Not sure about tensile strength, but I've seen polypropylene line commonly used for this purpose, probably because it's lightweight and floats and available in high visibility colors.
I think if conditions are such that the line may break, you might be better off if it does.
There's a huge Nordhavn (87ft?) trawler that I've seen anchored in Kelly's Cove multiple times, I don't think they were using a line thicker than 3/4".