Stephen, I like what you're saying and I wanna comment on this:

You said: The key problem on a boat is the child needs to have
opportunities to
explore what interests them. This could present some major challenges
to
the homeschooling parent on a boat.

Hey! Drop the phrase "on a boat." This is the key problem for a
homeschooling parent in New York City, suburban San Diego, or East
Podunk. It's also the key problem for any kid, schooled by any method,
in a school or otherwise.

As for it being a challenge for a homeschooler on a boat, that's
certainly true; but that's what the www is for. However, it's just as
true for a kid sitting at his desk in P.S. 101, prepping for the latest
round of "standardized testing" when what he wants desperately to
investigate is plate tectonics. The difference is that the homeschooler
can tell his folks that and off they go on an exploration of the world
of plate tectonics. Meanwhile, the kid at P.S. 101 is still stuck at
his desk learning how to give the "correct" answers on the latest
"measurement device" (test) to ensure funding under the "no kid is left
behind" extortion scheme. Behind what, I'm not sure.