Transom on the Tangent of 3 Degrees

Here you can see the transom hanging on to the jig and the keel coming in at more or less a right angle.




The tangent is equal to the ratio of the opposite side over the adjacent side of a right triangle.

Right now we are at 2 inches divided by 39 inches or about 2.9 degrees which is probably way close enough.

The tangent of 3 degrees equals 0.0524077793.





In the plans the designer specifies that the transom should be raked forward 3 degrees. Now I have a suspicion that when Graham was building the first EC 22 Southern Skimmer that he just tilted the transom in a wee bit and let it go at that. He could not really write that on the plans so he put down 3 degrees. Now I am going to spend an hour or two trying to set the transom within a couple of minutes of 3 degrees.










I know the stem of a boat can be difficult. The stem is often curved, it has rabbits, and bearding lines and plank landings. The stem can be complicated but a transom that is pretty much just a flat board stuck on the back of the boat. Right?


Well not quite!


Checking to see how the matched halves of the transom fit the pattern.


Here I am separating the halves and laying them out on the full size drawings. Hmmm any differences between the plywood and the drawings are due to humidity induced paper distortions.







Checking to make sure that I am keeping the edges of the transom square as I plane them down to the lines.






I clamped two pieces of plywood together and cut out both halves of the transom at the same time. I cut just outside the line using the circular saw set to a very shallow cut. Then I used a sharp plane to bring the pieces just down to the line.










I transferred the curve of the transom from the plans to a 2x8 that will support the transom on the jig and maintain the specified arc.

What Knot

I had two pieces of wood in mind for the keel. 3.5x1x20. One piece was free of knots but a poor grain orientation. The other piece has a nice flat grain but a knot or two. I decided the knots were too small to matter and went with the nice grain.



I waffled awhile.


Then I finally took a saw to the board and cut the knot out.


This kind of angled cut is not easy to make.


The saw roughs out the shape.


The plane brings the slope down to the lines and corrects any misalignment.

Many boatbuilders use an 8:1 scarf. The Gougeon Brothers recommend a 12:1.

The lower the angle the more difficult the scarf is to make, the more you shorten your board and the stronger the joint.

I went with a 10:1

The second photo shows the rough cut.

Then planing.

And the final fit.

Now with a little glue I will have a keel with nice grain and no knots.

The stem

The plans call for the stem to be made from solid stock. A full size pattern is included for cutting out the stem.

I decided that I would do a laminated stem.

I used the pattern to determine the shape of my mold.

Instead of just cutting out my mold I made one extra cut and this gave me three pieces.

The inner piece is the mold for the stem. It ties into the rest of the jig and helps to make it rigid. The holes are for the clamps that I will use to pull together the laminates.

The middle one represents the stem.

This came in handy because all measurements in the plans reference the forward end of the stem.

I think the outer piece will be useful when I begin to shape the laminated stem. I will be able to hold this piece up against the stem to insure that I shape the proper curve into the laminated stem.

I will post some more when I actually glue up the stem.

The stem is made up of 14 strips of wood each about 1 1/2 inches wide 1/8 inch thick and five feet long. The strips have to be thin so they will bend around the curve of the stem without breaking.

The first photo shows a dry run. Clamping the strips in place without epoxy gave me a chance to work out how I would be able to get all the strips in place. The strips were a little difficult to get in place the first time. They resisted taking the sharp curve, but after they spent a day clamped into position they got used to it. They went together much more easily the second time.









Here the epoxy has been spread on each strip and they are clamped in place.






The temperature in my boat shop was 55 F. The epoxy needs to be a little warmer to harden properly. I made a little tent and put a lamp under it.

Selling Out

I have been struggling with decisions that need to be made about which brand of plywood to purchase and from where. Does the BS1088 standard mean much anymore? Does Joubert still make a good product or have their standards slipped?

I sold my Whitewater Kayak so I could buy some sitka spruce for my mast. What will be next?

Warning

Just between you and me I only about half way know what I am doing. Some of the information in this blog could be useful some could be down right dangerous.

Be careful.


Joe

Pendulum or Plumb bob

The molds have been cut out. Now I am erecting them on the 2x6 frame. Each mold should be plumb and perpendicular to the long axis and the correct distance from the bow. Phew.


All the molds are in place.

You could say the jig is up!!

Resources

Well I am having difficulty getting my text to match with the photos. This is one big learning process.

Some of my resources.

In case you didn't recognize him that is Graham Byrnes the designer.

The book is the Gougeon Brothers on Boat Construction. Lots of detailed information on the combined use of wood, epoxy, and glass fiber in boat construction.

And of course


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