There is just something completely inconsistent in that statement.

The entire concept of 'bottom paint' - Anti-Fouling - is to 'reject
attachment'. That is to prevent the typical flora & fauna from growing on an
underwater structure. This is usually achieved by the use of some kind of
chemical COMBINED with a carrier that either sloughs off {Rosin's or
Ablative's}or is so 'slippery' {Teflon, Vinyl's}that anything has difficulty
attaching.

Therefore, it goes against reason that any kind of finish - let alone a
'Gloss Finish' - would be recommended over an Anti-Fouling coating.

There is one particular circumstance where I have used a 'Gloss Finish' on
the bottom of a sailboat. The boat was 'dry sailed' - that is it spent most
of the time out of the water, stored on it's trailer. A Gloss Finish was
applied - then, when thoroughly cured, it was heavily waxed. {There are even
special waxes that are used as an 'anti-fouling coating' in waters of low
fouling, or fresh water}. Even so, it spent no more than several days at a
time in the water - after which it was well washed.

Regards & Good Luck,
Ron Magen
Backyard Boatshop

"Old Nick" wrote
SNIP
The manufacturer says to apply primer, _then_ bottom paint, then gloss.