Measuring stray electrical currents

[Squeaky]

Good morning:

Over the years I have seen many comments concerning the need to bond all the skin fittings and seacocks to an anode to prevent damage from stray electrical currents in the water surrounding the yacht.

I have recently discovered some shoddy work on my yacht where the final bonding wire was simply shoved into a hole in the GRP stringer at the forward end of the engine giving the impression that it continued on and was connected to the anode at the aft end of the engine compartment. Assume it was considered too much trouble to empty the locker and finish the job which looked ok to the casual observer.

I have now "daisy chained" all sking fittings and tested for continuity and while doing so began to wonder if there is any simple way to check how much, if any, stray electrical current exists in the water surrounding my yacht.

Any advice/comments will be appreciated.

Cheers

Squeaky

 

[sailorman]

DO NOT bond skin fittings, they are isolated with no electrical connection you have now caused a potential ( Pun ) problem

Good morning:

Over the years I have seen many comments concerning the need to bond all the skin fittings and seacocks to an anode to prevent damage from stray electrical currents in the water surrounding the yacht.

I have recently discovered some shoddy work on my yacht where the final bonding wire was simply shoved into a hole in the GRP stringer at the forward end of the engine giving the impression that it continued on and was connected to the anode at the aft end of the engine compartment. Assume it was considered too much trouble to empty the locker and finish the job which looked ok to the casual observer.

I have now "daisy chained" all sking fittings and tested for continuity and while doing so began to wonder if there is any simple way to check how much, if any, stray electrical current exists in the water surrounding my yacht.

Any advice/comments will be appreciated.

Cheers

Squeaky

 

[rogerthebodger]

I agree with Sailorman, disconnect then now if it a GRP boat, different is metal hull like mine.

A friend did what you did and connected all his skin fittings and they all started to corrode. He then disconnected and cleaned all the corrosion and all was well.

The only reason IMHO the anode suppliers recommend bonding on GRP boats is to sell more anodes.

 

[prv]

The only reason IMHO the anode suppliers recommend bonding on GRP boats is to sell more anodes.

Well, bonding the stern gear makes sense, assuming you have the usual combination of a bronze prop on a stainless shaft. That's the purpose of the anode on a typical fibreglass boat. Seacocks should be all the same material, or insulated by the bearing material in the case of a ball valve, so don't need to be bonded.

I don't remember ever seeing any authoritative advice to bond seacocks, only reminders not to. I wonder where people get the idea from?

Pete

 

[alahol2]

I don't remember ever seeing any authoritative advice to bond seacocks, only reminders not to. I wonder where people get the idea from?

All the seacocks were bonded on my boat when I bought it, and, so far as I am aware, they have been bonded for the last 20 years or so. There is no sign of any untoward results so, for me, it's a case of 'if it's not broke, don't fix it'.

 

[Salty John]

In general terms there are three reasons to bond metal items together on a grp boat:
Corrosion resistence.
Lightning prevention.
To provide a good earth for electrical and communication systems.

The case against bonding comes from the possibility of introducing stray current corrosion. The ABYC (American Boat and Yacht Council) address this in their Standard E-2, Cathodic protection of boats. It's an interesting document.

They are generally in favour of bonding, but specifically state that bonding of seacocks and through hulls that are electrically isolated may not be justified.

To answer the OP's question, you can check for stray currents by detaching a bonding wire at a seacock and then measuring for current from wire to seacock. Current flow, if any, should be from seacock to wire and not from wire to seacock.

 

[VicS]

The reasons for the shift in opinion away from the previous policy of bonding all through hulls etc to the anodes can be understood by reading the MAIB report into the near loss of the fishing vessel Random Harvest some years ago.

One of the recommendations was that through hulls should be disconnected from the cathodic protection system.

 

[maby]

.....


To answer the OP's question, you can check for stray currents by detaching a bonding wire at a seacock and then measuring for current from wire to seacock. Current flow, if any, should be from seacock to wire and not from wire to seacock.

That will only measure the leakage current for that seacock - better to disconnect the bonding wire from the hull anode and measure current through the anode - that will pick up all leakage currents in one go.

 

[mitiempo]

Back when boats were either moored or in marinas without shorepower bonding was common. With the prevalence of shorepower now it's a bad idea for the reasons posted above. Bonding now can be asking for trouble.

Here is a link to an informative article on grounding:
http://www.sailmail.com/grounds.htm

 

[Squeaky]

Good morning:

If my reading of the above responses are correct, it looks like I got ahold of the wrong end of the stick and will be removing the bonding wires I connected recently.

Thanks to those who responded.

Cheers

Squeaky

 

[Squeaky]

Good afternoon:

Having read the very good link provided and while discussing this matter with my neighbour we came across another point that neither of us can answer and that is "why does his engine have an anode in the heat exchange which the intructions that should be checked every 4 months while my engine does not have an anode of any description?".

We are both trying to get our heads around the fact that bonding all the outlets to an anode is not a good idea having picked this theory up someplace over the years.

Further advice and comments will be appreciated.

Squeaky

 

[sailorman]

Your engine is higher quality marineizeation then his.
does he have a red engine

Good afternoon:

Having read the very good link provided and while discussing this matter with my neighbour we came across another point that neither of us can answer and that is "why does his engine have an anode in the heat exchange which the intructions that should be checked every 4 months while my engine does not have an anode of any description?".

We are both trying to get our heads around the fact that bonding all the outlets to an anode is not a good idea having picked this theory up someplace over the years.

Further advice and comments will be appreciated.

Squeaky

 

[VicS]

why does his engine have an anode in the heat exchange which the intructions that should be checked every 4 months while my engine does not have an anode of any description?

Some do some don't. It depends upon the materials used in the construction of the heat exchanger.
Difficult to explain if you have identical installations though unless of different ages.

We are both trying to get our heads around the fact that bonding all the outlets to an anode is not a good idea

Basically not necessay if the fittings are of a good corrosion resistant material eg a bronze or DZR

Best avoided for the reasons found in the Random Harvest investigation.

There was also case a year or two ago in which a forum members boat sank at its mooring due to electrolysis and failure of a skin fitting that had been bonded to the DC negative at a bilge pump, presumably in an attempt to bond everything together.

If you moor in a marina where there is a lot of stray current through the water it is possible that the current can take an easier ( lower resistance) path through the bonding wiring. Corrosion will occur of the fitting where it leaves and flows back into the water

 

[Kukri]

further to Vic's note (which I agree with) here is a link to the MAIB report on the loss of the "Random Harvest":

http://www.maib.gov.uk/cms_resources.cfm?file=/random harvest.pdf

As you certainly know, electrolytic corrosion is temperature related; warmer, saltier water (the Med!) makes it worse.