... I have a question though: What does "two
group 27 Trojan batteries" mean? How many batteries
are we talking about here? How many in a group?

This means you have 4 batteries, and two in each group. This sounds
like more batteries than I have expected. May be I can make do with a
12-volt motor with 2 batteries (of course with a small rowboat, not a
20-ft boat).

I have no clue how you got that.

Two as in the number of batteries.

I read the original message wrong. I thought you said "two groups
(plural) ... batteries" when you actually said "two group (singular)
.... batteries". I should have understood what you said as: Two
"group-27" Trojan batteries. Sorry for the confusion.

This means you only need 2 batteries to achieve the long run time. This
is very good to know. In that case, this makes sense to use a 24-volt
motor with 2 batteries (like what your setup is) in a rowboat as the
primary propelling force of the rowboat.

Again, thanks for clarifying your setup for me.

Jay Chan