Wednesday, August 7, 2013

Sailing with the new tramps

The deserted rigging lawn at DPSS, a glamour winter's day in Queensland. The boat has been on the water half a dozen times now, and looking fairly promising, though lining up against other moths has proved tricky.

A large part of this project has been designing and building the aerodynamic tramps for the boat. They are shaped quite carefully to maintain attached airflow around the lower surface when sailing upwind. The tramps are supposed to generate lift downward and to leeward, with a slight forward component, reducing drag and possibly even contributing to the driving force. Despite being complicated, heavy and generally troublesome, I like them. A few people have suggested that, as an alternative, i could have built the wings as rigid carbon structures, and I think there is merit in that idea. I went down this path because:
  • I wanted the option to disassemble and pack up the wings for transport
  • I didn't want to have to make all that tooling
  • I was happy in this instance to base the design on a tried and true structure
At this point I should thank Yancy Smith at Doyle Sails Queensland for teaching me everything I now know about sailmaking, letting me stay at his house, use his sewing machine / loft etc. I spent some time trying to 'work off' my debt doing sail repairs, so if yours was the luff tape I sewed on or the batten pocket I fixed etc, I apologise in advance for the sketchy workmanship. Totally out of character for an otherwise high performing loft.

With access to the sail plotter, I had the chance to experiment with ways of unwrapping / flattening the panels from the rhino model. Once in 2d, You can throw in the seam allowances and number the panels ready for plotting and cutting. I think it was the first time Yancy had done that with the plotter, and hopefully in the future it will streamline the process of making boat covers, bags, logos etc. Once everything was cut out, it was just a simple process of sticking it all up and sewing it together! A week later, I had the first set of tramps that everyone has seen already.

We initially went for a Technora laminate for both the top and bottom skins, with a luff pocket made of black luff sleeve material. As it became clear that fitting the bottom skin was going to be a challenge, I sewed it all together with just the top skin and went sailing. The Technora looked great, but had a couple of major flaws- it was slippery - soon overcome by adding taffeta film, and it was too stiff meaning that the few wrinkles from the luff pocket couldn't be pulled out. In the end though, it was the point loading near the seams that brought it undone, and it started falling apart after a couple of sails and one return trip on the highway.

I went back up to Yancy's and unpicked it all, replacing the top panel with some heavy black Dacron. We worked out how to tension the bottom skin to the bolt rope track, and it all went back together. The Dacron on top looked much tighter, (but obviously wasn't due to the extra stretch, the Technora had a great rigid feel despite being a bit wrinkly) and the sail shape in the bottom is 80% there.

Here's a bit of a montage of the tramps going together:

I've been sailing twice now with the full wing tramps, and it generally feels nice and clean. Definitely reduced air noise around the boat, though reaching and running you'd struggle to see a speed difference, possibly due to the extra couple of kilos in the tramps alone. Upwind though I think I have managed to get the flow to hook up a couple of times, and she feels like a rocket. I haven't really lined up against anyone who's super fast yet though, (no offence Rob!) so probably too early to make a call.

Practically, our efforts to get water to drain, tension to remain and things to be generally durable seem to be paying off, with the lower skin being hardly noticeable when sailing. I can't feel any real difference when righting from a capsize etc, though haven't been out in anything more than 10 knots and flat water. It's a fun experiment.

Here's a short video, marginal conditions, footage captured by Rob Green from the rescue boat. Check out my sail looking shitty! Next big item on the agenda is the rig, and between Yancy and I, we have a few ideas.

1 comment:

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