Marine Engine Ratings Guidelines

Ratings should be applied on the basis of vessel operation, and on the type boat or hull design. Vessel descriptions such as workboat, pilot boat, or ferry boat; and hull design such as displacement or planing hull do not define the operating conditions of the vessel or the power demands on the marine engine. More than one rating could apply to these descriptions, depending on how the vessel is operated. Listed below are descriptions of ratings A, B, C, D and E followed by an overview chart.

Unrestricted Continuous - A Ratings

For vessels operating at rated load and rated speed up to 100% of the time without interruption or load cycling (80% to 100% load factor).

Typical applications could include but are not limited to vessels such as freighters, tugboats, bottom drag trawlers, or deep river tugboats. Typical operation ranges from 5000 to 8000 hours per year.

For 3600 Marine Engines only:

  • Continuous Service (CS) Rating is suitable for continuous duty applications, including dredges, for operation without interruption or load cycling.
  • Maximum Continuous (MC) 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. Operating time at loads above the Continuous Service rating for a given RPM is limited to 1 hour in 12 or 8.3% of total operating hours.

Heavy Duty Marine Engine - B Ratings

For vessels operating at rated load and rated speed up to 80% of the time with some load cycling (40% to 80% load factor).

Typical applications could include but are not limited to vessels such as mid-water trawlers, purse seiner, crew and supply boats, ferries, or towboats. Typical operation ranges from 3000 to 5000 hours per year.

  • Some 3500 engines have "Bhp ratings" which are typically used in fast commercial and passenger vessels including catamarans and SWATH vessels with high load factors.
  • 3600 marine engines indicating "Fast Commercial Vessel Ratings (FCVR)" are typically used in high speed commercial vessel applications with approximate load profile: 85% of operating hours at rated power, 15% of hours at less than 50% rated power.

Maximum Continuous - C Ratings

For vessels operating at rated load and rated speed up to 50% of the time with cyclical load and speed (20% to 80% load factor).

Typical applications could include but are not limited to vessels such as ferries, harbor tugs, fishing boats, offshore service boats, displacement hull yachts, or short trip costal freighters. Typical operation ranges from 2000 to 4000 hours per year.>

  • Some 3500 engines have "Chp ratings" which are used in fast commercial and passenger vessels and cruising yachts with moderate load factors.

Intermittent Duty - D Ratings

For vessels operating at rated load and rated speed up to 16% of the time (up to 50% load factor).

Typical applications could include but are not limited to vessels such as offshore patrol boats, customs boats, police boats, some fishing, fireboats, or harbor tugs. Typical operation ranges from 1000 to 3000 hours per year.

  • Some 3500 marine engines have "Dhp ratings" which are used in patrol craft, fast passenger vessels, and cruising yachts with low load factors.
  • 3600 marine engines indicating a "Military Fast Vessel Rating (MFVR)" are typically used in patrol craft and other naval vessels with low load factors.

High Performance - E Ratings

For vessels operating at rated load and rated speed up to 8% of the time (up to 30% load factor).

Typical applications could include but are not limited to vessels such as pleasure craft, harbor patrol boats, harbor master boats, some fishing or patrol boats. Typical operation ranges from 250 to 1000 hours per year.

  • Some 3500 marine engines have "Ehp ratings" which are typically used in fast patrol craft and fast yachts with low load factors.

Rating Conditions for 3500 and smaller engines

Ratings are based on SAE J1228 standard conditions of 29.61 in Hg (100 kPa) and 77° F (25° C). These ratings also apply at ISO3046/1. ISO8665, DIN6271, and BS5514 conditions of 29.61 in Hg (100 kPa), 81° F (27°) and 60% relative humidity.

Fuel rates are based on fuel oil of 35° API [60° F (16° C)] gravity having an LHV of 18 390 Btu/lb (42 780 kJ/kg) when used at 85° F (29° C) and 60% relative humidity.>

Fuel rates are based on fuel oil of 35° API [60° F (16° C)] gravity having an LHV of 18 390 Btu/lb (42 780 kJ/kg) when used at 85° F (29° C) and weighing 7.001 lbs/U.S. gal (838.9 g/liter).

Rating Conditions for 3600 Engines

Ratings are based on SAE J1349 standard conditions of 29.61 in Hg (100 kPa) and 77° F (25°C). These ratings also apply at ISO3046/1, ISO8665, DIN6271 and BS5514 standard reference conditions. Ratings also meet classification society maximum temperature requirements of 113°F (45° C) temperature to turbo and 90° F (32° C) seawater temperature without derate.

Fuel consumption is based on ISO3046/1 with +5% tolerance at rated power for fuel having an LHV of 18,390 Btu/lb (42,780 kJ/kg) and weighing 7.001 lbs./U.S. gal. (838.9 g/liter). Includes engine mounted fresh water and lube oil pumps. SFOC without pumps 2% less.

Additional ratings may be available for specific customer requirements. Consult your Caterpillar® representative for details.

Performance Data

Performance along a typical fixed pitch propeller curve with a 3.0 exponent.

Power rated in accordance with NMMA procedure as crankshaft power. For units equipped with Caterpillar supplied marine gears, reduce crankshaft power by 3% for propeller shaft power.

All Cat Marine engines shipped on or after January 1, 2000 have ratings which meet IMO standards for nitrogen oxide emission limits in Regulation 13 of Annex VI of Marpol 73/78.