Repair enlarged bolt holes.

[mogmog2]

I've seen plenty of stuff on repairing stripped screw holes in GRP but wondered if there was anything else to do in repairing oversized rudder fastener holes?

I'm currently thinking of using epoxy with glass strands from from CSM or tape, cut up smallish.

My application is the lower rudder tube mounting bolts on a Centaur (the bolts are a bit loose and the holes may or may not be enlarged). Another application is a transom hung rudder on a friend's Vivacity. These have definitely enlarged quite badly.

Would I need a different approach where the holes are only slightly oversized to where they are significantly larger?

Thanks

 

[Graham376]

What material are the holes in? Is there enough meat to drill out for next size of bolt - e.g. 8mm out to 10mm?

 

[Fr J Hackett]

Are they through holes? If so drill out and sleeve with a suitably sized piece of tube.

 

[mogmog2]

In both cases the hulls are made of polyester glassfibre.
Going oversize may be a possibility, although it would mean drilling substantial stainless plates in both cases.

I haven't investigated mine yet as we've only just been craned out. My son had a look at the Vivacity's bolts and from what he said, I think they may need more than just going up a size, as his friend sailed all summer with a loose rudder, tightening them periodically. Conversely, our boat didn't go anywhere as the engine died in July, so I'm hopeful that our holes are ok: I had to remove our stiff rudder in the spring. It took a lot of robust effort to get it out and I think that may have broken the seal/loosened the bolts, as she was dry when we bought her.

 

[Poignard]

S/s Helicoils

 

[savageseadog]

If there's a "substantial" SS plate then drilling upsize would be the way to go. Otherwise flare the holes and fill with epoxy/glass fibre strands, don't use CSM.

 

[PaulRainbow]

Drill the holes out to a few mm bigger than they should be. Chamfer the holes from from both sides. Tape some stiff plastic to one side, a piece of old oil container or similar works well. Fill from the other side with P40. Remove the plastic and fill that side, if needed. Sand when cured. Some gelcoat over the P40 would make a pretty much invisible repair. Re-drill the holes, job done.

P40 is a polyester repair past containing chopped glass strands, similar to what the OP describes. It is almost indestructible.

 

[mogmog2]

If there's a "substantial" SS plate then drilling upsize would be the way to go. Otherwise flare the holes and fill with epoxy/glass fibre strands, don't use CSM.

What's the difference between 'glass fibre strands' and strands of glass fibre from deconstructed CSM or tape?

 

[mogmog2]

Drill the holes out to a few mm bigger than they should be. Chamfer the holes from from both sides. Tape some stiff plastic to one side, a piece of old oil container or similar works well. Fill from the other side with P40. Remove the plastic and fill that side, if needed. Sand when cured. Some gelcoat over the P40 would make a pretty much invisible repair. Re-drill the holes, job done.

P40 is a polyester repair past containing chopped glass strands, similar to what the OP describes. It is almost indestructible.

Thanks Paul & Savageseadog, chamfering the holes is the piece of information that satisfies.

 

[VicS]

I've seen plenty of stuff on repairing stripped screw holes in GRP but wondered if there was anything else to do in repairing oversized rudder fastener holes?

I'm currently thinking of using epoxy with glass strands from from CSM or tape, cut up smallish.

My application is the lower rudder tube mounting bolts on a Centaur (the bolts are a bit loose and the holes may or may not be enlarged). Another application is a transom hung rudder on a friend's Vivacity. These have definitely enlarged quite badly.

Would I need a different approach where the holes are only slightly oversized to where they are significantly larger?

Thanks

If yu use epoxy resin dont use ordinary CSM as the binder in it is not soluble in epoxy. It is only suitable for polyester resin. Strands from glass tape or cloth will be OK.

You might consider "micro fibres" or one of the other hard fillers from West Systems.
https://www.westsystem.com/filler-selection-guide/



Alternatively use Isopon P.40 which you will find in Halfords or any car spares/ accessories place. I'm sure it will be perfectly satisfactory and what I would use/ have used when i have not had epoxy to hand. ( you can warm it up to make it set in a few minutes too which is very handy when the weather is a bit on the cool side)

 

[mogmog2]

Thanks. P40 is a good option, especially factoring in postage for resin or lack of in p40 case, although I was hoping to minimise the amount of stuff I need to buy, given the shelf life of such stuff.

 

[Daydream believer]

When I had to re fix the chain plates to my Stella they rattled about & were extremely loose due to rot around the old bolts. The rep from Wessex advised that I drilled 25mm diam holes to give a wider spread of load & filled with west epoxy mixed with 404 filler. There was no need for any matt to be mixed in with it. Then drill to the correct size for the bolts. One can actually bed fixings direct to it but I think that drilling right through & backing pads would be better for a rudder.

 

[PaulRainbow]

Thanks. P40 is a good option, especially factoring in postage for resin or lack of in p40 case, although I was hoping to minimise the amount of stuff I need to buy, given the shelf life of such stuff.

A tin of P40 will last for a very long time if stored correctly.