A visit to Brewer Cove Haven Marina will pleasantly surprise you with its collection of America’s Cup boats that make this quality yard their home. The fact that these prized yachts rely on Brewer Cove Haven speaks volumes for the yard’s ability to maintain sophisticated racing yachts, as well as recreational vessels, in a first-class marina facility. The marina’s remote location is far removed from the RI boating scene, yet has a worldwide reputation for its work with 12 Meters, J-boats and other high performance racing sailboats. (Source)
For private property issues this cache is not located in the marina, but rather on the outskirts of the adjacent George Haines Memorial Park. You can catch a glimpse of some of the boats the marina has to show through the fence near the cache, including one named "Indian Princess."
You're looking for a small, black container. If you've found any 4Swans caches before you should know exactly what you're looking for. As mentioned earlier you will need to BYOP as well and replace the cache as found. Have fun! 