One corroded Green circular plate bolted to the boat: Eaten away / SSB

[Jamesuk]

Hi,

We had the SSB replaced but now we have one of our midship grounding plates looking like it probably fizzled when the SSB was being tested.

Set up:

Midship below nav station we have two circular grounding plates which are about 14cm in diameter. Looking at both, one seems to be connected to the inverter, the other has a copper strip leading up from it to a bolt which has all the electronics in the vicinity grounded to it Including a large wire that disappears off to another location. This on the hull is the heavily corroded one.

At the back of the boat we have two grounding plates fitted for the SSB 9 years ago around 20cm long each which look as they have always looked.

At the stern we have an anode on the prop that is worn away more than I have ever seen it on the propeller (Gori) the other anode above it looks fine but with the bar appearing to be rusty (could just be air that did that)

I tried a continuity test between the anodes/shaft and damaged grounding plate and I get no continuity. I am now inside the boat attempting to do the same but access is pretty awful.

Any thoughts or perhaps better a local sparky expert who can come and visit the boat would be much appreciated (Southampton)

Cheers

James

 

[VicS]

Hi,

We had the SSB replaced but now we have one of our midship grounding plates looking like it probably fizzled when the SSB was being tested.

Set up:

Midship below nav station we have two circular grounding plates which are about 14cm in diameter. Looking at both, one seems to be connected to the inverter, the other has a copper strip leading up from it to a bolt which has all the electronics in the vicinity grounded to it Including a large wire that disappears off to another location. This on the hull is the heavily corroded one.

At the back of the boat we have two grounding plates fitted for the SSB 9 years ago around 20cm long each which look as they have always looked.

At the stern we have an anode on the prop that is worn away more than I have ever seen it on the propeller (Gori) the other anode above it looks fine but with the bar appearing to be rusty (could just be air that did that)

I tried a continuity test between the anodes/shaft and damaged grounding plate and I get no continuity. I am now inside the boat attempting to do the same but access is pretty awful.

Any thoughts or perhaps better a local sparky expert who can come and visit the boat would be much appreciated (Southampton)

Cheers

James

Severe corrosion of a ( bronze ???) grounding plate is only likely to be caused by electrolysis due to a small ( or not so small if the damage has occurred quickly) current from the equipment attached to it passing through the water and back to battery negative via another under water appendage not directly connected to the affected one (eg the other nearby grounding plate if the two are not connected to each other)

This current could be the result of a poor negative connection to one of the bits of equipment connected to the affected plate, The plate, the water and the other underwater item then providean alternative path to the battery negative.

I would therefore be looking for this " stray" current in the connection to the grounding plate when various bits of equipment are in use ( and possibly even when they are not) or a measureable positive voltage on the affected plate compared with other underwater bits and pieces, esp the other nearby plate. If the boat is out of the water then be looking for this positive voltage, although there won't be any current flow.


This is the sort of thing that can happen with several under water items if they are not all bonded together directly and independently of the boats electrical system. If a loop is created, that includes the water , and a bit of voltage is created due to current through a poor connection something is likely to fizz.

If your older stern grounding plates are now redundant I would disconnect all wiring from them.

The mounting strap of the hull anode will suffer surface rusting when the boat is out of the water once the original zinc plating has gone.


Cannot comment at the moment on the more rapid than usual wastage of the prop anode.

 

[Jamesuk]

Thanks for the advice and PM.

 

[VicS]

Thanks for the advice and PM.

I am wondering if anyone out there can contribute some advice on the installation of SSB in particular the wiring of a ground plate and the use of a "DC Block"