rusty spots under underwater

[Admiral.snelson]

My boat has been in the water since April this year. Before it went in it had 4 coats of bitumen, however, I have just spotted lots of rusty orange spots under the water line. This is not good right? Any help greatly received.

[Ray T]

What sort of mooring do you have?

 

Are you connected to a land line without a galvanic isolator?

 

Are other boats in the vicinity similar?

 

Why I ask is this boat:

 

 

became a Anode when the boat next door but one had an electric fault and acted as a cathode

 

 

This boat had only been blacked a year previously

 

The "cathodic" boat developed a paste looking appearance around the hull:

 

 

The extent of the effect surprised me as three boats in our marina became anodes.

 

Not saying this is the problem but may be worth looking into.

[Admiral.snelson]

Hello, I am a continuous cruiser, so have never been hooked to shore power but use an ac generator regularly. My earth wire is just attached to the hull, is this wrong?

[Guest]

My generator is earthed in the same way without problems. Was the boat new in April? Mine did something similar in the first year and we decided it was millscale parting from the hull. It has been OK after other blackings (approaching ten years old.)

[Admiral.snelson]

The boat was new in 2003 but never touched water until 2013.

[Guest]

The boat was new in 2003 but never touched water until 2013.

Assuming that the hull has never been shotblasted, my money is on millscale parting from the hull. When ours did similar after 12 months immersion, you could see the millscale parting company under the pressure washer.

[Admiral.snelson]

Do I need to get it lifted and re blacked or does it eventually sort itself out?

[Guest]

Do I need to get it lifted and re blacked or does it eventually sort itself out?

I drydocked mine after it had been afloat for 12 months. We pressure washed it (that was when a lot of millscale came away) then gave it three coats of Rylards Rytex bitumen. It has been done since at two yearly intervals with Rytexand has been fine. We are having it grit blasted and two packed next spring for its tenth birthday.

[Neil2]

What sort of mooring do you have?

 

Are you connected to a land line without a galvanic isolator?

 

Are other boats in the vicinity similar?

 

Why I ask is this boat:

 

 

became a Anode when the boat next door but one had an electric fault and acted as a cathode

 

 

This boat had only been blacked a year previously

 

The "cathodic" boat developed a paste looking appearance around the hull:

 

 

The extent of the effect surprised me as three boats in our marina became anodes.

 

Not saying this is the problem but may be worth looking into.

 

Wow, that's a very graphic example of what seems to becoming a more and more common occurrence.

 

I was looking at buying a boat recently that has suffered the same issues, there was no inkling of the state of the hull until she was lifted out of the water, but the surveyor has insisted it cannot be refloated without a complete replate/overplate. It too had spent a long time hooked up to a land line without an isolator.

 

There does seem to be more and more yards offering epoxy coating these days, and even if you can't afford the full monty why not get just around the waterline area two packed? Blacking is easily dissolved by solvents floating on the canal surface and if you aren't on shore power, this is the most likely explanation.