|Subject: Re: beams and trailers|
|From: Mike Crawford |
|Date: 2/5/2006, 12:27 PM|
|To: rob dalton |
Roughly how I imagined it. You could use your boom as the gin poles and then use the two booms to make a a bipod to provide support for a lightweight block and tackle. Possibly the bipod and a block and tackle could do the original lift but I don't know if it would be quite long enough to lift the mast high enough to pivot it in position.With a 9m bipod it would be a piece of. The main difficulty is setting up the boat with various sockets and rope attachment points. Check out robs original Harry in the articles section for how he worked on a big schooner rigged wingmast.
Mike Crawford <email@example.com> wrote:<<I suppose the mast could be raised on a pivot at the base, when vertical remove the pivot and somehow make sure the whole thing doesn't fall down. >>
That's it. Or at least that's the way Franke does it on cat2fold.
The mast is supported by a roller at the top, and then pinned to a sleeve that gets inserted into the hole on deck. This sleeve extends about 10cm higher on one side than the other, "missing" half the sleeve on the aft side where the mast is inserted. Lines triangulate out to each side to provide lateral support, while a halyard goes over a gin pole and down to a winch, and another line runs from the mast to the boat in order to prevent the mast from tipping over once it reaches vertical.
He then winches the mast to vertical. Once it's there, he fastens the missing half of the sleeve to make it complete, grabbing the mast at its base. He then uses a neat little lift that's about one meter high and 30 cm wide with a crank at the top. The crank is a 1cm rod/axle that extends out to a handle that's maybe 30 cm long. A line wraps around this axle many times and then fastens to the mast. He "winches" the whole mast up few centimeters with the lift, removes the pin at the base, and then lowers it with the crank. With the 30:1 power of that handle, even an 80 kg mast wouldn't be an issue.
There would still be some problems adapting this to a proa, but I think it's possible.
rob dalton wrote:The akas can be made perpendicular. But even if they weren't it only needs the pivots to be parallel. The pivots do not need to be perpendicular to the beams. The ends of the beams can sit on a flat suface and be held down but better if they are in a notch. the ends of the beams can be tapered to perpendicular to the hulls as they would have to be for any system of sockets. James Shannahan's original version of the folding sysstem was very elegant but the extra complexity is a big expense apart from the weight. Also the bridge deck comes either level or below the bottom of the beams. To get the boat to trailering width the lw hull needs to tuck under the bridge deck, preferably on its side. This could be done fairly easily with the expandable trailer. My experience with putting very tall objects into close tolerance holes has not been easy. It needs a gantry to lift the masts from near to their pivot point from almost directly over the hole. I suppose the mast could be raised on a pivot at the base, when vertical remove the pivot and somehow make sure the whole thing doesn't fall down.
Mike Crawford <firstname.lastname@example.org> wrote:
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