Well I used a diluted household bleach on my dingy sails and sheets. Worked better on the sheets than the sails, but then I did let them soak over night.
Better change my name now in case your Zodiac goes pop!
Dettol mould and mildew does the same thing, except you do not think it is working and 10 mins later you have a very clean boat! The plus side is you can then eat your tea off it...