Transom repairs

[dog]

Long winded post, but please bear with it!!! Im currently converting a twin petrol engined boat to single diesel (outdrives). I need to fill the 2 holes left by the old outdrives before cutting in the new single. I have already had some very good advice from another forum member, but would like further views.

I would like to undertake the work myself, but am well aware of how good the finished job needs to be in terms of strength etc. I am competent with general joinery and GRP, so am not put off.....YET!

I had anticipated creating a rebated joint on either side of the transom (50mm thick ply/grp construction) and bonding/mechanically fixing 3 layers of new plywood to fill the holes to create a double lapped joint. I had then planned to grp mat/resin the inside face and epoxy/re-gel the outside.

Does this sound achievable or should I leave well alone? Any advice greatly appreciated.

Brian

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[andy_wilson]

If I understand what you intend doing correctly, you will be grinding back the grp inside and out, rebating 1/3 of thickness of ply from the inside and outside face so you will create a new laminate consisting of:-

a piece of ply the size of the current aperture epoxied in place, sandwiched inside and out by another slightly larger piece of ply epoxied in place, followed by a suitable lay-up of grp laminate, inside and out, followed by gel coat (on the outside at least).

Sounds great, will the new aperture be cut through your work or be in totally new area of transom?

Is the existing ply core OK?


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[dog]

Hi Andy, I must have made some sense as you have understood me correctly!!! Yes the ply core is sound, and yes the new aperature will cut into approx 1/3 of the width of the repairs (as seen from behind)- In theory the transom will still have sound, untouched material above and below the new hole, with a patch on either side. Any further comment?

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[boatmike]

In principle you have it covered but remember that any moisture in the ply or laminate will cock up the bond. It must be completely dry and you must work at a temperature in exess of 16degrees so get a wiggle on its getting colder! Don't be afraid to finish off with extra layers of GRP in the inside over a wider area. No one will see it!

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[graham]

would some glass cloth as well as just epoxy resin on the outside give a bit more protection to the plywood.

you could glass the outside of the ply before fixing it in place.



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[andy_wilson]

Further comment

Yeah, you mentioned epoxy and gel-coat on the outside. Polyester gelcoat won't go over epoxy. Double check the following.....

Bond the ply panels in with epoxy, and together with epoxy.

On the inside epoxy / glass laminate is OK unless you are flow coating with Gel afterwards.

If so, treat the inside and out by grinding away all excess epoxy, and roughly keying the exposed surface before adding GRP laminations, an gelcoat where required.

Stick to the instructions and leave no voids and it should be sound. The transom shield will spread the load well across and beyond the repaired area.

Good luck.

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[William_H]

Just 2 comments.If you put glass and resin on the outside of the ply put quite a few layers or thick glass so that it has strength in itself as it may tend tio delaminate from the ply over time. The thicker the glass the more structural strength. Grind some of the gel coat outside the hole circumference so that the glass is bigger than the hole but still fair. Use epoxy on the wood .You can get pigment that is suitable for epoxy as well as polyester however of course epoxy is not good in sunlight long term.
Good luck will

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[MLBURGE]

sounds ok - Did the same on ours (twin outdrives) we had to fill the original holes as the cut outs for the new drives would have left gaps. We ended up replacing the entire transom as the existing ply was fairly rotten, your way sounds ok as the ply is sound, just make sure all bonded bits are 'well' sanded and cleaned well with acetone and scratch the surface of the wood heavily with a cross cut hand saw and clean aswell.

good luck.

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