Bottom row, from left to right: Black streak removers from Armada, West Marine, Nautical Ease, Star brite, 3M Marine, and Heller Glanz. The product from Yacht Brite (far right) is a general cleaner that claims to remove black streaks. Top, from left to right: Marykate and Aurora black streak removers, and Marine Spray Nine’s general purpose cleaner.

Our test boats failed us.

Over the past three years, the Neptune 212 and Twin Vee Awesome 22 have served as guinea pigs for many a maintenance test, providing, for example, the barnacles, the rust stains, and the waterline stains we’ve needed to evaluate the marine industry’s dizzying array of specialized cleaning products. But the vessels could not give us the mystifying “black streaks” we need for, you guessed it, a test of black streak removers.

Black streaks occur when one boat’s black rubrail rubs against the gelcoat of another boat, right? Wrong. …