I've been there several times
It is a powerboat destination. Sailboats are almost out of place. I have anchored in the lake, and the depth is fine for a 5' draft. Be aware of the dogleg turn at the south end of Star Island and note that the channel is on the west side of Lake Montauk. Once you get past the private aids you can turn to the east and anchor. There is a 7-8' spot between cans 5 & 7 where I have seen sailboats anchored but there is shoal areas just outside the 7-8' spot and I don't know first-hand how if the holding is good.It is a long dinghy ride to the town docks from the lake and getting around on foot is a long walk everywhere.If I sound negative it's because I am. I honestly can't think of a good reason to visit Montauk in a sailboat.Now Watch Hill on the other hand is a very nice spot to visit. Good anchoring, lots of room, easy dinghy ride to the docks, interesting stores, merry-go-round, ice cream stores. Only a couple of decent restaurants but a bakery, store with old books, and one of the better beaches in the area. Swimming can be done on the ocean side or the bay side. There is a long narrow channel at the entrance that you need to keep in, but it is not difficult. There is a narrow point right at the entrance that looks a bit scary the first time you enter, but it is really quite easy.