Thought I'd throw this in for anybody who is looking for advice on cleaning your bimini. As part of crazy boat project I removed my entire bimini (two parts) and for the second time in a year threw it in my FRONT LOADING washer on the large object cycle with just a touch of detergent. It comes out looking like new. Works like a charm.
Disclaimer: I said FRONT LOADING washer because there is no agitator bar or anything to wrap the fabric around. Front loaders use friction of the material to get it clean and I also have the large or bulky setting that doesn't treat the thing like a red headed step child.
If you do not have one of these machines (get one they are the best washers we've ever had......better on energy and water usuage, cleaner clothes......) go to a laundrymat and use on of theirs.