Just going to put this here, I have the sea zones for naval locations. Essentially, if you are in the same zone, you can take certain actions like combat and such. The zone splitting may appear bizarre and uneven, but remember that this is Mercator's Projection, so everything near the equator is scrunched up whilst the Antarctic Ocean (Southern Ocean) is zoomed far out of normal proportion.
Here are the abbreviations that the sheet will use, and that you probably should too:
ARB Arabian Sea
ARG Argentine Coast
BAF Baffin Bay
BER Bering Sea
BLK Black Sea
BLT Baltic Sea
BNG Bay of Bengal
CAL Coast of California
CHL Coast of Chile
COR Coral Sea
CRB Caribbean Sea
CSP Caspian Sea
CST Cape of Storms
EAR Eastern Antarctic Ocean
ECH East China Sea
EIN East Indian Ocean
EMD Eastern Mediterranean
FES Far East Sea
GUY Coast of Guyana
HUD Hudson Bay
IVR Ivory Coast
JPN Sea of Japan
LAB Labrador Sea
MAR Mid Antarctic Ocean
NET Near Atlantic
NAT North Atlantic
NRT North Sea
NRW Norwegian Sea
OKH Sea of Okhotsk
PCI Pacific Islands
RED Red Sea
SAT South Atlantic
SCH South China Sea
SIN South Indian Ocean
SPC South Pacific
SWH Swahili Coast
TAS Tasman Sea
WAR Western Antarctic Ocean
WHT White Sea
WIN Western Indian Ocean
WMD Western Mediterranean