Bulkhead radius bad?

Posted by Laszlo on Oct 24, 2004

I was fitting the deckbeam to my wife's CH16LT yesterday and the instructions about the vertical placement seemed a bit ambiguous, so I rigged up a test.

I put the forward deckbeam temporarily into place and put a pipe along the centerline across the top of the 2 deckbeams and the forward bulkhead (pictures A & B). Since the deck is supposed to be a constant camber of 16" radius and plywood will only bend in 1 direction, that makes the deck the intersection of a 32" diameter cylinder and the hull's sheer line (which is why we have to plane the sheer clamps to a 16" radius). The bottom of the pipe shows what the deck line will be.

So, I found a gap between the top of the forward bulkhead and the bottom of the simulated deck when I put the deckbeam in the position shown in the manual. Not entirely unexpected, given the references I've seen to having to fill the gap between the deck and the bulkhead. I could make the gap go away if I lowered the deck beam (picture D), but then there wouldn't be much support for the beam against the sheer clamps.

I decided to simply add more wood to the top of the bulkhead, rather than fool around with patching the gap after the deck was on. I cut an arc that had a 16" radius of a length that would result in the gap being filled. When I dry fit it to the bulkhead, I found that the existing bulkhead did not have a 16" radius.

The bulkhead was cut by CLC on their CNC cutter, so it wasn't something I did. Just for consistency, I used the 16" planing guide that came with the kit and found:

1. The deckbeams (fore & aft) were 16" radius. 2. The bulkhead was not. It was less than 16" 3. The bulkhead pattern in the plans was not (picture E). It was less than 16".

Now unless I'm missing something, this pretty much guarantees a bulkhead/deck gap at least at the edges by the sheer clamps, since everything except the bulkhead itself is 16" radius.

So, my question is:

Am I missing something? Is this a deliberate design feature that I just don't understand?

Anybody got some words of wisdom on this?