That is not always the case though it was the case for me in the past when
I
did winter afloat. It happens that the boat yard where I winter actually
charges about the same for dry or wet storage. When one factors in a
quick
haul in the spring for checking things (such as seacocks, etc.) the
economics are reversed.

I have wintered afloat on the slightly saline Norfolk Broads for the past
seven years
with only the anti-fouling that came on the boat at purchase. Sometimes she
grew
some slime underneath and a few weed whiskers at the waterline. The weed was
easily
removed with a broom and the slime tended to come off after a good sail.

This year I sailed her round to the north Norfolk coast and she dried out
for the first time
on the sand. The bottom was as clean as a whistle with a minimal thickness
of old red anti-foul. However, within a month she started
growing barnacles despite only being afloat for some 4-5 hours in every 12.

I may try the coppercoat solution, not for economy but through sheer
laziness, should
cost about £300. Alternatively I may buy some epoxy resin and add the copper
powder myself,
it appears to be readily available but I haven't costed it nor looked at
minimum order levels.
I may have to order a ton of copper powder and that'll be more than the boat
is worth!

TonyB