Motor mount stringers

[Indymike]

'80 Wellcraft Nova 21 is getting the gut and redo. Getting ready to start building stringers and such.
Whats the preferred method for building the motor mounts. Dimensional lumber or laminated ply? They used dimensional lumber from the factory. Motor is a Mercruiser 350 V8.

Example

Thanks

 

[Boomyal]

Re: Motor mount stringers

I used dimensional lumber. I cut them to size, soaked them in CPES, glued them together, used peanut butter to anchor them, poured liquid epoxy down any voids around the stacked members, covered them over with biaxial mat and 10 0z cloth, drilled the motormount holes, kept pouring CPES into the holes until they quit absorbing it, pumped them partially full of 3m 4200 then rammed the stainless steel mounting lags into them.

The hull will disentigrate around those mounts before they rot or break loose.

 

[jeffengle]

Re: Motor mount stringers

I am replacing motor mount stringers also. I was advised by my brother to go to the lumber yard and order Spruce Boat Stringers. They don't twist or bow. That's what they always used in big horsepower Grand National Boats.

 

[klos]

Re: Motor mount stringers

I've used laminated ply. Plywood is much stronger but either will work.

 

[Boomyal]

Re: Motor mount stringers

I... was advised by my brother to go to the lumber yard and order Spruce Boat Stringers. They don't twist or bow.

Good consideration, that is why I bought kiln dried doug fir for mine. I hoped that that would be sufficient to eliminate twisting.

I would speculate that dimensional lumber would be easier to waterproof than stacked/laminated plywood.

 

[Indymike]

Re: Motor mount stringers

I would speculate that dimensional lumber would be easier to waterproof than stacked/laminated plywood.

I was thinking the ply would be easier to treat. More surface area to apply resin to as you do the layup of the laminations. And I believe the plywood will hold screws better.

Along the same lines why are lag bolts used rather than imbedding a machine screw ?

 

[Robj]

Re: Motor mount stringers

If you look at ply, it has many cracks as it is peeled from the core. These cracks are great for taking pressure treating, and also for absorbing resin. I used pt doug fir ply, it is straight, no crown. I think laminating ply is the way to go.