Since the Port are now full of Constitutions and Ingermanlands - I'd like to propose that the duration of ships is reliant on the quality of the ship.
Right now you can just buy a basic constitution, annoy the hell out of your enemy and if you have used all 5 durations of it you just buy another one.
To make the ships "worth" a little bit more without making them crazy overpriced I propose, that the quality of the ship dictates the duration of the ship
Meaning:
A Constitution:
Exceptional - 4 Dura
Mastercrafted - 3 Dura
FIne - 2 Dura
Common - 1 Dura
And the ones buyable in the shop have only 1 dura. So if you want a Consti with more than one dura you have to put some Mid Grade Notes in to get those Durations.
Same for bigger ships - sailing a basic Santi is a joke - Since 1st rates only have 1 Dura you only can craft exceptional ones - other qualities should not be able to be crafted.
3rd Rates could be made in:
Exceptional - 3 Dura
Mastercrafted - 2 Dura
Fine - 1 Dura
thats it.
Ultimately you put some worth in the ships quality and increase the benefits of "good" ships without taking away the possibility to craft a bad one, but you encourage better ships starting from the bigger ones.
Small Ships should use the same mode - Snow for example:
Exceptional - 5 Dura
Mastercrafted - 4 Dura
FIne - 3 Dura
Common - 2 Dura
Basic - 1 Dura
Maybe the countless tagging of 1st rate fleets with small ships like consties will be reduced because its not a basic one which loses its durations but an exceptional one.