anode on wooden boat

[davidsmith18]

hi
hope u can help?
had a huge problem recently with a bronze rudder post dissolving due to what looks like electrolysis ..
disaster!
have never had an anode on my boat before in my ownership ..
in fact no evidence has ever been one !
she was built in 1906, and has no engine (apart from outboard in well when used)
should I have an anode ?
and if so, where to attach to and would it need wiring to something ? (can't imagine what?)
any help much appreciated as am at a loss
many thanks
david

 

[johnlilley]

Take great care considering adding anodes to a timber vessel. They can cause major damage to timber structure whilst protecting the metal fittings. If the vessel has never had anodes then look for other problems that may have caused the rudder tube to corrode. By adding anodes you could find that the timber surrounding the rudder tube deteriorates as a result. Much less expensive to replace a rudder tube or stern tube than to replace the timber surrounding both.
Other problems could be things such as new electrical problems from faulty or new installations, any new fittings or recent repairs below the waterline, shore power problems or possible just a lower quality bronze tube naturally coming to the end of its life.
Don't create major new problems as a result of not investigating the existing fully.

 

[davidsmith18]

thank you for the response .. the bronze rudder post is less than 1 year old! .. it runs through a bronze rudder tube (through counter) and is attached to a stainless rudder stock under water .. the previous one had survived fr 109 years ... no idea what has caused this ... now in a marina for my sins, as have small family and thought it more practical ..
have no shore power .. limited electrics on board (isolated) .. and no engine .. only an outboard that drops thru a well .. could it be the marina? .... very expensive problem as rudder post has to be hollow to allow rudder lifting wire to go thru it, and not metric size (blah blah) ....
thank you
david

 

[davidsmith18]

.. to add .. I could attached the anode to the stainless rudder stock under the water ...
no need to bolt to hull ?
would this avoid damage to wood ?

 

[johnlilley]

If the rudder tube is bronze & in sound condition & no electrolysis or damage, then I would suspect the new bronze rudder post is the culprit in that it possibly is a very different bronze to the tube. Is there any doubt that it is bronze and not a brass shaft.
It might be possible to attach an anode to the rudder without causing timber problems, but I would try to revert to the original materials that obviously survived without the need for anodes. Originally your vessel was not fitted with a stainless rudder so not quite sure of the design, but certainly sounds like vastly incomparable metals in contact underwater. Bronze & stainless should be OK together but there are so many slight differences in both that it is possible to have extremes at both ends of the range thus causing problems that anodes can cure, but not without the risk of timber damage somewhere
|I would be inclined to check the deteriorated stock is not inferior material. There are occasional problems in marinas that affect vessels. Quite commonly a close by vessel with an unacceptable electrical mains leak. Even sometimes the marina electrics themselves.

 

[burgundyben]

Is there any doubt that it is bronze and not a brass shaft.

That's exactly what I was thinking as I read my way down the page.

 

[Lon nan Gruagach]

If the rudder tube is bronze & in sound condition & no electrolysis or damage, then I would suspect the new bronze rudder post is the culprit in that it possibly is a very different bronze to the tube. Is there any doubt that it is bronze and not a brass shaft.
It might be possible to attach an anode to the rudder without causing timber problems, but I would try to revert to the original materials that obviously survived without the need for anodes. Originally your vessel was not fitted with a stainless rudder so not quite sure of the design, but certainly sounds like vastly incomparable metals in contact underwater. Bronze & stainless should be OK together but there are so many slight differences in both that it is possible to have extremes at both ends of the range thus causing problems that anodes can cure, but not without the risk of timber damage somewhere
|I would be inclined to check the deteriorated stock is not inferior material. There are occasional problems in marinas that affect vessels. Quite commonly a close by vessel with an unacceptable electrical mains leak. Even sometimes the marina electrics themselves.

Bang on the money there.
If you want a replacement to last another 109?? years then get a sample of the old one or the tube to a metallurgist and have a composition drawn up. Then, when ordering new stock specify precisely what you need. Sounds expensive, but not as bad as a new post every year.

Another solution might be to make a new post out of stainless, again match to the rudder as accurately as possible.

 

[davidsmith18]

the rudder tube is bronze .. and 111 years old
the rudder stock is stainless and 50 years old
the rudder post was bronze and 111 years old ... failed last year and replaced with a new one ... also naval bronze
eaten away and snapped where joins to rudder stock (and exposed to the water) ... >
all leads to metal was wrong quality (new post, that is)..
very annoying in the meantime :-(

 

[davidsmith18]

have just got to that position myself .. (stainless post) .. if can find tube the right diameter and wall thickness .. then machine a section to fit top and attached to tiller head (also bronze) ...
should mean can then avoid using any anodes at all (which have avoided for 111 years to date) ...
thank you for all your input

 

[Motor_Sailor]

I don't think that Naval Bronze is a bronze at all. I think it's a brass like Manganese Bronze is a brass.

More recently suppliers have been encouraged to call it Naval Brass (not to be confused with Admiralty Brass). It does have a small amount of tin in it (~1%) which is where the 'bronze moniker came from. The tin was there to help with dezincification in the same way lead is added to DZR brasses.

I would check to see what your rudder post was made from. Naval Brass would have lasted about a year.

 

[burgundyben]

Always keep a copy of the Nigel Warren book to hand!

 

[DoubleEnder]

Also take a good look at marina electrics. I have a wooden boat. I once over wintered in a marina and when the boat came out in the spring the propellor nut was about 50% eaten away by electrolysis. I am now very suspicious about spending any length of time on marina pontoons

 

[vyv_cox]

I have replied to your question via YM. Motor Sailor is correct, the alloy you have used is not a bronze at all, it is a slightly modified brass. You should receive my full reply tomorrow.