The Harbor is located to the right of your farm. Captain Barnacle and Miss Tentacle will bring their Ship to the Harbor to offer to purchase your farm products for dollars, horseshoes, and experience points. The horseshoes you get from the Ship can be used at the Horse Ranch.
The Ship will dock at the Harbor for 6 hours or until you fill all 6 of Captain Barnacle's requests. Once the Ship departs, it will take 6 hours until the Ship comes back with a request for more farm products, The Ship will not appear in the Harbor unless you are logged in to the game, but the 6 hour departure timer will keep counting even if you are not logged in. Once you log in, the Ship will arrive and the 6 hour timer will begin.
Captain Barnacle will always request 6 different items. The first 4 items will be products will be produced on your 3 permanent farms (Main, Gourmet, and Flower). The products requested can be anything that your farm is able to produce even if you choose not to produce the item. For example, a Donkey Stable can be built at Level 29. Captain Barnacle will not ask for donkeys if you are Level 1-28, but once you reach Level 29, he will begin to ask for donkeys even if you do not build a Donkey Stable on your Gourmet Farm.
The last 2 items will produced by your Greenhouse. When the Island Farm event is running, the Ship will ask for Greenhouse products available from the Island Farm or from the Seashell Trader. When the Viking Farm event is running, the Ship will ask for Greenhouse products available from the Viking Farm or from the Runestone Trader.