Calculating Sail Area/mast height?

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NLOM1

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Hi

I have a 22ft unidentified gaff under restoration
but no original spars or rigging and no plans.

How do I go about calculating mast, boom, gaff and bowsprit dimensions and sail-plan etc?

many thanks
 
There are two routes: the "proper" one - go to a professional designer, or the DIY route. Presumably as you ask you want the second?
Have you read up anything about Centre of Lateral Resistance and Centre of Effort? There are two fundamental starting points - one is the CLR, which will be determined by the hull shape, and trim. The other is the total sail area aimed at. That will depend on hull stability, ie how much sail it can carry. i would suggest looking at other boats, and doing some readings and getting a picture of common sail areas for a boat of your size and shape.
Then you need to do lots of scale drawings, playing with different sail plans, calculating where they place the Centre of Effort, and seeing how that position realates to the CLR. They should be close-ish, but there is a lot of subtlety in the relative positions and spacing.
When after a lot of reading, drawing, redrawing, talking, I would set about getting some cheap secondhand worn out sails of something similar to your design, and trying it out.

But then as I said, there are many who will be horrified at an amateur even contemplating doing this himself. But are you willing to pay, or do you want the fun or cheapness of doing it yourself and learning from mistakes?
 
As Clifford has said there are two ways to go. I would go by the D.I.Y. route, partly because I can't afford to pay anyone to do anything, and partly because I have learned so much by doing everything myself. A very good reference here is Howard Chapelle's 'Yacht Designing and Planning', and another is John Leather's 'Gaff Rig Handbook'. "Chap" will give you diameters of spars once you know the length. You could start with a mast length equal to the length of the boat's deck, and work from there. Once you have absorbed both of those books [they are both worth buying, not borrowing] your questions will become much more refined.
Peter.
 
John Leather is excellent. So much information, lots of pictures, I can endlessly re-read it for sheer pleasure, let alone finding out useful things like conventional ratios of mast diameters, etc.
Perhaps the first step is to stand back from the boat and decide what sort of style appeals most to you, having regard to the kind of boat it is or you intend it to be. Is it a yacht, or an ex-working boat, or some kind of conversion, or an unfinished home-made project. What shape of hull does it have. Will it ever be a performance sailer, worth driving hard with optimum tuned rig? Or is it tub for messing around in with the family and going out for a day's fishing? You can't turn it into something it is not, but you ought I think to try and do justice to whatever qualities it has, and presumably attracted you to the boat in the first place.

Lots of reading I would suggest in the first place, and comparing pictures. Then try designing a sail plan by eye, and then measuring to see what area that produces and where its CE is. Tinker with it and observe the effects of longer/shorter bowsprit, longer/shorter boom, higher peaked gaff, single or double foresails, etc.
Above all, have fun!
 
Does it look anything like this, for example?

xenia.jpg
 
Hi

THanks for your useful comments and apologies for such a clumsy question which I wanted to be as 'open' as possible.

After much research and help from others I have come to the conclusion that she is a one off homebuild, very similar to a Deben 4 T but with keel stepped mast coming through the coachroof and no forward facing portholes.

Looks like I have some reaading to do.............

thanks again
 
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