malcp
Member
Some advice please concerning possible stray current corrosion of underwater fittings.
On haulout a week ago I found:-
Antifoul and primer covering the seacocks was gone (I've seen this each haulout for the past 6 years from new, but much worse this year).
Metal (bronze) on seacocks was brightish, except engine w/c intake bonded to anode which was grey but still missing its paint. With the exception of 1 seacock (see below) no fitting was observed.
Heads basin seacock showed some internal signs of actual corrosion (ball valve type). This observed by looking up from underneath.
Colour of seacocks yellowish colour, not pink, except for heads basin seacock in area of corrosion which was slightly pink and engine w/c one which was grey.
Rope cutter (Stripper) fixed (stern tube clamp mounted) showed worse crevice corrosion than previous. This is isolated. Just clamps onto stern tube.
Anode slightly more eroded than usual but pretty minimal none the less.
Boat is GRP, foam cored double skinned (Starlight35).
Only underwater fittings bonded to anode is the engine w/c intake and prop shaft via gearbox (VolvoMD2030 MS2A). Everything else is isolated (no bonding wires)(I shall check this this w/e that this is in fact true, using a sensitive ohm meter).
Each year seacocks painted with International Interprotect epoxy primer followed by Micron A/F.
No water in bilges.
Boat is 6 years old
Boat kept in Chichester Marina. Mains power plugged in usually.
No isolation diodes for mains earth to boat earth fitted. In fact it seems there's no low impedance connection from mains earth to boat earth. There is a high impedance connection of about 6k ohms.
Boat has mains battery charger fitted. (Sterling).
New next door neighbour this year, with new boat.
Any ideas on this? Do I have a problem? If nothing else can anyone suggest someone knowledgable and reliable on this subject for advice.
Thanks in advance.
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On haulout a week ago I found:-
Antifoul and primer covering the seacocks was gone (I've seen this each haulout for the past 6 years from new, but much worse this year).
Metal (bronze) on seacocks was brightish, except engine w/c intake bonded to anode which was grey but still missing its paint. With the exception of 1 seacock (see below) no fitting was observed.
Heads basin seacock showed some internal signs of actual corrosion (ball valve type). This observed by looking up from underneath.
Colour of seacocks yellowish colour, not pink, except for heads basin seacock in area of corrosion which was slightly pink and engine w/c one which was grey.
Rope cutter (Stripper) fixed (stern tube clamp mounted) showed worse crevice corrosion than previous. This is isolated. Just clamps onto stern tube.
Anode slightly more eroded than usual but pretty minimal none the less.
Boat is GRP, foam cored double skinned (Starlight35).
Only underwater fittings bonded to anode is the engine w/c intake and prop shaft via gearbox (VolvoMD2030 MS2A). Everything else is isolated (no bonding wires)(I shall check this this w/e that this is in fact true, using a sensitive ohm meter).
Each year seacocks painted with International Interprotect epoxy primer followed by Micron A/F.
No water in bilges.
Boat is 6 years old
Boat kept in Chichester Marina. Mains power plugged in usually.
No isolation diodes for mains earth to boat earth fitted. In fact it seems there's no low impedance connection from mains earth to boat earth. There is a high impedance connection of about 6k ohms.
Boat has mains battery charger fitted. (Sterling).
New next door neighbour this year, with new boat.
Any ideas on this? Do I have a problem? If nothing else can anyone suggest someone knowledgable and reliable on this subject for advice.
Thanks in advance.
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