Bubbles under anti-foul on keel.

[Auntie Podes]

:confused
I don't know if anybody has experienced this sort of thing but I thought I'd try my luck. Everybody I talk to seems to have
different ideas. It is apparent to me that there are many degrees of understanding from patent mis- through to reasonably good but, so far, not complete. I've found info on the web - some good info - mostly very lengthy - but nothing which fits my case.

I have a problem with my lead keel - the anti-fouling blisters quite badly and comes off in patches. I had it ground back and
epoxied prior to a/f'ing - twice - but the same problem recurred. From what I can gather it could be due to electrolysis within
my own boat or electrolysis connected with my being on a marina and close to other boats.

I really cannot see how other boats on the marina can be a factor as I do not normally connect to shore power. The only time I
do use shore power, which is rare, is when using power tools on the boat, drill, soldering iron etc or when charging a battery. I normally charge bat's at home where I can keep an eye on the process. In view of this I find it hard to believe that the marina environment is a factor.

My boat (f****** I happen to like the stuff!) has a metal plate, presumably bronze, fitted flush into the underside of the hull and to which zincs are attached outboard. A couple of hefty bolts welded to this plate extend through the hull and the engine and batteries are wired ("grounded") to these.
There is also a hefty wire (more of which in a minute) running from a keel bolt (which shows no resistance to the other keel bolts - i.e. there's clearly good connection through the keel to the rest of the bolts) and back to the plate-bolts. The zinc on the plate is "working" - it wears out - but not at a great rate of knots. The engine etc, as far as I know & can tell, isn't rotting away !?!?! I also have a zinc mounted on the prop shaft and this "works" - not excessively. This is NOT electrically connected to the engine - it's "decoupled" at a flexible coupling which is not strapped across.

Now - this wire - keel to plate. I cannot be certain that, when I bought the boat, this was connected because I later found that the wire was chopped under a floorboard. When it was chopped I do not know - nor do I know whether it was done deliberately or not. I have since tried connecting it - disconnecting it - hanging a "guppie" over the side from the keel bolts and so on but have not been able to distinguish any effect on the blistering problem on the keel.

SO - what the heck should I do? I'm just having the keel re-painted from scratch - complete with burnishing and "treating" with various acids, potions and unctions. My current thinking is that I should isolate the keel - i.e. disconnect this wire and again see what happens following the paint job. If it is isolated - there's nothing for it to react with - save the (presumed) ironwork inside it - bolts etc.
All contributions will be gratefully receieved.
Thanks
Auntie Podes.
P.S. For those fortunate enough not to have come across me before - I'm a HE! The Auntie Podes thing is a pun.

[Classic Boatworks - Maine]

It definitely sounds like an electrolysis problem. However, it may still be coming from somewhere in the marina and not on your boat. We have heard of cases where boats have been affected by other boats 3 or 4 slips away to the point of dissolving fastenings in short order. Even on boats which have not electricity at all!
We can relate horror stories all day but that won't help. Have the boat tested when it is in the water by someone competent in marine electronics. They can test for stray voltage flow (mini-volts).

[Ed Harrow]

Ditto CBM.

[John B]

Get a marine electrician to come down and test it.
oops... too slow.

[This message has been edited by John B (edited 11-06-2001).]

[dale o]

This is an interesting problem. Lead is pretty far down on the EMF table. Lead is resistant to corrosion from seawater. You say you have epoxied the lead keel before painting with the antifouling paint. Maybe the failure is due to an adherance problem there. You have protected the other metal with sacrificial zinc anodes. Why not skip the epoxy coating and apply the antifouling directly to the lead keel? Lead is slightly sacrificial to copper. You may want to remove that bonding jumper between the keel and the bronze plate and check for stray currents.

[ford]

I had the same problem with a timber boat, blistering on the lead ballast, checked the boat with a multimeter and found 250 milliamps running through her.
Seem that the different mix of metals below the waterline, stainless steel keelbolts and copper nails etc, turned her into a large battery.She is now undergoing a major reconstruction.
Check the metals below the waterline.