the boat needs to be fully scrubbed with a wax and grease remover then sanded with 150-220 grit paper then primed with awlgrip 545 primer min 2 coats. the the primer needs to be sanded with 320 the painted with the awlgrip 2-3 coats. Plus to mention any scratches of cracks needs to be filled and sanded smooth. If your going to paint a dark color take your time with the prep work. every little mark will show, so take extra special care in the prep work.
why not consider rolling and tipping, people all the time get the same professional sprayed results with this method, yes it takes longer but you can do it on your own. And i would make sure to talk to your marina about you doing the prep work and them painting. I can easily see them have a poor finish and blame it on the prep work not the painter.