Originally Posted by settingsun
Smacksman - I am still trying to visualize this setup. At the universal joint, do the poles cross each other, one sitting above the other, or do the two ends meet? Do you have any issues of chafe on the inboard ends of the poles? Also, for 18' poles, what would be a reasonable diameter of the pole?
Here is a pic of the final Mk.2 universal in a rope
crucifix form -
The loops of the crucifix are a little long so the overlap is a bit too much but it still worked beautifully allowing the poles to rotate laterally and axially. The pole ends were being chewed by the expensive stainless Mk1 universal so I leathered the ends in Cape Town
(excellent shop in town sells hides and leather off-cuts, palm, needles and waxed twine).
Letting the pole ends overlap takes the stress out of the universal after the first Mk1 design was trying to force the pole ends to a point which soon distorted the pole end fittings.
Alma's poles were about 16ft. long and 'reverse engineered' starting with the pole end fittings that were available in Lanzarotti, a short length of ally tube with i/d that would fit and then the body of the pole was tube that would fit the o/d of the end poles. It ended up about 2"/50mm diameter thick walled (about 3mm) ally tube for the middle section like ally scaffold pole with the sections pop riveted together. Very cheap
and cheerful. The poles also did a good job spreading the awning in harbour.
The compressive loads on the poles are not anywhere near those of a spinnaker
pole on a close reach. Here is a clip
of me pulling the ends of the poles apart in 20 knots or so of Trades. I would never
be able to do that with a bag up in that strength of wind!
@Dockhead - That is exactly what I would do for bigger sails of heavier working cloth and if I had only one furling gear
then I would set it up in harbour and set off with it rolled and ready for action. If circumstances and weather
changed and you had to beat with it then sailing close hauled with one of the twins nestling inside the other works well for a few hours. I wouldn't like to do it much longer than that for fear of chafe on the stitching. Anyway, engines are for windward work
Also a good argument for twin roller reefing forestays. Excellent flexibility for choice of sailplan and good insurance
Slightly off-topic but with reference to furling gear
. If the sections of the foil are secured with grub screws and not pop rivets, make sure that the grub screws are glued in with Loktite or similar. From new furling gear fitted in Knysna, South Africa
to the time we arrived in Brazil
, a quarter of the grub screws were lost
forever and many of the remainder had unscrewed so that the top swiveler would not slide down the foil and therefore sail could not be dropped. This is a potentially dangerous situation. End of lecture.