Caterpillar Marine Propulsion Engines are available in five rating classes, tailored to your needs.

Continuous A Rating
Load factor: 80% to 100% time at rated rpm. Typical hours/year: 5000 - 8000. "A" rating typical applications: for heavy-duty service in vessels such as freighters, tugboats, bottom drag trawlwers and deep river towboats when the engine is operated at rated load and speed up to 100% of the time without interruption or load cycling. For 3600 engines only: Continuous Service Rating is suitable for continuous duty applications, including dredges, for operation without interruption or load cycling. Maximum Continuous Rating is generally used for vessel applications involving varying loads. The engine power actually produced is limited by application guidelines, leaving a power reserve for unusual operating conditions.

Medium Duty B Ratings
Load factor: 40% to 80%. Up to 80% time at rated rpm. "B" rating typical time at full load: 10 hours out of 12. Typical hours/year: 3000 - 5000. Typical applications: Vessels such as midwater trawlers, purse seiners, crew and supply boats, ferries and towboats where locks, sandbars and curves dictate frequent slowing and engine load and speed are constant with some cycling.

Intermittent C Ratings
Load factor: 20% to 80%. Up to 50% time at rated rpm. Typical time at full load: 6 hours our of 12. "C" rating typical applications: Vessels such as ferries, harbor tugs, fishing boats moving at higher speeds out and back (i.e. lobster, crayfish and tuna) off shore service boats and also displacement hull yachts and short trip coastal freighters where engine load and speed are cyclical. Chp - Fast commercial and passenger vessels and cruising yachts with moderate load factors.

Patrol Craft D Ratings
Load factor: Up to 50%. Up to 16% time at rated rpm. Typical time at full load: 2 hours out of 12. Typical hours/year 1000 - 3000. "D" rating typical application: Planing hull vessels such as off-shore patrol boats, customs, police and some fire and fishing boats. Also used for bow and stern thrusters.

Dhp - Patrol craft, fast passenger vessels and cruising yachts with low load factors ( 2 out of 12 hours)

Military Fast Vessel Ratings - (3612, 3616) For patrol craft and other naval vessels with low load factors.

High Performance E Ratings
Load factor: Up to 30%. Up to 8% time at rated rpm. Typical time at full load: 1/2 hour out of 6. Typical hours/year 250 to 1000. "E" rating typical applications: Planing hull vessels such as pleasure craft, harbor patrol, harbor master and some fishing and pilot boats.

Ehp - Fast patrol craft and fast yachts with low load factors (1/2 hour out of 6)