The Arctic Tern Project

Volume 3 Issue No. 12 January 1, 2007

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Knees and Beams

Last month we got the foredeck beams more or less done. This month was spent mostly trying to get the knees that define the side-deck sorted out. It’s critical that these are correct because they define the curve of the side-deck, the height of the side-deck and the curve of the cabin side. It took me half a dozen attempts to get the patterns right. It was that old problem about figuring out what to measure from and which measurements are most critical. I think in the back of my mind I always knew the method I should be using but it took numerous attempts at making the patterns before I finally decided there was really no other way to make them accurate enough. Anyway, here’s the way I think they should be done.

Knees

First off, I cut a slot in the sheer batten down to the horizontal where the knees need to go. Ok, this is a pretty messy cut but it will be covered by the knee eventually.

I make up a camber ruler laid out to the camber of the deck (3 inches in 8 feet) with the beam width and side deck widths marked for each of the stations (where the knees go).

I place the camber ruler in the slot and take my measurements for the knees from this.

After the patterns are cut I fit them to the boat. I’m using a laser level to check the vertical positioning of the pattern. You could also use a string line here. In fact a string line is better because it doesn’t depend on the boat being absolutely level. Because everything is laid out to the inside of the planking the string line should go through the slot you cut and just touch to top edge of the inside of the plywood hull panel.

After I’m satisfied with the patterns I use them to mark out the knees on the real stuff. A word about patterns: If you make them out of door-skin you can use a steel ruler and a utility knife to cut them out. This gives a really accurate pattern that you can happily use to mark out the real thing. Then I fit the knees to the boat. Here I’m still using the laser level put eventually I switch over to a string line. Use a really thin, strong string for best results.

Here I’ve switched over to the superior string method.

Once I’m happy with the fit I pin the knees in place with braces, nails, etc. so when they’re smeared with epoxy they won’t be sliding around everywhere and I won’t have to worry about lining them up. I’ve left those little triangles on the bottom of the port knees for positioning purposes, they’ll be cut off after the epoxy cures.

I rough up the spots where the knees will glue in for extra strength because I don’t think I’m going to glass these in.

Then they get epoxied in place. I put a small fillet down each side.

Cabin Bulkheads

The next thing I did was cut out the front and back cabin bulkheads. I use the two-sticks/three-nails method for drawing the camber in the top of the bulkhead.

More Beams

Next thing I did was make up the interior cabin braces (beams). These are made out of Yellow Cedar which is an absolute joy to work with. Looks good, smells good, feels good. I use the fore-deck beam as a pattern for the front brace.

Can you spot the mistake in the forward brace? The middle right screw hole is two inches to far to the right. Hmmm.

My initial plan was to terminate this forward brace where it will meet the carling. After I did the aft brace though I realized that it makes more sense to carry them all the way out to the sheer batten and just notch the carling into them. Originally I was going to notch the carling into the cabin bulkhead itself but this doesn’t really make sense. Better to just notch them into the brace. …So, the next day I re-did the forward brace. I took this opportunity to put the screw hole in the right place too. My scrap-rate for this yellow cedar is running about 50% right now. Ouch.

The next thing I did was the top brace for the forward bulkhead. I use the forward bulkhead as a pattern for the top curve. I want the brace to be narrower at the ends that in the middle (bottom curve flatter than top curve) because this looks nice. To get the bottom curve I thought I’d just use a batten and three nails. I was being lazy here. I really should have made a camber tracer. Notice how the batten kind of flattens out as it approaches the edges. The curve of the batten really needs to continue beyond the edge nails in order to get a fair curve. I was aware of this at the time but thought the curve would still look ok.

I was wrong. The curve looked terrible after it was cut out. Notice how the brace looks kind of fat near the ends.

There was not getting around it. I needed to use a camber tracer to get a decent curve. So I banged out a quick template using a camber tracer and reshaped the brace. See how different the curve is.

Looks ok now.

Next Time

More braces, cabin framing, etc.