Although technically, once you get a ship with a cannon, you can make money by sinking sea monsters and pirate ships and collecting the salvage. But carrying cargo from port to port is a recommended way to increase your doubloons, and becomes more valuable as larger ships can carry more.
(see related question)
You can get doubloons by sinking other ships, monsters and by selling cargo.
The Cargo Master (Bouffant Bay) increases cargo space of any ship by 50%.
All you do there is to hire the Cargo Master, when you can afford him (salary 15,000 doubloons).
you go around to each place and sell your cargo
"Cash" on Skullduggery Island is your doubloon count. You earn doubloons by salvage or by trading, and you can borrow some from the Golden Harbor bank. When you buy cargo, you spend your cash, and when you sell it, you make a profit. If your ship is sunk, you lose aprt of your doubloons and part of your cargo. You need doubloons to buy larger ships and hire skilled crewmen. (see related question)
He is at Bouffant Bay in the warehouse. You can hire him for 15,000 doubloons (one-time payment), and he will increase any ship's cargo space by 50%.
You have to defeat ships and sea monsters and pick up the cargo that they leave behind when they sink.
skullduggery island!
well you need to beat other ships to gain not only doubloons but cargo as well. this might depend on your ship if you have the first ship then it might be hard to beat other ships but you know, you can trade cargo for money and you can roam the seas for cargo and money to sell, sorry but i have not found any cheat for this island yet!
Nothing immediately. You need to get the largest ship, the Phoenix warbird, and hire the Shipwright and the Cannoneer. Once you have defeated Captain Crawfish, you can go back to the governor and get the directions to the treasure buried on the small island.
Fort Ridley is the first place you go on Skullduggery Island. Its impossible to miss it.
Bouffant Bay is located northeast of Fort Ridley on Skullduggery island Poptropica.com