Thursday, November 10, 2011

Crossbeam Hinge

It's time to make my outrigger foldable.  I'll do this by hinging the crossbeams so that the ama can be lifted and pivoted over the main hull, thus reducing the overall beam to a legal trailerable width and avoiding the lashing and unlashing that gets old fast.
I've built a mockup of my Va'a Motu's forward crossbeam and am using 1/8" (3mm) plywood in place of the stainless steel plate I will use on the real hinge.

The beam is hollow with 3/4" (19mm) timber top and bottom with 1/4" (6mm) ply on the sides.  The timber on the Va'a Motu beam is actually two layers of 3/8" laminated together.

I drew a careful line where the beam will be cut and glued on two 1/8" plywood spacers that allow the hinge parts to slide past each other.

The 1/8" ply pieces that you see will be stainless steel plate and the fiberglass pins will be 5/16" stainless. I drilled pilot holes for the fasteners to make sure that the beam stays straight when it is reassembled.

I cut the beam in half with a thin kerf pull saw.

A bulkhead and side blocking to a depth of 4" (100mm) are glued into the cut ends of the beam to reinforce it.

The hinge plates are screwed into place and the pivot pins installed.  The real hinge will use epoxy bonded machine screws for fasteners.  The pivot pins will be drilled for locking pins and you only need to remove the bottom pin for the hinge to operate.

And there it is.  It seems stable enough for the job, so I'll hunt down some stainless plate and get to work on the real thing.
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