A water separator for use in a marine exhaust system comprises a horizontally disposed, generally cylindrical housing including a wet exhaust inlet, a dry exhaust outlet, and a water outlet. Wet exhaust entering the wet exhaust inlet is constrained against the inner housing wall by a variable geometry vane or baffle which causes the wet exhaust to accelerate such that centrifugal force causes the entrained water to separate from the exhaust gas. Separated water encounters a longitudinally disposed barrier and flows to the water outlet for discharge from the vessel. A tubular dry exhaust pipe is longitudinally disposed within the housing and includes an inlet disposed in proximity to a first end thereof, and an outlet projecting from a second end thereof.