Light air performance priority...which one?

[sharpii2]

Originally Posted by Omeron

It is generally well known that for a sailboat to perform well, certain ratios
have to be within certain bands.
I guess the most common are, Displ/LWL, SA/Displ, SA/wetted surface,
and perhaps Ballast Ratio.

If you were designing a boat around 38 ft overall, and would want her to have v.good light air, upwind performance (up to 10 knts) which of the
above ratios, or any other ratio would be your top priority to get it right? Why?
And how would you rank the others in order of importance.
And if you think this is a valid argument, you can state your optimal figures to be achieved.

As a note,the boat is to be used/raced (IRC) mostly in protected coastal waters, minimum creature comforts, no exotic materials or building techniques.

First, I would get the basics down.

Good helm ballance would be a good place to start.

Next, I would go for a high heft factor 20 vol./(Length*beam^2). I would consider a Hf of 1.0 about average and one of 2.0 to be very high. The reason I would go for this is to have good momentum to plow through the inevitable slop. A boat with even a high Hf can also have a very low DL. It can do this by being very narrow and having a long waterline.

Next, I would pile on as much actual sail as I could get away with within the rule.

After that, I would either give it widely spaced floats or a deep, high AR keel.
This would be, of course, to hold all that sail up.

Finally, I would chose a rig with the least amount of working sails, or one with one sail being bigger than all the others combined. One very large sail would be most effective if not always most practical. And, I might add, I would probably spend at least one dollar on the sail maker for every two I spent on the boat builder.

So, I guess, in answer to your question, In priority of ratios, I would go with: S/D (which will usually take care of SA/WS all by itself), Hf, D/L, then, if really limited in sail area, Prismatic Coefficient, or cP. These numbers, by themselves don't really tell you that much, with the exception of S/D.

Bob

[Paul Scott]

Mr. Pedersen- so you've seen the tiller, eh? Where does your brother play?

I know the WS loading idea is expressed elsewhere, but.....

Paul, who also comes from the -sen neck of the scandinavian woods.

[mgpedersen]

My brother plays in NYC. He enjoys the city, and there's more than enough opportunities to play at weddings, etc. so he can pretty much make it as a starving musician.

He's always lusted after an Amati of the musical kind, but I'm not sure that's in the cards. I think he would enjoy the whimsy of the tiller though.

Matt

[Paul Scott]

Amati cost a lot less than an Amati! As close as I'll get.

Paul

[sharpii2]

Omeron,

I just came up with a basic idea to illustrate my earlier point.

I thought of a boat with a 5000kg weight budget. It would be 38ft long, have a beam of 9ft max at the gunwhales, and have a 1.83m draft. It would be sloop rigged with a 600sf main and a 225 sf jib. The main sail would be a modern gaff rig which might get some kind treatment from the rule. the 1800kg ballast should not raise too many eyebrows either.
The D/L would be less than 120 and the S/D would be around 25. The S/D is a little high but hardly outrageous. The Heft factor would be around 1.0, which should make this boat buildable without going to exotic matterials.

The boat should be sharp enough and have enough weight behind it to slice through slop without having really unballanced ends.

Bob