In Australia it's called mates rates. Friends helping friends.

If a sailing buddy needs help then, if you can, offer to help without
sticking your hand out for $$ in return.

we do the same thing here. however, strangers are not usually considered
"mates" or "friends". they are also not considered slave laborers available
for use by anyone who says he requires help.

unpaid crew is a learning experience for inexperienced crew. For this kind of
crew the owner is responsible for providing food and port fees and all boat
costs.

for experience crew, the owner also pays a reasonable rate, plus transportation
to/from.