Motor Yacht Stern Gear Arrangement

[DivingDarin]

I have become sensitive to signs of corrosion since I fitted an inverter on my vessel not least because of the science around earthing when at sea. AA recent inspection revealed corrosion apparently on the what i imagine to be the the stern gland between the water lubricated seal and the




stern tube as shown
Can anyone shed light On what the assembly looks like i.e. schema/diagram? I have tried and failed to find a diagram illustrating the stern tube on the Fairline Phantom 37 circa 1994. Is there a metal tube ? what is the apparent steel bar ? should the assembly be bonded (though looking at the bonding wires they too are corroded)?

I can clean the surface corrosion but if I need to replace parts it will be really helpful to know what I am dealing with.

Many thanks in anticipation

 

[Tranona]

If you are worried about then it is quite normal to see this on bronze housings such as this. Nothing sinister just damp on the surface.

The bar is however a concern. This part of the cathodic protection system for the propellers and is missing the vital part. This explains what it is mgduff.co.uk/knowledge-base/electro-eliminators As you can see yours is missing the sprung loaded brushes which you can by separately . These are essintial to bond your propeller and shaft to the external anode. Note that the bonding wire should be attached to the brush carrier not to the stern tube housing.

This system is nothing to do with your boat's AC or DC systems.

 

[DivingDarin]

If you are worried about then it is quite normal to see this on bronze housings such as this. Nothing sinister just damp on the surface.

The bar is however a concern. This part of the cathodic protection system for the propellers and is missing the vital part. This explains what it is mgduff.co.uk/knowledge-base/electro-eliminators As you can see yours is missing the sprung loaded brushes which you can by separately . These are essintial to bond your propeller and shaft to the external anode. Note that the bonding wire should be attached to the brush carrier not to the stern tube housing.

This system is nothing to do with your boat's AC or DC systems.

Thank you Tranona...I'll follow up with the mgduff bushes

 

[Boaty_Pete]

Agree with what's written above.
However despite the low res photo, it looks like the brush carrier is in the background att he base of the carrier rod.
They are really important on most installations.
For a long time we had excellent bonding through the gearbox despite the oil, but over the years its diminished and we're now reliant on the brushes that we added.

Replace all the local bonding. Corrosion gets into the lugs between the crimp and the wire. One solution can be to make new ones and then solder them, to prevent that.
Once done, check with a digital multimeter between the engine and the shaft, the shaft and the stern tube (your green bit)
Ensure the brushes are helping by ensuring all the bonding connected to them is good too.
If you really want to get into it (you kinda should)
Try to locate your Anode mount bolts, where they come through the hull -they'll have bonding wires too, and check between one of those and your shaft too.
If that's all good, you're done.

When you get into it, it's a job to be done everytime the boat is out of the water and due to be launched.

If the green bothers you, clean it up with a soft wire brush and all some marine grease occasionally.

 

[spannerman]

I would recommend that anyone who has this brush system check that the arms are free and the spring pulls the brush against the shaft. I have often seen these where the arm pivot is seized and it looks as though the brush is in contact with the shaft but in reality aren’t. So I always pull them to see if they snap back and lube the pivots with WD40 or similar.

 

[DivingDarin]

Agree with what's written above.
However despite the low res photo, it looks like the brush carrier is in the background att he base of the carrier rod.
They are really important on most installations.
For a long time we had excellent bonding through the gearbox despite the oil, but over the years its diminished and we're now reliant on the brushes that we added.

Replace all the local bonding. Corrosion gets into the lugs between the crimp and the wire. One solution can be to make new ones and then solder them, to prevent that.
Once done, check with a digital multimeter between the engine and the shaft, the shaft and the stern tube (your green bit)
Ensure the brushes are helping by ensuring all the bonding connected to them is good too.
If you really want to get into it (you kinda should)
Try to locate your Anode mount bolts, where they come through the hull -they'll have bonding wires too, and check between one of those and your shaft too.
If that's all good, you're done.

When you get into it, it's a job to be done everytime the boat is out of the water and due to be launched.

If the green bothers you, clean it up with a soft wire brush and all some marine grease occasionally.

Thank you