fitting inwale - breasthook - knees

[ChuckG]

Once again, it's not the geometry, it's the joinery. Could I have some suggestions for the best technique for making the inwale fits to the breasthook and the quarter knees? This is an open 14 foot lapstrake boat that will have an inwale and a rub rail sandwiching the top edge of the sheerstrake and the frame ends.

It seems as if there are two basic options:
1. Cut the notches in both the breasthook and the knee, fit one end of the inwale, then use the notch at the other end of the boat to mark the end of the inwale, and cut it, praying that it's not too short.
2. Conversely, use the pre-cut ends of the inwale to mark and cut the notches in the knees/breasthook, praying that the notches don't get too big.

Which is best?

I'm aware of the technique of using a thin pull saw to fit the joint (kerfing), but relying too much on that is what creates the risk of getting things too loose.

Other drawbacks to kerfing the joint include the danger of even touching the saw to the shoulder of the joint and thereby leaving a small, but oh, so visible bit of kerf right where you don't want it, and also the fact that a thin saw tends to wobble slightly in the joint, leaving less than an absolutely straight line. But using a dozuki, rather than a ryoba, might make the cut straighter.

What I'd like to be able to do is "measure twice, cut once" and be done with it.

Any other suggestions or techniques out there?

Thanks,
Chuck

[DougC]

Use option one. Also consider making a pattern from a short piece of inwale stock and fit it to the quarter knee to make sure you have the angles right (actually much harder than getting the length right). In any case it is a tricky procedure.
Doug

[Brian Palmer]

Tom Hill explains how to do this in Ultralight Boatbuilding and it worked well for me on a canoe with breast hooks at both ends of the boat.

-- Brian

[Bob Smalser]

Lay the overlong inwale on your bench and use it to mark its rabbet in the breasthook and knees before they are installed. Cut those rabbets.

Then cut the breasthook end of the still-overlong inwale. If there is a whole lot of short-radius bend along the sheer in the last couple feet of inwale, then angle the cut a half degree or so off of the normal 90 degrees with the bevel on the sheer side of the inwale. Not too much, just a hair....because if the rabbet is 2" or so long, the rabbet will be dead flat but even once riveted, the inwale will have a tad of bend in it.

Install breasthook and knees and rivet in the still-overlong inwale to the breasthook, leaving the inwale a couple inches long and overlapping the stern knee rabbet by that amount, laying atop the rabbet.

Rivet inwale to thwart knees and frames starting at the breasthook and working sternwards....stopping just before you can no longer spring out the stern knee overlap enuf to cut it.

Clamp the inwale to any frames not yet riveted and mark where you will cut the inwale end to fit the stern knee rabbet. Mark all four surfaces by removing clamps and springing the inwale outwards using a block jammed between sheerstrake and inwale to hold it clear for marking and cutting.

Cut outboard of your lines....how far outboard depends upon your confidence. When in doubt, cut it long, then bring it on for a looksee, then block it back out and gradually pare with a block plane by trial and error for a perfect fit.

[Bruce Hooke]

I would certainly lean towards method 1. I think it will be much easier to accurately cut a piece to length then to cut a notch to fit. So, I would cut the notch first and then cut the inwale to length. Once you have the knee and breasthook in place and as much of the inwale as you can fastened in place then you can mark the inwale to length and cut it carefully. One way to gain some comfort with the process would be to get the breasthook and knee in place and then temporarily clamp a 2' scarp of inwale size stock in place overlapping either the knee or breasthook (whichever is going to be the end you cut to fit) and cut the test piece "to length" as if it were the inwale. This will give you some practice and warn you if your marking technique is off.

[Bob Perkins]

I did this exact thing in my Fundementals of Boat Building class at WoodenBoat School.

It is much easier than you would think using patterns. Get "Building Small Boats" by Greg Rossell and he covers it very clearly.

His answer in the book is better than I can write here..

Take Care,
BOb

[Paul Scheuer]

I'll vote #1. Then if you cut the quarter knee rabbet at a slight angle, or maybe even an angle that matches the transom angle, it will be easier to trim the inwale end as you do the trial fits. Once you have a perfect fit, you can make the final, final trim to the top of the inwale.

Let us know what you end up doing. Pics too.

[Jack Heinlen]

Second getting ahold of Tom Hill's book, Ultralight Boatbuilding . Absolutely the simplest, most direct way to get a good fit I've ever seen. Too long to explain, plus pictures really help.

[Jon Etheredge]

It seems as if there are two basic options:
1. Cut the notches in both the breasthook and the knee, fit one end of the inwale, then use the notch at the other end of the boat to mark the end of the inwale, and cut it, praying that it's not too short.
Chuck,

Your method 1 is close. But I can almost guarantee that the inwale won't fit until you do some fiddling with the joint.

Here is one method that will produce an exact fit on the first try:

1) Notch the breasthook and stern knee and install them in the boat.

2) Take a 2-3 foot long piece of scrap inwale stock (or other scrap that is the same size as the inwale) and fit it exactly to the notch in the stern knee. Cut a clean, square end on the opposite end.

3) After you have this piece fitted to the stern knee notch, put a tick mark on the sheer at the point where the square end stops. Remove the pattern piece from the boat and set it aside.

4) Fit one end of the actual inwale stock to the notch in the breasthook. Spring the inwale into the boat and pick up the tick mark that you put on the sheer in step 3.

5) Take your inwale stock to the bench. Align the pattern piece exactly with the tick mark you picked up in step 4. Using a comination square, transfer the four intersections formed by the beveled end of the pattern and the corners of the stock to the corresponding corners on the inwale. Connect the transfered marks to give you the straight lines that define the bevel.

6) Cut to the lines.

If your layout and cutting are done carefully, the inwale will fit perfectly on the first shot with no guesswork or fitting required.

After you've done the pattern method a few times you'll figure out how to do the same job more quickly with a tick stick and your bevel gauge.

Oops, I almost forgot to mention one other thing...

It is helpful if the end of the notch in the stern knee or breasthook (both if you like) is cut with an angle slightly greater than 90 degrees. This just makes it easier to get the inwale sprung in to place after it is cut to the exact length.

[ 03-03-2004, 04:21 PM: Message edited by: Jon Etheredge ]

[ChuckG]

Thank you , everybody, for the responses. I tried some things last night on the port side inwale. A few observations:
1. "Kerfing," even as described by Rossel, seems like a desparation measure. Rossel would have you leave the inwale a quarter too long, and use kerfing to march it in. I tried that, and it ends up with a pretty ragged-looking joint, as I feared in my first post. (Not to be critical of Rossel at all, it's me, I'm sure)
2. Leaving a bit of a bevel in the the end of the inwale allows the inwale to fall into place when it's ready, rather than having a press fit into a 90 degree joint.
3. I'm going to try a tick-strip and Bob's suggestion of using a block plane for final fitting on the starboard side.

Also, I'm about to order "Ultralight Boatbuilding" from Amazon - it isn't the book I thought it was (isn't there one out there about using fabric to cover a frame or something?) and even the preview teasers Amazon gives you are informative.

So once again, I'm obliged to you all. Thanks!

cg

[Keith Wilson]

Method 1, cut it a little long, and then use a belt sander to take a couple of thou at a time off the end of the inwale until it fits. Not elegant, but it works for me.

[abe]

Joe Etheredge's method works well. I am now an expert. I used this exact method two days ago. Dry fit yesterday on the starboard side.

abe

[Brian Palmer]

Jon Etheridge's method is the same as described by Tom Hill. He obviously explained it well.

-- brian