Preheating works better, the boat will hold most of the heat whilst the paint is applied so flash-off is quicker, a shorter flash-off deminishes the risk of dust etc contaminating the fresh paint, re-fire the heat once the paint has tacked off.

A few tips if your doing this at home ;

Jet-fire heaters:
awesome heat source but they have a drawback, they stir up the dust in your shed which then falls onto your paint
solution pre-heat the boat / allow a short period to let the air become still / spray / wait for tack-off and then re-heat

radiant heaters:
another excellent heater but they usually don't heat large areas that well, fine for a car door for example but useless for the entire side of the car, so a 16foot hull will be unevenly heated resulting in patchy paint.


DUST
simple solution really..... hang a large plastic sheet over your work area and wet the floor down with water before spraying, also pays to wipe down air-lines etc, and your clothing needs to be clean and dust free too...... don't forget the hair-net


when I set up my "booth" I have 3 wires across the shed which form a 'tent' over my work when the plastic sheet is slid over them, I usually pre-heat first and wet the floor at the same time, once I have the heat in my work I shut down the heater and then draw the sheet over my work, then spray ..... once it tacks-off I re-dampen the floor & run the heater again


Dust and airborne particles are your biggest killer, preparation work to minimise this is just as important as the prep work on the boat itself.


Kingy