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Strawberry View Drop Down
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    Posted: 07 Feb 06 at 12:35pm
However, the 400 could be a hell of alot quicker without changing any key dimensions. It's almost been "de-tuned", as a compromise more polarised towards easier sailing over speed (the downfall of the SMOD). You couldn't expect this to happen in a dev class, where everyone will be seeking pure speed. And the Tasars seem to manage to plane upwind without traps, and I wouldn't call them an extreme design. More of an "efficient" design.
Cherub 2649 "Dangerous Strawberry
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Chew my RS View Drop Down
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Posts: 790 		Post Options Post Options   Quote Chew my RS Quote  Post ReplyReply Direct Link To This Post Posted: 07 Feb 06 at 12:26pm

Aarrgh! Are you trying to be provocative, Strawbs?

Speed is a relative thing. Eveb your Cherub is slow compared to my car, which is slow compared to a jumbo jet. The RS400 does not plane upwind in winds where planing downwind becomes possible. But it isn't a slooooow boat unless you consider all boats pre 1992 slow. The Tasar, on the other hand, can plane upwnd when its windy enough. But it is a slower boat than the 400 (nice, nonetheless). So upwind planing does not mean, per se, a quick boat. And as I didn't want an 'extreme' boat, with twin wires and all carbon construction, generating enough righting moment to plane upwind would be tricky - though if you can do it under the rule formula good luck to you. The idea proposed at the start of the thread was for a 400 style class, therefore 400 style performance. I have already admitted that the formula may not be as good as a simple box rule - I just thought I'd share my thoughts.

 
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Posts: 1337 		Post Options Post Options   Quote Strawberry Quote  Post ReplyReply Direct Link To This Post Posted: 07 Feb 06 at 11:56am
Originally posted by Chew my RS

Originally posted by Strawberry

Originally posted by Chew my RS

Downdwind the formula doesn't really hold - as the boat would potentially be planing

May I suggest that if your design doesn't plane upwind (in conditons when your planing down) then your gonna be sloooooooooow.

No, you can't.

Another well thought out and intellectual repsonse from another SMOD sailor.



Edited by Strawberry
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Posts: 790 		Post Options Post Options   Quote Chew my RS Quote  Post ReplyReply Direct Link To This Post Posted: 07 Feb 06 at 11:51am
Originally posted by Strawberry

Originally posted by Chew my RS

Downdwind the formula doesn't really hold - as the boat would potentially be planing

May I suggest that if your design doesn't plane upwind (in conditons when your planing down) then your gonna be sloooooooooow.

No, you can't.
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Posts: 1337 		Post Options Post Options   Quote Strawberry Quote  Post ReplyReply Direct Link To This Post Posted: 07 Feb 06 at 11:48am

Originally posted by Chew my RS

Downdwind the formula doesn't really hold - as the boat would potentially be planing

May I suggest that if your design doesn't plane upwind (in conditons when your planing down) then your gonna be sloooooooooow.
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Posts: 790 		Post Options Post Options   Quote Chew my RS Quote  Post ReplyReply Direct Link To This Post Posted: 07 Feb 06 at 11:45am
Originally posted by Strawberry

[quote=Chew my RS]Downwind all the boats would have the same sized kite, which is the totally dominant sail.

That's not true. You spend loads more time going upwind than you going down with the kite up. Therefore upwind speed makes a loads bigger difference.

I meant going downwind the kite is dominant, therefore whilst going downwind the size of the main and jib is of secondary importance.  Upwind speed is important, but sail area is just one function of upwind speed.  The formula lets you chose the combination of length, weight and sail area that you personally think will provide the best upwind speed in a range of conditions.  Downdwind the formula doesn't really hold - as the boat would potentially be planing, hence the proposed kite area rule (as kite area is the dominant factor downwind, go to start of post, collect £200...).  Obviously a lighter boat would help the downwind speed as well, but at the expense of length or upwind sail area.



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Posts: 1337 		Post Options Post Options   Quote Strawberry Quote  Post ReplyReply Direct Link To This Post Posted: 07 Feb 06 at 11:30am

Originally posted by Chew my RS

Downwind all the boats would have the same sized kite, which is the totally dominant sail.

That's not true. You spend loads more time going upwind than you going down with the kite up. Therefore upwind speed makes a loads bigger difference.

Originally posted by Isis

How much cloth am I allowed on a 6ft hull?

Originally posted by Chew my RS

A 6 foot boat with all up weight (inc crew) of 200kg could have 30m2 of sail. Now that I'd like to see! 

Sounds like a challenge! (Bit heavy tho)



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Posts: 790 		Post Options Post Options   Quote Chew my RS Quote  Post ReplyReply Direct Link To This Post Posted: 07 Feb 06 at 8:12am

That's one reason I wasn't so keen on it, but there's only so much rag you can hold on a 2m beam without trapezes. Downwind all the boats would have the same sized kite, which is the totally dominant sail.  I don't think a big main is that much use downwind. The RS400 doesn't plane upwind effectively anyway, so the formula is only rating this type of boat in displacement mode (I guess the 59er probably can plane upwind though).

A 6 foot boat with all up weight (inc crew) of 200kg could have 30m2 of sail. Now that I'd like to see!  In practise, holding more than 15m2 would be tricky so there's no point being shorter than about 14 foot, with higher low end speeds likely on a 15-16 footer.
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Posts: 2753 		Post Options Post Options   Quote Isis Quote  Post ReplyReply Direct Link To This Post Posted: 06 Feb 06 at 4:56pm
I dont think trading length for sail area has the intended effect in planing dinghies tbh, although its a nice idea.
In displacement mode a longer hull is worthwhile but once you start planing length starts to matter less (except for controlability) and rag starts to matter more.

How much cloth am I allowed on a 6ft hull?
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Posts: 790 		Post Options Post Options   Quote Chew my RS Quote  Post ReplyReply Direct Link To This Post Posted: 06 Feb 06 at 2:17pm

Getting back on thread...

Based on America's Cup rules, how about:

length + 1.25*(upwind sail area)^0.5 - 9.8*(total displacement)^0.333 <=3.00m

and

kite area =17m2

max beam = 2.0m

This system allows for a wider variation in designs (trading length for sail area etc), but I'm not sure whether that is a good or a bad thing. Probably bad in this instance as it might lead to a greater rate of change of design and correspondingly high cost. The simple rules proposed by Jim are probably better, but this offers an interesting (to me at least!) alternative.

For information the RS400 comes out with a value of 2.91, the Topper Xenon 2.77 (with a crew weight of 150kg) and the 59er 2.97 (based on a heavier crew). All are 2.0m wide, but the 400 and Xenon could trade up to a bigger kite whilst the 59er would need a smaller one. I'm not suggesting that the Xenon could seriously race the 59er over the water, but it does illustrate the point that most of the big manufacturers have produced boats in this area of the market. Wouldn't it be better if they united behind one class rather than creating three smaller ones?
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