Technology offers navies detection capability not available in the past. Still, this question is important, how did navies find each other before planes and radar? From reddit:
The biggest most impressive naval battles all happened at important ports, near important water channels or river mouths. The Battles of Salamis, Trafalgar, the Nile, The burning of the Spanish Armada, and numerous others all occurred in important strategic locations. It wasn’t really an issue of finding each other. The modern development of radar, and the use of airplanes, for finding ships has really been used to take naval warfare away from land, though most naval battles still occur near strategic locations such as the World War II battles of Midway, Coral Sea, Leyte Gulf, and the Naval battles surrounding Guadalcanal.
I guess what I’m trying to say is that it wasn’t actually that hard to find the enemy fleet. You defended your strategic locations until they showed up, or you attacked their strategic locations and found them defending.
Do go read the discussion of Mahan. The father of the big Navy.