In our 75 -85*F water in Pacific Mexico a boat left for 3 years without cleaning there would be tons of growth...literally. As for your electrolysis problem as you probably know the issue may be on board or with a neighbor boat or "hot dock" At Port Townsend Marina they checked for "hot boats" The staff would give the offender an oppurtunity to fix or they would cut their power. Most marinas I have been don't bother checking. When Tappan Zee is at a dock we don't plug in unless it is cloudy and no wind so our on board systems can't keep the batteries up. I know you are skilled but perhaps contacting a marine electrician in your area would help clarify were the electrolysis issue is.
Tom Evans
SV Tappan Zee
La Paz Mexico