Mystery rash on bottom paint

[thekeip]

OK, here's one for the guru's:

The ist time I saw this condition, a J-109 came into the yard with a severely corroded / erroded sail drive unit and the bottom paint looked to be burnt. The boat is probably 3-5 yrs old. The original bottom paint was Trinidad SR, overcoated with some sort of carbon 'race finish'. The whole surface, but localized just above the keel and including the keel and the sail drive unit, for an oval shaped area of about 5ft, was covered with something akin to prickely-heat on a kid's bottom. The destroyed sail drive problem was a grounding issue, and seems to be corrected and may not be related.

The 2nd time was (is) an Olson-25 with the same paint condition...but only on the stbd. side, and not affecting the rudder at all, which is as smooth as a baby's rear end. It's a different marina. AC power is probably not an obvious cause either...the boat and shore power connections seem perfect and go to the right places, and the system has been in place for many years.

The yard thinks it's most likely an 'electrical' issue; I think more a paint incompatability problem...any guesses???

[sailingdog]

Can you post photos of this???

[thekeip]

I think so...tomorrow evening.
thekeip

[Fstbttms]

I have seen this phenomenon with Trinidad-painted boats many, many times. Most frequently with black Trinidad. It seems the paint is reacting with the metal it is in contact with, such as bronze thru-hull or a saildrive housing. The paint discolors and loses efficacy in an ever-widening circle around the object in question. I don't know the specifics of why it happens, but I do know that the people at Interlux are aware of the issue. I wouldn't count on a lot of support from them, however.