You could also consider
Float-a-Coat ... as the name suggests, it is a non water soluble oil based paint....[usually black]....
Just fill the bath 2/3 full with standard cold tap water .......place the vessel in the bath & ballast her to the intended waterline......without too much splashing.........add a few gallons of
Float-a-CoatGently & squarely lift the vessel from the water & the black
Float-a-Coat will leave a perfectly level waterline & also represent the black antifouling over the entire under surface of the hull
Perfect job well done....not sure who will clean the bath though
Derek
PS.....
Float-a-Coat is now also available in a
TBTO [Tributyltinoxide] formulation which is has excellent cacogenic properties to minimise weed & mollusc growth on underwater hull surfaces