repairing the fiberglass engine bed

[arecuk]

Hello,

I'm going to repower my 35ft sailboat, currently with volvo penta md11c, with volvo penta d1-30, and want to keep my current engine bed:
1) I can get repowering brackets, so that I don't need to change the engine bed; this is fine.
2) However, at the same time I know that some screw holes of the fiberglass engine bed are worn out, meaning I cant tighten the bolts attaching the silent blocks with brackets to the engine bed itself.

I wonder if there are glassed-in nuts in the bed that got loose, or if there is simply a thread in the fiberglass material itself? Either way, any ideas on how to fix this, so that I can bolt down the brackets properly when replacing the engine?

Thank you so much, Tomas

[nuku34]

Hello,
It might help the forum if you gave the make and model of your boat.
Not knowing that, I can say that generally speaking, on fibreglass boats the engine bearers are actually heavy wooden beams that are glued to the hull and then glassed over to keep the water out. I suggest you drill a small test hole and see if you get wood chips coming up.

If it is a wood bearer, many people use coach screws (also called lag bolts) which are big screws with hex heads. for your size engine, I would use 10mm diameter and maybe 75mm long.

Occasionally, there is a piece of steel flat bar on top of the wood bearer and that is tapped for machine bolts.
BTW, what you call "silent blocks" are normally called anti-vibration engine mounts.
If any of the mounting holes in your new engine mounts happen to line up with holes already in the bearers, the bearers are wood, and you will be using coach screws, you can just fill the existing holes with epoxy mixed with glue powder and then re-drill the holes.
Good luck,

[arecuk]

Hello,

thank you for your tips. My boat is fiberglass built in 1980, small local production in Spain, Visiers 35.

I'm pretty sure the engine bed is from fiberglass, no wood, and prefabricated by volvo penta. See an example pics attached.

I want to keep the current engine bed, get repowering brackets that I would bolt down using the current holes, and on of that new engine mounts for the new engine. See attached.

[Reefmagnet]

Use bigger diameter and longer coach screws into the original bearer, after suitably preparing the holes for the new bolts.

It's also possible the core of the beds is mush. In this case you'd need to partially (at least) rebuild the beds. If doing this, you can embed flat bar into the new beds that have holes drilled and tapped to fit the new mounts. A mock engine mount template constructed from mdf and dowels makes this an easier job than it would, at first consideration, seem.

[Turtle Blues]

To reuse existing worn bolt holes in a wood or glass stringer: get new lag bolts same diameter, slightly longer, wrap bolt with single layer of teflon tape, partially fill bolt hole with epoxy, thread in bolt snug, not overly tight but make sure it reaches required depth. let epoxy cure and then you can remove bolts, set base and refasten to required torque.
In badly worn stringers I have used expansion anchors filled with epoxy in the same sequence.

[DougR]

The fiberglass engine bed is manufactured with a small square steel plate glassed to the underside of the bed at the location of each bolt hole. The plate is approximately 5 cm x 5 cm and 7 or 8mm thick. Then the plate is drilled and tapped to the required thread at the required location.

If you have some of the threads in the plates stripped, the easiest fix is probably to drill the plate hole oversize and re-tap the threads. Then drill out the re-power bracket hole to match the new fastener size.