Bermuda to Gaff conversion on dinghy

magnocain · #1 10-11-2012

I have a 8' El Toro frakenboat. It is currently rigged with the typical Bermuda rig, the sail coming from a Sabot dinghy. The mainsail has a 10'-8" luff, and a 7'-2" foot. The sail is not perfectly triangular, so I estimate the sail area to be about 45 sqft.

This is my boat to play around with. I want to make a gaff sail. I plan to make it out of polytarp. I think I have figured out how the rig works, but I don't know what size to make the sail. I know the Gaffs are not as tall as Bermudas, but I do not know the particulars.

How long should the Luff be? The Foot? What angle should the head be at? Are there any other info that I am forgetting that I need to know?

Thank You.

peterchech · #2 10-12-2012

I love gaff rigs, though one would add complication and weight up high on such a small boat. My suggestion is to try it out, doesn't get cheaper and easier than poly tarp!

I have built several small sails from instructions on wooden boat forum, that is the place to ask this question. If u go with poly tarp, may I recommend you use the white uv resistant stuff? Costs the same practically but looks so much better. Also, there is no need to sew such a sail together. Just buy white, high quality duct tape (the really cheap grey stuff stiffens and falls off too soon) and some grommets. Tape all the edges, reinforce the corners with extra tape, and be sure the align the weave of the tarp with the leach of the sail!

Here's a video of my duct taped poly tarp jib from my previous boat, clearly the stuff works:

fast wa'apa outrigger canoe sailing - YouTube

magnocain · #3 10-12-2012

Any tips on dimensions? I found conversion ratios on the internet once, but I can't seem to locate it again. My centerboard and rudder are heavily weighted, so some topweight shouldn't be a problem.

paulk · #4 10-12-2012

I would not be concerned with topweight affecting the boat's stabiity so much as the possibility that the increased sail area (30% more than what's there now?) may make the boat very tender. You may be forced to reef the sail in order to be able to keep the boat upright. This somewhat defeats the purpose of having a bigger sail, if you can't use it fully deployed much of the time. The other issue would be the center of effort of the sail moving aft with the new Gaff rig. Generally the CE of the sail is designed to be fairly close to (perhaps a teensy bit aft of) the center of lateral resistance of the boat. This makes it so the boat has a little bit of windward helm going upwind. This is a safety feature: if the wind blows hard, the boat will tend to turn into the wind and not be knocked over. If the sail's center of effort is moved aft (which is what a Gaff sail would do here) the boat would REALLY tend to point into the wind all the time - like a weathervane. You might need to move the centerboard aft in order to compensate for the new sail, to keep the boat from immediately swinging into the wind whenever you pull in the sail. Moving the board would be an expensive hassle. The blue poly tarps also disintegrate in the sun because of the UV rays. Your time might be better spent finding and rigging a real El Toro mast & sail.

magnocain · #5 10-21-2012

After reading about different mast building techniques, my budget, and my experience level, I'm looking at a reenforced PVC mast. The mast goes 16" into the hull into a step, and an additional 18" to be high enough to not hit me on the head. What should should the dimensions on the mast, spars, and sail be to give me roughly the same power?