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Pacific Seacraft 40 - electrical ground/keel barrier coat failure?

2K views 8 replies 5 participants last post by  rschaedel 
#1 ·
I have a Pacific Seacraft 40.
Starting in 2007 the Interprotect barrier coat has chipped off at several isolated locations on the sides of the lead keel.
Twice during the subsequent years the chipped areas have been ground down to the lead and then re-coated with 4 layers of Interprotect barrier coat. Nevertheless the re-coated spots fail again after approximately a year.

It is always the same locations and fortunately not a problem on the surface of the rest of the keel

It has been suggested to me that maybe this is (or was) caused by electrolysis. While using a Corrosion Reference Electrode to check for electrolysis it was noted that when the associated digital multimeter was connected to the rigging and mast step that the readings were significantly different than when connected to the battery negative or engine. However both readings were in the correct range of -750 t0 -1000mV indicating that there is satisfactory cathodic protection.

The PS owners' manual states that the rig is connected to a keel bolt for lightning protection. Does this imply that there is not a common ground to which everything is connected? If so, is this o.k.?

Any thoughts you have on this issue would be appreciated.
Bob
 
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#2 ·
If everything was connected to one ground, everything would have been fried for sure when struck by lightening. Having two separate ways of grounding would likely lower the probability of the rest of the boat getting fried if your mast was struck. Probably your boat is set up that way.
I would rather suspect the lead surface preparation or the new coating material not sticking right, than an inherent electric problem. No reason for the current to come out just in these spots time after time. It is one solid hunk of metal. However, the current will flow along the line of least resistance. If the new coating on the keel has lower electric resistance than the rest of the keel, that could indeed be related to the grounding issue.
 
#3 ·
On my boat, the Bayfield 36, there is a plate on the keel that the rig is grounded to. You are not supposed to paint that plate which would, I assume, interfere with its ability to ground the rig. I wonder if you have something like that occurring?
 
#6 ·
On my 1990 Pacific Seacraft Crealock 37 there is a external ground plate on the hull ( not the keel ) that the ground wire from the mast is bolted to. That wire is somewhat heavy gauge ( maybe AWG6 ) and goes from a masthead connection all the way to the ground plate stud. These connection studs are on the inside of the bilge near the forward (speed) transducer. The ground plate is not painted with bottom paint. There are no connections to the keel bolts, by the way.
I know this isn't related directly to your issue, but mentioned as superfluous information :smile
 
#7 ·
Bill:
Thanks for describing the ground plate which is the type that I am familiar with and I assume that Gladrags1 has on the Bayfield 36 as noted in his reply yesterday.
Your reply is not at all superfluous. My PS40 does not have an external ground plate. The base plate below the mast step has cables attached to it which I assume lead from the shrouds and stays. I also assume that the screws on this base plate may connect it to the lead keel. What I do not know is whether the engine ground is just the shaft and prop in the water.
If so, then then the difference (-150mV) in test for electrolysis when measuring from the rig as compared to the battery negative post and the engine may be explained in that the rig/keel circuit is just not as robust as the engine shaft.
Whether this is anything to be concerned about is what I do not know.
Bob
 
#8 ·
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