What size anodes should I fit, please?

[Grace and Favour]

Hi chaps!

 

Can anyone help please?

 

When our boat is next out of the water I intend to fit new magnesium anodes..

 

What I don't know is whether there is an optimum size (unless it's purely governed by my wallet?)

 

 

As they are wasting anodes - - should I assume that a 2Kg lump will waste at the same loss rate as a 1Kg lump - - or is there some devilishly clever electrical reason (possibly known as "The Galvanic Rule of The Galaxy") that governs it?

 

And, as far as I know, wasting anodes are normally located fore and aft, would there be any advantage in welding a pair on amidships (and am aware that I'd need be careful I don't clout them when moving/mooring)?

 

Any help will be appreciated - thanks

 

Dave

[Robbo]

Not sure about the size, but having a few mid ship as well as front / back is recommended if they are not prone to getting knocked off!

[BEngo]

Hi chaps!

 

Can anyone help please?

 

When our boat is next out of the water I intend to fit new magnesium anodes..

 

What I don't know is whether there is an optimum size (unless it's purely governed by my wallet?)

 

 

As they are wasting anodes - - should I assume that a 2Kg lump will waste at the same loss rate as a 1Kg lump - - or is there some devilishly clever electrical reason (possibly known as "The Galvanic Rule of The Galaxy") that governs it?

 

And, as far as I know, wasting anodes are normally located fore and aft, would there be any advantage in welding a pair on amidships (and am aware that I'd need be careful I don't clout them when moving/mooring)?

 

Any help will be appreciated - thanks

 

Dave

 

 

The optimum size for a steel narrowboat is governed by your wallet, the frequency of lift-out for inspection/renewal and the effect they will have on your beam/draft. Since there are practical limits to the size you can buy and the popular sizes last 5-10 years on a reasonably well blacked boat in fresh water, I would buy the biggest you can afford/fit.

 

The loss rate is complicated, involving potential differences, water conductivity, the shape and surface area of the electrodes, the price of fish in Grimsby on Bank Holiday Tuesdays and the shape of Rhode Island Red chicken entrails after being thrown at least 6ft onto a firm surface. However 10 Kg electrodes in practice last about twice as long as 5 Kg ones!

 

The effective range of an anode is, empirically, about 6 ft. The logical spacing is therefore about 10ft apart. However that is OK if you can afford/safely fit enough of them. If not the major bits of bent steel, which (in the very broadest and most general terms) are more susceptible to corrosion than flat bits, are at the front and the back so they are good starting points if your budget/space will not run to lots.

 

MC will have them at 20% off on Freaky Friday if you are not desperate. See the FF thread for the next date.

 

Three is a good deal of corrosion science out there and you'd need to understand it to produce an optimal anode layout, but the above are reasonable approximations from practical observations.

 

 

N

[nb Innisfree]

When we reblacked in 2006 we came across a few small pits exactly midway along our 60´ nb, no sign of them since but as a precaution we fitted a couple of anodes midway on top of the bottom plate chine.

[Grace and Favour]

BENgo and NB Innisfree

 

 

Many thanks indeedy chaps!

[blackrose]

See if you can find some flat anodes to weld on amidships.

 

I found some at Crick made by Amber Boats. They're protected by the overhang of the baseplate (the one at the bow is a standard anode).

 

 

I've also got an anode on each side of my uxter plate. My reasoning is that it's just below the waterline so susceptible to corrosion. At least with other parts of the hull at the waterline I can see if rust appears.

Edited March 29, 2013 by blackrose

[Grace and Favour]

Thanks Mike . . . . .

 

I shall do just that

 

Freaky Friday's order is just about to get a bit heavier

[J R ALSOP]

put as many on the bottom as you put on the sides, I see lots of boats out of the water and believe me the bottom does get affected, have it grit blasted and two pack coated. only had mine out twice in 34 years and is as goo as new unlike some 10 year olds that have had nothing done to them, only the sides.

[FadeToScarlet]

This is where it's handy having a banged about wrought iron hull, I have enough dents and corrugations to put anodes in without them being exposed and vulnerable.