Earthing brushes on prop shaft

[CalicoJack]

I have previously posted about earthing my prop shaft to the anode. It has been suggested that I use earthing brushes mounted on the prop shaft; there is no room for an anode mounted on the shaft in the water.

I met a friend today who thought he had seen an article about making a set using brushes from a washing machine, but he could not remember where he saw this. Anyone come across this article?

 

[Topcat47]

The best way is to run a strap across the coupling. One side is part of the engine. the other clamped to the shaft and perhaps keyed and or grubscrewed in place.

 

[markdj]

The best way is to run a strap across the coupling. One side is part of the engine. the other clamped to the shaft and perhaps keyed and or grubscrewed in place.

Have to agree.

A shaft earthing brushes setup is a complete waste of time and is quite likely to get knocked about and is difficult to mount. Measuring with a good connection and a clean bright stainless steel shaft it has a high resistance at the best of times giving very poor galvanic protection. It is far superior to simply use a flexible multistranded tinned electrical cable across the flexible coupling.

 

[VicS]

Earthing to the gearbox and bridging the flexible coupling is the simplest solution but you are then relying on completing the electrical path though the hopefully well oiled bearings of the gear box!

A properly built , installed and maintained brush system such as MG Duffs electro-eliminator should give a reliable connection to the shaft and does not have in insulating film off oil preventing a good low resistance connection. I see no reason why brushes on the shaft should not be satisfactory. They are used on all manner of rotating electrical machinery from small electric motors to large power station generators.

I see no reason why someone with good engineering skills should not make a perfectly adequate system using readly available bushes.

 

[NorthUp]

Have to agree.

A shaft earthing brushes setup is a complete waste of time and is quite likely to get knocked about and is difficult to mount. Measuring with a good connection and a clean bright stainless steel shaft it has a high resistance at the best of times giving very poor galvanic protection. It is far superior to simply use a flexible multistranded tinned electrical cable across the flexible coupling.

I disagree, and have fitted several boats, both mobos and yachts with shaft brushes, boats which had serious, measurable, corrosion problems involving propellers. Brushes cured the problems. Wiring across the flexible couplings will not always cure the problem, as there is resistance through the bearings in the gearboxes, probably caused by the oil film on the bearings.

 

[omega2]

www.clementsmarine.co.uk

 

[nedmin]

Earthing brushes

Its not as easy as putting an earthing strap across the flex. coupling.I was having a prob. with de-zincing. on the prop.on my steel boat.The flex. coupling was strapped across but I was still getting a m/amp reading between prop shaft and the boat earth.This can only have come from the oil on the bearings in the gearbox insulating the earth return, from boat earth to propshaft.occasionally this would obviously make contact with a miniscule current across the bearing so what was it doing to the bearing assuming there was a miniscule "arc". I obtained one brush holder from an old black and decker drill and mounted it to run on the outside edge of the flex. coupling,the bit connected to the propshaft.then connect to boat earth.If you can you need a starter motor brush as they are high in copper content.File to suit size of brush holder.You may be able to beg an old one from an auto electrician.My readings are now OK ,and prop also.