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Plastic or synthetics that bond with epoxy

AaronD

.
Aug 10, 2014
538
Catalina 22 9874 Newberg, OR / Olympia, WA
I'm filling in a concave space in a locker to mount a battery; a previous owner had just set a battery there, and I'd left it thus far (adding a battery box, at least). But the hull is rounded enough that the battery is only supported at the ends, and I'd rather fill in the void beneath to provide a better support (and real tie-downs).

I plan to put a flat G10 board underneath the battery box, and fill the rounded space beneath with ???

Options: 1) Marine plywood soaked with epoxy - this would probably be fine, but since it's at a low spot in the hull, I'd prefer something that won't rot if it ever collects moisture (water shouldn't penetrate a top layer of epoxy, but bolts for the tie-down anchors would provide a route in). 2) I can do it all in G10 board, which won't ever rot, but is heavy and somewhat expensive. 3) G/Flex epoxy would bond Starboard, but I can't really justify buying the G/Flex when I have plenty of regular West System.

Is there some other material that would work with regular West System epoxy and save a few pounds (and isn't hugely expensive)? Note that it will only be stressed in compression, so material strength isn't a big deal.

Mostly I'm just curious - I'm not a racer, so I'd probably never actually notice a few extra few pounds of G10, but if there's another good option, I'd like to learn. After all, the purpose of winter is for learning about boats, right?
 
Jan 11, 2014
7,853
Sabre 362 113 Fair Haven, NY
Filling the void will cause a hard spot in the hull to form. The hull around the void will flex ever so slightly, but under the battery, it won't. That may cause stress cracks to form at the edges of the now filled void.

One way to address this by fiberglassing 2 cleats on to the hull and then laying a piece of plywood or G10 across the cleats. Half inch cabinet grade plywood (sometimes sold as birch veneer) will probably work. It could be glassed in or simply screwed to the cleats. Coating in West System is one option, another is a decent polyurethane varnish (like Minwax). This is likely not an area that will get wet, so epoxy may be overkill.
 

AaronD

.
Aug 10, 2014
538
Catalina 22 9874 Newberg, OR / Olympia, WA
Filling the void will cause a hard spot in the hull to form. The hull around the void will flex ever so slightly, but under the battery, it won't. That may cause stress cracks to form at the edges of the now filled void./QUOTE]

Thanks - I hadn't thought of that.
 
Mar 26, 2011
2,939
Corsair F-24 MK I Deale, MD
I'm filling in a concave space in a locker to mount a battery; a previous owner had just set a battery there, and I'd left it thus far (adding a battery box, at least). But the hull is rounded enough that the battery is only supported at the ends, and I'd rather fill in the void beneath to provide a better support (and real tie-downs).

I plan to put a flat G10 board underneath the battery box, and fill the rounded space beneath with ???

Options: 1) Marine plywood soaked with epoxy - this would probably be fine, but since it's at a low spot in the hull, I'd prefer something that won't rot if it ever collects moisture (water shouldn't penetrate a top layer of epoxy, but bolts for the tie-down anchors would provide a route in). 2) I can do it all in G10 board, which won't ever rot, but is heavy and somewhat expensive. 3) G/Flex epoxy would bond Starboard, but I can't really justify buying the G/Flex when I have plenty of regular West System.

Is there some other material that would work with regular West System epoxy and save a few pounds (and isn't hugely expensive)? Note that it will only be stressed in compression, so material strength isn't a big deal.

Mostly I'm just curious - I'm not a racer, so I'd probably never actually notice a few extra few pounds of G10, but if there's another good option, I'd like to learn. After all, the purpose of winter is for learning about boats, right?






a. There is no reason to use G10 for applications that do not require thread holding ability or massive (far more than most fiberglass laminates) comprehensive strength. Structural grade fiberglass is stronger than the rest of the structure of the boat and 1/2 the price. G10 is a neat material, but it is not what you build boats with.

b. Use structural FRP for the underlying structure.

c. You can probably go thinner than you think. 3/16" is probably plenty with such high strength material. Good fillets and taping spread the load.

I've used 1/4 structural FRP for steps and stuff I intended to jump on. It is way stronger than what you need.


McMaster Carr has this, as do others.
 

AaronD

.
Aug 10, 2014
538
Catalina 22 9874 Newberg, OR / Olympia, WA
Thanks, Drew. That's just what I was hoping to learn. Structural FRP probably won't save much weight vs G10, but I'll sure take the cost savings!