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Thinner, stiffer, faster: evolution of International 14 & Merlin Rocket masts

by Mark Jardine 20 Jul 2016 13:50 BST 20 July 2016
Katie Nurton & Nigel Ash win the International 14 Prince of Wales Cup © Mary Pudney

We spoke with Graeme Willcox of Selden Mast about their success at International 14 PoW Week where Selden spars won the PoW Cup as Katie Nurton became the first female helm to win the trophy, and the week overall where Stu Bithell & Sam Pascoe won on Glen Truswell's Concours d'Elegance winning boat. Graeme has also been involved with the Merlin Rocket fleet, where the mast section diameter has reduced significantly in recent years and Andy 'Taxi' Davies crewed by Alex Warren have just won with a day to spare Salcombe Merlin Week.

Mark: Can you tell me a little bit about the evolution of International 14 rigs, with the square top mainsails, and what that means for mast production at Selden?

Graeme: In the last ten or so years the rigs have moved from pin tops or small square heads to large square heads, which means the mast needs to be stiffer. We've achieved this by moving from a slightly larger section in the lower carbon modulus to a smaller section in higher modulus carbon.

Mark: The International 14s are now running huge tensions - how does the mast stand up to that?

Graeme: With the increased stiffness in the tube, it's a lot of UD (uni-directional) tapes running up and down the sides - that's how it takes the extra load.

Mark: Have you made these developments in conjunction with the sailors?

Graeme: Yes, in the early days we were working with guys like Rob Greenhalgh and Ben McGrane and getting their feedback on how their rigs were working.

Mark: It must have been quite a transitional period where you're going from effectively traditional carbon rigs which were replicating an aluminum rig to now rigs which can carry far, far bigger sail areas on the head. How has it been watching this transition and being such an integral part of it?

Graeme: It's been quite an exciting time. Moving from traditional fairly full sails with soft rigs, all the way up to now where these rigs are close on 45 - 50% stiffer than the were before. Sails are a lot flatter, working a lot more like a windsurfer sail instead of the traditional dinghy mast.

Mark: Moving on to the Merlin Rockets, the mast sections have gone from what you would regard as the traditional size of an aluminum section to now incredibly skinny masts. What challenges has that brought for Selden as a manufacturer?

Graeme: As you drop down in size on the section, you have to try and keep the strength up - that's always been the challenge. We've come down two sections in the last seven or eight years, down to about 45 millimetre tube but the mast wall is a lot thicker than it used to be, just trying to keep its strength up.

Mark: What was the mast diameter beforehand?

Graeme: Series 3 which is 65mm fore and aft and about 50mm sideways.

Mark: Is it stiffer than the previous masts even though it's thinner?

Graeme: Yes, we have gone up in stiffness, not as drastically as the 14s but they are definitely a bit stiffer nowadays. We also put a carbon fibre track up the back, instead of the traditional PVC, which has allowed us to add a bit more stiffness in a more efficient way.

Mark: What's the future? Is this trend going to continue?

Graeme: I don't know how much smaller we can go! But yes, it's definitely the smaller you go, the less windage you have, so the sailors all they want is less windage but then you get a bit of a trade off with weight.

Merlin Rocket sailor David Hayes talked about the differences the new sections had made to sailing in this high-technology development class.

Mark: What have you seen happen in the class with reference to the section size dropping and what that has meant to sailing the boats?

David: The Merlin has a very different kind of requirement, say from the International 14, because the rig loads aren't necessarily that high. The Merlin uses what they call a one-string system which allows you to put the rig in any position while you're racing, from forward to right back. It's also got a tiny jib so it is a very specific boat, so you are able to depower it if you wish. Because it's got a small jib you don't need hugely high loads. The evolution over the years to go smaller in section is more about drag and flow than it has necessarily been about holding huge rig tensions. The drag and flow component has been quite substantial so the fleet has changed dramatically over the last two years to a smaller section.

Mark: As a sailor, what major differences do you notice, apart from drag, with having a smaller section and the fore and aft stiffness?

David: Well that's the thing in a way, because actually the inertia numbers are very similar to the trusted favorite product, which was the Chipstow - a hand-built beautiful product - but it was just bigger and less consistent, so actually what we're offering with this particular product is consistency. We're actually able to replicate the first mast to be as good as the 10th mast off the mandrill by a machine downstairs. That's great for us and it's good for the competitors because we are getting repeatability.

Graeme then ran us through the process of building the stunning carbon spreader brackets onto these masts.

Mark: Many of the spreader brackets on the Merlin Rockets and International 14s are made of carbon. How is that done?

Graeme: We make them in a two-piece female mold. We laminate the carbon on the inside, put the mold together and bag it up in a vacuum bag and put it in the autoclave, which gives us quite a nice, consolidated, pretty fitting.

Andy 'Taxi' Davies gave us his thoughts after a major nose-dive prior to a race in Salcombe

Mark: Can you tell us what happened with your capsize in Salcombe?

Taxi: Are you sure that was me? (laughing) I'm trying to deny that I capsized! I was pretty impressed with the mast. When I was sat at the back of the bus watching the bow go down I was looking at the rig around the spreaders and thinking, 'is it going to go?' but it didn't even flinch.

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