All of those private owned marinas is just a matter of the right timing. You can be on a list forever. But if you go there, they like you, it's yours.
30' might be tough to fit in Ralph's it's pretty tight in there as it is, but it's worth a try. If you cannot get a slip, ask for a transient slip, they will charge you by the week. If that doesn't work, try a mooring. Not that bad.
Old Man in Stonybrook usually has availability, but the problem there is you cannot get out at low tide.

Old Man in Stonybrook usually has availability, but the problem there is you cannot get out at low tide.
