I don't know why it took me so long to figure this out, considering I figured out the rest of the event data months ago. I was playing around with the map loading event's zz value, and realized that it covers all the modes of transportation. This means that you can load the ship! See the attached picture for proof. Unfortunately, it doesn't work as an actual sailing ship -- it passes through all terrain, and you can't exit it. But I was just wondering yesterday how I was going to do the ship event in my hack, and here's the solution. I can do as many as I want, even create shipping lines if I want to. It turned out to be easier to change than I thought it would, at the least. Here's the key for that event hex:
FE aa xx yy zz Load map aa at position (xx, yy) with transportation/world zz
zz: 01 = Yellow Chocobo
02 = Black Chocobo
03 = Hovercraft
04 = Enterprise
05 = Falcon
06 = Lunar Whale
07-1F = Ship
20 = load map without pixelation transition
40 = for airships, don't use the dust entrance or take-off animations
80 = Underground/Moon
Notes: bit 7 of xx and yy in location maps is unknown
If event flag 36 is set, the Enterprise can use the hook
If event flag 39 is set, the Falcon can go over lava
If event flag 3D is set, the Falcon will have the drill
The modes not normally available on a map (e.g. Chocobos in the Underground or airships on the Moon) don't really work. Either you can move but the graphics aren't there, or the graphics are there but you can't move. The Lunar Whale works on all maps; funnily enough, using the Crystal in the Underground moves you to the Overworld. Also, be careful about loading a Black Chocobo not in a forest. It will return to the spot it came from, but won't be able to land. It's kind of funny to watch it bob up and down forever, actually, but not something you'd want in your game.
Edit: Figured out bits 5 and 6 of zz, and which event flags determine the airship properties