Thursday, May 2, 2013

The Utility, part 2: The Keel

The Utility's keel is made from a 1" x 3" x 8' board, laminated on the inner surface with an additional 1/4" x 3" x 8' plywood backing piece. Optionally, the builder can substitute a 1-1/4" thick solid board. I chose the standard laminating method.

This is where I ran into a little trouble. 

Firstly, I had cut the frame notches as precisely as possible, as-drawn on the plans. For the keel notch, it was 1-1/4" deep. 

Secondly, the "1-inch" mahogany board I'd bought for the keel was in fact only 3/4" thick. (I touched on this in my last post.) So, after laminating on the 1/4" plywood keel backing, the keel was at this point only 1" thick overall.

I briefly considered scrapping the keel and buying a full 1-inch mahogany board to re-build it. The problem there is that mahogany is quite expensive. Also, as you'll read in other boatbuilding blogs (and certainly this one), problems arise. It's a given. If you re-start every time a problem arises, it will take you forever to get the boat built. What I've found is that boat construction, particularly for the first-time builder, involves a lot of troubleshooting. Frankly, that's part of the fun. At least, I think so.

I decided to simply add a second lamination of plywood in order to make up the needed thickness to match the 1-1/4" notch. I did still have some left-over 1/4" marine plywood, but not enough to cut a full 8' length. So, I decided to try my hand at a scarf joint.

Instructions for making scarf joints were included in the plans. Basically, to scarf two sections of 1/4" material, you bevel the ends of each piece along a 3" span. Then, you flip one piece over, fit one diagonal bevel over the other, and glue the two together with epoxy. Creating the bevel is probably best done with a plane, but I didn't have one at the time. So, I used a small Black and Decker sander.

Scarf joint before being glued.
Scarf joint after gluing.

I glued the scarf joint together and added the second keel backing with Poxy-Shield thickened with #2 Silica. The end result wasn't exactly pretty, but it was functional and felt very solid along the full length of the keel.

As with the Squirt, the Utility's transom is raked backward at a 12 degree angle. Notches in the transom frame members must be cut before fastening all the transom parts together. This is because the keel and floor battens do not pass through the transom. Instead, they butt up against the transom. Ideally, the transom frame notches should be cut in such a way so as to match the fitted angle of the transom.

I did not do this. Instead, I simply made perpendicular cuts into the transom frame members. As a result, when the assembled transom was fitted to the construction form, my notches turned "downward" 12 degrees. This meant that for proper fitting, I would need to bevel the ends of the keel and floor battens. I did this using a circular mitre saw cutting on a bias, in addition to using a rasp, file and sander.

In the end, it worked out fine. However, I'd recommend cutting the frame notches at an angle if possible. I believe the final joint would be stronger.

Aft end of keel after beveling.

Beveled keel fit into its transom frame notch.

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