Rot near gunwale

  • Patrick
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13 Jul 2009 17:57 #20533 by Patrick
Rot near gunwale was created by Patrick
Hi

I think I have finally discovered my leak into the back bouyancy tank. On Saturday I noticed a dark stain in the wood near the gunwale towards the left-back end of my Mirror just above this bouyancy tank. Poking around I then proceeded to put my finger through a rotten patch and now have a hole the size of my fist. It looks as if rain water has been getting under the cover and in-between the ply that fits into gunwale. The rot doesn't seem to extend down any further but I am going to have to investigate and possibly cut out a section to make sure....I am fairly handy with wood but I don't know the thickness of marine ply needed and the best technique to ensure its a nice fit.

Anyone any thoughts/suggestions

P



P

PD

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14 Jul 2009 09:04 #16568 by Martin Egan
Replied by Martin Egan on topic Rot near gunwale
Hi Patrick,

Boats were originally (i.e. 1960's) 3/16" (=4.7mm), then changed to 5mm ply so depends how old yours is. Normally gaboon marine ply was used, but you will find it hard to source as it is an unusual size, 4mm and 6mm are far more common. So you may have to go for 6mm and plane it down, or maybe some 4mm that is on the thick side (it's never exactly 4mm) would be OK.

Two methods for fixing are;
1) Scarf join it to surronding ply by chamfering the surronding ply and the patch. I chamfer for 1" when I do this. As you are handy with wood this is a good method as the patch can be almost invisible. Needless to say, you need to get the grain to run the same way where it is varnished and if you can colour match it even better. No need to scarf where it goes between the inner and outer gunwale. You should be able to slide the new patch up or down into the gap left by the rotten ply.

2) Put a backing plate, or, in your case plates inside the tank and inside the side panels. Snag is the backing plates can be seen, but involves less intricate woodwork than scarfing. Backing plates need to overlap the existing ply, and the new ply. So you cut out the rot leaving a neat hole. Fit the backing plates which are, say, 1/2" larger than the hole all round (so you can glue them to existing ply). Inside tanks backing plates can have holes in if you are worried about weight. Then glue ply patch to the backing plate which is visible inside the hole.

I'm understand that it is good engineering practice for patches like this to have rounded corners. But this makes it a bit of a challange on the woodwork front.



Edited by - MartinEgan on 14 July 2009 10:25:57

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