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Rabbet cutting question....


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Being a first time builder and approaching the cutting of the rabbet. I thought it best to ask a couple of questions and perhaps some advice. I do have a build log going but wanted to reach a wider audience so decided to post in this forum.

 

I have just finished gluing the sections of the false keel together. The beardline and rabbet line have been transferred from the plans to the false keel and I will next began cutting out and dry fitting the bulkheads before cutting the rabbet.

 

I have spent time looking through the build logs, instructions and reference books but found little devoted to cutting the rabbet. I would think this procedure is critical to fitting the hull planks correctly. While I don’t want to get too far ahead of myself, I do realize that each step taken will affect the next step

 

Question 1:

Should the stern post be fitted before cutting? This isn't clear to me.

 

Question 2:

I notice in various logs that on more than a few occasions the bottom edge of some bulkheads either do not reach the drawn bearding line or extend past it. My question is; Should the bulkheads be modified to match this line or should the line be altered to follow the bottom edge of the bulkheads?

 

Thanks in advance for any information or advice passed along.

 

Dave

Edited by CPDDET
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Ad 1: I think it would be lot easier to cut the rabbet before any bulkheads fitted. The reason is that the angle typically is shallower as you can get with with tools, as the bulkheads would allow (depends on the technique though). Conversely, you will need to fit the stem and stern posts, as the rabbet usually continues along the posts and the keel, so should have the same depth all around.

 

Ad 2: If the bulkhead finishes before the bearding line, you may have to cut away from the wood of the keel in order to continue with a smooth profile up to the depth of the rabbet. Conversely, if the bulkhead reach below the bearding line, then something is wrong with the bulkheads. It could be that they are notched too deeply or the profile in the lower part is wrong. If you have a plan, check against it.

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I'd suggest you assemble your "backbone" (keel, stem, and sternpost) and your bulkheads/frames and make sure your bulkheads are perfectly straight and true. Then make yourself a "fid stick" (sometimes called a "fit stick,") which is simply a small piece of wood the same thickness as your planking. Place the fit stick against  each bulkhead and slide it down until it hits the side of the keel, or wherever else your rabbet is going to be running and tick off a mark with a pencil.  Where the inboard corner of the fit stick hits the keel is the top of your back rabbet. The outboard corner, once the rabbet is cut so the fit stick fits in the rabbet you will cut, is going to be your rabbet line. The fit stick should lay perfectly flat against the bulkhead and the back rabbet when the rabbet is cut.

 

If you make a small length of rabbet at each bulkhead with your fit stick(s), and then you draw a fair line between the rabbet lines with a batten, and cut the rest of the rabbet along those lines, you should have a perfect rabbet. As the back rabbet is a rolling angle dependent upon the shape of the hull above it, trying to mark a rabbet line from a plan is almost always a disaster. You have to "work from the boat," and not "from the plans" in a lot of instances. A rabbet is a three dimensional creature and all you've got are two dimensional plans. Without a fit stick, you are pretty much flying blind, whether a rabbet line is on the plans or not. Rabbet lines on plans are basically there to illustrate the extent of the planked surface and never the depth and angle of the rabbet itself, which is defined by 1) the thickness of the planking and 2) the angle at which the plank hangs as defined by the frame or bulkhead. If you have a station construction drawing that includes the rabbet, you will see how the shape of the rabbet is different at any point along its length.

 

Hope this helps.

Edited by Bob Cleek
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For this approach you have to be sure that the bulkheads are running correctly into the keel-plank for the envisaged plank thickness. In the original question, this was exactly the problem. The outside, i.e. lower, rabbet-line is defined by the plan, while the inside line depends on the angle with which the frame/bulkhead runs into the keel. I agree, that this line is best worked out on the model itself.

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