BoatHowTo · video

What this video covers

A viewer measures 0.6 volts between a gearbox and a propeller shaft on a boat fitted with a flexible coupling and asks whether the elastomer insert is conducting rather than isolating.0:27 Nigel Calder explains the coupling itself is not the source — a properly installed rubber insert does not conduct.0:49 The more likely explanation is that zinc or aluminum sacrificial anodes on a stainless steel prop shaft impress a small galvanic voltage across the system, which a meter will pick up even with the coupling in place.1:04 Calder notes other system factors could also produce the reading and that further investigation is needed to identify the exact source.0:58 The key point: a 0.6-volt reading in this location is not a cause for concern and does not indicate a faulty or conductive coupling.1:37

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