How would knowing your latitude and longitude help you find your way at sea?

Knowing where you are is only one part of getting to where you're going.

-- If you know your own latitude and longitude, AND the latitude and longitude of

where you want to go, then you can calculate the DIRECTION you need to sail in

order to get there by the shortest route, and exactly how far that is.

-- If you only know your own latitude and longitude and nothing else, then perhaps

the most useful application of that knowledge takes place when you need to radio

the Coast Guard and ask them to come out and rescue you. If you can give them

that information, then they don't have to hunt for you when they get to the general

area.