For cleaning gel-coat topsides, I have always used a product called 'Gel Gloss' ... Formulated for bathtubs and shower
stalls, this product contains an extremely mild abrasive and premium wax content found in many top quality automotive waxes.
It can be found in many hardware
stores or bathtub sales stores and is much cheaper than products marketed strictly for marine
use. Easy to apply and even easier to wipe off, it leaves an excellent finish.
I clean my topsides twice per year and get many compliments on the result of my efforts. My boat hull
was manufactured over 30 years ago and still looks awesome.
I have teak
decks so I can't comment on non-skid gel-coat, with the exception of my cockpit
floor. On this, I use a soft scrub brush with this same product. But then I also have a teak
grid covering it so it doesn't really get wear and tear, only foreign material that falls thru the grid.