Motor and Motor Bracket, Part 4, Backing Plate, Construction

The backing plate for the transom plate, dry-fitted into place
Having constructed the transom plate for the motor bracket, it was now time to construct the backing plate for it. To use the singular in this context is something of a misnomer, because this part of the project actually involved the construction of four different backing plates. The most prominent one was of aluminum. The other three, which were somewhat disguised, were of plywood. In this posting I describe how I constructed these four different backing plates for Oystercatcher, my Ericson 25.
As I said in my last posting, I purchased two separate pieces of aluminum from Both were 3/16 inch thick. The larger one was 2 ft by 2 ft square. The smaller was 1 ft x 4 ft. The larger I used for the transom plate. The smaller I used for one of the backing plates - the one visible in the cockpit in the picture above.
In case you need a reminder, here's what this project as a whole looked like at the end of my last posting.
To create the aluminum backing plate, I began by determining the angles of the space by means of a bevel gauge.

I transferred these angles to a piece of cardboard.
I then created a cardboard mock-up.
I took measurements of the mock-up and recorded them on a piece of paper.
Using these measurements and the cardboard mock-up, I created the first backing plate, this one out of 1/2 inch exterior grade plywood.

I then used this plywood backing plate to create the aluminum backing plate.
For these cuts I again used my Makita jigsaw and cutting oil.
This time I used a different type of blade - the Bosch T118B, which was designed specifically for cutting metal.
These blades worked well, but just as was the case with the other Bosch blades that I had used for the transom plate, it was easy to wear them out, even with lots of oil.

After I had finished making both of these backing plates, I began by temporarily installing the plywood one. Through this plywood I drilled holes, using the existing holes in the aluminum transom plate as guides.
I then used the holes in this plywood backing plate to mark the spots for the holes in the aluminum backing plate.
Back in the boat I checked to make sure all these holes lined up.
Then I created an additional cardboard mock-up, this one to to fill the gap in the cutout between the transom plate and the plywood backing plate.
This gap was a little over 1/2 inch in thickness. My plan was to use the cardboard mock-up to create one out of 1/2 inch plywood. This I would join to the other plywood backing plate with screws and epoxy. I figured that by the time I finished epoxy coating all of this plywood it would be just the right thickness for this gap.
Before moving forward with anything else, I decided to cut a new plywood backing plate to replace the one I had previously created for the aluminum backing plate. I had discovered in the first one a void that would have made it weaker than it should have been.
The new one was nice and solid.
While I was at it, I decided to reshape this piece of plywood. The more I had thought about it, the more I disliked the appearance of the pointed corner on the existing piece. When I cut this corner off and rounded the other three corners, the backing plate became much more pleasing in appearance.
Then I drilled the holes in the appropriate places. It's difficult to see in this picture, but between the plywood and the aluminum transom plate is the small piece of plywood that I had created to fill the gap in the cutout.
Now it was clear that I needed an additional screw in the transom plate. This one would help to pull everything together into a nice, compact aluminum and plywood sandwich of sorts.
I drilled a small pilot hole to ensure that the hole on the cockpit side was going to be exactly where I thought it would be.
Then I drilled the real hole. Two holes up from the new hole you'll notice a certain hole that is somewhat distorted in appearance. Recall that in my last posting I said I had to widen a hole or two when I dry-fit the transom plate and the motor bracket. This was one of those trouble spots. The problem was that the aluminum shifted slightly when I installed the screws and tightened them down. This shifting was unavoidable on account of the slight curvature of the transom. To put it simply, I was putting a flat piece of aluminum on a curved surface
I countersunk this new hole, just as I had countersunk all the others around the perimeter of the transom plate.

Now it was time to modify the aluminum backing plate on the cockpit side of the transom.
Just as I had removed the pointed corner from the plywood backing plate, I did the same to the aluminum one.

This made the whole set-up much more professional looking.
This led me to soften up the appearance of the transom plate.
The rounded corners gave it a much more shippy appearance.

See the file? I used this to remove the rough edges that remained from my cuts.
The last thing I needed to do in terms of the backing plates was to construct a small one out of plywood for the lazarette.
There were several screws that would require washers and nuts in this area beneath the cockpit sole.
This area would have been impossible for me to access if I had not earlier removed the original battery bank and water tank. Even with these two things out of the way, it was not easy for me to climb in and out of this space, but climb in and out of it I did - many times - as I slowly custom cut this piece of plywood to fit snugly against this small part of the transom.
Having constructed these three plywood backing plates and the one aluminum backing plate, I could now call this part of the project complete. This ends this posting on how I accomplished these backing plate tasks for Oystercatcher, my Ericson 25.

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