What does a marine engine model number mean?

Formula, assumptions, and limits

Formula

The decoder’s arithmetic is the engine’s total output at the family’s rating:

where $n_{cyl}$ is the cylinder count read from the designation and $P_{cyl}$ is the maker’s tabulated rating per cylinder in kW at the rated speed $n$ in rpm. Two figures follow from the bore $B$ and stroke $S$ in meters, and the drawings use both:

$V_s$ is the swept volume of one cylinder in m³ (times 1,000 for liters) and $c_m$ the mean piston speed in m/s. The full specification under the drawings adds two more. The output in horsepower, as ship sale descriptions still quote it, and the mean effective pressure the rating implies:

One metric horsepower is 735.4988 W and one horsepower of 550 ft·lbf/s is 745.6999 W, from NIST’s Guide to the SI, Appendix B.9.¹⁰ In $p_{me}$, $k$ is 1 for a two-stroke, which fires once per turn, and 2 for a four-stroke; with $P_{cyl}$ in kW and $V_s$ in m³ the result is in kPa, and 100 kPa is 1 bar. Each maker’s program tables the mean effective pressure at its rating point, and this figure reproduces it: 21.0 bar for the S60ME-C10.7 at L1 in the Everllence 2026 program.¹ Where the two differ, the maker’s figure is for another mark or rating point.

Everything else on the page is lookup: bore, stroke, rating, speed and the cylinder counts on offer come from the maker’s published tables.

Derivation

Each maker publishes a key to its own designations, and the decoder holds one grammar per key. The Everllence two-stroke key in the Marine engine programme 2026 reads, in order, the number of cylinders, the stroke letter (G for ultra long, S for super long), the bore in cm, the engine concept (ME-C), the mark and dot number, the fuel injection concept (GI, LGIA, LGIM, LGIMe, LGIP, GIE) and the Tier III technology (EGRTC, EcoEGR, EGRBP, HPSCR, LPSCR).¹ WinGD’s key in its Engine Booklet 2026 reads cylinders, X, the bore in cm, DF, the fuel application (M, A, P or HP), S for short stroke, then the technology and update levels.² J-ENG’s key in the UE catalogue 2026 reads cylinders, UEC, the bore in cm and the development code (LSJ, LSJA, LSJM, LSGH), then the Tier III technology.³

The grammars are tried in a fixed order: the two-stroke makers first, because their prefixes are distinctive, then the medium-speed makers, then the high-speed engines and gas turbines. The first grammar that fits returns the segments, and the family key built from them (S60, G70ME-C10.5, X72DF-2.1, H32/40V) indexes the ratings. The maker tables give totals equal to $n_{cyl} \times P_{cyl}$ for every family checked: the Everllence G70ME-C10.7 lists 6 × 3,770 = 22,620 kW.¹

Assumptions

• The rating is the family’s top rating point from the maker’s program: L1 for Everllence B&W, R1 for WinGD and P1 for J-ENG.^1,2,3 The HiMSEN H21/32 figure held is HD HHI-EMD’s higher power rating of 220 kW per cylinder at 1,000 rpm, against a standard rating of 200 kW at that speed.⁴
• Every cylinder carries that rating. An engine specified at a lower rating point on the layout diagram, or derated, gives less.
• A vee engine with no entry of its own carries its in-line family’s rating per cylinder.
• Units follow each maker’s key: centimeters for every bore and stroke in the Everllence, WinGD, J-ENG and HiMSEN names.^1,2,3,4 Wärtsilä publishes no key; its product documents give the Wärtsilä 31 a 310 mm bore, which matches the number read as centimeters.⁵
• Where a mark has left the current program, the rating comes from the last program that listed it: the G70ME-C9.5 from MAN Energy Solutions’ 2021 program.⁹

Worked example

6S60ME-C10.7: 6 cylinders, S for super long stroke, a 60 cm bore, ME-C, mark 10.7. The family key S60 returns 2,490 kW per cylinder at 105 rpm (L1) and a 2,400 mm stroke from page 29 of the Everllence Marine engine programme 2026, so¹

which is the six-cylinder figure the program prints. One cylinder sweeps $\frac{\pi}{4} \times 0.6^2 \times 2.4 = 0.679$ m³, 679 liters, and the mean piston speed at 105 rpm is $2 \times 2.4 \times 105 / 60 = 8.4$ m/s. The rating implies $p_{me} = 2{,}490 / (0.679 \times 105 / 60) = 2{,}097$ kPa, 21.0 bar, and 14,940 kW is $14{,}940{,}000 / 735.4988 = 20{,}313$ metric hp.

HiMSEN 12H32/40VP: the brand is removed, then 12 cylinders, H, a 32 cm bore and 40 cm stroke, V for vee and P for propulsion. The key H32/40V returns 500 kW per cylinder at 750 rpm from HD HHI-EMD’s 2026 program, so $P_{total} = 12 \times 500 = 6{,}000$ kW, the 12-cylinder end of the program’s 6,000 to 10,000 kW range for the H32/40V.⁴

Edge cases and limits

• A mark changes the rating. 6G70ME-C9.5 returns 3,640 kW per cylinder at 83 rpm from the 2021 program, 21,840 kW in all; 6G70ME-C10.5-GI returns 3,170 kW at 80 rpm, 19,020 kW; 6G70ME-C10.7 returns 3,770 kW at 86 rpm, 22,620 kW.^9,1 A name typed without a mark takes the current mark’s rating.
• Families with no traced rating decode by grammar only, and the result says no rating is held.
• Designations that are in no maker document, such as H46DF, decode with a note that the model is not in the maker’s program.
• A cylinder count the family is not offered in. 99S60ME-C10.7 still fits the grammar, but the Everllence 2026 program lists the S60ME-C10.7 with 5 to 8 cylinders, so the decoder gives the rating per cylinder and no total, and offers only the listed counts on its slider.¹
• Two ratings under one name. HD HHI-EMD rates the H21/32 at 1,000 rpm at 200 kW per cylinder as standard and 220 kW as a higher power rating, and the Wärtsilä 31 at 630 kW per cylinder at 720 rpm and 650 kW at 750 rpm.^4,5 The decoder holds one figure per family and names it in the rating basis line.
• Gas turbines carry no cylinders and fall outside MARPOL Annex VI Regulation 13, which covers marine diesel engines.⁶

Regulatory basis

The designation is the engine’s identity in the NOx certification that MARPOL Annex VI Regulation 13 requires. Regulation 13.1.1 applies to each marine diesel engine with a power output of more than 130 kW installed on a ship, with exclusions in 13.1.2 for engines used solely for emergencies, lifeboat engines and, under conditions the Administration sets, engines on ships on domestic voyages only.⁶ A ship’s engine of 130 kW or less is outside the regulation, so the decoder prints no limit for it. The EIAPP certificate in Appendix 1 of the NOx Technical Code 2008, resolution MEPC.177(58), names the engine in its Model number column beside the rated power and speed, the Supplement repeats it in field 1.6, and paragraph 2.4.1.3 puts the rated speed and power in the engine’s Technical File.⁷

The rated speed sets the limit. For $130 \le n < 2{,}000$ rpm, Tier II allows $44 \cdot n^{-0.23}$ g/kWh and Tier III allows $9 \cdot n^{-0.2}$ g/kWh, which at 1,000 rpm give 8.98 and 2.26 g/kWh. Under 130 rpm the limits are 14.4 and 3.4 g/kWh, which covers the large-bore two-strokes; an S35ME-C at 167 rpm takes the formula limits.⁶ Tier II applies to ships constructed on or after 1 January 2011. Tier III applies while a ship operates in a NOx Tier III emission control area and was constructed on or after 1 January 2016 for the North American and US Caribbean Sea areas, or on or after 1 January 2021 for the Baltic Sea and North Sea areas (Regulation 13.5.1 as revised by resolution MEPC.328(76)).^6,8

Common errors

1. Reading bore and stroke as millimeters. 48/60CR is 480 × 600 mm and H32/40 is 320 × 400 mm; both keys say centimeters.^1,4
2. Putting the vee letter in the wrong place. Everllence writes the V before the bore, as in 12V28/33D STC; HiMSEN writes it after the stroke and the fuel letters, as in 18H32/40VP-LM.^1,4
3. Dropping the mark. 6G70ME-C and 6G70ME-C10.5-GI are 22,620 kW and 19,020 kW engines; the mark is the difference.¹
4. Taking a propulsion rating for a generator. HiMSEN’s H35DFP propulsion engine is rated 500 kW per cylinder, its H35DF generator set 480 kW.⁴
5. Reading the WinGD version as a mark. In X72DF-2.1 the 2 is the technology level and the 1 the update level, and the X72DF-2.2 is a different engine: 2,600 kW per cylinder at 79 rpm against 3,225 kW at 89 rpm.²

Designation keys by maker

The Everllence 2026 key lists only the G and S stroke letters and the ME-C concept. Earlier engines carry K for short stroke, L for long stroke and the MC and MC-C camshaft concepts, which the decoder reads from the older programs. Wärtsilä publishes no designation key: the number in W31 matches the 310 mm bore given in its brochure, read as centimeters, and the decoder keeps the letters after it, as in W31DF, as part of the model name.⁵

Rating points and what the output means

The output on this page is the top of the family’s rating field, the point the program tabulates. Everllence B&W engines are rated at L1, and the G70ME-C10.7 can be laid out anywhere from 63 to 86 rpm below it; WinGD’s X72DF-2.1 is rated at R1, 89 rpm; J-ENG’s UEC50LSJ at P1, 1,780 kW per cylinder at 108 rpm, with P4 at 81 rpm.^1,2,3 An engine contracted at a lower point keeps its designation, so two ships with a 6G70ME-C10.7 can have different rated powers.

Medium-speed engines carry a different split. HD HHI-EMD rates the H32/40V at the same 500 kW per cylinder at 720 and 750 rpm, while the H21/32 has a standard and a higher power rating, and the Wärtsilä 31 gives 630 kW per cylinder at 720 rpm and 650 kW at 750 rpm.^4,5

Where to find the engine model on board

The builder’s nameplate on the engine carries the designation and the serial number. The EIAPP certificate is the record that has been checked: its face lists the engine manufacturer, model number, serial number, test cycle, rated power and speed and the engine approval number, and field 1.6 of its Supplement repeats the engine type and model number.⁷ The NOx Technical File holds the engine’s rated speed and rated power under paragraph 2.4.1.3, and definition 1.3.12 of the NOx Technical Code ties the rated speed to the nameplate.⁷ Class machinery records and the ship’s particulars repeat the designation, often without the mark and the suffixes, which changes the rating the decoder returns.