Fun with lathes (Starwind 860 centre pins)

More supplies, more parts- my Starwind 860 trimaran project is, slowly, progressing.

In addition to the eight strut hinge pins from the last post, I've now finished the bearing sleeves and pins for the two crossbeam centre hinges.

The crossbeams of the Starwind 860 are hinged on the centreline. When the outriggers are retracted, the crossbeams fold into an inverted V shape, but remain connected so that the port and starboard outriggers move together. The joint is one of the most highly loaded spots on the boat, and so the centre bearing assembly must be suitably beefy.

The outer sleeves are of 2.5" OD aluminum tube, and they'll become part of the crossbeams. The inner sleeve serves as the hinge pin when the boat folds for trailering, and the centre pin locks the entire assembly into the two adjacent bulkheads when the boat's on the water.

In theory, the boat cannot exert enough force to damage this assembly (it would take several times her all-up weight to tear one of these pins out). In a collision, the outrigger hulls, and eventually the crossbeam outer ends, would fail long before these bearings are overloaded. This is similar to the "crumple zone" model used in cars; the outermost parts are the weakest, and absorb most of the energy of a collision as they progressively fail. Structural components closer to the passenger area (or, in this case, the centre of the main hull) are stronger, and because the outer regions have dampened the collision forces, these critical components should still be just fine even if a collision damages the outrigger.

Each centre bearing assembly took me about 2.5 h to make; as I've mentioned in previous posts, an experienced machinist with good tools would be much faster.



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