Preparing for throughhulls on a ply-epoxy boat.

[whipper_snapper]

I need to drill some holes under the waterline on a Wharram cat built in epoxy-soaked marine ply. One task is to fit a dynaplate*, I also need to re-seat some dodgy seacocks.

Having drilled a hole, should I seal it with resin to prevent seepage into the ply? Or is that not necessary? My instinct is to drill way oversize, fill with resin/chopped glass, let cure and redrill. But that would make it impossible without lifting out which I hope to avoid. If I just drill to fit the bolts, then anything I squirt into the hole would be of little use as it will be pushed out by the bolts. The dynaplate instructions advise sikaflex on the inside but specifically say NOT on the outside.

Any suggestions ? As far as I can see the hull is very sound and built with top quality ply.

Thanks


(*which I tell everyone else they don't need!!)

 

[john_morris_uk]

Why can't you drill the holes and just give the raw edges a couple of coats of epoxy to seal them. I don't see how you are going to do this without hauling the craft out though.

 

[boatmike]

Your instincts are good. Getting water ingress into the end grain of the ply is something you really don't want. When I have fitted dynaplates on larger vessels they have usually sat about 1/8" away from the hull on spacer washers which have been sealed on both sides a bit like an anode mount. I think its mainly to get the maximum electrically conductive area, but also if it suffers electrolysis it won't affect the hull.
Probably why they say don't sikaflex the outside.
Don't see why you should not do the same.

 

[oldsaltoz]

G'day whipper_snapper,

You could oversize the holes, then apply epoxy thinned with meto to 30% by weight, this will penetrate into the end grain much faster and deeper, you will have to apply several coats as the end will suck it up.

When this finished, fill the hole with a mix of epoxy resin and Micro-fibres, very strong and water resistant.

Use stainless steel washers to cover the holes when you pass the bolt thru', and another on the inside. Clean up any material that squeezes out because this stuff is murder to sand after it cures.

With the above you will not need any other sealant and should you have to remove it at some point in the future, just apply heat to the bolt and the epoxy will soften enough to remove it.

Remember everthing MUST be bone dry before you start.

Hope this helps.

Avagoodweekend......

 

[whipper_snapper]

I like it, thanks.


What is 'meto' ?


W_S

 

[oldsaltoz]

OOps that should read Metho (Methylated Spirits).

Avagoodweekend......