Just been trying out a another product for cleanig boats. This stuff is called Muc-Off and is pretty good at removinng all sorts of dirt, green algie and streaks from the gell coat. What is amazing is that it does what it say on the label. Just spray on neat and agitate with a brush and wash off 3-4 minutes later.
It is sold in 1 litre spray bottle and also in a 5 litre container for £19. I manage d to buy it when I was threw at Bosun's Locker at Port Edgar marina. A litre will do a boat of 30 ft long.