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S&S Swan Maintenance - P bracket corrosion 411
12 February 2020 - 21:52
#1
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paul bond
Join Date: 19 July 2007
Posts: 66

P bracket corrosion 411

Hi All

for the 11 years of ownership we have had no issues with corrosion of the underwater hull fittings. The shaft anode has typically lost 50% and been changed each season the propellor boss anode lasting 5 years.the seacocks are dismantled and checked each winter and  show no signs of corrosion.

in the past the boat has been kept on a mooring and shore electrical power has been only connected for short periods when in marinas.

last year the boat spent some time in a marina berth but except for 5 days in the French port of Vannes the shore power connection was only used for a short time to recharge batteries and then disconnected.

As can be seen in the photos, there is significant corrosion on the lower aft end of the P bracket. and also rust like stains around the cutlass bearing edge. there are no signs of corrosion anywhere else on the underwater hull the shaft adjacent to the P bracket is unmarked as is the propellor boss. the shaft anode has lost a simlar amount to previous seasons.I am assuming this damage is from stray currents whilst in a marina

Has anyone else had such locallised corrosion?

Any thoughts would be appreciated.

Paul bond

Hierro 411  042
13 February 2020 - 07:32
#2
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the professor
Join Date: 02 January 2008
Posts: 1547

 

Dear Paul
 
There has been a strong current flowing from the P-bracket to an underwater metal object when shore power was connected, i.e. a serious fault in the shore power system.
 
If there is a grounding cable connected to the bracket on the inside, removing it will prevent further corrosion.
 
You should also check the bottom of the keel and the rudder stock lower end for similar damage. If there is a grounding cable connected to the rudder stock, remove it also. The keel is used as boat ground and must not be disconnected.
 
These grounding cables were specified by S&S, but are not used on the newer models. It is preferable that the underwater components are not interconnected, as they will then not be affected by such faults in the electrical system.
Kind regards
Lars
13 February 2020 - 11:23
#3
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paul bond
Join Date: 19 July 2007
Posts: 66

Dear Lars.

Thanks for your reply.  I was suprised to find this corrosion,so localised, as I have followed Nautor'(and your ) advice. The rig grounding cables are connected to the keel, no other grounds are in place so the P bracket and rudder are isolated. It shows the dangers of shore power systems in marina situations.

Thanks.

Paul
13 February 2020 - 12:00
#4
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the professor
Join Date: 02 January 2008
Posts: 1547

Paul
In some way or another the P-bracket has been part of an electrical circuit when the corrosion occurred.
Or has your yacht been moored close to steel piling or a big steel ship? Some of them have impressed current corrosion protection feeding strong current into the water nearby. Avoid swimming there, this can paralyze the muscles.
Lars
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