The Medium Weight Sails increase the carry weight of the ship it is placed on.
|Medium Weight Sail|
Sail value : 1.7
The "Sail Max Movement Weight" stat that comes from blueprints gives a percentage based bonus to the weight. The bonus calculation is based on the base value of the sail and not the ship.
A medium weight sail with a "Sail Max Movement Weight" bonus of 110% will be calculated as 2500 * 1.10 = 2750 weight for that sail.