100' of extension + a couple connections +30 feet shore power cord + x ft of internal wiring? You are looking at a significant voltage drop over that distance. Assuming you had at least 110 VAC (not a given in a boat yard) at the outlet, you could be getting into the realm of where the charger no longer can function properly. A 100' 14ga extension cord will cost you about 6% of your voltage. All the other wiring will cause more and cumulative loses.
Check the AC voltage at the charger when at the boat and post up what you have. The further you are from 110-120 VAC the more issues you will have.
yep, I feel silly for not checking that first. The charger says it will function down to 100VAC but like you said we could be well under that. Hopefully we don’t have a problem at all and I’m chasing a ghost