surfdabbler

Well, Christmas is over, time to catch up on my build log.

I’ve mostly been busy on the keel and the canting mechanism.

First the keel itself – my original straight balsa keel was nowhere near strong enough to support a 1 kg weight on the end, so I remade it with ‘stringers’. This helped a lot, but still not strong enough. With a single layer of 1.5oz cloth, there was still a fair amount of flex in the keel. I measured the flex by measuring the force required to bend 5cm along the full 40cm length. This was longer than the final keel, but was a good reference point. Anyhow, here’s the measurements I got as I added more and more cloth to get the strength I needed. The measurements are rough, as I can’t find my written measurements, and I’m typing this from memory…

Weights to flex 5cm over 40cm length…
1 x 1.5oz cloth = 250 gms
2 x 1.5oz = 350 gms
2 x 1.5 + 1 x 4oz cloth = 500gms
2 x 1.5 + 2 x 4oz cloth = 900gms. Now we’re getting somewhere!

I figured this is sufficient strength. My keel bulb is about 1kg, and the final keel length is going to be 25cm at most, so it’s shorter than my full test piece. If the canting keel works well, I may even shorten the keel to between 15-20cm, for closer to the correct scale length. The keel was also reaching just over 5.5mm thick with all that glass, so I don’t want to go thicker. Anyway, we’re probably looking at only a couple of cm flex on a horizontal keel, so that’s strong enough for me.

The next stage was the canting keel mechanism. After tossing around a few ideas, I decided to get some sealed stainless steel bearings to mount the keel. I fitted these into the tube at the bottom of the keelslot. A friend of mine is a man-arts teacher, so he made up some nice ends and axles to fit. This whole setup will allow the keel slot to be removeable/replaceable if required later, so that’ll be nice. There’s a photo of the exploded keel slot below. Once this was all done, and the end pieces were fitted to the hull, the whole lot was epoxied into the hull.

The keel bulb was also drilled out to fit the keel, and the keel epoxied into the bulb. I discovered that lead is really not easy to drill. The metal is really soft, and the drill bit jams easily. On my first hole, the drill jammed and twisted the whole lot out of my hand and slammed it against the post of the drill-press, bending the trailing edge of the bulb, as shown in the photo. I had to hammer it back into shape.

The keel is epoxied into the hull, and drying now, so hopefully it won’t be long before I can fit it all together. I’ve also squared off the top section of the keel, so that it will fit snugly in the keelslot. With a canting keel, I’ll also need dagger boards, so you can see a couple of those in the keel photo.

By the way, this keel assembly is by no means meant to be waterproof yet. Waterproofing will come later.