How to: check and replace an anode (zinc) - Yachting Monthly - YouTube

Hello and welcome to Yachting Monthly's How To series

brought to you in association with GJW Direct.

I'm Matthew Sheahan and over the course of 13 episodes

we're going to be dealing with some of the key issues when it comes to maintenance

and talking to some of the experts to get their tips.

In this episode we're going to look at what the anode does on our boat,

how to check it's working, and how to make sure the key items on your boat are nicely bonded.

So we're going to talk a little bit now about galvanic corrosion.

It's a phenomenon that affects the majority of

boats out there and you absolutely don't have to

understand the chemistry behind it but it is good just to have a bit of an

understanding so that you know what to look for and how

to prevent it attacking your boat.

The very simple chemistry of it is that you have two dissimilar metals,

so think of a common seacock or other type of through hull.

One part of it might be made of bronze or a brass alloy

and another part of it such as the handle might be made of stainless steel.

If you have those two dissimilar metals – and they must have an electrical

connection between them so be in contact with each other –

if they are then in salt water the salt water acts as an electrolyte

and the less noble of the two metals, in this case the bronze,

will corrode and before too long you can have a serious leak in your hull.

So galvanic corrosion the decaying of the less noble metal to

the more noble metal is something that we have to protect against

So the simple solution to prevent galvanic corrosion

is to add in another metal which is even less noble

than the one that might have got corroded.

So this is zinc which is one of the least noble metals of all.

This is attached to our hull, possibly also

to your prop shaft, your sail drive. Your boat will have a number of different

places where it may or may not have a zinc anode

and the zinc becomes the anode rather than the bronze the zinc decays

and the bronze and the stainless steel, your through hull or your seacock,

is prevented from having corrosion.

So here we've pulled the boat out now and we can actually see

one of the zinc anodes that we talked about previously.

We can see that it's had lots of corrosion to it, which is a good sign.

It means it's been doing its job and it's been corroding

rather than the noble metals such as the bronze or the brass alloys on our through hull fittings.

When you first pull the boat out what you're really

looking for is to see that that hasn't corroded more

than about 50 percent. The size of the anode is important:

you don't need to know more of the science of it

but just if it's corroded more than 50 you could probably look at upgrading

your anodes slightly.

So it's quite a simple process now to take off the anode.

We've loosened these off 15mm nuts already.

Just obviously be careful as you take them off you're not going to let

anything drop off.

Although the spring-loaded washers come off with them good practice is to

replace those washers before you put the new one on.

This one's got a protective matting behind it which just protects the hull

of the boat as the anode corrodes so you end up with a nice flat surface.

Here's our new anode, there's the protective matting

that goes behind it and then it's a simple matter putting

the new anode on,

a nice set of new spring-loaded washers and the nuts. We will usually put a bit

of medium strength loctite onto these nuts before we put them on,

which just ensures that they stay in place through the course of the season.

It's then just a matter of giving the anode a good tightening up

and we're ready to start looking inside and checking the rest of the bonding system.

On the shaft you'll often find one or two of these anodes here,

very simple mechanism, they come in a split.

You put them either side and bolt them up, again remembering to use some loctite

or similar thread sealant to make sure they stay on through the

course of the season. Again you're hoping that these anodes will last you through

the season because they're obviously not that easy

to replace once the boat's in the water and they should that's why we put two of

them on usually so that it lasts through the season.

If you're sailing in more brackish water such as in the baltic you may find that

your anodes actually not only run out faster but

might need to be switched to magnesium anodes.

You might also – it depends on which boat you're on – but you might well also find this skeg

plate here has an anode as well, which is another one just to look out for.

So here you have a typical keel cooling setup

where you have these porous blocks and this is used for refrigeration

for freezers and for some generators as well – especially useful if you're sailing

in the warmer climates and you have these porous blocks here

through which the refrigerant is passed and the sea water cools it.

And these donut anodes here are used to protect the various metal parts of the

circuit. They can corrode quite quickly so it's important to give them a really

good check at the start and end of the season.

You will see there are two approaches to bonding in the maritime industry.

There are those who believe in bonding every metallic item

that goes through the hull, and there are those who believe in bonding the minimum number of items.

As with anything, if there was a clear right or wrong it

would have been answered, so this is really down to a matter of personal preference.

The argument for bonding everything is

that if you do have any dissimilar metals or

stray current having every metallic item attached to the zinc

will protect it from corrosion. The argument for not bonding every item

is that if the items are not prone to corrosion

you are simply giving them a metallic connection

to something which is prone to corrosion and you might be

introducing a problem into the system that wasn't there previously. [NOTE: Bonding anodes in wooden boats can cause electrolysis within the timber. Take specialist advice.]

Increasingly modern day through hulls

and mechanical items have got rid of a lot of the problems of dissimilar metal

and that has reduced the problems with galvanic corrosion.

So it's very much a matter of picking from your boat and your systems whether

you believe the bonding should be to all the items

or only to the essential items. So it is possible in a marina

environment that there could be stray current in the water

either from their 240 volt system or for another boats' 240 volt system.

If there is, your metallic through hulls become a source of danger to you.

Your bonding system, if your through hulls are bonded,

will also be connected to your negative battery bus bar. This gives a quick and

easy route to ground for any stray current,

rather than posing a danger to any humans on board who might touch those through hulls.

There is also an increasing move towards

high strength plastic through hulls and these

obviously negate the need for any type of bonding at all.

So here we can see the studs of the anode coming up

through the hull. Attached to them is the thick

bonding wire, which in this instance connects to the gearbox

adapter plate, the item being protected by the anode.

Now it's not enough just to check that the visually check that the wire is in

place because it could have breaks in it or

corrosion in it which is reducing its effectiveness.

So we need to use our multimeter and put it onto the resistance setting

or the continuity setting and we put either probe – it doesn't matter which one –

on the stud of the anode and the other one on the item being protected in this

case the gearbox plate. And we need to see from the multimeter

that resistance is zero or you might hear its audible tone

telling you that there's good continuity. Here we can see that we can

see the resistance is zero and we know that the item is being well protected

by the anode. Now if there are other items also being bonded

you can simply daisy chain this process. So this time one of the probes will go

on the engine that we know is already bonded and the other probe

might go on the through hull that's being bonded.

Again we're just looking for continuity in the process.

Well thanks for watching. I hope that was a help. Make sure that you like us.

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