Friday, November 4, 2011

back on the horse

Its been about 10 months since the worlds. A pretty good amount of time to rest, digest new information, work on other things etc etc. But, the itch to go sailing is back and I now have a Doink-built Alpha shell (thanks mate!) sitting in the garage waiting to get turned into a new boat.

So, the plan was to start with the most outrageous contraption possible, and gradually change it into something that sort of worked. I'm not sure about that plan anymore, due to day to day time constraints and the pressures of modern life and whatever else. So, I've decided to go with something more conventional. Evolutionary rather than revolutionary, and maybe then try and put a wing on it.

But, it seems like a waste to just chuck ideas away, so I decided to post some things I've been thinking about on here, maybe generate a bit of discussion and possibly inspire someone else to take it a step or two further. They might trickle in, but here's the first one.

The canting foil.
After an initial thought experiment and then some basic 2d cad "calculations," I decided that this would probably be worth a try. But a discussing it with Nick and Markla, we came to the conclusion that it was going to be a lot of work and structural compromise for no a huge gain. Markla did a few proper numbers to illustrate this point. Anyway, I'm still not completely discouraged and it will just go on the back burner I think!

The system I arrived at to make this work is as follows: The foil cants side to side about a bearing mounted at deck level. Very important to have the bearing on the deck, as you seem to get absolutely no advantage over a fixed foil with it at the keel. The bearing needs to be pretty snug, so there are replaceable nylon inserts inside the carbon tube. The centreboard case is supported from the top, but a sliding 'car' that runs along a bit of aluminium bike rim acts as a third point in case you hit a sand bank. I was initially thinking of using a stainless lead screw to control the cant, but decided there was too much machining involved, so I went for an 8:1 purchase system running through laminated-in thimbles. The purchase would need a serious amount of pre-tension in the form of a big bungee to compensate for the changes in line length between 'centred' and 'canted'. Even so, you would never achieve the stiffness from the foil that you get from a fixed centreboard case. That's probably the biggest trade-off. Another issue is that you're left with a large hole in the bottom of the boat, which is among other things a structural problem. This is overcome by some longditudinal bulkheads that tie the fore and aft bearings into the chines and act as beams to stop the hull from snapping. A laterally sliding carbon plate, flexible in one direction only, sits around the base of the foil and fits into a specially moulded carbon groove at the front and back of the hole (not modeled, quite difficult to draw actually) and a small fixed venturi drains it.

In the end, the foil can cant through about 15 degrees comfortably, which is all you would need. From a sailing point of view, i envisaged that the controls would be quite lightly loaded and accurately adjustable. You would probably just centre it in the tacks and when sailing downwind. its an upwind device really.

Wednesday, February 16, 2011


Finally got around to watching my interview from the worlds. Knowing full well that i'm a pretty rough looking bloke I was putting off watching at it in the name of self esteem, but now I've seen it and i think the worlds media team really did a great job so i thought I should share it. The particular 'some guy' mentioned I think was Bill Olsen (with probably the nicest paint in the fleet) - don't think we'd met at that stage.

Sunday, January 23, 2011


thanks very much to Thierry Martinez for the shot.

Without going into too much detail, I had a great time at Belmont. It was especially good to meet so many moth people for the first time. Thanks to John Harris and Clive Watts for helping me get set up with a rig that worked, and cheers to the guys like Andrew Stevo, Bruce Gault, Bill Olsen and Al Goddard who generally hung around the repair shed and were really generous with their advice and bits of carbon. It was also cool to meet Dave Lister and check out some of his genius carbon work on the 'monstro' and likewise Luka with the scalpel and John Ilett with his latest prowler. All three are lovely looking boats with great ideas and top blokes behind them.

So anyway I didnt do very well on paper - 34th in the silver fleet and I think over the regatta i had as many DNFs and i had places. In one race i did manage a 15th in silver, which I was quite happy about in breeze. Also i logged a new top speed on the speed puck of 27.2 knots. I was really pleased, but I heard later that the fast guys average that on a downwind, so again i need to find another gear.

The boat performed reasonably. I cant say I had it right on its game because I was stuffing around with the foil angle of attack the whole regatta, and never quite got it right. I noticed after the first day's racing that my boat was sailing around with the flap fully down, which cant be fast. The refinement process was complicated when I snapped the strut in one very windy race, after the gudgeons on the gantry came apart and the rudder parted company. I could say I was a victim of the weed clumps, but the reality is that I needed a carbon spar in the strut. On Bruce's advice I hollowed it all out and glued a stack of carbon rods in the break, then scarfed the laminate back over it and she's probably stronger and stiffer now than before.

for reference, A good angle of attack for my main foil design is 2.0 - 2.5 degrees from what I have seen and what people suggest.

I got more DNFs for other stupid things - my vang strop came undone at one point and I had to sail in to fix it. The sail got chafed on the concrete and wore through the webbing strap at the top, causing it to fall down the mast and I lost 3 races I think. Angus had a similar issue and we were both at the sailmakers on the same day. Probably the dumbest was when I went out after racing was cancelled in a gusty 25 - 30knots, and blew up the vang, causing the sidestay to get overloaded and rip the front wingbar off the boat. the rescue was a bit difficult and I felt a bit bad for going out and causing drama when I should have stayed on shore. the wingbar will be sleeved together in good time, but after that I called it a regatta. It was actually pretty fun sitting in the club on the last day watching the racing. probably the best spectator sailing ive ever seen - and ive watched a lot of match and team racing!

So as a way of capping off this post, heres a diagram of something I was keeping a bit secret. Its my integrated hinge concept. It has never worked in the past, but I fixed it I think. It survived the nationals and worlds anyway. The trick is to make the centre 70mm or so a standard sikaflex hinge like a bladerider, and then have a couple of narrow points, about 5mm wide (section a) along the span to stop the hinge going 's shaped'. section b shows the normal 10mm gap to allow the carbon surface to bend around a decent radius. A few people mentioned that it might work better if the seamless surface was on the bottom, which is fine, as long as you keep the hinge dead straight so it wont bind up.