Motor and Motor Bracket, Part 5, Motor Mount Pad, Mahogany and Aluminum, Construction

The mahogany and aluminum motor mount pad, dry-fitted to the motor bracket
Having constructed the aluminum transom plate and the aluminum and plywood backing plates, it was now time to construct the mahogany and aluminum motor mount pad for the motor bracket. The Garelick heavy duty motor bracket came with a plastic pad. This pad was thick and sturdy, but unfortunately it was rather small, and it offered no means of securely bolting the motor to it. Therefore, I resolved to construct my own sturdy motor mount pad, one that was the appropriate size for the Yamaha 9.9 High Thrust motor, and one that would allow me to bolt this motor to it. How I did this is for Oystercatcher, my Ericson 25, is the subject of this posting.
You'll recall from my earlier posting that I was inspired by the photograph below to purchase the Garelick heavy duty motor bracket. Let's take a look at this photograph again, this time paying close attention to the plastic motor mount pad.
You'll notice that the owner has hand-tightened the Yamaha clamps to secure the motor to the plastic motor mount pad. I have circled the one visible clamp, i.e., the port side clamp, in yellow. Aft of this you'll notice an orange circle. This I have placed around what appears to be a bolt of some sort. This owner, apparently concerned about the security of his Yamaha, has attempted in some fashion to secure the motor to the pad by means of a bolt. That this bolt is awkward looking is a testimony to the fact that the plastic mounting pad is not designed to accept a bolt.
You'll also notice a red circle at the bottom. This I have placed around that portion of the Yamaha bracket itself which extends beyond the rather small Garelick plastic mounting pad. This portion of the Yamaha bracket has a hole in it. There is an identically sized hole (not visible in this picture) on the other side of the bracket. These holes, like the other holes in the Yamaha bracket, are designed to accept bolts for the bolting of the motor to a transom or some other object.
Garelick, apparently conscious of the fact that their motor mount pad was rather small on average, included a stainless steel cable. This cable was described in the literature as a safety tether of sorts. It was meant to be secured from one of the holes in the motor bracket to the transom of the boat. In the event that the motor came off of the plastic motor pad, this safety tether was said to prevent the motor from sinking to the bottom of the water and thus being lost.
None of this sounded very appealing to me. What a horrible situation that would be to have a heavy four-stroke motor underneath the boat, dangling from a tether. Why not just take steps to ensure that this never happens in the first place? Why not construct a motor mount pad that is capable of receiving bolts? Others must have had similar concerns, because when I looked around the internet I found at least one person who had removed the plastic mounting pad from the Garelick heavy duty bracket.
This person, as I recall, had started out with a sold piece of mahogany. Also, as I recall, this set-up failed when the mahogany, despite it's thickness, split and broke free from the Garelick bracket. This sent this person's motor to the bottom of the water.
Also, as I recall, this person started all over with another piece of mahogany, but this time he sandwiched it between two pieces of aluminum. This set-up worked.
With this in mind, I determined that I would replace my own plastic mounting pad with something similar.
Garelick had joined the plastic pad to the bracket with carriage bolts. I was able to remove three of the four bolts without any problems. One of them, however, was a real headache. The nut for this bolt was excessively tight. When I applied the necessary torque to loosen the nut, the carriage bolt damaged the square-shaped recess in the plastic pad that had held the carriage bolt in place. This caused the carriage bolt to spin freely. This in turn prevented me from loosening the nut. Therefore, I had no choice but to cut the bolt.
I used a cutting wheel on an angle grinder for this job.

One of the other problems with this Garelick plastic pad that I've not yet mentioned was that the plastic was very slick. My guess was that it was HDPE, the same type of plastic that you find in the marine lumber popularly known as "Starboard." If you've ever worked with Starboard, you'll know that it is super slick. This slickness was yet another reason why I did not feel comfortable mounting my brand new Yamaha to this pad without any means of securely bolting it in place.
To construct my own heavy duty pad, I began, as I usually do, by making a mock-up, this one out of a scrap piece of pine.
After I had cut it to size, the first thing I needed to do was to drill two large holes in it. These would serve as the recesses for the springs.

I didn't take the time to figure out why the springs for this bracket were configured in this fashion. They had nothing to do with the pad that I was constructing.
All I knew was that I had to create room for them.
Next, I drilled the holes for the mounting of the pad to the black aluminum bracket. I also rounded the corners on the pad to give it a more curvy and thus shippy appearance.
Satisfied with this mock-up, I turned my attention to the aluminum plates that would sandwich it.
You'll recall from my previous two postings that I had ordered small sheets of 3/16 inch aluminum for this project. One of the sheets measured 1 ft x 4 ft. I used part of this sheet to construct the cockpit backing plate for the transom plate. The part that remained from this sheet I would use to construct the two pieces of aluminum for this motor mount pad.
For these cuts I used both types of blades that I have described in previous postings - the Bosch Plexiglass blades and the Bosch metal-cutting blades.
Both of these, as I have said, are effective on 3/16 aluminum, as long as you use plenty of cutting oil.

Even with the oil, however, these blades quickly grow dull.
Consequently, it's necessary to have several new blades on hand at any given time.

Everything was starting to come together, but there was still a long way to go.
First, I needed to cut holes in one of the aluminum plates for the springs.
For this, I used a Lennox brand bi-metal hole saw.

Then I drilled the bolt holes in the aluminum plates.

At this point I stopped and dry-fit everything together.

The edges of the aluminum were sharp from the recent cuts that I had made. I softened up these edges with a piece of 40 grit sandpaper.
I didn't mind scratching the aluminum. I would later be roughing up this aluminum and applying some two-part polyurethane paint.
I used the Dremel with a 50 grit sanding drum to soften up the edges of the large holes.
Notice that I only drilled large holes through one of the plates. The opposite plate would conceal and protect the springs.
To even out the two different plates and make them perfectly symmetrical I ran the quarter-sheet sander back and forth over both edges at the same time.
Yes, 40 grit paper will wear down aluminum. This is the same grade paper that I have always used to sand epoxy and mahogany.
Now it was time to cut the mahogany. I used a scrap piece left over from my companionway hatch project. This piece was almost two inches thick.
The mock-up piece of pine provided an excellent pattern for me to follow.
In my construction of the mock-up I had realized that it was unnecessary for me to cut the large spring holes all the way through the wood. In other words, shallower holes would work just fine. So for the cutting of these holes I used a Forstner bit, a bit specifically made for drilling shallow holes (as opposed to through holes) in material.

Once I had gotten the holes started, I removed the mock-up and got to work on the mahogany.

I drilled each hole approximately 1-5/8 inch deep. This left almost 3/8 inch worth of mahogany in the almost 2 inch thick board.

After I had drilled the holes I used an angle grinder to round the edges of the mahogany and the aluminum plates.
Then I test-fitted the motor mount pad to the bracket to ensure that everything lined up well. This required a little bit of extra drilling on my part.
This caused the plates and the mahogany to become slightly misaligned.
To remedy the problem, I used an angle grinder to make everything flush once again.

The file helped me take down the rough edges on the aluminum.
The quarter-sheet sander with 40 grit paper gave it a finished appearance.

Now that I was close to the end of this part of the project, I started to become a bit concerned about the thickness of this pad. The Yamaha bracket would tolerate a pad of 2-1/2 inches, but at almost 2-3/8 inches, this pad was pushing it.
I therefore reluctantly decided to set up the planer and take off almost 1/4 inch from the mahogany.
This would probably make it easier for me to install the motor on the pad, and it would allow me to make a few extra turns on the manual clamps on the Yamaha bracket. It also made the whole set-up a tad lighter in weight, which wasn't a bad thing.
By the time I called this part of the project complete, I was satisfied with my work. It was not only functional, but also pleasing to the eye.
This ends this posting on how I constructed a custom motor mount pad of mahogany and aluminum for Oystercatcher, my Ericson 25.

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