I agree a modern, self-contained car alternator is a much better
alternative than this money ripoff boat nonsense with the $300
regulators. Batteries are just too simple...float 'em and they work
great. .

This got my attention.

An older sailboat ('79) I just purchased, has two West Marine SeaVolt
gel batteries and what appears to be the stock alternator that came with
the Perkins 4-108. I see no external regulator.

Should I replace this old alternator? If so, can I use an automobile
regulator? I was pricing exactly what you panned - marine alternators
like Balmar with external regulators and echo chargers linking house to
starting battery.

It certainly would be far cheaper if I could use a car alternator.

TIA for any info.