Probably not necessary on a boat with all the other things you can use to maintain muscle.
Most of you have two speed winches etc......you can just do things the hard way. Don't use a winch
to raise and lower the sails
until absolutely necessary
Plus, with yoga exercises you can use your body to make things hard.
Also, you can do pullups off the boom or just jump overboard
and reenter the boat the hard way. I use the stern railing to pull myself up.
Then there's hiking with a pack once you reach your destination
. I have a kayak
rather than a dinghy
which I unload manually then row wherever I want to go. It's a great workout.
My 16'6" kayak
is a folding kayak which you can disassemble and store below if you need to.
Be creative ...............