Building a Carbon Front Beam from America’s Cup Mast Sections
This one started with two projects running in parallel. Anna was up in the sail loft recutting a fractional kite while Shayne was in the grinding bay with sections of an America’s Cup mast, working out how to turn them into a front beam.
The original aluminium front beam had to go. Not just for weight — the new carbon system would be structurally superior, and it would give Paikea things she didn’t have before: a proper attachment point for an inner forestay and a bowsprit to fly modern asymmetric sails from. The whole front end of the boat was being rethought.
The material was sections of mast from a former America’s Cup challenger — the same high-modulus carbon that was already going into Paikea’s rotating rig. The longest section became the longeron, the bowsprit that runs forward from the beam. Two shorter, thicker sections became the port and starboard beams that connect through the hulls. Shayne spent the day grinding the mast channel along the full length of the sections — a lot of work before the build even starts.
The structural joints between cylindrical mast sections at precise angles need careful filling. Shayne’s approach is a mix he makes himself — short strands of uni cut to make milled fibre, combined with microspheres for volume without weight, and cabosil to control the consistency. Microspheres alone and the mix droops and hangs. Cabosil makes it thixotropic — it holds its shape, stays where you put it. The milled fibre is what gives the cove its structural integrity, bonding the joint without cracking. It’s stringy and difficult to work with but there’s no shortcut in a joint like that.
The beam went in glued and lined up perfectly. By the next morning one end had slipped — not much, a few millimetres to port, but enough that it wasn’t centred. That’s the reality of a build under time pressure. It got fixed. The crane was coming and the whole assembly needed to be structurally sound before the boat went back in the water.
In the Series
The full front end rebuild — load paths, vacuum bagging, forestay fittings, seagull striker, martingale, trampoline — is all documented in the series Paikea’s Carbon Front End Rebuild. If you want to see behind the scenes photos in more detail, that’s what the members’ technical library is for. Join here.