Many powerboats and nearly all PWC are equipped with two-stroke engines. Conventional two-stroke engines produce roughly 14 times as much ozone-forming pollution as four-stroke engines. Also, 25–30% of the fuel and oil mixture of two-stroke engines is discharged unburned with a portion lingering in the water column for a period of time.
New federal emission standards for marine engines are being phased in gradually. Many manufacturers are meeting these requirements currently with clean-burning engines already available. The new technology provides easier starting, faster acceleration, quicker throttle response, improved fuel economy, and a reduction in fumes and noise.
Even though vessel engines currently in use are not affected by the phase-in, retiring them will help aquatic environments.