Do you connect the Anodes to battery ?

[Dave-Fethiye]

Hi,
I have recently got myself a 40' wooden motor yacht. It needs a fair bit of work but I am keen on learning it all.

A local boat engineer who was looking at my engine said that the oxidation on the water exhaust manifold (which is aluminium) was due to the fact that the engine should be connected to the sacrificial anodes with a cable.

The boat is out of the water at present while I do the servicing. I have bought a new zinc anode as the present ones look a bit used up. The engine is a Perkins 80hp deisel.

Is this advice correct ? After all the engine is connected to the -ve side of the main battery stack.

Someone said that as the old anodes had some white oxidation on, I should check the current flow with a meter. I have a multimeter - does anyone know how to do this.

I'll appreciate any advice.

Thanks,
Dave
Fethiye
Turkey.

[Les Schuldt]

Dave,

Here's how to build an "Anode Tester".

Buy a voltmeter with a millivolt range, a length (1-2 meter) of copper tubing or rod, a couple 3 meter (or longer) pieces of wire and some alligator clips.

Adapt the wires to your meter "bannana jacks" and add the alligator clips to the ends. These long wires allow you to wander around the boat to test protection.

Connect one alligator clip to the copper tubing and suspend the tubing in the water your boat is floating in. (Only the copper should touch the water, not the alligator clip.)

Touch the other alligator clip to any item that you wish to check the protection, ie: engine block, exhaust manifold, etc.

Your meter should indicate 900 millivolts (.9 volt) if the zinc is doing it's job and all connections are sound. A lower reading (or zero) would indicate a degraded zinc or a bad connection to the zinc.

Regarding the engine being connected to the (-) side of the battery; the boat's electrical system CAN cause corrosion, but what the zinc is really protecting against is corrosion caused by dissimilar metals reacting in the salt water environment. This is called galvanic corrosion and the "least noble" metal will corrode away. Aluminum is very low on the scale, so you need zinc (even lower) to be sacrificed.

The zinc anode should not be connected to the battery. It should be connected to the item you wish to protect, in this case the exhaust manifold, then the zinc should be suspended in the water. Sometimes manifolds have zincs that screw in (they kind of look like a "chapstick" tube.) Then the water circulating through the manifold touches the zinc and protects the manifold.

Fair winds,
Les

[Dave-Fethiye]

Thanks - great post.

Just to make sure I understand this.

The 2 systems are separate.

First system:
I have three anodes fastened to the outside of my boat. They are connected to the propellor, the bolts that protrude the hull and hold the boat together, the brass water outlets and the rudder assembly.
The connection is with 6mm copper wire. This is what I check as you described with the millivolt meter.

Second
I do NOT connect the engine (which is connected to the -ve battery) to the daisy-chained exterior anode system. The engine should have its own zinc anode.

I think I may have seen the anode. I have a Perkins Prima 500 series and there is a plug type screw in that is on the top of the exhoust manifold. I guess thats it. I will check it out, maybe I need a new one or it needs cleaning. Is that a common problem ?

Again thanks for your informative post, and please correct me if I have not understood it.

Dave

[Les Schuldt]

Dave,

I must correct myself. Yes, your block should be connected to a zinc, and yes, it is connect to the (-) side of the battery.

The zinc in your block/manifold will tend to be relatively small and might degrade faster than other, larger zincs. It's a good idea to check all zincs at least once a year and replace when they start to get worn.

Les

[sdowney717]

http://www.yachtsurvey.com/diesel_engines.htm

read it and weep, Pascoe says aluminum is terrible for marine engines.

Can you switch to cast iron?

[nedL]

I seem to remember something about the sacrificial anodes for use with aluminum are not actually zinc. Zinc and aluminum are very close on the galvanic scale. I think it might be something like a magnesium alloy, but I don't remember for certain. You want to look into this with more detail. (What are the anodes made for outboards & inboard-outboards made of?)