Epoxy galvanic insulation

[PabloPicasso]

Would epoxy work as a good galvanic insulator?

 

[VicS]

Would epoxy work as a good galvanic insulator?

ITYWF that it is a good electrical insulator.

 

[PabloPicasso]

I've had a problem with the hub anodes corroding too fast on the hub of a Volvo sail drive folding prop. If I epoxy coated the hub, except for bearing surfaces and anode mounting places, would it reduce the rate at which the anodes corrode and improve protection?

 

[Neil_Y]

Yes, as the rate is down to exposed surface area. Just make sure there is a good electrical connection to the metal you want to protect, corossion of the anode shows it is protecting something.

 

[PabloPicasso]

Will epoxy unbalance the hub?

 

[MYStargazer]

I was told epoxying a bronze rudder would expose the uncovered rudder shaft-gland interface to a concentration of severe galvanic action?

 

[macd]

I was told epoxying a bronze rudder would expose the uncovered rudder shaft-gland interface to a concentration of severe galvanic action?

I'm no expert in galvanic action and am happy to be put right, but can't see that at all: assuming the bits you're worrying about are less noble than bronze, isolating the rudder can surely only be a good thing. Besides, you happily antifouled it, didn't you? The effect is much the same.

 

[vyv_cox]

It is well established that painting a cathodic component will reduce the rate of loss of an anode. A well-known example is an aluminium rivet in a steel plate, which will disappear quite quickly underwater. Painting the plate delays loss of the rivet (anode) quite considerably.

Anything on the hub is unlikely to cause much of a balance problem but a coat of paint on it even less so. I paint all of my prop, which has no discernable effect on vibration.

 

[MYStargazer]

I paint all of my prop, which has no discernable effect on vibration.

Could - indeed should - all metal underwater parts be coated in epoxy primer and a durable top coat? Why are so many props and prop shafts left bare?

 

[MYStargazer]

assuming the bits you're worrying about are less noble than bronze, isolating the rudder can surely only be a good thing.

It's not the bronze I'm worried about - it's the mild steel p-bracket and stainless steel prop shafts.

Besides, you happily antifouled it, didn't you? The effect is much the same.

Nope! My bronze rudders have always been just bare bronze. Was never sure why, though!

 

[vyv_cox]

Could - indeed should - all metal underwater parts be coated in epoxy primer and a durable top coat? Why are so many props and prop shafts left bare?

I have been unable to get epoxy primer to stick to bronze/brass parts reliably, it seems that an etch primer is needed. I do find that Hammerite non-ferrous metals primer works well. In combination with Velox antifouling it has been pretty effective. This photo is from last year, when using the recommended four coats of Velox seems to have been too much and it chipped off under the influence of cavitation. This year I only used two coats with almost no chipping.

2013 season, P-bracket also painted with Velox. Photo taken before pressure washing, four months afloat in Greece.

 

[macd]

It's not the bronze I'm worried about - it's the mild steel p-bracket and stainless steel prop shafts.

You miss my point. Of course it's not the bronze you're worried about. But if the bronze is isolated there can be no galvanic couple between it and less noble metals.

If you'd been a little less cryptic about your "rudder shaft-gland interface", someone would probably have come along to tell you that your stainless prop shaft would probably be happy as Larry, but the galvanic difference between it and your P-bracket is greater than that between mild steel and whatever sort of bronze your rudder is constructed from.

 

[macd]

It's not the bronze I'm worried about - it's the mild steel p-bracket and stainless steel prop shafts.

You miss my point. Of course it's not the bronze you're worried about. But if the bronze is isolated there can be no galvanic couple between it and less noble metals.

If you'd been a little less cryptic about your "rudder shaft-gland interface", someone would probably have come along to tell you that your stainless prop shaft would probably be happy as Larry, but the galvanic difference between it and your P-bracket is greater than that between mild steel and whatever sort of bronze your rudder is constructed from.

 

[PabloPicasso]

Hmmmm. My sail drive is protected by a big thick ring anode. It's the anodes for the hub on my folding prop that corrode fast