drilling hole in balsa-sandwich deck

Ric

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I would like to fit solar panels onto the coach house roof of my boat. I would need to pass the cables through the roof, which is grp/balsa sandwich. Is there a fool-proof way of doing this without risking getting water into the balsa sandwich? I don't really trust some of the usual glands etc that are available for passing cables through decks as these seem more designed for simple grp decks. Is there anything available specifically for sandwich decks?

It's an expensive one to get wrong...
 

bigwow

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When drilling a hole in a sandwich construction deck it is a must that the sides of the hole are sealed, I use epoxy when making holes in mine.
 

Noddy

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I've just repaired a 2 ft hole in my balsa sandwich coachroof.

Terrified when I started more confident now.

You are right in saying that you want to keep the water out as it does travel.

I would just make the hole and remove some of the balsa, pack in some epoxy (sealing the balsa in) and then redrill the hole.

If you need load bearing then remove more balsa and put in a harder wood (marine ply is OK) and glass over again. This is to prevent crushing (which was the cause of my problems). Then support the fitting in the normal way.

Most of the DIY boat books will have pictures and explanations.

Good Luck
Paul
 
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You mean they know how to drill holes? Or are they an advertising agency?
 

savageseadog

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I drill right through with a 6mm drill then use a hole saw approx 20-25mm to cut away one side of the GRP and the basa core, stop when you cut through to the other GRP layer. The hole is then filled with an epoxy filler mix, I use West with colloidal silica or whatever. I do this from underneath so preserving the deck. Use tape to hold the epoxy in place, it is possible to inject the filler into the hole from above with a syringe if you want to be posh. This also has the benefit of strengthening the deck where you need it.
 

john_morris_uk

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Another 'approved' way is to drill deck through and to use a bent nail or similar on a drill to make a void in the balsa core of the deck all around the hole. Use a vacuum and a bit of wire to poke/suck as many bits of balsa out as possible. Now tape over the lower hole and inject epoxy through the top hole. (A syringe is useful for this and works amazingly well.)

Wait for epoxy to harden and then re-drill your hole for the gland at the correct size. Easy-peasy and you get a nice bit of 'solid' deck to mount the gland on and guaranteed waterproof deck if you fill it with epoxy properly. (Even if the gland leaks.)
 

oldsaltoz

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G'day Richard,

The small hole and hole saw or the small hole and bent nail (Should read old allen key) are fine fir this, however I would use resin mixed with micro fibres, this will provide a lot more strength.

I prefer the single hole and allen key and tape over the lower hole and inject the mix slowly. clean up any excess when still wet, it's very hard to sand after curing.

Avagoodweekend......
 

1317

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Simoncr. Those brothers popularised "West System" epoxy builds/repairs and essentially wrote the book on DIY marine applications. I am retired from the Ad business and don't know of any company trading in Ads with that name. However, I defer to any Scot/Pole knowledge that would set me straight.
It is common practice in North America to "ream" the hole with a bent nail and fill the void with epoxy and re-drilling the correct size for the fastener. Not enough GRP's for you?
 

1317

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Simoncr, sorry, shouldn't use jargon in an open discussion. GRP's is short for GROSS RATING POINTS and is determined by measuring reach and frequency in media evaluations.
 

DorsetPete

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Hi there
'john-morris-uk' above has hit the nail right on the head!
I have followed this way of doing itfdor years and as he says it is easy-peasy.
Highly recomended
Good luck
 

William_H

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Hello Ric if it is a mobo then solar panels on the roof may be ok. I found with a smaller sail boat that solar pannels are just to susceptible to damage especially when racing with someone swing a spin pole around. After several damaged panels I have successfully settled on attaching my panels onto the top of the boom cover using bungee. The cables run to a connector on the outside of the bulkhead and are always removed beffore sailing. This also allows for a little tilt toward the most sun. North for me, south for you. of course if you are on a swing mooring then put em flat as best compromise. good luck olewill
 

boatmike

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By far the best way of passing cables through any deck is to use a proper cable gland. You can buy them in any chandler for a few bob and it enables you to create a perfectly waterproof joint and you can remove the cable whenever you want. By all means drill the hole and seal around the hole first if you want belt and braces. It is an excellent idea to drill the hole a bit bigger than you need it first and get a plain bit of rod (an old bolt or something like it) wipe some vaseline around it and pump Sikaflex in the hole around it. I would not use Epoxy as it is not very flexible and can crack in time. Sikaflex never will. If you can undercut the balsa even better. When the Sikaflex has hardened, remove the bolt and fit the gland using more Sikaflex to seal the base. Much more work perhaps but a more professional job. As an aside, contrary to popular lore, end grain balsa does not actually soak up water very well anyway if it is properly bonded to the deck. The big problem is that on many boats it isnt and there are voids and it is these voids that the water travels down.
 

vyv_cox

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Deckfittings.jpg


From the book Glassfibre Boat Manual, editor Bo Streiffert.

Here's a method I have used for heavier fittings, specifically my windlass. Possibly too much for your needs but it might be useful. For lighter fittings you can omit the back-filling and instead cover the holes with the plastic caps used to blank pre-drilled holes in self-assembly furniture.
 

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