Marine Engine Rating Classifications

See also M-rating.

Source IMPC corporation.

Continuous Duty

• For use in applications requiring uninterrupted and unlimited service at full power.
• Load Factor: 80% to 100%
• Typical Annual Operation Hours: 5000 to 8000 hours
• Typical Hull Forms: Displacement
• Typical Applications: Freighters, tugboats, bottom drag trawlers, or deep river tugboats, dredges

Heavy Duty

• For nearly continuous use in variable load applications where full power is limited to 8 hours out of every 10 hours of operation.
• Load Factor: 40% to 80%
• Typical Annual Operation Hours: 3000 to 5000 hours
• Typical Hull Forms: Displacement
• Typical Applications: Mid-water fishing trawlers, crew and supply boats, ferries, purse seiners, and towboats. Or auxiliary applications like thrusters and cargo pumps in dynamic positioning.

Medium Duty

• For moderate use in variable load applications where full power is limited to 6 hours out of every 12 hours of operation.
• Load Factor: 20% to 80%
• Typical Annual Operation Hours: 2000 to 4000 hours
• Typical Hull Forms: Semi-displacement and displacement
• Typical Applications: Ferries, harbor tugs, fishing boats (designed for high speed), offshore service boats, (non-cargo) displacement hull yachts, or short trip coastal freighters.

Light Duty

• For intermittent use in variable load applications where full power is limited to two hours out of every eight hours of operation.
• Load Factor: Up to 50%
• Typical Annual Operation Hours: 1000 to 3000 hours per year
• Typical Hull Forms: Planing and semi-displacement
• Typical Applications: Offshore patrol boats, customs boats, police boats, some non-net fishing, fireboats, military and police vessels, or harbor tugs. Or auxiliary applications like emergency fire pumps and hydraulic power packs.

Pleasure Duty

• For infrequent use in variable load applications where full power is limited to one hour out of every eight hours of operation.
• Load Factor: Up to 30%
• Typical Annual Operation Hours: 250 to 1000 hours
• Typical Hull Forms: Planing
• Typical Applications: Pleasure craft, harbor patrol boats, harbor master boats, some fishing or patrol boats, sportfishers, motoryachts, and cruisers.