Well I'm not familiar with "Post Marine" bottom paint ( bet its Interlux in a different can)
But a copolymer ablative paint allows for season to season use with out recoating (as long as there is still paint on the surface) since it "washes" away during use .... your constantly getting fresh protection ....as long as you use the boat. The copoly ablatives can come in and out of the water with out harming the anti fouling properties (they do however scuff up very easily ....hence the suggestion for a different color underneath you finish coat color to see when its time to touch up) .. initial coating is usually like 3 coats
A "hard" bottom paint (i.e. modified epoxys) Does suffer from extended periods exposed to air ....and after a winter of sitting out generally need to be recoated to get the proper protection. Its a more "brittle" finish and will chip if it wasn’t applied properly.... generally boats painted with this stuff need to see the water within a month (that varies from a couple days to 2 months)
We have used both .... which is better... I don’t think we ever came to a conclusion about that ....the ablative would wear away ....but never chipped away .... the hard stuff ...if not prepped right would chip and needed to be recoated every year
Hard paints build up season after season .....ablatives gradually wear away ....so the build up isn’t the same
The easiest way is to paint over what you have …naturally. If it really needs attention strip it, fix any blister, barrier coat it, and paint it ( this is what they do in the boat yards here)
Boat yards …. Typically they will put on the hard stuff …..its cheaper … if you want different you tell them what you want and pay.
Compatibility chart for Interlux anitfouling