Sunday, April 8, 2007

Keel foam shaping

I spent some time Friday evening and Saturday shaping the keel foam on both floats. This was more tricky than I thought it would be -- it's easy enough to sand the keel down to the supplied template shapes, but that only tells you what three spots (form frames #2, 7, and 11) should look like. Making the rest of the keel nice, smooth, and uniform with those three spots is all your (my) responsibility. My new sander worked great, by quickly taking down all of the rough stuff. Once you're down close to the right shape though, it seemed difficult to me to really tell how you're doing. I really hope I did not take too much off anywhere -- we'll see. There's also the usual issue with the putty between the planks being much harder to sand than the surrounding foam -- if you lean in hard with the sander to take down some cured putty, you almost always end up digging out more foam than you wanted to. This is frustrating but I don't know a good way to avoid the problem. On a flat surface a good planer might work but on these curved keels, no way.

I started off with the keels looking like this:

Here is a mid-way progress shot:

And another:

And a picture from underneath the transoms (the one on the left looks pretty good; the right one needs more curvature):

By the time I decided it was good enough to stop (on Saturday morning), things were looking like this:

I don't think I'm 100% done shaping the keels, but I decided to save the final fine-tuning for after the decks are attached and I'm pre-fairing the entire hull. And I'm done with using the sander on the keels - next time will be all longboard (I'm afraid of going too far, as I mentioned).

By the way, I don't want to give the impression that I spent sixteen hours on this task -- it was more like three to four hours total, and a lot of that was on careful sanding of problem areas. It seems clear to me that Ian designed the building procedure this way (vertical keel plank\batten combined with post-float-join shaping) in order to avoid any tricky tight thermoforming around the keel area. If that was his goal then he succeeded, but I'm not yet sure if the new method is any better - but I'll tell you in a year when the boat is done :). (And I wonder why he designed the F22 float keels with less of a knife-edge that his other trimarans seem to have?)

Lastly, the resonance of the sander on the hulls makes a curious thrumming sound. My wife says it sounds like there's a full-scale light saber war going on outside. No sightings of any storm troopers, thankfully.

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