The Starwind 860 trimaran's crossbeams are joined on the boat's centreline by a massive hinge pin. This mechanism ensures that the two outriggers fold in sync. The peak load on the centre bearing could be up to 41 kN (about four tons) port-starboard or 11 kN up-down, and the structures around it need to reflect that.

Safety first! Here's Katy showing off the latest fashion in shop-safe eyewear.

The blocks she's cutting are to join the starboard crossbeam's tang, here sitting on its own, to the rest of the starboard crossbeam. The port crossbeam's clevis is already in place.

Clamping the two crossbeams together, with the strut bearings and outrigger mounting flanges aligned, ensures that we're keeping things more-or-less symmetrical.

The tang is in place, dry-fitted. We always dry-fit every part, to ensure it all lines up correctly, before adding any epoxy.

The centreline bearing has three concentric layers. The outer aluminum sleeves are integrated into the crossbeam centre blocks. The inner sleeve, shown here, joins the port and starboard crossbeams, allowing them to pivot freely. When the boat's in operating configuration, with the outriggers extended, a pin is inserted through the centre of this sleeve to lock this joint to the bulkheads on either side of it.

The outer sleeves must be parallel and concentric. Using the inner sleeve as a guide while gluing up the tang is a good way to do this.

Once all that's done, these layers of 6 mm okoume ply will be bent and laminated to form the top and bottom flanges of the crossbeam box section.