Experimental sail for 'Alegra':A while ago I bought a second hand jib sail with the idea in mind that I could re-cut it and use it as a mainsail for one of my dinghies. The luff was too long to hoist as-is on a mast just over 5m long. The solution that occurred to me, was to cut off the head of the jib and make it into a square-top main. North sails agreed it could be done and did the work, adding battens etc.
The "Alegra" last had a Gunter rig with shrouds and lots of control lines. This time I was going for something super quick to rig.
So a free standing mast was required, one straight aluminum tube , so the sail could be set sliding up the mast on 'hoops'. I did not want a mast section with luff groove for reasons of economy and not wanting to alter the luff as well.
The lower end of the mast had to be thick walled, but if I carried it right to the top there would be a weight penalty and the length would be a problem when trailering. So a two-piece mast was needed with the upper portion being a thinner-walled tube, but the same OD as the lower end.
I had suitable tubes. For the lower part I used 2"OD x 1/8" (51mm OD x3.18mm), a bit light for an unsupported mast, but a 1.8m long solid pine internal plug in the lower end brought stiffness up to required level. Sleeving the two mast pieces was done with a stepped wooden plug to fit the two different internal diameters (the upper end has 1/16" (1.6mm) wall thickness.
The sail has eyelets along the luff, into which stainless steel wire hoops fit. The stainless steel wire hoops idea is as devised by Ned Macintosh for his Merrimac design. Hamish Laird, who used it on his Aludink "Amazon" explained the basic principle to me.
I formed the hoops using stainless steel MIG wire, which was to hand. To reduce friction, I fitted polyprop braid over the MIG wire hoops. A sprit boom made sense as it makes the rig self-vanging and simple.
Sail area is 5.25m2 (56sqft), fine for the stronger winds we have here at the Cape of Storms. In practice, although the hoops are made so one can un-clip them from the mast, I just drop the sail and leave it on the mast, then lower the whole rig complete with sprit boom by lifting it out. The upper mast section slips out and is stored in the boat, mast etc. are carried on top of the dinghy. Rigging is the reverse and takes minutes as everything remains attached.
|The 1.8m long pine plug being installed. It is pushed in until flush and then another 140mm.||The stepped pine plug is 12" (300mm) long. It was made by rotating in a jig with a router doing the carving. It got a bit slack on the smaller diameter, a layer of 2oz glass fixed that.|
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