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
Wouter Hijink Formula 16 NED 243 (one-off; homebuild) The Netherlands
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Re: A choice to make ...
[Re: Wouter]
#96002 01/13/0707:59 AM01/13/0707:59 AM
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.
Dermot Catapult 265
Re: A choice to make ...
[Re: Dermot]
#96003 01/13/0709:07 AM01/13/0709:07 AM
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
Wouter Hijink Formula 16 NED 243 (one-off; homebuild) The Netherlands
Re: A choice to make ...
[Re: Wouter]
#96004 01/13/0709:35 AM01/13/0709:35 AM
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
Re: A choice to make ...
[Re: grob]
#96005 01/13/0705:46 PM01/13/0705:46 PM
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
12ft might be more practical for home building - using 8ft sheets of ply. Less waste wood.
Dermot Catapult 265
Re: A choice to make ...
[Re: Dermot]
#96006 01/13/0706:23 PM01/13/0706:23 PM
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
Matt Harper
Homebuilt Taipan 4.9
AUS 329 'GOT WOOD' SEEDY PIRATES RACING TEAM
Re: A choice to make ...
[Re: mattaipan]
#96007 01/13/0707:02 PM01/13/0707:02 PM
F12 Great Idea! <img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />
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="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />
"House prices have risen by nearly 25 percent over the past two years. Although speculative activity has increased in some areas, at a national level these price increases largely reflect strong economic fundamentals." – Ben Bernanke – 2005
Re: A choice to make ...
[Re: Buccaneer]
#96009 01/13/0710:01 PM01/13/0710:01 PM
F12 Great Idea! <img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />
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.
Dermot Catapult 265
Re: A choice to make ...
[Re: Wouter]
#96010 01/13/0710:22 PM01/13/0710:22 PM
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?
Re: A choice to make ...
[Re: Dermot]
#96011 01/13/0710:26 PM01/13/0710:26 PM
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
Matt Harper
Homebuilt Taipan 4.9
AUS 329 'GOT WOOD' SEEDY PIRATES RACING TEAM
Re: A choice to make ...
[Re: mattaipan]
#96012 01/14/0712:42 AM01/14/0712:42 AM
This Hobie Teddy looks to be about 12' with skags but uses a jib for improved tacking. <img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />
"House prices have risen by nearly 25 percent over the past two years. Although speculative activity has increased in some areas, at a national level these price increases largely reflect strong economic fundamentals." – Ben Bernanke – 2005
Re: A choice to make ...
[Re: Buccaneer]
#96013 01/14/0712:46 AM01/14/0712:46 AM
This one looks even smaller. <img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />
"House prices have risen by nearly 25 percent over the past two years. Although speculative activity has increased in some areas, at a national level these price increases largely reflect strong economic fundamentals." – Ben Bernanke – 2005
Re: A choice to make ...
[Re: Buccaneer]
#96014 01/14/0704:30 AM01/14/0704:30 AM
This Hobie Teddy looks to be about 12' with skags but uses a jib for improved tacking. <img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />
I saw one once - I think that it has the inverted T shaped skegs that Mary mentioned - made it look a bit agricultural.
Dermot Catapult 265
Re: A choice to make ...
[Re: Buccaneer]
#96015 01/14/0704:36 AM01/14/0704:36 AM
The Teddy looks a lot like a scaled down Hobie Tiger with skegs. Is the jib self tacking?
I know that the voices in my head aint real, but they have some pretty good ideas. There is no such thing as a quick fix and I've never had free lunch!
Re: A choice to make ...
[Re: phill]
#96016 01/14/0704:43 AM01/14/0704:43 AM
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
I know that the voices in my head aint real, but they have some pretty good ideas. There is no such thing as a quick fix and I've never had free lunch!
Re: A choice to make ...
[Re: phill]
#96017 01/14/0705:06 AM01/14/0705:06 AM
Here's one of the skegs.. <img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />
Last edited by Buccaneer; 01/14/0706:30 AM.
"House prices have risen by nearly 25 percent over the past two years. Although speculative activity has increased in some areas, at a national level these price increases largely reflect strong economic fundamentals." – Ben Bernanke – 2005
Re: A choice to make ...
[Re: Buccaneer]
#96019 01/14/0706:48 AM01/14/0706:48 AM
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="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />
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="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />
Last edited by Mary; 01/14/0706:50 AM.
Re: A choice to make ...
[Re: Mary]
#96020 01/14/0706:57 AM01/14/0706:57 AM
Just don’t mention that to my wife… <img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />
"House prices have risen by nearly 25 percent over the past two years. Although speculative activity has increased in some areas, at a national level these price increases largely reflect strong economic fundamentals." – Ben Bernanke – 2005