Technical
You start at 30 per cent
Seldén Mast continues to perfect the art of delivering fast lightweight carbon spars... and at accessible levels of cost
If there’s one area where the benefits of weight saving are frequently underestimated, it must surely be in the rig. When it comes to the additional performance-sapping inertia that is created when a boat is heeling or pitching, weight aloft has an exponential effect the further it is from the waterline. Rig experts Seldén know this well and like many other spar manufacturers they have invested considerably in carbon spar building technology to reduce weight aloft. But the gains go much further. Seldén’ s starting point when
compared with an equivalent alloy mast is a 30 per cent reduction in weight. But this is just the headline figure, refining the design can improve the savings considerably. And while the motivation to reduce weight is the same for all carbon spar builders, the Seldén approach to building carbon spars is significantly different and has been delivering impressive results. ‘We describe our process as
mandrel filament moulding (MFM) in which we lay towpreg [pre- impregnated fibre] around a male aluminium mandrel,’ explains Seldén’ s head of sales, Sam
68 SEAHORSE
Vaughan. ‘We then put the tube into our autoclave where the laminate cures under pressure. The heat also causes the aluminium mandrel to expand, which achieves further compression on the laminate against the shrink wrap that we put around the tube before it goes into the autoclave. This ensures a great consolidation of laminate and a very low resin content at around 33 per cent. Once cured and out of the autoclave, the mandrel shrinks down and we pull it out from the cured tube with a big hydraulic ram.’ This single section method of construction provides a further advantage when it comes to joining tubes. ‘We can build single tubes up to 21m, beyond that a join is going to be required’ Vaughan continues. ‘But unlike our competitors, who have a front and back section that are joined either side along their entire length, our join is typically 600-700mm long for a 24m mast which offers a big weight saving.’ And while Seldén are justifiably
proud of their production technique, they point to the accuracy, repeatability and reliability of the system as the three key benefits
Above: for the Farr X2, like any one- design class, there is an obvious benefit in using a mast builder who can deliver spars with identical weight and bend qualities. But Seldén’s precision also lends itself well to producing optimised full custom rigs
that place their spars apart from their competition. ‘Laying the towpreg onto the
mandrel is computer controlled and is extremely accurate’ Vaughan says. ‘The machine will lay down fibres at certain orientations depending on the design of the tube. And while this is a very efficient and cost-effective way of building carbon tubes, the biggest advantages to many of our customers in the one design scene are the accuracy of build and the repeatability of the weight and bend characteristics of our spars. ‘A good example of that goes
back to when we were developing the spars for a contender for the new women’s Olympic skiff class, the RS900. Here, consistency is one of the key criteria for any new Olympic one-design class. We built four rigs over a three to four-month period, all to the same specification and when they were bend tested the variance was just two per cent. It’s not difficult to see why the accuracy and repeatability is appealing to one-design builders, but the process of using aluminium mandrels and filament winding also
MATT CUMMING/VICSAIL
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