Which is stronger: epoxy or steel?

[rsallo]

Hi all,

I've got an old refrigeration system on the boat, an Origo MarinCool, which works with a cooling plate attached to the outside of the hull (under the water line). The plate is bonded to the hull with adhesive/sealant (don't know if polysulphide or polyurethane) and 8 screws.

The plate is pretty well bonded and I plan to carry on using it, but I'd like to make sure there are no leaks through the screw holes. What would happen if the holes where filled with thickened epoxy, instead of screws with sealant? I'm not sure about the idea and will probably carry on using the screws, but was wondering what would you do.

 

[30boat]

I'd stay with the screws but it might be a good idea to re bed them in new sealant.If they get moist where they go through the plate and hull they will waste very quickly,assuming they're stainless.Epoxy resin is brittle and any movement between the plate and hull could break it and allow water in.

 

[William_H]

Epoxy

As said epoxy is not in itself very strong. Being brittle. It's strength is often adequate as an adhesive where the epoxy is quite thin bit over a large area. Epoxy can however make substrate like fibreglass carbon fibre, kevlar or boron very strong. Each substrate giving a different kind of strength. ie stiffness for carbon. tensile strength for kevlar.
So if you wanted to pursue the replacement of bolts with epoxy your best bet would be to fill the hole with kevlar strands which spread out around the hole on both sides to give good tensile strength in the pulling direction plate from hull. No I am not suggesting you actually do that just how in theory.
In practice either refit the screws should be no real sealing problem or rely on the adhesive. good luck olewill

 

[electrosys]

Epoxy doesn't have to be brittle. I use General Purpose Lay-Up Epoxy Resin from ABL (Stevens) in Cheshire. www.resin-supplies.co.uk

It remains slightly flexible when set - a tad more flexible than Rapid Araldite, if you're familiar with that. In my opinion, it's a lot better (and somewhat cheaper) than the equivalent West Systems product.

ABL also do UV-resistant epoxy and a lot more besides - worth a visit.

 

[BabaYaga]

Hi all,

I've got an old refrigeration system on the boat, an Origo MarinCool, which works with a cooling plate attached to the outside of the hull (under the water line). The plate is bonded to the hull with adhesive/sealant (don't know if polysulphide or polyurethane) and 8 screws.

The plate is pretty well bonded and I plan to carry on using it, but I'd like to make sure there are no leaks through the screw holes. What would happen if the holes where filled with thickened epoxy, instead of screws with sealant? I'm not sure about the idea and will probably carry on using the screws, but was wondering what would you do.

Hi, I have got the same installation onboard Baba Yaga. I would definitely keep the bolts, as they are the only things that attaches the whole unit to the hull, apart from the sealant. There is no threaded ring/nut on the inside, as is the case on a normal though hull fitting. And the hole is big, 80 mm diameter IIRC. You would sink quickly if it fell off.
The sealant BTW should be Sikaflex, at least that was what the manufacturer recommended.
Are there any signs of water leaking in though the bolt holes? If not, best to leave it alone, in my opinion. On the inside, the eight nuts are probably not accessible without cutting into the isolating foam? Therefore, trying to tighten the bolts from the outside, might actually create leaks, by breaking the bonds to the sealant.

 

[rsallo]

Thanks to everyone for your replies, I'll ditch the "epoxy only" idea and use the screws instead.

BabaYaga, it's nice to find someone with a MarinCool! I believe it was not sold in the UK so there aren't many around here. How well does it work on your boat?

The reason I started working on it is because the sealant around the plate started peeling off, and the surveyor recommended removing it and making it good with epoxy.

Re. the nuts, I don't know if they leaked or not, but the isolating foam was wet at the bottom and released quite a bit of water when pressed. It could be a leak from a nut or it could be from the water dripping through the inside of the hull due to condensation, I don't know.

As I plan to do some extended cruising, I didn't want to have something on the boat I wasn't sure how it worked or if there was a problem with it, so I removed all the insulation (took me a few hours to strip it!) and I'm now in the process of putting it together again. I'll fill the holes with epoxy and drill again, to make sure it's as watertight as possible.

 

[BabaYaga]

Thanks to everyone for your replies, I'll ditch the "epoxy only" idea and use the screws instead.

BabaYaga, it's nice to find someone with a MarinCool! I believe it was not sold in the UK so there aren't many around here. How well does it work on your boat?

The reason I started working on it is because the sealant around the plate started peeling off, and the surveyor recommended removing it and making it good with epoxy.

Re. the nuts, I don't know if they leaked or not, but the isolating foam was wet at the bottom and released quite a bit of water when pressed. It could be a leak from a nut or it could be from the water dripping through the inside of the hull due to condensation, I don't know.

As I plan to do some extended cruising, I didn't want to have something on the boat I wasn't sure how it worked or if there was a problem with it, so I removed all the insulation (took me a few hours to strip it!) and I'm now in the process of putting it together again. I'll fill the holes with epoxy and drill again, to make sure it's as watertight as possible.

You might be interested to know that the MarinCool is still around, but now under the name of OzCooler:

http://www.ozmarine.se/

This is the inventor's own business, he took the cooler back and renamed it when Origo dropped the product some years ago. The OzCooler is not marketed very actively though (the company concentrates on electric propulsion), but I am sure you could get some good advice on how to revamp the installation if you contacted them directly.

My wild guess would be the wet foam has to do with condensation rather than seawater leaking in. Regarding the peeling sealant AROUND the plate, my advice would be to remove and renew. It has no sealing funtction, it is there only to improve the waterflow over the plate.

After fourteen years my own unit simly keeps on working and hopefully will continue to do so a good number of years (knock, knock...)