Steel Boats and Anodes

  • Thread starter Thread starter hlb
  • Start date Start date
hlb

hlb

RIP
Joined
16 May 2001
Messages
26,773
Location
Any Pub Lancashire or Wales
Visit site
Just had the barge lifted after three years and anodes are unworn. Yet it has been on shore power all the time. Yard says some boats dont burn anodes but they are going to check the grounding. Theres no prop or shaft pitting, as far as we can see. So it all looks ok, but I'm not sure. My anodes would be shattered in 12 months or less. Is fresh water different.
 
[Is fresh water different.]

Centainly is and a different type of anode should be used for it. More Alluminium I believe if my memory serves me correctly.

Your yard is right some boats don't burn Anodes no reason why but best to get a check any way.
 
Magnesium for freshwater

Aluminium usually used in brackish water, though Mercruiser now supply all their drives with Aluminium for salt water use
 
Best is magnesium for fresh water, although I currently have zinc in fresh and very slow to degrade too. Other factors probably work in our favour and against us depending on other boats and condition of shore supply and so on.
 
Twat! /forums/images/graemlins/grin.gif
Wasn't talking to you.

GRP boats in freshwater get osmosis quicker. Steel boats like delph no problem. Person you need to talk to is Ships_Cat, he understands this stuff better than most.
 
Yes fresh water is different, your steel boat is better off in fresh rather than in salt and I suspect that you haven't much to worry about if there is no problem evident in the hull. The rate of wastage of the anodes is less in fresh water too and all the talk that people say about if anodes not dissolving (whether in salt or in fresh) then they are not working is bunkum.

That is the plain answer for what was asked for. If interested beyond that, read on /forums/images/graemlins/smile.gif.

Limiting my comments to steel boats (as that is what the question was about) then the anodes will deplete more slowly in fresh water. This is because it is not much of an electrolyte and so the "battery effect" between dissimilar metals is much less. As far as I am aware, zinc anodes are fine in fresh water, comments on using other anode materials being mainly relevant to aluminium parts such as out drives.

A well built small vessel will need very little anode protection in any event (even in saltwater) as it all depends on the galvanic compatability of the metals used in its construction. Just as one example (and I always get cried down on this, but it is so) if correct materials are used for the propellor and shaft (and especially if they are also insulated from the hull and engine) then no shaft anode is required - that applies to glass and timber boats too, of course.

The type and condition of the coatings on the hull also determine the rate that anodes disappear as if the steel is painted a high resistance path exists between it and the electrolyte (the water) and then to the anode.

As an example, our own 40 foot yacht living all year round in salt water is steel (is only lifted out for a couple of days every second year). It has one only teardrop anode on one side of the keel (nothing on shaft or anything else). That anode easily lasts 2 years. In fresh I would be surprised if much happened to it at all.

John
 
Shorepower

Doing this by itself because a different issue.

Shorepower is only a problem if ones boat hull is connected through the AC shore cable to the AC ground on shore and thence by a similar shorepower route to another boat. Then only if ones own boat is not isolated from the shore earth by use of an isolating transformer or a galvanic isolator in ones own shorepower cable earth connection.

Again, the problem is much less, possibly non existant, in fresh water because for a problem to exist there has to be an electrolyte between ones own boat and the others to which it is electrically connected via the shore earth. Fresh water is not a very good electrolyte being of high resistance.

John
 
You must log in or register to reply here.

Share this page

Top