Dewport is the capital of your land. Dewport Harbor is part of this point of interest and provides you with frequent shipment of goods (e.g. Shards, Forge Materials, Gold, Potions of Knowledge).
In Dewport Harbor you can also choose to buy a Merchant Ship offer (or 5 at a time) for Gold; or a Smuggler Ship or Imperial Ship for Diamonds. The higher the price, the better the cargo!
There is also a free Merchant Ship waiting for you every 4 hours, and a free Smuggler Ship every 48 hours. Make sure to pick them up in time!