If it's pretty much that water stain scum line I use starbrite hull cleaner. I put it in a spray bottle and spray it on and use a soft bristle brush and move it around. You can spray it on and watch it turn white right in front if you. That's what I use. If you have growth on your boat it won't take it off.

Fountain of Youth Power One is the best hull cleaner I ever tried...


http://www.fountainofyouthrestore.com/power1.html

scrubbing bubbles!!!

Says right on the can great for fiberglass surounds!!!

Been using it for years, started with my old jet boat that stayed in the water over the weekends.

Wet the with water, spray on scubbing bubbles, wait a few minutes, towel off :)

Now not sure how well this works for boats in the water longer then a weekend, and of course depending on the water too :)

No fumes, easy on the hands and comes in a spray can so no leaking fluids

Is it scum or a yellowish brown stain in the gel????

If its a stain in the gel, Sno Bowl or The Works toilet bowl cleaner will take it off easily and cheaply.

we used to use Zing at the dealership when I was there...but beware it is some strong stuff..

I agree. Been using The Works for years. When I first started using it some friends doubted me. Now they all use it instead of the specialty products..

+1 for Power One.

+1... 50/50 with water in a sprayer

Agreed. It's nasty stuff, but works amazingly well.

on off is great but watch it close on the concrete it'll eat up...also if you have an aluminum trailer. If what you have is just scum line...(i'll get a brownish stain in the canal i live on sometimes), just use Nu-hull it takes it off easily. just my .02