A LONGBOAT carries colonists over open sea and puts them ashore.
It sails FIVE tiles a turn and founds a city on any coast it reaches, exactly as SETTLERS do on land — and is spent doing so.
Requires MAP MAKING.
Costs one point of city POPULATION, like Settlers.
It cannot fight, treat with anyone, or carry other units. A longboat is a one-way journey, not a navy.
For a people whose land runs out at the shore, it is the only expansion there is.