Cleaning the stern locker out the other day after laying up Chuckles for the rest of the winter, I noticed a black wire which seems to be connected to something down below, the P bracket I think. As it doesn't seem to be connected to anything I'm wondering if it should be connected to the engine and therefore through the prop shaft to the one sacrificial anode that we seem to have. Are we missing an anode maybe. What do other inboard boats have I wonder? I'd appreciate it if anybody could have a look and tell me where this wire goes, and maybe what the standard set-up should be.

Cheers,

Jez
Chuckles Too
GBR 7139

Hi Jez,
I believe the theory is that if you have an anode everything that is metal and below the waterline should be connected to it. That said Genghis Khan has never has an anode fitted (as far as I know) and having checked all seacocks (I check and service them every winter) they are showing no signs of pitting or any other probems.

I have however seen the pitting that can be caused to a propeller if not properly protected by an anode so it's worth keeping an eye on.

I havn't fitted an anode as so-far no problems, I think it may depend on where you moor and how much metal there is around??

Hope this ramble helps???

Hope to see you in the new season. G

On Forethought the stainless prop shaft has anodes on it. That is because it is connected directly to the brass propellor.
The previous propellor began to corrode when the anodes failed to work (coated in concretion)

One idea seems to be that only items that 'see' each other are really candidates for electrolysis. They also need to be connected to each other to complete the circuit. A GRP hull doesnt conduct as well as wet wood, so there isnt a good circuit for electrolysis. Adding a bondwire and an anode will protect the items, but if the anode fails the items will be less protected because of the wire

Another factor comes in with marinas and shorepower and entire boats being at different DC voltages but then the typical GK24 isnt involved much in that

On Forethought the P bracket is not connected to anything, as the cutless bearing is rubber. This is also because the P bracket is a retrofit , 4 years after the boat was built.

The engine was connected to the prop shaft by a wire across the semiflexible coupling but that wire commits suicide all the time.

There are no bonding wires on other fittings.

Cheers Guys,

No need to be paranoid then! It's the prop that's the problem really, there's no bonding at all on the sea cocks and this doesn't seem to be causing any pitting. I might connect the P bracket to the engine just to make sure.

Moving to our outer harbour fore and aft mooring seems to have done a power of good as the marina berth that we had before was eating a 3/4" shaft anode at least every six months, a combination of electricity and brackish water I suppose.

Hi Jez
'Upgrade' came to me in Jan 07 with an inboard 1GM10 & an anode on a wire, which the previous owner used to hang off the back rail into the water when moored. At that time, it had no prop shaft anode fitted, so I put one on and it eroded approx 33% in one year to Jan 08.
I failed to replace the internal engine anode [behind the alternator] in Jan 07 and when I did it recently [Feb 08] it had almost completely gone [2 year's wear]. Hope this may help.
Cheers
John

Since posting a confident "no problem"
I have had to replace the P bracket on Forethought. It was thoroughly dezincified and brittle around the cutless bearing.
The replacement was horrible hard work. But it only took 2 days out of a 4 day MDL special offer lift out.

I have now bonded it electrically to the engine and made sure that there is a bit of Monel wire wrapped round the semiflexible coupler on the propellor shaft. So that is also bonded .

I now hang a big lump of zinc teardrop anode off the pushpit which is also bonded to the earth. Interestingly the steel strip in the anode has become highly magnetized - probably induced current from a nearby lightning strike. It really affects the autopilot.