Anodes

[single]

What am i missing here? I can understand the anode protecting the prop shaft,steel rudder etc (bits in the water) but why does the engine need bonding to the anode? Its nice and dry inside the boat and no different to the car being parked right next to the sea.

 

[VicS]

What am i missing here? I can understand the anode protecting the prop shaft,steel rudder etc (bits in the water) but why does the engine need bonding to the anode? Its nice and dry inside the boat and no different to the car being parked right next to the sea.

A hull anode is often connected to the prop and shaft by bonding it to the engine and gear box and bridging any flexible shaft coupling. The connection must exist for the anode to do its job but it is also possible to make the connection via brushes running on the shaft. (eg MG Duffs "electro eliminator" qv)

Props and shafts may alternatively be protected by shaft anodes or prop nuts etc

Folding props usually incorporate their own anodes.

A raw water cooled engine will probably have one one or more internal anodes in the water passages, which should be renewed when necessary.

A fresh water cooled engine may have an anode in the seawater side of the heat excahnger

 

[single]

Maybe thats why my coolant looks rusty.The boat is now in fresh/brackish water so the zinc anodes don't work.I'm changing to ally. now.

 

[vyv_cox]

Some people seem to be under the impression that electrons can be exchanged between an external anode and an engine via the seawater inlet hose. The reality is that this does not happen. Electrons travel pretty much in straight lines in water, hence the instruction that anodes must be able to 'see' the object they are protecting. As VicS says, raw water cooled engines can only be protected by internal anodes and in general indirectly cooled ones need no anode.

 

[VicS]

Maybe thats why my coolant looks rusty.The boat is now in fresh/brackish water so the zinc anodes don't work.I'm changing to ally. now.

Confused.

What engine are we talking about?

If your engine has "coolant" it implies the it is indirectly cooled. That coolant shoulbe a normal antifreeze mixture which will contain corrosion inhibitors.

There are basically two types of ethylene glycol based antifreeze. The conventional low silicate type used by older engines which should be changed annually, or the advanced, long life or OAT type used by more modern engines where specified and which requires less frequent changing. (the two types should not be mixed)
An indirectly cooled engine is protected from corrosion by the inhibitors and does not require the protection of an anode any more than your car engine does.

However there may be an anode in the raw water side of the heat exchanger. Some have one, some do not. In your case fit an aluminium one is needed and is available

If your engine is directly cooled it will probably have one or more anodes in its cooling passages but some older engines do not have anodes. If applicable and available an aluminium anode would be the first choice for brackish water.