sail plans

[bilgepump]

Could anyone offer advice on square footage for a 15'x58" double ender? I am leaning towards a cat ketch rig or a yawl rig but if anyone can offer any insite I would be most obliged....Thank you

[TeddyDiver]

Can you give any additional information about your boat? Displacement, keel, ballast, VCG, drawings, photos..

[bilgepump]

Well its still mostly in my head but the closest I could get would be the CLC Skerry if that help any?

[TeddyDiver]

http://www.clcboats.com/shop/boats/r...LC-SKERRY.html In their pages in the picture of the sail package it's marked 56sqf

[Eric Sponberg]

B-P,

How much sail area depends on what your displacement is. You consider the Sail Area-to-Displacement ratio. Sail area is in square feet, and displacement is in cubic feet, and more correctly, this is called the "volume of displacement". It is the displacement in pounds divided by 64 to convert pounds of displacement to cubic feet of seawater. But you have to raise Volume of displacement to the 2/3rds power (i.e. 0.667), which can be done on most calculators. Specifically, the ratio is:

SA/Vol^2/3

Calculate this number, and it should be more than about 17, and probably not more than about 23. This is the average range. Others may have other opinions, but that is what I typically use, and my later designs have all been over 20.

I recommend that you get a book on boat design such as the following, which explain boat design ratios like the above more clearly:

Ted Brewer Explains Sailboat Design, by Ted Brewer

The Nature of Boats, by Dave Gerr

Cruising Sailboat Kinetics, by Danny Greene

I hope that helps,

Eric

[bilgepump]

Thank you Eric and Teddy its a little confusing but I will definatly research it more. As far as the Skerry plans go I'm aware of their recomandation for 56sqf but to convert that to a yawl rig how do I figure out the size of the mizzen? Also should the main be moved forward?

[timothy22]

I highly recommend the following
http://dan.pfeiffer.net/boat/ratios.htm
more information than you thought you wanted to know, and all in one place.

[bilgepump]

Thanks dude your right I thought it would be simple but as usual I'm wrong again thank the gods for this site!!!!!!!

[alan white]

Eric is right that displacement matters. My boat is 15' x 5' 6" and her sail area is 186 sq ft, which is a bit high even for my preferences (it's how I bought her). However, I have at least 600# of lead in the keel and the sail is a gaff type.
Sail area can vary wildly if length and beam are the only variables considered. Even at the same length and beam and displacement, overhangs vary, and bottom shapes run the gamut from flare-sided to Bolgeresque square-chine and everything in between.
Then there are the intended use, locale, ease of stowing spars, rig height, and on and on.
All of those factors affect sail area. And in addition to the aforementioned, there is also ease of reefing/furling, where a boat having a more easily struck rig is likely to carry a somewhat larger sailplan.
All of these considerations take into account the ease with which a boat can achieve her best average speed without too much fuss. When the wind is light, it's nice to have a big sail, but how often is the wind light in your locale, and in which months?
I personally like my boat over-canvassed (by typical standards, she should carry about 150 sq ft). Especially in August, around here, there's not as much breeze. If it does pipe up, I can reef or douse the jib, taking me down to maybe 100 sq ft. I'll be changing my rig to a yawl pretty soon too, which will be about 170 sq ft total, but with only about 110 in the main. The advantage is, I can sail with jib and mizzen alone, at about 60 sq ft, in perfect balance.

[bilgepump]

Thank you Alan do you have any pics of your rig? Just for a referance.

[alan white]

Here's Black Rose without the jib up. As you can see, it's a large rig, and tall too, at 20 ft from foot to peak. At the time this picture was taken, I hadn't yet received my new jib. I was using a smaller jib borrowed from my other boat (prob about 22 sq ft), and that day I had it stowed.

[bilgepump]

Absolutely gorgeous Alan BRAVO! What design? You made me miss the coast of Maine like you wouldnt believe!!! Thank you for your help!

[alan white]

Thanks! The design is a one-of-a-kind I'm sure. Interestingly, the hull is glass. There the plastic ends. The spars and everything else are wood.
When I bought her, she had no sprit. The boat was a cat with 155 sq ft.
I moved the mast back 14 inches (which helped the shroud angles), and added white oak coamings and a new foredeck, tiller, sheer clamps, etc. Basically, the whole boat is new above the glass.
So I guess she's partially my design.
One thing I'd like to do down the line is to build leeboards. She's got a shoal keel that draws only 2 ft, though the keel is long. I'd like to sail closer than 55-60 degrees off the wind, and I believe the leeboards will accomplish that.
I wouldn't ever give up the open cockpit, which is what makes this boat a keeper. It's at least as comfortable as a Herreshoff 12 1/2, but with longer and wider seats, which you can sleep on.

[PAR]

No offense intended Bilgepump, but your questions are so basic in nature, that you'll need considerable education, before expecting reasonable balance from a rig/hull form combination or selection. The books mentioned by Eric are easy to read and understand without all the math and head scratching stuff of the more involved texts.

This would also apply to the rest of the design ( . . . it's still mostly in my" . . . ), which of course requires a fair understanding of the concepts, principles, dynamics and engineering associated with a vessel as complex as a 58' double ended sailing yacht.

The book store on this site has a good selection of design references, though all could be had from an on line seller or your local book store too. Build up your library and juice up your understanding of the various subjects you need a much better handle on.

[bilgepump]

No offense to you either but if you read what I had said I'm building a 15 foot(') by 58 inch ("), so pordon my lack of education in this feild. The only way to gain knowledge about anything is to ask questions and not let pride or arrogance keep your questions from being too "basic in nature" The whole reason I joined the site was to try and glean as much information and advice as I could.