I have used several Halfords Aerosol spray
cans on boats over the recent years.
In each case I have sanded the hull down to bare wood as the boats were vintage ones and did have coats
on them that could not be identified.
Best to use thin applications of both primer
up on that after leaving 24 hours between each coat.
Another good point is that Halfords also stock plastic primer
in their paints
range which is ideal if your boat has a polystyrene
hull or you have plastic fittings