Not Pretty in Pink......

Canopy Locked

Canopy Locked

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Well..the pics says it all.... my prop has been subject to (I think) Galvanitic corrosion.

What I am trying to establish is WHY?

She's been on hook up all year, but she was on hook up all summer before that with no problems.

I assume she has a Galvanitic isolator (not sure what one looks like!!), she has brushes on the shaft and all the earthing wires to the anode seem okay - need to check them

Of the external anodes... the hull bar anode was fine as was one of the trim tabs and the skeg anode - however one of the trim tab anodes was very badly pitted and eaten.

I have a sparks coming to have an investigation next week, but I would be very grateful to receive the wisdom of the forum in these matters so that I can be sure I cover all angles next week.

Is it likely to be an electric problem from my boat? What would the most likely culprit be?
Should I have an anode on the prop shaft? Could my boat have been affected by another in the harbour? How could I check for that?

My thanks for ideas, suggestions and observations

Rob
 
robmchugh said:
Well..the pics says it all.... my prop has been subject to (I think) Galvanitic corrosion.

What I am trying to establish is WHY?

She's been on hook up all year, but she was on hook up all summer before that with no problems.

I assume she has a Galvanitic isolator (not sure what one looks like!!), she has brushes on the shaft and all the earthing wires to the anode seem okay - need to check them

Of the external anodes... the hull bar anode was fine as was one of the trim tabs and the skeg anode - however one of the trim tab anodes was very badly pitted and eaten.

I have a sparks coming to have an investigation next week, but I would be very grateful to receive the wisdom of the forum in these matters so that I can be sure I cover all angles next week.

Is it likely to be an electric problem from my boat? What would the most likely culprit be?
Should I have an anode on the prop shaft? Could my boat have been affected by another in the harbour? How could I check for that?

My thanks for ideas, suggestions and observations

Rob
Click to expand...

deffo shaft anode if you have space or on the rudder support
battery charger always on
neighbour has a fault
are you moored near a pile
 
sailorman said:
deffo shaft anode if you have space or on the rudder support
battery charger always on
neighbour has a fault
are you moored near a pile
Click to expand...

battery charger is almost never on - the dehumidifier is plugged in on a timer - hence the reason she is on shore power hook up.

A new boat has arrived in the harbour, but they only came in maybe 6-8 weeks ago.

No
 
Last edited:
robmchugh said:
Well..the pics says it all.... my prop has been subject to (I think) Galvanitic corrosion.

What I am trying to establish is WHY?

She's been on hook up all year, but she was on hook up all summer before that with no problems.

I assume she has a Galvanitic isolator (not sure what one looks like!!), she has brushes on the shaft and all the earthing wires to the anode seem okay - need to check them

Of the external anodes... the hull bar anode was fine as was one of the trim tabs and the skeg anode - however one of the trim tab anodes was very badly pitted and eaten.

I have a sparks coming to have an investigation next week, but I would be very grateful to receive the wisdom of the forum in these matters so that I can be sure I cover all angles next week.

Is it likely to be an electric problem from my boat? What would the most likely culprit be?
Should I have an anode on the prop shaft? Could my boat have been affected by another in the harbour? How could I check for that?

My thanks for ideas, suggestions and observations

Rob
Click to expand...


I would check that there really is a galvanic isolator and get it checked out to ensure that it is correctly fitted working properly.

Check the brush system on the prop shaft.

IF this is galvanic corrosion due to the shorepower connection and an absent or non functioning galvanic isolator it is a puzzle that some of the anodes are Ok while others are not. I'd get the anode bonding where applicable checked out.
 
I believe that you can check whether you have a galvanic isolator by unplugging the shore power line and using a multimeter to measure the resistance (the ohms settiing on the multimeter) between the earth on your boats shore power line and something on the boat which is connected to the boat earth (usually the negative side of the battery). The engine block would be a suitable point.

If the multimeter shows that there is a connection between these two points then you do not have an isolator fitted, or if you do, it is not working.

If the multimeter shows that there is no electrical connection between these points then you either have an isolator fitted, which is great, or your boat's earth wiring (or lack of it) is potentially dangerous. You therefore need to search for the isolator for your peace of mind.

If the above is not totally correct, I am sure someone more knowledgeable than me will be along shortly! ;)

Richard
 
The best way to check if you have a galvanic isolator is to look at the shore power connection on your boat and trace the earth wire between the connection point and the main panel. If there is a galvanic isolator it has to be fitted into the earth wire, as its job is to "break" the earth connection to low voltages, whilst allowing mains voltage to pass. A multimeter check may work, depending on the voltage of the meter's internal battery, as anything over 1.2 volts will pass most isolators, though Safeshore make one with a double set of diodes that stops up to 2.4 volts, and I have that one fitted.

The way galvanic isolators work is by having diodes in circuit, which allow current to flow only one way, but as diodes need a small initial voltage to let any current pass they effectively block very low voltage leakages to earth. A pair of diodes pointing in opposite directions allow AC current at mains voltage to pass safely.

There is a better explanation on the Safeshore Marine website.
 
I'm not sure what I am looking at in your photo. It appears to be some pink coloured shell-type fouling on the surface of the prop, but maybe I am not seeing it right. It doesn't look anything like dezincification to me. There are some examples down the page at http://coxengineering.sharepoint.com/Pages/BrassandBronze.aspx where you can see the real thing.

To answer another question above, DZ affects the surface first and moves into the metal. Abrading or filing the pink areas will perhaps remove it all, in which case the underlying metal will be the usual brass colour. When it gets bad on propellers, for example, small chunks of metal will be lost from the trailing edge, as the remaining copper is porous and has very little strength.
 
I know it's natural to assume the problem is with you and your boat. But we've had a similar experience in Plymouth last year with boats loosing propellors and anodes at a HUGE rate. Anything and everything that was in the water, and therefore in circuit, was vulnerable. It turned out to be badly-wired shore power circuits leaking to earth. Even up-river, outside of a marina, the same can happen depending on local industry, population, etc

Prevention seems to be better than cure, so extra-big sacrificial anodes are a must. Maybe even replacing bronze propellors with stainless or carbon fibre equivalents.
 
My website chose the moment I made my previous post to lose almost all it's photos. Restoration will be a long term job that I am unlikely to do for some months. Sorry.

Imagine a brass fitting on a copper pipe. Now imagine that it is in fact a single piece of metal. That is what dezincification looks like. The DZ area will be the colour of copper when compared with the original brass (which is what most props are made of, despite the name manganese bronze).
 
Whatever the prop has it has a problem

attached another pic, slightly zoomed in..... still does not show the pitting that well, but the brown areas are the original surface of the prop and the "pinkish" areas are the pitted.

When you tap the prop, there is no "ding"... just a thud
 
OK, with your new photo I understand what I'm looking at. The colour suggests severe dezincification but pitting is not normal with this type of failure. Some electrical problem seems like a possibility. I would have suggested that the composition is faulty but it looks like a quality item, so unlikely. I'll be interested to hear the verdict.
 
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