Hi Phillip and welcome to the forum.
I don't ACTUALLY know what size chain you would need but probably as small as you can get. The pound shops , or similar, for cheap costume jewellery are a good source of chain.
Unless someone has built thgis size of model and can tell us, then I would just go for "small"…this may mean 1mm or less, and it is possible that chain to the proper scale does not look right, as the links are too small to see especially once painted and it just looks like cotton , but that's just a thought.
Build the boat up to the point where you really need the chain and then start looking is what I would do. Lay some on and decide if you like the look.
Ashley