Thursday, September 30, 2010


I'm still spending my weekends up helping my Dad on his boat, but I've continued to push ahead on free evenings after work.

I started placing the battens with the thought, "I'm going to use fewer than I did on the floats." But it didn't work out that way. Bending over convex shapes seems to beg for more to smooth things out -- too few and the transition is too sharp.  Sucking the foam into a concave shape, especially when it may not have been thermoformed completely requires some holding power -- and a couple extra battens spreads this out.  Where do you stop?  I think I used more than necessary once again.

I'm planning on vacuum-bagging this time (the surface is too tall and far to reach it easily for the 'poor man's' technique I used on the floats) so I added an extra batten along the top to extend the foam for sealant tape attachment. I also thought about the placement of the battens in relationship to where I will be installing the centerboard case.  As noted by others, the gunwale section forward of the forward beam mount are straight and therefore discontinuous with the aft battens.

With the complicated shape I spent more time trying to make sure the resulting surface was fair. A lot is happening with compound bends and twists to the battens in some areas. It's amazing how one batten will be more stiff than those next to it, or have to start twisting in a new direction -- and this will make it stand higher or lower than it should.  In several areas I attached very thin, flexible, strips under the battens (parallel to the forms) which smoothed these areas out (picture later).  It's possible that placing the foam does something similar, but I wanted to do everything I could.

Also, since the battens extend unsupported past form #1 (and they don't all want to do the same thing), I added extra support to position them how I though they should be.

At one point I remember seeing a wrist band with magnets that held fasteners at the ready. A magnet in the pocket allowed the screws to be handy when stooping (crawling?) underneath. My version below:

When doing the floats I tried to thermoform the foam and place it such that there was no tension on the battens. The soft (cheap) batten material I was using could be pulled out of shape if the foam was just forced into place and held with screws. I started with the same plan for the main hull, but I found that several factors made this more difficult to achieve.

The screws that I've been using don't really penetrate the foam very far. In some places I found myself expecting them to hold better than they could, so I went to longer screws that I held back with washers because the next size up was too long.  Of course, now I found some tips that were just penetrating the surface (which won't do for VB'ing). I circled these and then replaced close by, with the hole enlarged and later filled.

I plan on joining the strips of foam by placing bog between them - just like I did on the floats. Because of the size and gentle curve on the floats, I was able to place a shallow bevel with a router table and a dovetail bit after thermoforming (thermoforming after this step puts a cusp on the edge).  These strips have too big a curve to do this effectively.  Most builders use a Dremel tool to place this groove after attaching, which is likely what I'll do.

My previous experience was that the foam strips which weren't quite together allowed a small amount of material to push through - which was easily removed when fairing the exterior foam prior to glassing. On the other hand, those strips which butted close together were 'dry' on the exterior. I had to open and backfill some of these before glassing.  This time I'm using small shims between the strips to keep them slightly open and to encourage the gap to be filled all the way through. It's possible that with vacuum bagging (vs. hand lay-up) the exterior, any dry areas between the foam would be filled with epoxy, and therefore not require backfilling. I'll evaluate this when I get to that step.

Otherwise not much new.  Thermoform, scribe, cut to shape, trace edge onto battens.  Place packing tape, drill holes, pre-place screws from under side. (Behind the tape you can see the 'equalizing' strip attached underneath).

Then screw in place . . .

. . . and if you're lucky, someone will be happy to help.

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