If you have paid back your debt to the King, you are allowed to buy a boat.
When you own a boat you can travel the sea and find undiscovered land, conquer and rebuild it.To buy a boat your bank account has to be over 5,000,000 and you also have to bring several nets.
If you want to put off and your boat is lying at another port, you will have to transport it back for a little fee, proportional to the distance your boat is away.
You can develop your boat further, but costs raise (both silvers and nets) with each level. A boat will travel the number of cells equal to its level per click. (For example, a level 3 boat will use up only one click for every 3 cells traveled.) Note also, that it will cost slightly more to transport back higher level boats.
Tip: Always take a sense ball with you for your journey.