Another vote for a quality pressure washer--three weeks ago I asked/received marina permission to PW the entire deck of S/V Beyond_the_Arc (also asked slipmates & neighbors). In two hours (and two tanks of gas!) thirty+ years of dirt and grime were removed and flushed away--water only! Boat looks almost new, the white is white!, the tan non-skid is clearly tan and the blue stripping is beautiful. Waxed & polished the gelcoat and now, almost a month later, she's still beautiful! And for a near-geezer (I was at Woodstock!), I could easily stand and do the work--much easier than the scrub-a-dub I tried in April (to no real success) using many of the aforementioned cleaners.
Just my own experience.
Smooth sailing!