Most of the fishermen around Portishead use rope rodes, with a short length of chain for the anchor. They also have electric winches!

I have a manual windlass and I anchor a lot - I carry 45m 10mm chain, with 60m rope spliced to that. To get a 3:1 scope over HW in the upper BC I would usually have to use all the chain, and if it was windy/strong current I would use half the rope as well. The problem is changing over from the drum to the gypsy so I don't use the rope unless I have to, which is why I would ideally like about 75m chain!

"75m shock horror!" I hear some cry

Personally I would find it easier to have all-chain, and I can cope with the weight forward (which many boats couldn't), but whatever you use, if you only have 20m in total then IMO it is about 25% of what you should be carrying for anything but a calm day in shallow water.