Bonding blues

[sailcruiser]

OK
The fact you have a motor/saildrive propulsion changes things -- always a risk of long distance diagnosis.

Bonding the other underwater metals to the motor/saildrive will lead to accelerated wasting of the saildrive anode because the anode will be protecting the saildrive and the other underwater metals in addition. Volvo did not intend that the sail drive anode should be protecting anything except saildrive. But they claim the drive is electrically isolated from the motor.

Check any motor/drive manual to verify whether the manufacturer permits bonding of other metals to the motor bock/saildrive and if so then whether additional anodes are recommended.

Be certain to keep the saildrive anode fresh, clean, and working.

As to the paint - two questions: what is the hull made of and did the paint fall off altogether or is there still paint under the effected area ?

Charles

Hi Charles, I will check my shop manual. I know some engines like Yanmar had pencil type anodes but I haven't found any reference to this with Volvo.

I do watch my anode carefully. Our season is about 4 months long so usually (so far) 1 anode is consumed per season. I change it annually before launch.

The hull is fiberglass. And it did appear the paint was gone. I think what is left is barrier coat and maybe paint remnants. The through hulls are marine grade bronze. The brand escapes me but it was one of my first stops looking at the boat. My first guess is Conbraco but I'd need to double check that. I haven't been on my boat in months.

SC

 

[Charles Erwin]

OK

Motor internal (pencil) anodes, heat exchanger anodes, etc. will have no influence in your case. In the manual -- look for any cautions like "Do not connect saildrive to vessel grounding/bonding system."

The paint failure photo looks more like the coating underneath the VC 17 failed and carried the VC 17 away with it. If it were DC current, I would expect the process to stop once the paint fell away such that the paint was no longer touching the metal through hull. Also the outer edge of the failure is looks very abrupt - not a gradual fade into the intact paint.

Find out what is between the bare hull surface and the VC17? Is there a barrier coat? Was the hull painted with something else before VC 17? Were the metals cleaned and epoxy coated before anti foul was applied?

Charles

ps Check your messages.

 

[sailcruiser]

OK

Motor internal (pencil) anodes, heat exchanger anodes, etc. will have no influence in your case. In the manual -- look for any cautions like "Do not connect saildrive to vessel grounding/bonding system."

The paint failure photo looks more like the coating underneath the VC 17 failed and carried the VC 17 away with it. If it were DC current, I would expect the process to stop once the paint fell away such that the paint was no longer touching the metal through hull. Also the outer edge of the failure is looks very abrupt - not a gradual fade into the intact paint.

Find out what is between the bare hull surface and the VC17? Is there a barrier coat? Was the hull painted with something else before VC 17? Were the metals cleaned and epoxy coated before anti foul was applied?

Charles

ps Check your messages.

There is a barrier coat under the VC17. As far as I know and have seen there hasn't been anything else. And no he underwater metals were not cleaned and epoxied. They were taped off though. I will be cleaning them up here soon and doing just that as soon as it is warm enough.
Thanks! SC

 

[Charles Erwin]

OK
I don't understand "taping off."
If you tape off the exposed metal and paint -- then when you pull the tape you have a fragile broken edge Water can/will get under the new paint.
An epoxy (barrier) coating over the metal surface extended onto the hull surface, followed by top coat of anti foul over the hull and the fitting guarantees water cannot get under the paint nor between the fitting and the hull surface either.
The tape, paint, pulling tape method creates a pathway for water to get under the hull paint.
By the way anti foul will not harm bronze through hulls even if you did not coat the metal with epoxy first.

Charles

 

[sailcruiser]

Ok with the boat finally in the water we were able to measure the hull potential with a silver corrosion reference electrode and found it high with everything unplugged, batteries off etc. we got a reading of 1280 millivolts where the book gives us a range of 900-1050 millivolts. What it doesn't say is what this means or how to correct it.

This was measured off the bonding system that is giving us problems. The problem is currently thought to be because this bonding system lacks an anode tied to it. We leave the sail drive isolated which has the only anode on board. Right now the plan is to remove the system all together but I want to understand the problem regardless.

Thanks!
SC

 

[anchorclanker]

Bonding:

http://en.wikipedia.org/wiki/Electrical_bonding

Not everything, but a good primer