Actually, Gateway Marina in Brooklyn might work. The downside is that it is just west of JFK, so the only practical way to Garden City is by car. 25 minutes door to door--except the two highways you'll have to use both bog down regularly with any excuse. And as a NYC resident, you may be liable to NYC income taxes, which are much higher than Nassau or Suffolk county.
Northport and Port Jeff could be hour-long commutes, ugh.