Re: What size and type of rope for a mooring strop??
Im wondering the same thing myself. Boat has always been on a pontoon and now thinking about a sheltered mooring on trots is a quite fast flowing tidal river.
For what its worth, I will probably go with chain. This will take away the common worry of chaffe, which no matter what you do, is difficult to feel confident you have dealt with. This said, chain has no stretch, so I will have a secondary nylon line which will take the strain. Should this fail (through chaffe or whatever) the chain will be there to take up the strain.
As to the size of the nylon rope... my feeling is as big a diameter as the cleats on your boat will sensibly cope with.
All of this said, Im still on the pontoon and have no ahhh... proof of the pudding, if you know what I mean.
What ever you decide...if it lets you sleep at night, its right for you.
I'd rather bodge it myself than pay an expert to bodge it for me.