Guys,
We have a choice to make I'm afraid.
I won't go into details right now but because of the short hull length this F12 will have a more narrow crew weight range then larger catamarans. We need to decide where to place this range.
I worked out the underlaying scalings law and as such can give you all a feeling of what we are talking about.
As the reference I put forward an F18 sailed from 115 kg to 180 kg, with 155 kg being optimal. Lets assume that all F18 crews in this range are more or less competitive and experience enjoyable sailing, meaning, neither heavily overpowered nor sluggish and underpowered.
If the F12 is exactly 12 feet long = 3.66 mtr then its characteric weights (similar to F18 above) are :
range = 31 to 50 kg with 43 kg optimal
if the F12 is 3.90 mtr long then its characteric weights (similar to F18 above) are :
range = 49 to 72 kg with 63 kg optimal.
if the F12 is 4.00 mtr long then its characteric weights (similar to F18 above) are :
range = 57 to 82 kg with 73 kg optimal.
All above boats have been scaled to not perform worse then the F18 when not looking at the other issues associated with scaling like the pitching moment problem (= dive happy).
Additionally, from the point of drag it is always better to sail an boat underweight then overweight. Meaning that being 10 kg overweight is just as bad as being 20 kg underweight. The overweightness just hits harder.
Be sure to note how only 0.1 mtr (= 4 inches) difference in hull length, (from 3.9 to 4.0) moves all characteristics weights up by 10 kg's ! 0.1 differenc in length is nothing on a F18 but it is the world on a F12.
The point of this post is that we need to decide what the F12 should carry in crew weights a choice here will have a direct impact on the required MINIMAL length of the hulls.
Please everybody give your opinions on this, I'll provide my own opinion at the very end of the discussion.
Wouter
I know nothing about working out such figures, but my instinct says go for the greater buoyancy. It can still be called a F12, even if the length is closer to 13ft. When I see a Hobie 14 with it's hull so low in the water, I get worried about a 12ft cat. Even though I know that the hull shapes are different.
Don't look at the H14.
Picture yourself an F18 or Spitfire / F16.
I'm using the same scaling laws as I did with the F16's
In principle this would lead to a F12 with the same performance as the F18, despite being much smaller. But for true equality it would have to be fitted with jib and spi. Sadly there is a thing that I call the Quad-problem and it limits the amount of sail area you can put on the F12 before it turns into a right submarine. Therefor we are not going to achieve full F18 performance. But I have a feeling that we'll discuss this soon enough.
Wouter
Stick with 3.6m don't get so hung up on performance. Make the hulls wider to get the increased crew weight. A 12ft boat will be lighter and more practical.
Gareth
Gareth
12ft might be more practical for home building - using 8ft sheets of ply. Less waste wood.
Gday
12ft = 3.660m, so I would go 3.7m max, I wouldn't go anymore than that, it will start getting further from the objective if you go more.
I don't think theres any need to make them comparable to F18's, F16's or whatever to terms of performance, remember theres a lot of things that they have that this F12 won't.
Regards
What would you name as our objectives ?
Also in an earlier posting you referred to some Aussies having other idea's about the F12, can you elaborate.
Wouter
F12 Great Idea! <img src=
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I’d guess drag is not the big challenge as short boardless cats are a much more difficult to tack, especially without a jib! Rocking horse effect is another matter. What makes you think this design will be any different?
Ease of tacking is an essential element in training new sailors and one reason why the Opti is so popular (less run away boats!).
I suppose a hull design using ultra low profile boards would be make a major difference in the handling characteristics. <img src=
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I’d guess drag is not the big challenge as short boardless cats are a much more difficult to tack, especially without a jib! Rocking horse effect is another matter. What makes you think this design will be any different?
Ease of tacking is an essential element in training new sailors and one reason why the Opti is so popular (less run away boats!).
The boardless Dart 16 is amazingly responsive. No problem tacking.
A MAJOR objective, IMHO, would be no boards of any kind. Skegs only.
By the way, has anybody ever heard of a
shoe
? An exremely low-profile
keel
that has been used on cruising catamarans? When I say
low profile,
I mean it is only a few inches deep below the bottom of a 35-foot-long boat. It has kind of a fat, upside-down-T shape. The boat we sailed pointed very well with VERY little leeway, and it tacked on a dime. Would that work on a smaller boat, too?
Hi Wouter
Well I guess the main objective was a 12ft cat, increasing its length to make it suitable for a larger weight range, you may as well build a Paper Tiger or an Arrow.
I spoke offline to another forum user, who to is interested in introducing a more modern 12ft cat for trainers, for their junior fleet, as we had said earlier, we would prefer and his own kids would prefer to have the option of a trapeze, and probably an optional jib to allow their friends to continue to sail with them after they get the hang of it. We didn't really discuss hull shapes or profiles, but the boat I'm working on, would be tortured ply design, not that I'm a designers little toe, but I'm having a crack at it, I don't find tortured ply difficult at all, when I try to explain it to someone who hasn't a clue what I mean, I think its sounds more technical than it really is.
Regards
This Hobie Teddy looks to be about 12' with skags but uses a jib for improved tacking. <img src=
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This one looks even smaller. <img src=
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I saw one once - I think that it has the inverted T shaped skegs that Mary mentioned - made it look a bit agricultural.
The Teddy looks a lot like a scaled down Hobie Tiger
with skegs.
Is the jib self tacking?
Just took another look.
The jib does not appear to be self tacking but then I don't
think the Tiger's jib was self tacking first up.
I think the 12ft target audience needs something much simpler to maintain the advantages of the 12 ft size.
Just a personal view.
Regards,
Phill
The Hobie Teddy looks alright, nice clearance under the sail for moving around, never seen one til now.
Regards
Here's one of the skegs.. <img src=
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Yes, I think that 'shoe keel' is what I was talking about. It worked phenomenally well on the Witness 35(?). What difference does it make if it LOOKS agricultural but works great? You guys are SO superficial. <img src=
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Didn't you ever hear that song that goes:
If you want to be happy for the rest of your life, make an ugly woman your wife
? <img src=
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Just don’t mention that to my wife… <img src=
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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
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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=
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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.
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Didn't you ever hear that song that goes:
If you want to be happy for the rest of your life, make an ugly woman your wife
? <img src=
alt=
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Because if you want kids to be interested it has to also look
Cool
.
Tiger Mike
What would you name as our objectives ?
Wouter
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:/
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.