"An alternative cleaning method would be to wash the boat with fresh water and hand scrub after a cruise. After the boat dries you can spot clean any stains with your cleaner of choice and wipe up the residue without creating a discharge."

Your problem isn't "dirt" you accumulate on a cruise, it's dirt that lands on your boat when it's in the marina. Maybe you have to go sailing and do your rub a dub dub at sea, well out of kayak range.