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Old 20 March 2003, 20:05   #21
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Country: UK - England
Town: SOUTHAMPTON
Boat name: Won't get Fooled Again
Make: Ribtec
Length: 6.5
Engine: Honda 130
Join Date: Mar 2002
Posts: 888
Thanks Guys, my goodness this is informative.

To answer some questions ,

The boats was only in the water for 7 weeks and has been in the same Marina Berth for the last two years on and off without such problems. The longest continuous period is probably 4 months. however the bottom gets furry in the water so it was usually pulled out at least every month for a clean.

Anodes were in good nick, they don't exist anymore obviously

Boat was tied to the Pontoon..no chainis , not moored to another boat and surrounded by other craft. Cabin cruisers, Gin palaces and Yachts all with mains feeds.

My boat was not connected to the mains and the batteries were isolated but the Auto bilge pump was left on.

Yup it has a stainless prop.

The Marina has a manufacturer of Turbine generators on the grounds which produce enough Electricity on site to supply some surplus to the National grid.

Our Optimax on the Scorpion has lost lost the majority of it's anodes and they were only three months old. It was immersed for about 6 weeks.

Yes I have legal protectin built in to the insurance. I guess it is Digital Camera and Multimeter time.

Cheers
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Old 22 March 2003, 09:42   #22
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Country: Ireland
Town: Dublin
Boat name: wizzard
Make: REDBAY
Length: 7m +
Engine: 225 optimax
Join Date: Sep 2002
Posts: 835
corrosion

Current will only flow if it has a path, and will take the path of least resistance,remember all the boats sitting around you some with electrical leaks manifesting themselves on the various boats will result in corrosion , but only local corrison.I dont believe that shore power being ac will flow tro the water and up tro the honda gearbox and cause corrosion, all the boats are at the same potential once they are sitting in the water, this is not to say a leak like this couldnt happen , but flowing from a distant boat tro your boat is not going to happen.It will take the easiest path, therefore a leak will find a path back much closer ,almost immediate to the leak I would have thought and if it did find a way to your boat it would have to find a different path back to where it came from to complete the circuit.There are possibly two problems here, your battery isolation is completly useless as long as you have an electrical load fed from it ie a bilge pump.In this instance voltage is present at the pump which is normally low down and usually wet, secondaly outboard anodes must be in the water to operate correctly.A small leak electrical leak from the bilge pump could travel along wet surfaces of the boat conduct along outboard metalwork and cause this problem of a stray current flow, a small flow of current is enough to eat metalwork.Another problem is this if you have metal fittings ie stainless in a salt water soultion and a different type of metal elsewhere in the solution, ie an outboard made of alu, you have effectively created a battery.A battery in its simplest form is 2 dissimilar metals in a sailine solution.In this instance the so called battery will create current flow and the corrosion can be dealt with by having the anodes immersed in the water,they will then safely corrode.I would be reluctant to look to the marina I think your permanetly fed bilge pump is leaking to earth .Hopefully you find spares cheaper gavin
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Old 22 March 2003, 11:11   #23
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Country: Other
Make: FB 55
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Join Date: May 2001
Posts: 1,711
Maybe some puffins had a go.........
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Old 22 March 2003, 17:26   #24
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Country: UK - Scotland
Make: HumberOceanOffshore
Length: 8m +
Engine: Volvo KAD300/DPX
Join Date: Oct 2002
Posts: 4,962
I'm feeling pedantic tonight, pedantic tonight

A battery in its simplest form is 2 dissimilar metals in a sailine solution.

Read cell for battery. A battery is a group of cells.
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Old 23 March 2003, 12:58   #25
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Country: Ireland
Town: Dublin
Boat name: wizzard
Make: REDBAY
Length: 7m +
Engine: 225 optimax
Join Date: Sep 2002
Posts: 835
batteries

Batteries as we know for boats cars etc are made up of groups of cells, however mono cell batteries do exist which however small the potential difference across the positive and negative is ,enough to produce current flow,in your car battery you have 6 cells as you know each dropping 2 volts, by combining these you get 12 volts, but one on its own gives you 2 volts across its positive and its negative.You dont need 12 volts milivolts are enough to produce current flow gavin
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