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



Ain't that the truth !

Wouter

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

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


I had two immediate reactions to both statements

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

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

Wouter

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

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

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

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

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

Wouter

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

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

Wouter,

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

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

How can it not fit the box rule?
regards

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

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

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

Wouter

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

Regards,
Bob

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Wouter "

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

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

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

Wouter

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

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

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

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

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

Wouter

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

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

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

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

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

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

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

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

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

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

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

I hope this clear enough.

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

Just more useless mathematics I guess !

Wouter

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

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