rot in transom, sterndrive boat

[Elessar]

I'm swapping my Mercruiser V8 petrol with Alpha 1 Sterndrive for a 6cyl diesel with Bravo3. I've got all the bits and have removed the old engine and drive.

Unfortunately there has been water ingress to the transom plywood core. The wood around the hole at the worst point is soft for about 4", at the best point is solid.

I've seen this www.rotdoc.com . (how do you make that a "clickable" link?) The recommended quantities with shipping but not import duties will cost US$340.

Anyone any experience of this, thoughts on this solution or a better idea?

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[chippie]

As the transom is a relatively flat area you could cut out the rot and then determine the size of patch you need. You then mark the outline of your patch on the transom and with a router machine a flange to half thickness of your ply and a corresponding flange on your patch . saturate the whole lot in epoxy with particular care to the edges and then mix epoxy glue and fit the patch like a lid with a few square drive screws which you can later remove and fill and fair it all and you have a very strong repair with both inner and outer surfaces flush.
I have done this on plywood boats with success. The diagram gives the general idea. Good Luck

.. .... ^^^^^xxxx^^^^^.... .. patch

TTTxxxxx ............... xxxxxTTT transom


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[arran]

It may be helpful to look at here for your other question.

Hope this helps

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[gjgm]

is the ply glassed into the transom ? I believe the ply is there to take the considerable forces applied to the transom by the leg. I m a bit surprised you havent experienced some delamination as the outer fibreglass starts to flex against the ply. Id suggest its a bit different from repairing a ply boat because in this case the ply is a farily intsrinsic part of the transom structure. It is reapirable of course, but not sure its not for a specialist (and specialist costs!)

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[oldsaltoz]

Have to agree with Chippie, very good advice, have replaced part and whole transoms on power boats and cats in the past myself.

As you have good access to both sides of the transom it should be pretty straight forward.

Mark the area you want to remove and screw some battens on to guide the router. run a drill through the battens before you remove them and relocate them on the other side of the transom and this time secure them with bolts, this will ensure both cuts line up perfectly.

Just remember to over size any and all holes in the transom re-fill with a mixture of epoxy and fibre just below the surface (It's very hard to sand), or fill it and grind off after then fair with epoxy and micro-balloons or 'Q' cells, you need "Closed Cell" fillers.

Have a talk to your local fibreglass supplier about the best fibre to add to the resin to provide high bond strength.

You may find the ply is wet well past the soft area, I make a point of removing all wet, rotten and more important, dry but stained material, as this indicates it has been wet and may not be as strong as the material around it.

You can thin epoxy resin with metholated spirits, up to 50/50 by volume to give you a mix that will soak in and penetrate any suspect areas.

Hope this helps...

<hr width=100% size=1> Old Salt Oz /forums/images/icons/cool.gif Growing old is unavoidable. However, growing up is still optional.

 

[Blue_Blazes]

As a fellow wood-butcher I agree with both Chippie and Oldsaltoz, especially the bit about removing any darkened wood beyond the soft areas. I would be carefull about thinning epoxy. West system do not recommend it, check out their website, sorry don't know the URL. Also beware of saturating rotten wood with epoxy. It will make softened wood hard again but will not restore structural strength, something which it is vital for you to do in the case of a sterndrive mounting area.

Best of luck,

Bill.

<hr width=100% size=1>One of these days I'll have a boat that WORKS

 

[oldharry]

Think about it - your transom is structural and is supporting to some extent the weight and thrust of the saildrive. No wood 'freezer' will restore the strength of the original timber, so chop it out and replace the damaged area. It might be easier and better to simply replace the entire transom, then there will be no doubt about its structural integrity. There is a rule of thumb with rot in hardwood, that you cut back to sound timber plus a foot. (Oh, allright - 33cms if you must!) This ensures that you remove any potentially infected material - it takes very few rot spores to start the process off again.

Thinning epoxy reduces its strength, and it has to be extremely thin to penetrate timber to more than a few mm depth. How can you be certain that it has fully saturated the timber anyway before it goes off. You only get one shot at that one! There is no way of checking it has gone right in - short of cutting through it! And if it has not - how do you access the unwetted rotten core to treat it once the stuff has gone off?

There is only one treatment for rotten structural timbers - new wood.

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[Elessar]

I wish this advice didn't sound so sensible........

However, there must be people with old boats out there that haven't paid to have the who transom romoved?

What did you do? How are you getting away with it?

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[chippie]

At least three of us who replied to your post gave advice on repairing the transom without replacing it as long as there is some good wood left to work with.

Advice is what we ask for when we know the answer but wish we didnt.

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[oldharry]

<.... that haven't paid to have the whole transom romoved..?>

If you are planning a DIY job then you might find it easier to replace the whole transom rather than fiddling around trying to get it right - only you know if you have the skills to make a decent serviceable job of repair or replacement.

If on the other hand you are paying a chippie or boat builder to fix it - then you only need to know how much he will charge to fix it! You can (hopefully) leave the technical bits to him - thats what you are paying for!

My main point is that encapsulating rotten timber in epoxy or some 'wonder gunk' simply will not do for structural repairs.

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