Rheilly, Thanks for your answer. Yes, it looks more like the fizzing
of a soft drink than a boiling kettel. The batteries are not wired in
parallel. They are Trojan 105 Golf cart 6V batteries. Negative pole is
wired to positive pole in both pairs. Alternator charges them at 14.1
volts. The manual of the regulator states also to charge at 14.1. So I
thought I was doing the right thing. I am going to the boat only on
Saturday. Is this something I should go there immediately before a
major explotion occurs? Once again, thanks for your attention. Roy

Batteries normally "bubble" when fully charged (Like at the end of the
charge), however I would say it is more like the fizzing of a soft
carbonated drink than "boiling". If it looks like the inside of a boiling
kettel then you mave have a bit of a problem :-). If the batteries are wired
in parallel (all pos posts connected together and all neg posts the same)
then it is only neccessary to connect anywhere convenient to a neg and pos
battery terminal ofm the group.
It would be a good idea to take hydrometer readings of all the batteries
after they have stood fully charged overnight to check their degree of
charge and if there is any variations between them.