I'm going to tell you the number one best way to remove mold and mildew from your boat canvas, or any canvas material for that matter. It will not use any harsh chemicals, toxic smelling products, or highly labour intensive proceedures. You will only be using fresh water and a little bit of arm movement.
I have the type of canvas on my boat that does not breath all that well, it has some sort of coating underneath that makes it extremely waterproof, but when the canvas is closed up, it traps moisture, and therefore mold can grow. I have spent many labor intensive hours trying many products to remove mold and mildew, from expensive made for boat products, to bleach, ajax, vinegar, and pine-sol. Some of those solutions worked to a degree, but I was never completely satisfied.
So while putting on my canvas one spring getting ready for launch, I noticed that my canvas once again was not its cleanest. Later that day, a good friend was walking into the boat yard with a sale item they bought at a local hardware store. It was actually a small handheld Shark Steamer.
I can't remember how I got the new steamer out of her hands and onto my flybridge trying out different attachments, but I did, and after 5 minutes of use, I left the boat yard to go and purchase my own steamer.
The process was as follows. Use a small bristle brush attachment where the steam still comes out with some force, and you are able to lightly brush the fibres of the canvas as the steam is doing its work on the mold. When an area of about 3'x3' is done, take a clean cotton rag and wipe down the area. Repeat if necessary. That's it. Just take a look at the before and after pictures.
Before
After
I have never had as good a result with any other product or solution. It isn't like new in my case because my canvas is older, and the mold has discolored the canvas backing just a little, but it is 99.9% better than it was. Every boat owner with canvas, needs a small steamer like this one. I wonder what else this little steamer will come in handy for?