Here are some rules I developed in case you want to add current or set to a scenario (it can be especially interesting if there is land involved).

Current (set): To represent the effect of current, the Current Indicator card is placed on the board and all vessels involved in the engagement feel the effect. At the start of each turn, each vessel places the Current Movement card on the corner or edge of their base furthest downstream, and moves the base in the direction of the Current Indicator’s arrow the distance of the Current’s indicated speed, without changing the ship’s orientation.

The Current cards with the royal blue arrows indicate localized currents and the border arrows define the boundaries. Any portion of a ship’s base within the boundary means the ship feels the effect of the localized current. A ship can only be affected by one current per turn.

Current Cards 1.pdf
Current Cards 2.pdf
Current Cards 3.pdf