Making the Breasthook

Cabinet makers have it relatively easy, in that most of the corners and joints are at right angles.  In building a boat, there are very few right angles.  Most of the joints are at some kind of weird angle.  The breasthook is a perfect example of that. (That being said, I’ll be the first to admit that I’m not a very good cabinet maker).

The breasthook is a triangular-shaped piece of wood fitted to the top of each of the sheerstrakes and the stem.  (Sheerstrakes and stem – whatzat??  See Ya Gotta Learn the Lingo! at the top of the page) The ‘hook is a structural member that ties the bow of the boat together.  The first step is to make a pattern from scrap 1/4″ plywood so we have an idea of what we’re aiming for.

2017 06 18 Lofting the breasthook.

The plywood is laid on top of the sheer, with the flat top edge against the stem.  A pencil is then held under the plywood and traces the inside edge of each sheer.  The lengths of the “tabs” at the bottom of the breasthook are given on the plans; these tabs will be used when it comes time to glue the inwales to the boat.  A batten was used to draw a nice curve on the left side, and some simple lofting was used to transfer a couple of points on the curve to the right side, and draw a mirror image of the curve.

2017 06 18 Breasthook pieces and spline, ready to be epoxied.

The breasthook is made of two pieces of lumber, joined so that the grain runs with the sheer.  The center joint will require joining two pieces on the end grain, so this joint is strengthened by the use of a plywood spline. A dado is cut down the middle of each piece, and half the width of the spline will fit in each slot.

2017 06 18 Breasthook epoxied.

The two halves of the breasthook are epoxied together.  Note that the completed blank is oversize when laid on top of the pattern; that’s a good thing.

2017 06 25 Determining the angle where the breasthook meets the stem.

The stem is not absolutely plumb, and like any classic boat, the sheer is tilted up at the bow.  That means where the breasthook meets the stem is some angle that is not 90 degrees.  Plywood is laid across the sheer, and a bevel gage is used to pick up the angle.

2017 06 25 Test fitting the breasthook against the stem.

The top of the breasthook blank is cut off, and the bevel cut into the face that meets the stem.  There’s still a little too much gap in this photo; the front end needs a little more trimming.

The sides of the breasthook also have a bevel, but these are a little more complicated.  The top edge of the sheerstrake has flare; it is canted toward the outside.  However, the flare is not constant.  The sheerstrake has a little flare near the bow, but as you move aft, the flare increases appreciably.  I’ll have to cut a rolling bevel to handle this changing flare.

I started out by laying the blank up against the stem, on top of the sheer, and like I did for the pattern, traced the inside edge of the sheer onto the bottom of the blank.

The depth of the inwale is 7/8″, while the designer states to make the blank 1-1/8″ thick.  That leaves 1/4″ extra, which will sit above the sheer and be shaped later to form a camber.  After cutting the blank to the lines I just drew, I then drew a line 7/8″ up from the bottom of the breasthook on each side.

2017 07 03 Determining the flare along the sheer.

To determine the shape of the rolling bevel, I picked off four points along each side.  One near the front, one at the rear, and two in the middle.  In the photo above, I’m determining the bevel at one of the points I laid off.  The metal bar sits tight against the sheerstrake, and the black portion of the bevel gage lays on plywood going across the shear.  The angle formed is the amount of flare at that location.

2017 07 03 Rolling bevel along the sheer

On the bottom side of the breasthook, I mark the amount of bevel at each of the locations and draw a line.  This line tells me the bottom edge of the breasthook.  If I take my plane and take off the wood between this line and the earlier line that I drew on each side that was 7/8″ above the bottom, I’ll have the rolling bevel.

2017 07 03 Rolling bevels cut on each side.

When the rolling bevels are cut on each side, the breasthook will (hopefully) fit between the two sheerstrakes and against the stem.  You can see the 1/4″ extra left above the sheer.

2017 07 03 Rough cut to shape.

With the pattern as a guide, the shape of the breasthook can be laid out and cut.  Lay out the shape of the breasthook on the bottom of the blank, not the top!  Why is that important?  It has to do with the inwale.  The inwale will be installed parallel to the sheer along the entire length of the boat, but instead of being glued directly to the sheer, will be separated by spacer blocks.  The back portion of the breasthook (the “tab”) is the width of the spacer blocks, which in this case is 5/8″.  The side of the tab must also be cut so that it is parallel to the flare of the sheer.  If I had measured the width of the tab from the top of the blank instead of the bottom, by the time I cut the side of the tab to match the flare, the top width would be less than 5/8″.  But by laying out the pattern from the bottom of the blank, the bottom width of the tab is 5/8″, and I can trim the tab to be parallel to the flare and also 5/8″ wide at the top.

2017 07 05 Final shaped; held in place with temporary screws.

Finally, the breasthook is shaped to form a small crown or camber on top, curving down to land flush with the sheer.  The breasthook is held in place with temporary screws; I don’t want to epoxy it in place just yet.  Prior to doing that, I need to seal the bottom of the breasthook with several coats of varnish, as it will be difficult to get to the underside of the ‘hook once it’s glued in place.

4 thoughts on “Making the Breasthook”

  1. Well, I see the procedure and understand…… NOW, I shall return to what I know best…. Sail making…. you are the master Bro Al….. she’s looking great, and I am impressed !!!!!

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  2. It’s not clear to me how the rolling bevels taken from the sheerstrake and plywood across the sheer were transferred to the bottom of the workpiece.

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