Should I earth bond my new P-bracket ?

[Boo2]

Sunrunner's original P-bracket was suffering from "electrolysis" (the Engineer's words, not mine) so given that I've got absolutely everything out of the way (tank, engine, drains etc) and that a new one at £370 inc is small beer in the general engine replacement scheme of things, I've decided to replace it.

The new one is from Teignbridge and made in Nickle Aluminium Bronze (BS 1400 AB2), my question really is as title : do I need to earth bond the P-Bracket, given the old one suffered from electrolysis ? I know it's normal not to bond skin fittings, but the P-Bracket is very close to the prop shaft which will be earthed, so...?

(Note: by "earth" I mean battery -ve terminal, Sunrunner's shore power supply is a work in progress but when complete will have its earth bonded to battery negative too.)

Thanks,

Boo2

 

[sailorman]

Sunrunner's original P-bracket was suffering from "electrolysis" (the Engineer's words, not mine) so given that I've got absolutely everything out of the way (tank, engine, drains etc) and that a new one at £370 inc is small beer in the general engine replacement scheme of things, I've decided to replace it.

The new one is from Teignbridge and made in Nickle Aluminium Bronze (BS 1400 AB2), my question really is as title : do I need to earth bond the P-Bracket, given the old one suffered from electrolysis ? I know it's normal not to bond skin fittings, but the P-Bracket is very close to the prop shaft which will be earthed, so...?

(Note: by "earth" I mean battery -ve terminal, Sunrunner's shore power supply is a work in progress but when complete will have its earth bonded to battery negative too.)

Thanks,

Boo2

bolt a 50m/m disc anode on it

 

[prv]

I can see the merit in connecting it to an anode, possibly the same anode as the shaft. I think mention of the DC system is a red herring.

Pete

 

[michael_w]

When I bought my boat the P bracket wasn't connected to the anode circuit; it showed signs of dezincification, this was ground off. I replaced the engine and had the fuel tank out too, the internal support for the P bracket was exposed for the first time in 23 years. Made sense to bond the P bracket to the anode circuit. This done, the P bracket has remained suitably bronze coloured. Do it, you'll only worry!

 

[VicS]

Hopefully your engineer was wrong about electrolysis. It would require connection to a positive DC source for electrolysys to occur. The effect would be rapid and catastrophic!

NiAl bronze is a verty corrosion resistant alloy it should not require any form of cathodic protection if not electrically bonded to anything else less anodic.

An anode bolted directly to it will be consumed fairly quickly, even though serving no useful purpose.

I think bonding to the same hull anode as the prop and shaft would be a mistake. It will then, as a consequence, be directly connected to the shaft which will be closer to it than the anode. NiAl Bronze is anodic ( by between 0.1 and 0.2 volt) to stainless steel and might as a result suffer from galvanic corrosion.

 

[vyv_cox]

VicS is correct. If the P-bracket really is nickel-aluminium bronze it is constructed from perhaps the best of all corrosion-resistant, relatively strong materials. Every ship's propeller and the best mobo ones are made from it. None of these require anodes for protection. I suspect that the problem with your old one is that it is made in manganese bronze which, despite its name, is a brass with very minor additions of other metals. Most P-brackets have been made from this, accounting for the frequent cases of dezincification that they suffer.