Why not just make a simple parallelogram with the two beams so that the two hulls lie alongside each other? Since one hull is longer than the other, this would result in little or no extra length of the folded boat. The only alteration would be in the ends of the beams, with seams or breaks in the middle of the beams. The hulls and beams could be held in the open, deployed configuration with a simple X setup of cables.
You could make hinges at each end of the beams, but even better would be to make the beam sockets open on one side. A little difficult to explain without illustration, but something like this: Suppose the end of a beam is a tube of 200 mm diameter. The socket might be a pie shaped indentation in a hull, 200 mm high and perhaps 1000 mm deep and wedge shaped, so that one side is perpendicular to the hull centerline and the other side is parallel to the centerline. A single vertical pin through the beam allows it to rotate, but when sailing, the stress is transferred directly from the beam to the hull socket. The wedge shaped openings face forward in one hull and aft in the other.
An improvement at the cost of more complicated construction would be if the pin through the beam was at 500 mm of the 1000 mm socket. The socket would then have to be "butterfly" or "bow tie" shaped, with one end of the socket open on one side and the other end of the socket open on the other side. Then, when the boat is opened to sailing mode, about 400 mm of the beam is pressing on the forward side of the socket and about 400 mm of the beam is pressing on the aft side of the socket. A wire stay holds the beam in exactly the correct location, and the vertical pin through the beam is only used when the boat is folded together.
You could make hinges at each end of the beams, but even better would be to make the beam sockets open on one side. A little difficult to explain without illustration, but something like this: Suppose the end of a beam is a tube of 200 mm diameter. The socket might be a pie shaped indentation in a hull, 200 mm high and perhaps 1000 mm deep and wedge shaped, so that one side is perpendicular to the hull centerline and the other side is parallel to the centerline. A single vertical pin through the beam allows it to rotate, but when sailing, the stress is transferred directly from the beam to the hull socket. The wedge shaped openings face forward in one hull and aft in the other.
An improvement at the cost of more complicated construction would be if the pin through the beam was at 500 mm of the 1000 mm socket. The socket would then have to be "butterfly" or "bow tie" shaped, with one end of the socket open on one side and the other end of the socket open on the other side. Then, when the boat is opened to sailing mode, about 400 mm of the beam is pressing on the forward side of the socket and about 400 mm of the beam is pressing on the aft side of the socket. A wire stay holds the beam in exactly the correct location, and the vertical pin through the beam is only used when the boat is folded together.
Hope that makes sense.
Larry Forgy
On Thu, Jun 11, 2015 at 8:43 PM, Michael Gehl mike@vail.net [harryproa] <harryproa@yahoogroups.com.au> wrote:
Perhaps a 4-bar linkage (i.e. Farrier type) anchored to a central “toy chest” might do the trick. It would keep the hulls upright when folding.
I suspect the scissor beams would carry a significant weight penalty, whereas the 4-bar has strut triangulation on its side.On Jun 11, 2015, at 5:01 PM, Mike Crawford mcrawf@nuomo.com [harryproa] <harryproa@yahoogroups.com.au> wrote:
The Farrier system would probably end up dumping parts of one or both hulls into the water as it folds -- it's more suited to a trimaran than a boat with two hulls. Plus, I'm not sure about it handling the sailing loads from the mast. And if you want to collapse the boat for a marina slip, there's a lot to be said about not having to apply antifouling paint to the hull sides.
It would be easier to go with either telescoping beams or a scissors-beam like the cat2fold catamaran.
The telescoping beams would be simpler and lighter, and would costs less -- not just because of their simplicity, but also because the scissors beams are patented and would require a $1,200 license.
However, I'd go with the scissors style to make collapsing the boat on the water as easy as possible while singlehanded.
- Mike
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Posted by: Larry Forgy <larryforgy@gmail.com>
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