[Anosmiac]

Yamaha-
I believe you are asking about the white gelcoat portion of the hull above the antifouling paint and below the black gelcoat. If so, it might be a matter of additional prep. If this boat is kept in the water for extended periods of time, variuos types of particulates and overall "crub" can become caked onto the surface of the gelcoat. If not properly removed, it could cause the problem you are describing. As a prep, I would wash this area with a Dawn/water mix. This should break down most of the gunk, and remove any old wax. I would then look to claybar the hull, starting with a light level bar. Try a small area first to make certain there are no adverse effects. Hopefully, this clears out the remaining "crud", and you can then apply a good quality marine wax for protection and shine (I prefer Collinite's products).

Good luck!