Thinking Ahead to Glassing in a Bottom Thru-Hull

[klb67pgh]

I filled the depth transducer hole in my E25 when I switched to a DST800 and only needed 1 thruhull, not 2. I was surprised in how quickly the original thruhull and transducer plug disintegrated when I started removing it. It wasn't leaking, but it certainly could have failed if something hit it.

I found the layup to be fairly straight forward and used online resources/YouTube to make decisions on the layup process.

 

[gabriel]

This may not be the right way to do it (would love to hear opinions on it) but why not simply epoxy a 1/2” plate of g10 over inside opening, epoxy a circular g10 disk (same diameter as opening) to fill outside opening , fair, sand, barrier coat etc?The thinking is that g10 is superior to any hand layup. Just my 02.

 

[tenders]

I would say that gluing chunks of G10 into a hole will not have the same degree of adhesion and stress absorption that stacked layers of cloth will. There will be hard spots that will tend to fail.

 

[David Vaughn]

There would be two issues with using layers of G10 instead of glass cloth.

The main issue is the type of bond.
When glass cloth is properly saturated and laid on another layer of saturated glass cloth, the epoxy in the first layer mixes with the epoxy in the second layer and so on. When that has fully cured the result is a single solid mass. This is why, for the strongest repair of this type, one layers from both the outside and the inside.

With just G10, you’re relying on the abraded surface of the G10 to hold on to the epoxy. It’s not absorbed into the already solid material. Cured epoxy by itself is brittle. Under the right loads there would the potential for one or more layers to sheer and the repair fail.

The other issue would be the epoxy itself. If I’m mixing several small batches to wet out the cloth, there’s more room for error if one batch is slightly off (not enough hardener for instance). If using G10 and that batch is off, the bond may never set properly and be even weaker than it would have been.

Above the waterline you could probably get away with that depending on where the repair was and the loads it had to handle. Below the waterline? No, I don’t think I’d want to try that.

 

[bigd14]

I understand the concerns about fillers, and should clarify that I only used the G10 disc in one or two repairs in a particularly thick section of hull where a full thickness taper and layering up didn’t seem worth it. I did taper the hull out but not 12:1. The G10 disc was well abraded with 40 grit, cleaned with acetone then the remaining thickness of the hole was patched in the usual manner with progressively larger circles of 1708 (8-10 layers likely in total) and then capped inside and out with a larger square of 1708 to bond it all together. I am satisfied that perhaps barring a strong impact with a thru-hull sized pointy object in the exact location of the former thru hull that it will never be an issue.

I agree that using just G10 as described would be risky.