Props eroded.

[Andydent2000]

We've been in the water since July last year. Knowing it was time for a lift I decided to dive down to take a look. (preparation to minimise the time out of the water).

I got a bit of a shock when I discovered the starboard prop had a chunk out of it and severe electrolytic erosion.
The anodes (which were fine) are dissolved down to the bar both port and starboard. The rudder anodes have gone too.

Obviously they have done their job but what on earth can have caused them to erode so quickly?

I mean, the props are beyond repair! Good job I checked. I don't think they would last another decent journey.

 

[andy59]

Do you leave boat connected to shorepower ?

 

[sharpness]

In less than a year, seems a very high wear rate, especially if now eating your propellors.
Are you permanately connected to the shorepower as i believe this can increase the wear rate, i understand fitting a galvanic isolator to the boats 240v circuit can make a difference.
You say all anodes appear to be showing correct wear, do you have anodes on your shafts or do you have the brush system for the shafts (located in engineroom near couplings) and if so are the bonding cables all secure, and good connectivity to the hull anodes.

I'm sure more specific advise will follow, and with you being located on the hamble, someone may be able to say if this is the norm or not.

 

[Andydent2000]

Do you leave boat connected to shorepower ?

The boat is connected to shore power but there is a rocker switch to turn it off on the boat. Weekdays it is off. Weekends it is on unless we are going somewhere.

 

[Andydent2000]

You say all anodes appear to be showing correct wear, do you have anodes on your shafts or do you have the brush system for the shafts (located in engineroom near couplings) and if so are the bonding cables all secure, and good connectivity to the hull anodes.

yes there are brushes on the shafts. They were tested with a multimeter before the boat was relaunched last July. Visual inspection shows that the brushes are fine and the wires look to be still ok.

It does seem high but I must admit I was not aware that shore power could still be a factor when isolated.

 

[omega2]

Are the gearbox/shaft couplings bridged?? if using R&D they must have a bond across the joint. Shaft anodes are as much use as a chocolate teapot. IMHO

 

[andy59]

If you turn off the shore power on the boat with a rocker switch , i would be pretty certain that its a double pole switch , so even when its of the earth circuit is still connected and so you are effectively connecting your annodes to anything else connected to the pontoon , ie other boats and any metalwork that is bonded on the pontoon electrical installation . When leaving mine off i allways pull the plug out of the boat and in winter leave the heaters connected directly to the shore power lead so as to leave the boat isolated . One day i will get round to fitting a galvanic isolator .

 

[VicS]

The boat is connected to shore power but there is a rocker switch to turn it off on the boat. Weekdays it is off. Weekends it is on unless we are going somewhere.

If you leave it connected, even if not in use and switched off at the circuit breaker the earth is still, as Andy59 says, connected.

That is very likely the cause of your problem. Either unplug from the supply completely or fit a galvanic isolator.
A galvanic isolator will block currents from the low the voltage sources that cause galvanic corrosion while allowing current from high voltage sources to pass so maintaining the effectiveness of the earth connection as a safety feature of the shorepower installation.

In view of the damage to the propellers I think I would also check the DC system for possible faults that could lead to electrolysis unless you are completely isolating the batteries when leaving the boat. A galvanic isolator will not stop electrolysis caused by a faulty 12 volt installation.


A while back a forumites boat sank on its mooring due to electrolysis of a skin fitting that had been wired to the negative connection of a bilge pump.

 

[Andydent2000]

Thanks for all the good advice. I am arranging a lift out and will go through everything with a fine tooth comb.

I must admit it did not occur to me that the earth would still be connected to shore power. I will be unplugging the lead from now on.

 

[kashurst]

sounds like your anodes and props are serving your neighbors and the pontoon piles too.

I leave my shore power on all the time to maintain the batteries.
I fitted a galvanic isolator about 14 months ago now. Anodes are dissolving but much much more slowly, I'm still on the same set and I think another 6 months+ at current rate. Cost @ £80 and easy peasy to it.

 

[Bandit]

A good policy when you get a new/secondhand boat is to lift it and check all underwater parts after 6 months with a quick lift to see condition of anodes and skin fittings.

If i was you i would get a good marine electrcian to cheak through your bonding to confirm connectivity of everything underwater, prop/shafts, p brackets rudders and all sknin fittings and valves. Also electriacian to check boat when back on normal berth to make sure there is not a problem with 240 volt on pontoon leaking to sea or a problem with neighbouring boats. If not fitted fit a galvanic isolator.

Also chech bronze fittings for going pink or carrotty and replace if nescesary.

Belt and braces I use shaft brushes and shaft anodes with a jubilee clip above and below stop them sliding up or down.

If valves are marked cw617n they are brass possibly a sivery nickel coated and should be replaced with bronze or DZR fittings If so or valves with red plastic levers suspect brass and also skin fittings and replace.

If brass fittings they will loose the zinc and go soft and crumble eventually.

 

[VicS]

If i was you i would get a good marine electrcian to cheak through your bonding to confirm connectivity of everything underwater, prop/shafts, p brackets rudders and all sknin fittings and valves.

It is not now considered correct or wise to bond everything underwater in this fashion. Only items that require the protection of anodes should be bonded to them.

Bronze and DZR through hulls do not need the protection of anodes and should not be bonded to anything, or even to each other.
Interconnecting underwater fittings can provide a low resistance path through the vessel for stray currents in the water.

Anything going pink is doing so due to dezincification. Bronze does not suffer from this because it does not contain zinc. It is something that only happens to brass.
Anything showing signs of zincification is therefore brass is best replaced with bronze or at least with dezincification resistant (DZR) brass if the effect is more than surface deep

Be aware however that there is now a trend for builders to fit brass through hulls with a life expectancy of 5 years!

 

[jimmy_the_builder]

Another vote for a galvanic isolator. The anodes on my d6 outdrives only used to last about 8 months, and since I've fitted the galvanic isolator I now get comfortably over a year.

When I was installing it, just out of interest I put an ammeter into the earth circuit. 30mA. Yikes.

Cheers
Jimmy

 

[volvopaul]

My boats moored in front of andys, I too nearly lost props to the location, when I was lifted this year the anodes were wasted completely , I'd say it's down to the location.

I'm going to speak to the Marina, I never leave my shore power lead plugged in yet anodes gone in 11 months, my props were ok but it worries me that should the pontoons wiring and supply have a problem then it's going to cost us.

Andys boat is also next to a pontoon post which is metal, maybe that's caused the erosion , I did all his bonding wiring and shaft brush checking last may , all was well and checked out before the boat went in the water prior to coming here.

 

[VicS]

Another vote for a galvanic isolator. The anodes on my d6 outdrives only used to last about 8 months, and since I've fitted the galvanic isolator I now get comfortably over a year.

When I was installing it, just out of interest I put an ammeter into the earth circuit. 30mA. Yikes.

Cheers
Jimmy

You can work out from that how much zinc you'd expect to lose in a year.

 

[ripvan1]

It is not now considered correct or wise to bond everything underwater in this fashion. Only items that require the protection of anodes should be bonded to them.

Bronze and DZR through hulls do not need the protection of anodes and should not be bonded to anything, or even to each other.
Interconnecting underwater fittings can provide a low resistance path through the vessel for stray currents in the water.

Anything going pink is doing so due to dezincification. Bronze does not suffer from this because it does not contain zinc. It is something that only happens to brass.
Anything showing signs of zincification is therefore brass is best replaced with bronze or at least with dezincification resistant (DZR) brass if the effect is more than surface deep

Be aware however that there is now a trend for builders to fit brass through hulls with a life expectancy of 5 years!

Vic - that's very interesting - I have all bronze underwater fittings, prop and shaft, p/bracket, rudder and shaft and 1 through hull.

I'm about to launch soon and have been asking around about anoding and general consensus is that I need to employ some. (I bought the boat as resto project and out of the water - she was previously only in freshwater I believe, so no anodes present)

Can you point me in the direction of some literature that backs up your views please?

Thanks