New motor mount board recommendation

[Salty19]

I'm a bit weary of continuing to use the plastic motor mount board that came with the Garelick motor mount.  Too many stories of them across the web shearing off without notice.
I value our outboard too much to loose it--they don't make two strokes anymore!

So, I want to make a marine plywood version.  I'm looking for recommendation on the following:

-Marine plywood type and vendor. Seems to be a myriad available.  Surely someone here has had good and bad to say about a certain type or another.
-Construction method.

I was thinking about epoxying the plywood together after cutting the boards to rough shape and thickness. Then once they are bonded, do the final shaping and encapsulate the entire board in epoxy and paint with something like enamel or perhaps bildge paint. Maybe, just maybe, fiberglass between layers (24oz roving) or on the outside or both.

What do you guys suggest for a an optimal construction method?  My design goals are it needs to be as strong as possible and as low maintenance as possible.  I don't care if how hard it is to construct...once done I expect to never have to fool with it again.   As I've never fussed with fiberglass before, this could be a fun and learning experience if I choose that route.


Suggestions on materials and construction method are appreciated!

[skip1930]

Captain Rank on Wind Rover has to do this before next season. His has come apart, mostly because the wood is varnished and was never sealed in epoxy and the engine clamps have been over tightened and that opened up and splayed out and dented in the edges of the wood allowing years of water and rot to work.

Wind Rover's Com Pac supplied motor mount is very old but has a wood laminated Plywood construction.
Suggest it be sealed water tight so I'm thinking any marine quality plywood and glue will do for the basic material.
The more layers the better as this 'piles' on the glue [which is where the strength is] layer after layer.
This is how Peterson Boat Builders in our little town constructed nonmetallic, wooden Mine Sweepers for the U.S. Navy.

Say 1/4 inch North-South and the next layer East-West, then North-South...and keep going until the desired thickness is achieved.
Criss Crossing grains stops warping.
It's going to be an epoxy laminate. It's going to be very strong.
Cut and dry fit all the pieces up.
Get your clamps ready.
And mix up some West System Epoxy/[and if you can find it], polyester* blended two componet goop or Marine-Tex with some sawdust to thicken the mix.
Roll the epoxy on both sides, slap it together, might want to use a gig with saran wrap or waxed paper between the gig and the laminate.
Clamp it and roll the squeezed out excess away, no drips, go away for two days.
Keep it clamped but do the perimeter edge again with fresh epoxy.
Drill and epoxy the holes and bolt it on to the back plate angles.

Speaking of which now is a good time to cut a new, full backing plate to lower and push-off the engine mounting board and that moves the engine off the transom and if you want, down into the water. New and longer arms on the mount itself would allow the engine to raise and tilt without hitting the rub rail astern.

skip.
* epoxy does not do well in sunlight. Polyester blends were created to combat U.V.

[ontarioSuncat]

I was fortunate that I hade a scrap of ¾ marine plywood left over from a previous boat. Where I made the rudder and CB from a 4x8 sheet.  Marine Plywood has thinner layers and are not supposed to have any voids in the layers. And it is put together with waterproof glue. I cut two parts that from the ¾ sheet and then added a piece of standard ½ inch ply in between. I glued and clamped them together using West System Epoxy. Once cured the part was shaped to size and the edged where eased etc. I measured and drilled the mounting holes to be over sized. The mounting holes where filled with thickened West System Epoxy. Once cured they where drilled to the correct size. This way the hole is sealed and the wood protected.  The complete board is coated with three coats of West System. Final step is to sand the part and coat with two coats of premium UV stable Varnish.
Now the part is stable to UV, rain, water and is strong. After a few years the board may show wear around the motor clamps. Just apply some epoxy and varnish.  I expect that failure would only occur after the board started to show signs of delamination. This would be very easy to visually inspect. Whereas the broken plastic mounts that I saw looked perfectly good. There were no visible signs of stress around the break. There was no way of knowing when it would break.

[capt_nemo]

Salty19,

Recommend "Meranti" Marine Grade Ply made in accordance with BS 1088 (BS = british Standard). It is lightweight and very strong, especially when laminated, and costs less than the lightweight, strong, and expensive Okume Plywood.

Cut required layers to pattern and assemble as you described above. Coat exterior with Epoxy and finish it off with a Marine Polyurethane such as Interlux Brightsides.

My homemade sailboat, pictured below, was made using Meranti Ply and finished off with Brightsides. Several components were made by laminating several layers of either 1/4" or 3/8" ply, such as the foredeck and the very thick 2 1/2" Rudder Head (6 layers of 1/4" Ply).







Hope this helps.

capt_nemo

[Ted]

Show off.

Just kidding.... Boat looks awesome!

[Salty19]

Awesome gentlemen.  Thanks for the tips.

Skip, I was thinking about making the board a tad wider and notching out the forward upper piece for the engine bracket clamps. This will move the outboard back the same amount. It's actually not hitting anything but a wee bit more clearance will be added.

Nemo..you're boat has me intrigued, and I totally want one!!  I live next to a very small dirt/rock boatramp off a lake--that little ship would be perfect for the offseason up north when the docks are removed for winter. Why, I bet the lawn tractor could launch it     Are there plans available for it, or is this your creation?

[Bob23]

   As an aside, I've seen Capt Nemos boat in person when we met up last spring on a trip to Punta Gorda, Fla-di-da. Or was it the spring before? Anyway, it is more beautiful in person than the pics could show.
   For the gudgeon extension on my 23 which was added to accomodate my rudder downhaul, I epoxy coated 5/8" exterior plywood, not CDX and painted with Brightsides. It's been in place for 2 seasons with no signs of water intrusion or delamination.
   Mike: You could get really creative with this motor mount- why don't you make it in the shape of a mermaid- she could be holding up the motor with her...her...well- you get the idea!
Bob23

[capt_nemo]

Salty19,

I made the boat from plans obtained from Selway-Fisher (UK). It is called the HIGHLANDER 12, and was chosen after looking at quite a few small boat design plans.
The rowing configuration (without sailing components) weighs only 120 lbs. I made  a few design changes, but overall, I'm quite pleased with the way the boat turned out. It sails quite well.

I made ALL the rigging components the old fashioned way, after first researching and learning some of the techniques and skills required. It was truly a labor of love and I enjoyed every moment of it!

Here are a few more pics.