Marignon CotS - What's the hook?

[PvK]

Sailing is a very different advantage from underwater ability. On some maps, it can be very useful. Not just for islands and hops over water to otherwise-blocked continents, but also when there are seas which border on many land provinces - this can let you sail an army a land-distance of many provinces in one turn. So the value can depend a lot on the map.

PvK