What wood to use for motor mount?

dlochner · Jul 17, 2024

No to pine, too soft. White Oak or Ash would be good choices. Seal the wood with epoxy and paint or varnish to protect from UV.

thinwater · Jul 17, 2024

I used to worry about rot and would look to fiberglass and plastics for motor mounts. But I've had a few motors vibrate loose, and now the idea of an easily replaced, sacrificial layer that the motor can bite into is starting to seem like a good idea. For that set up, I'm thinking pressure treated deck wood might be perfect. It's not a heavy motor.

People laugh at this one because they are young girls, but I bet 50:1 that dad mounted the motor and they did nothing wrong. I feel for them. That could have been my daughter, and it would have been my fault.
Motor comes off

kappykaplan · Jul 17, 2024

FeelinMorgan22 said:
I can buy an 8ft board 2in thick 10in wide of pressure treated Southern Pine for $16.

Sacrificial or not, southern pine is still too soft, in my opinion. Doesn't matter how many coats of epoxy, etc., you put on it.

jssailem · Jul 17, 2024

Easily found at a box store is stair Tread. They can be soft or hard wood. It will be boards glued together to form a 12 by 36" board. $10 here in Pacific NW. Yo can get several pieces out of a 3 ft piece.
You can use for plywood. Get the B/C piece for the better glue. Or Exterior plywood. Most of the box stores will have small cut pieces they call "Project Cut".

@thinwater struck truth, that that wood provides a better group for the motor mount and that is serves like a zinc as sacrificial. It may outlast your ownership of the boat.

Project_Mayhem · Jul 17, 2024

I picked up a green 2x12 about eight years ago and have been cutting it down little by little for every boat. No issues so far. Much better than plastic. They do see water as the stern squats at WOT. Be sure to check the clamps of the motor every few minutes when you first install it. Then every 30 minutes, hour, etc. By the second or third outing, it should be secured. I had a motor go for a swim once because I forgot to do this.

dLj · Jul 17, 2024

An excellent choice is black locust. Should be available in the Erie area.

dj

jibes138 · Jul 17, 2024

Why not use plywood? Just epoxy glue pieces together to get the thickness you want. It will be stronger than a pine board yet still some softness to let the clamps bite into it. Always attach a safety cable to your motor to prevent it going swimming.
Look at the transom of an inflatable boat, the industry has already perfected this solution.

SFS · Jul 17, 2024

StarBoard won't rot, or suffer from water incursion. Buy it once and never worry about it.

east coaster · Jul 18, 2024

If due the soft wood used and vibration encountered that would cause the motor to come loose, why not secure the motor mounts on the motor to each other or tie them together to a nearby strong point. This would prevent them coming loose risking the loss of the motor. I think starboard would be an excellent choice. Or am I not understanding the problem.

dlochner · Jul 18, 2024

east coaster said:
If due the soft wood used and vibration encountered that would cause the motor to come loose, why not secure the motor mounts on the motor to each other or tie them together to a nearby strong point. This would prevent them coming loose risking the loss of the motor. I think starboard would be an excellent choice. Or am I not understanding the problem.

The problem with soft wood is the compression developed by the mounting screws which crushes the wood fibers making it difficult get the screws tight enough. Some motor mounts provide for through bolting which could be an option.

The problem with starboard is thickness, the max thickness is 1" at that thickness I wonder if it is strong enough. Gluing up several layers to build thickness really isn't an option with starboard.

kappykaplan · Jul 18, 2024

dlochner said:
The problem with soft wood is the compression developed by the mounting screws which crushes the wood fibers making it difficult get the screws tight enough.

Exactly!

jibes138 · Jul 18, 2024

For those cross bolts you will be drilling holes. Plywood is laminated wood with each layer glued. Epoxy gluing pieces together will just be adding more layers. The epoxy joints will probably be stronger than the wood. The plywood assembly will be a lot stronger than a PT pine board. Plus your clamping force of the motor is further putting the joints in compression. If you are considering plastic use G10 and laminate that to the thickness you want. G10 is fiber reinforced plastic, way stronger than starboard. You can still drill and cut it but it is tough stuff and very strong. Counterbore two holes maybe 3/16 deep with a spade drill for the clamps to be securely retained. G10 won’t compress the way wood does.

SFS · Jul 18, 2024

Excellent points, and I completely forgot G10. OP, you might want to spec out the cost of laying that up vs. plywood. It might be worth checking your local big box store for plywood offcuts, which could be really cheap. Don't forget the cost of your epoxy, and (if you care) the value of your time.

StarBoard is available in a 1.5 inch thickness.

LloydB · Jul 19, 2024

I used a recycled plastic 2x4 from a local lumberyard. I recall at the time being somewhat surprised it actually cost a bit more more than a 8 foot stud.

Project_Mayhem · Jul 19, 2024

G10 will cost a fortune. Plywood is glued together with well, glue and you'd have to find a UV resistant epoxy to get it water resistant. So your glue and epoxy both have a limited lifespan even with UV inhibitors.

I'd look at plastic lumber or outdoor lumber. I'd lean more towards outdoor as it wont compress as much. Whatever you go for, remember to re-tighten the clamps for the first few outings. They will loosen much like a soft aluminum car rim

What wood to use for motor mount?

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