Hi ,
no look for a spot where one ship can reach several cities , put it one blockade , number two ship same spot is on guard , number three has medic for example and is on blockade also , number four goes in and out of the stack to raid ships or fishing boats , a stack like this is worth its money
then within reach of that pile is an other one ( max tiles a turn minus one ) that does the same or make stacks that border each other at the blockade range
now remember , why minus one turn , if you loose your blockade ship you want it to be replaced the same turn , and you have to wait an other turn if you cant designate it to blockade the same turn , thats a turn of less money , ...
now what you can also do if you are sure about naval control is indeed to just put a ship in each water tile , ...
but if you do that , be sure the AI will come after your ships , and this you want to exploit , while they are building ships you come in over land , start to pick on those units in the city , ...
a lot of people forget sea patrol , so play the RFC mod as Japan for example or try a few maps where you are on an island , ...
Have a nice tuesday