Shiver Metimbers
Well-Known Member
I have a cast iron keel with a lead bulb (dissimilar metals) therefore should the keel be protected by bonding it to the hull anode?
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Cast iron keel with Lead bulb
- Thread starter Shiver Metimbers
- Start date
Tranona
Well-Known Member
No. Lead and iron are fairly close on the galvanic scale and the keel will be painted so the junction between the two will not be in seawater.
Shiver Metimbers
Well-Known Member
Would it harm to bolt an anode on the keel anyway as there is a tapped hole from where the previous owner had an anode?
vyv_cox
Well-Known Member
There is about 0.6 volts between lead and cast iron in the galvanic series in seawater, more than between cast iron/steel and zinc. A zinc anode might well do some good. Do you see any corrosion of the iron?
Shiver Metimbers
Well-Known Member
There are some small rickety contours on the trailing edge of the keel, this could be corrosion or galvanic damage I'm not sure. But the previous owner has a bond between the bottom of one of the stantion bases to one of the keel bolts which I intend to remove.
VicS
Well-Known Member
You will need anodes both sides as one will not protect the side of the keel it cannot see. The same would apply to hull anodes
Id think anodes nearish to the lead bulb will be more effective than up on the hull as that will be where any corrosion the lead causes will be most severe
I wonder what is the object of the connection to the stanchion base.
Shiver Metimbers
Well-Known Member
The bond to the main Anode had corroded off at the point were the builder (Gibsea) had buried the bond into the gelcoat floor and the terminals of the anode could not be seen as they were buried too. Maybe the previous owner thought the bond from the stanchion base would be an alternative. Or maybe his idea of a lightning conductor?
I have drilled down into the anode stud and tapped it out so I can reattach the bond from the engine block and shaft stuffing box. Hence I'll be removing the bond to the keel bolt.
VicS
Well-Known Member
bond to the shaft stuffing box ????
Shiver Metimbers
Well-Known Member
It has sea water on it's external end and could touch the shaft?
Mark Taylor
Well-Known Member
Whilst at anchor or berthed I have seen some owners hang an anode over the side of their boat on a stainless wire, clipped onto the stanchion base. Presumably they then bond the stanchion to the keel, or stern tube or wherever? I suspect a previous owner has had a similar arrangement on this Gibsea. Tends to be more prevalent on racing boats but certainly a couple of the cruisers in Troon use they same system for added protection.
Quandary
Well-Known Member
No need to worry. All Sigma 38s have a composite keel, top half iron, bottom half lead, joint still close to invisible, most were made in the late 80s so are now nearing forty years old, if there was a problem I think it might have shown up by now.
I did use a hanging anode on mine, fitted to replace a high drag big lump of a hull anode as all the seacocks etc. were bonded so I wanted to connect the circuit to something, it was was just the redundant hull anode on a wire, never seemed to degrade, unlike the shaft anodes.
I did use a hanging anode on mine, fitted to replace a high drag big lump of a hull anode as all the seacocks etc. were bonded so I wanted to connect the circuit to something, it was was just the redundant hull anode on a wire, never seemed to degrade, unlike the shaft anodes.