Scurvy would affect both crew and passengers. There could be a high mortality rate.
Affected ships would be reduced in speed and defence as there would be few crew remaining healthy enough to man the vessel.
This would have to be a long time period effect - 72 hours or whatever may be a maximum limit.
The British Navy introduced limes and lemons into the rations to provide vitamin C (the lack of which caused the scurvy in the first place).
Hence the nickname: limeys for British sailors.
Therefore maybe British fighting vessels may be immune to this card.
Passengers (immigrants) would be lost.
Open this idea for discussion and maybe other attributes could be included.
Historically this was a major killer on long sea voyages.