version made from a minimal amount of 4x8 sheet material. I agree with the notion of replacing the originals with a faster design and passing down the starter hulls.

Tacking ability edges out looks for a starter hull design, especially from a newbie standpoint.

Because if you want kids to be interested it has to also look "Cool".

Tiger Mike

Has anybody actually put the projects stated objectives in a concise document??? I may have missed it (perhaps a sticky at the top of the forum would be a good idea) but a brainstorming session and then the aggreed objectives put into 1 post will help people to stay on track.

Tiger Mike

http://www.xs4all.nl/~whijink/formula_12/The_Formula_12_sailboat_project.doc

But that is my take on it.

Wouter

Would it be possible/practical for a F12 to vary the beam(width) according to crew weight?

sail area may be better because we don't want to make small childrens boats less stable.

I think enough time has passed for others to answer first and so I would like to give my own answer to this issue.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Wouter

I would call that a Formula 13. Or maybe they could sail in the Formula 14 class. IMHO, a Formula 12 should have 12 feet (or about 3.6 meters) as the MAXIMUM for the class. If you are going to have a Formula 13, then even the Wave could sail in it.

Also, weren't some talking about the boat being cartoppable?

I think there is a major disconnect here between the concept of Formula 12 and the concept of designing a new boat for young kids. <img src="http://www.catsailor.com/forums/images/graemlins/crazy.gif" alt="" />

In this post I wish to reply to the points made by others.




The 3.66 mtr hull will only be 0.555 kg = say 0.6 kg lighter then the 3.90 mtr hull. I worked that out with the design software. So in total the longer is 1.2 kg heavier overall. So this can not be a major point.

Making the hulls wider is a solution to getting the weight carrying ability both together with the severe limits on the sail area that can be carried because of pushing the bows under it will be slower then the Hobie wave and even the laser 1 dinghy. That are serious considerations.





The boat will never be build out of less then 2 sheets of ply. An additional sheet of ply is less then 50 Euro's including taxes. The difference in area between the 3.66 and 3.90 is 0.157 sq. mtr. per hull. That is 400x400 mm. This suggest that unless the 3.66 only just fits into 2 sheet then the 3.90 can be made from 2 sheets as well. I think both can be made out of 2 sheets, but a more in depth analysis must still be made here. But for an additional 50 bucks (shipping is already paid on the other 2 sheets) I don't think having to use a 3rd sheet is any serious obstacle.






My objective to have a design that can also be sailed by teenagers and small to medium adults and not only kids. The reasons for this is that kids grow into teenagers and adults and they won't rif the bike with training wheels for more then 2 years either. Also it is must easier for a parent to justify buying / building a F12 is he (she) can sail it himself as well. Additionally I want to be able to have kids sail the boat doublehanded as well. And I would really love to see this boat being sailed on an apparent wind policy. All these points are much better serviced by 3.90 then 3.66 mtr.

With respect to comparable to F18's and F16's, you misunderstood my point here. The F12 is not, with the possible exception of teaching sailors apparent wind sailing. What the comparison to f18 was intended to show is that a 35 and 50 crew on a 3.66 mtr F12 will perform relative to eachother as an F18 sailed at 115 kg and 180 kg. Meaning that even relatively small weight differences in the F12 will result in performance differences quickly. This is not something older kids and teenagers will appreciate very much after they learned to sail it. Young kids may not care at all but when the grow up in only a few years then they will care. At 3000 US or 2300 Euro investment the F12 better be succesful in keeping the kids interested for more then 2 to 3 years.






Different style of rig and as of yet I'm not using skegs on the hulls. This F12 is much more like the Supercat line of boats (like SC15 and SC17) then skeg boats. Without the skeg the hulls should tack noticebly better. Additionally my F12 isn't using sharp V-ed keel lines, it is much flatter on the keel. The rig will move forward when releasing the sheet and move back when sheeting tight. In effect the load on the rudders will be less during a tack when the sheet is released. The movement is the result of the flexing of the mast and not of any mechanical setup.

Currently my version of the F12 doesn't have a trapeze and I'm not looking at adding one. This makes quick tacking alot more viable thus spotting shifts and tacking is a more serious consideration then on a larger cat.

Ultra low profile boards are called skegs I think. But indeed short permanent stubs can put on the keel. Running a ground is not a real problem as short stubs will be very strong. But as of yet I want to try the no skeg or stubs approach. Afterall the Supercats aren't regarded as slow boats.





I sailed several hobie cats that had them. The Pacific (rip-off tiger) was aweful to tack. The shorter versions like the Dragoon where actually quite alright in tacking.





The paper tiger is long still and by much more then the 3.90 is longer then the 3.66 (compare 240mm to 370mm). But the F12 I see it is not so much different in the hulls but in all other things like the rig and the dolphinstriker less mainbeam, not having stays and the sleeved sail. As such it will always be much different (and I suspect much simpler as well) then the paper tiger and Arrow. Afterall the Paper tiger is also a VERY technical boat to sail with the baby stays and such. I don't think your comparison does justice to what we are really looking at here with the F12.

Adding a trapeze involves alot more then just adding a steel cable with a handle and ring. Most inmediate result will be that the mainbeam will have to be fitted with a dolphinstriker setup. And more volume needs to be moved to the bow to prevent the boat from pushing its bows down under the increased sail forces. In effect having a trapeze on the 3.66 mtr hull is having the worst of both worlds. I'm not writing off the trapeze completely but there are a few very serious points arguing against it. One of which is my own experience with the Hobie dragoon. At 80 kg I couldn't trapeze as it would immediately put its bows in. To kids at 40 kg trapezing would have nearly the same result. Also the trapeze is serious obstacle to quick tacking on shifts (coaching ?). I'm far more interesting in making the boat a little wider then adding a trapeze. Also we musn't forget that the F12 sails are much smaller in area and luff length. It will require alot of wind to even have to trapeze.


Wouter

Yes, isn't this far more determine by platform weight then length ?

Currently the platform (now rig and rudders etc) is 40 kg with stirdy hulls. Again a optimist hull is 35 kg and alot of parent car top that.





Please elaborate.

But also note that from the beginning a large part of the group didn't specify YOUNG children as the target group while another part did. Personally I don't see much point at all in having YOUNG children (6-11) singlehanding a sailboat. I think they much rather sail doublehanded and even a much smaller boat like the optimist isn't very suited to them. And then to top things off they grow into full sized (thrill seeking) teenagers in the span of only a few years.

If the F12 is aimed (solely) at young kids then it will be a bad feeder into larger cat classes as they will come off it at age 12 and 50 kg which is too young and light for the larger cat classes like the Hobie 16 etc.

Even you yourself wanted to sail an F12 to catch up with the kids on their waves. That is impossible if the F12 is optimized for 6-11 year olds. You will need a powerboat to catch up with them then.

All that for only 10 inches difference in hull length. I'm not sure if that is a wise decision.

Wouter

That is an excellent post John !

Good info. I can really use that.



Can you elaborate on that please.

Why is too much too handle ? What are the problem points ? What goes wrong ?


Wouter

Bear with me, I haven't had a play to work the quote jigger on here, but I refer to the reply a couple of posts back to my paper tiger/arrow post.

I think you missed my point, Wouter. The original idea, I thought, but correct me if I'm wrong, because I am more often than not, was to introduce or design a 12ft cat, 13ft is around the 3.95m mark, etc..

I don't think changing the length of the boat is the answer, if it doesn't suit your design, or the parameters you set for yourself earlier, such as sail area, etc..
If I were to design a boat, then found it optimal at 4m would I be able to call it an f12?

I'm not trying to be critical, but goal posts seem to be moving.

And I have seen a young woman, I would estimate to be 50-60 kg, sail an Arafura Cadet competitively (i.e national level) and the boat had no problem with her being on the wire, and boss's son and a friend who owned the same Impara at different times, were on the wire as much as any other class.

Regards

Wouter,

I don't know if this has been discussed or if it belongs in this thread, but will the rig be without stays and similar to a windsurfer (obviously without the the universal joint) or more traditional? I ask because of ease of set-up. Also, the sail material for windsurfers looks sexier, and probably is, faster.

Thoughts?

Bill Nieuwkerk

I can reply for him. The stock F12 would have an unstayed mast like the class 5 land yacht. This is comprised of sections of Al tubing. Sort of like a laser mast. An optional configuration/mast would be to use a windsurfing rig. The front beam would have a stub that would secure the windsurfing mast.

It wasn't.

The idea was to have a really simple and inexpensive cat that kids and youths (like teenagers) could sail, thus providing an feeder class toward catamarans as the Laser and optimists are tp dinghies and skiffs. Later an extra was added after noticing that kids were more drawn to cats then mono's. Several posts by Phill and somebody else also refer to that.

The idea for a 12 footer was derived from the initial feeling that that would probably be a good length for such a goal.

Of course after doing numbers crunching one finds the initial parameters set for the project validated or not.

I think that is what happened to the 12.00 foot length with respect to the 12.78 foot length. The difference is still pretty small though. We're not talking about adding something like adding 2 feet. It is only 9 inches.





What are you trying to say here ?




There have been a surfboard brand that called itself F10, short for force 10 because that was when the real surfboarders went out. No way the boards were 10 feet long.

Maybe F12 stands for formula 12 as in ready made for 12 years and older. Give it some spin. anything will do for me. I'm just trying to get to be best design possible considering the goals. If that happens to be at 4.00 mtr then that is what I will go for personally. Sticking with 12 feet solely because that was our initial gamble at the hull length doesn't seem to be beneficial.




This is pretty normal when a design develops and may not be a bad thing at all. One gets more data on which to justify or disguard earlier assumptions.

Maybe after more info they move back again.

However my design goals really haven't changed much.

Maybe it is your expection of what they were that is now more clearly to be show to at odds with the goals.

I still don't really understand what the aussies around you (and yourself) want out off this design.

Maybe you can elaborate on that further and we can get to the bottom of this.




Can you provide me with the specs for the Arafura. As many as possible. I could find them on the net.

Regards

Wouter

Thanks Bob:

I'm assuming that the sail slip on like a windsurfer's sail and wouldn't require hoisting - correct?

Bill