Foam strip construction

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 <img src="<>/smirk.gif" alt="smirk" title="smirk" height="15" width="15" />

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). 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 ! <img src="<>/eek.gif" alt="eek" title="eek" height="15" width="15" />

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 ! <img src="<>/grin.gif" alt="grin" title="grin" height="15" width="15" />

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