Mariner Fighting Style

This feat is to mechanically apply the following since it is not possible to create a new fighting style.

From Unearthed Arcana, Waterborne Adventures, 5/4/2015:

The following new option can be selected by fighters, paladins, and rangers for the Fighting Style class feature. Whether a buccaneer, an experienced sailor, or a specially trained marine, a mariner can scale a ship’s rigging and swim through choppy water with ease. Adapted to wearing light and medium armor, mariners can defend themselves without relying on heavy armor or bulky shields. Most of them thus wield two‐handed weapons or fight with a pair of blades.

Mariner: As long as you are not wearing heavy armor or using a shield, you have a swimming speed and a climbing speed equal to your normal speed, and you gain a +1 bonus to AC.