Spoiler (click to reveal)
Curses that trigger following a sail action: 'Feverish' causes you to remove a good from a ship's hold after every sail action, and 'Possessed' causes you to take a damage if you don't sail through dangerous waters with a sail action.
I assume these would trigger only if the sail action is taken for that particular ship. (But the wording on the Guild pages might suggest that if the sail action is taken, both ships take it - and the curses WOULD trigger - discuss with your play group, or geekmail RobDaviau for clarification.)
In either case, as Chris Boote mentioned above, you can only load/unload goods before or after taking a "sail action" with a ship. It makes sense that you wouldn't have to sail one space out and one back to accomplish this (but you still have to use it as one of your 2 guild actions. BUT, I imagine that if you are loading/unloading goods from your cursed ship, the curse would trigger (because that ship is officially taking part in the "sail action"). And I think that the curse triggers immediately after the sail part of the action.
So with an empty ship that is Feverish/Possessed, you could:
1. Sail nowhere
2. Lose a non-existent good/take a damage
3. Load goods aboard
With a full ship that is Feverish, you could:
1. Unload all your goods
2. Sail nowhere
3. Lose a non-existent good/take a damage