Backing plates

[rajjes]

What's the best backing plate for mounting a thru hull fitting? I've read that wood is best as if some water seeps in it swells and seals it off, while other sources recommend GRP plates.

I'm refitting all thru hulls and I'm thinking of building up the backing plates with GRP laminates which will be permanentely bonded to the hull.

 

[steve_cronin]

Your GRP option is the best and is now used by most commercial builders.

Timber - usually plywood WILL swell if it gets wet. If the skin fitting is plastic for a log or sounder this can (*& DOES) snap the outer flange off resulting in a hole in the bottom of the boat!

* 1987 with family on board heading out of Poole Fairway bound for Alderney, our log flange broke off and the boat started to fill. Walloped a bung into the hole and made it back to Sandbanks where we dried out against a jetty, got a spare from SYC, fitted it at low water (midnight) and set off again next day. Had it happened thirty miles further south!!!

Steve Cronin

 

[petery]

I bonded a wooden pad onto the hull and then covered that with GRP and expoxy resin when I replaced my Blakes thru hull fittings. I thought it gave me the best of both worlds - ie the swelling and the strength.

 

[steve_cronin]

No the swelling is BAD news

See my posting below.

Steve Cronin

 

[petery]

Re: No the swelling is BAD news

I basically followed the suggestions given by Blakes for their bronze fittings. I accept that it may not be the right solution for plastic.

 

[oldsaltoz]

G'day Rajjes, and welcome to the YBW.com forums,

Fibreglass will be just fine, but consider the following.

Remove ALL paint and other contaminants from the area to be glassed.

Use epoxy resin only and no chopped strand,

Cut out fibreglass material before you mix any resin and make sure each shape is at least 40 mm smaller than the previous one, this will give a feathered edge and avoid hard spots in the hull.

Don't lay up more than 4 or 5 layers at one time or too much heating may cause problems.

Measure your fittings and overdrill the holes to provide a 2 mm gap (Minimum) around the new fitting. Coat the inside of the hole with epoxy resin to prevent water entering the exposed glass, if you mix any filler with the resin, make sure it is a closed cell type.

When all has cured (24 Hrs) re drill and insert fitting, sealant etc.

Hope this helps.

Avagoodweekend Old Salt Oz......../forums/images/icons/cool.gif