how to install a P-bracket?

[Ivan R]

I am trying to find info on glassing in a prop shaft bracket.I bought a 39' balsa cored, unfinished sail boat.The 2003T volvo was already mounted.But the bronze P-bracket that I had gotten from the widow of the builder is yet to be mounted to the hull.Should the bracket be drilled and through bolted with a backing plate,or just glassed in place?I know that alignment is critical,and that I have some room for ajustment at the engine mounts.

[B. Hamm]

Ok, first this is the shaft strut you're talking about? Holds the prop shaft externally near the prop?

[B. Hamm]

Assuming this is the prop strut, it should be thru bolted to a preferably glassed in backing plate, but since the hull is balsa cored you need to do some prep work too. After the holes are drilled for the strut, the holes thru the balsa need sealed to prevent water migration thru the core (no matter how well you think you've got the holes caulked they will eventually leak). Easy way is to open up the holes inside the hull slightly so you can route out the core, perhaps twice their orriginal drilled size, then fill those holes thru to the inside with a thicked epoxy mixture, then once cured you can bond in the backing plate, redrill thru the epoxy plugs and the backing plate and bolt the strut in place, properly bedded. Btw, if you tape up the holes in the bottom of the hull with masking tape, it'll hold the epoxy in place and the tape doesn't stick to the epoxy.

Bill H.

[Ivan R]

Thank you for your response.The hull area were the strut is to be mounted is solid frp. so hole prep is simplified.The strut is not drilled yet.Would it be best to tap the holes and use,say 1/2"stainless bolts? Or would it be better to drill and countersink the strut holes and use,say 3/8" s.s.or bronze flat heads? Also the angle of the strut is a few degs. off from what is needed can a wedge be used to fix this? Sorry for my ignorance, but what is the proper way to bed the strut (thickened epoxy?,or polysulphide?3M 5200?).
Thanks again,
Ivan R

[B. Hamm]

First, don't mix metals. Since the strut is bronze, the bolts must be too or you're building a battery, bad idea.

Flat heads will work, you'll need an assistant to hold the strut and the bolts as you tighten inside.

Polysulfide will work, I don't like using 5200 for anything you might want to remove later, since it's a wonderful glue, good sealant though. Don't tighten all at once, just barely snug the screws till the sealant sets up then torque to the proper spec for the bolts you're using. Makes a gasket this way, if you tighten all at once it's easy to squeeze all the compound out and make a leak.

Sure a wedge will work, I'd make it from solid glass, might take a little time to lay it up.

Btw, this install is alot easier if you pre-install the shaft connected to the engine and out thru the strut, otherwise you're guessing on the alignment and that's not a good thing to do.

Bill H.

[Ivan R]

Thanks Bill,
I think I'm ready to tackle this project now! I guess the backing plate should also be bronze.Would 1/4"plate do,or would 3/8"be better?I assume it should be about 3"s wider and longer than the mounting base of the strut? The shaft was already in, but I think it needs to be shortend.It ends only a few inchs from the skeg. Do you happen to know what the minimum clearance from a prop to a skeg should be?
Thanks,
Ivan R.

[B. Hamm]

1/4" plate should easily be enough. I'd ask your prop supplier for their recommendations on prop clearances.

Bill H.