Anode bolts

mad_boater

mad_boater

Well-Known Member
Joined
14 Oct 2002
Messages
616
Location
staffordshire
Visit site
All the years I have been boating when it comes to changing the anodes the bolts are always rusted up and have to be replaced and resealed.Why can't stainless ones be used ? On my boat it's right faff as the lazzerette (hope that's how it's spelt) and all it's contents plus a big screwed down storage box have to be removed to get at them GRRRR.
 
As far as I'm aware, the general train of thought is not to use stainless steel fixtures or fitting under water because of the possibility of crevice corrosion occurring in the absence of air.

For this reason the tendency is to use non stainless steel through-hull bolts. I've seen people use extra nuts in order to cover any threaded section of bolt to make them easier to remove. After removal of the boat from water the rate of corrosion on the bolts will rapidly increase, so replacing anodes soon after hauling out makes sense.
 
If your anode bolts are rusting, you have some difficult questions to answer - the anodes are there to stop things rusting - if they are not working on the bolts, what good are they doing for the drive shaft?
 
maby said:
If your anode bolts are rusting, you have some difficult questions to answer - the anodes are there to stop things rusting - if they are not working on the bolts, what good are they doing for the drive shaft?
Click to expand...

I would have thought as the bolts are directly attached to the anodes they would be the first thing to be protected.
 
LittleShip said:
I have stainless threaded bar through my hull with stainless nuts underwater. It's against lots of advice you will receive re stainless in an airless environment but it's been fine for me.

Vic will probably be the best to advise.

Tom.
Click to expand...

I once put a stainless bolt in place of the more expensive anode fittings and was surprised and concerned to find that it had virtually disappeared when I next went to change the anode.

I now stick to the fittings sold specifically for anodes, don't want the risk of a big hole in the hull letting in water!
 
Stainless steel uniquely occupies two positions on the Nobility scale - Passive high and Active very low. If the metal cannot form its barrier it becomes active and is as corrodable as mild steel, and close to aluminium. The specific rate of corrosion will depend upon what other more noble metals are present, and what galvanic / stray currents are flowing.

Mild steel used with a well electrically connected zinc anode should not corrode at all as long as the anode remains with corrodable metal present, and it might even gain a light zinc coating. This bi-polar feature of stainless steel is why it is unpredictable in underwater situations.
 
mad_boater said:
All the years I have been boating when it comes to changing the anodes the bolts are always rusted up and have to be replaced and resealed.Why can't stainless ones be used ? On my boat it's right faff as the lazzerette (hope that's how it's spelt) and all it's contents plus a big screwed down storage box have to be removed to get at them GRRRR.
Click to expand...

The standard anode fixing studs are zinc plated steel. The zinc plating, while it remains, should prevent ordinary rusting while the boat is out of the water. While afloat the anode will protect the studs from corrosion when the zinc plating has been lost.

Stainless steel anode fixings are available if you want them. http://www.mgduff.co.uk/mgduff-product-catalog/Ancillaries/Ancillary+Item+Studs/M10BSS.html

If stainless studs are used they should be carefully sealed where they pass through the hull to ensure that no crevice can exist. If it does then water trapped in the crevice will slowly lose its dissolved oxygen and the stud will lose its protective oxide film. This results in the part of the stud passing through the hull becoming anodic to the part in fully oxygenated seawater. The galvanic corrosion cell formed will result in crevice corrosion of the stud. This is the process to which Superheat and LongjohnS refers
to above
 
You must log in or register to reply here.

Share this page

Top