Engine Nomenclature — Decode MAN, Sulzer, Daihatsu & Spec Sheets
Every letter on the engine plate is a dimension, a duty or a revision — read the code and you already know the engine.
Key Principles at a Glance 5 points
- MAN B&W codes read left to right: cylinders, concept letters, stroke class, bore in cm, then program and revision marks.
- K/L/S/G are stroke-to-bore ratio bands — G near 4 (ultra-long, slow, big propeller) down to K near 2 (short, fast).
- Sulzer 7RTA84M decodes as 7 cylinders, welded bedplate, superlong stroke, first series, 840 mm bore, modified.
- Aux codes carry duty letters: L for marine auxiliary, W for Tier-2 NOx, A for 900/1000 rpm range, DV for supercharge degree.
- A spec sheet is five numbers plus two consumptions: MEP, Pmax, SFOC, liner wear per 1000 h, cylinder-oil rate — read them before touching the engine.
1. MAN B&W — Read the Code Left to Right
The maker's project guide prints the code as boxes with leader lines — each position is one fact. The pattern below is assembled from the PDF's worked examples (774VT2BF, 7K74EF, 7L80GFCA, 6S80ME-C GI TII) plus Nithin's ship spec sheet (6S80MC-C):
| Letter | Meaning in the PDF examples |
|---|---|
| First number | Cylinder count (6, 7, 8…) |
| V / T | Crosshead frame: V-frame / tie-rod construction |
| K / L / S / G | Stroke class — §2 below |
| Bore number | Bore in cm (74 = 740 mm, 80 = 800 mm) |
| E / F / A | Design series / programme generation (7K74EF, 7L80GFCA) |
| M / C | Concept and programme: M = MAN lineage, C = compact/second programme |
| GI / TII | Gas injection variant; Tier II NOx compliance |
2. Stroke Classes — K, L, S, G Set the Engine Speed
Stroke-to-bore ratio fixes character: a long stroke means a slow-turning engine swinging a large-diameter propeller efficiently; a short stroke means a faster, more compact engine. The PDF bands:
Exam move: given any MAN code, state cylinders, class, bore, then compute S/B from the spec sheet and confirm the class letter matches — a mismatch means you misread the bore.
3. Sulzer RTA & Aux Makers — Same Logic, Different Letters
Sulzer uses the identical left-to-right grammar with its own alphabet; aux makers (Yanmar, Daihatsu) add duty letters because a generator engine and a propulsion engine with the same bore are different products:
Sulzer's 7RTA84M spec sheet in the PDF is also the template for §4: bore 840, stroke 2800, 23000 BHP at 92 rpm — every field below appears on it.
4. Read the Spec Sheet — Five Numbers, Two Consumptions
A spec sheet answers the surveyor's five questions — how hard does it push (MEP), how hard can it peak (Pmax), how thirsty (SFOC), how fast does it wear (liner), how much oil does it drink (cylinder oil) — with the Sulzer and Nithin sheets as the worked examples:
| Field (PDF example) | What it means | Exam read |
|---|---|---|
| MEP 17.2 bar | Mean effective pressure — average push on the piston | Higher MEP = harder-working engine at same size |
| Pmax 135 bar | Peak firing pressure | Over-limit Pmax overloads crosshead bearings |
| SFOC 115 g/bhp/h (MAN: 150–160 g/bhp/h band) | Fuel per brake-horsepower-hour | Compare like with like — bore, load and fuel change the number |
| Liner wear 0.05–0.7/1000 h | Bore growth rate | 0.6–0.8% bore growth condemns (see liner overhaul topic) |
| Cyl-oil 0.85 g/kW/h (e.g. 240 kg/24 h = 10 kg/h) | Cylinder-oil feed rate | Feed follows sulphur and load — too little scuffs, too much fouls |
Generator: Daihatsu 8DK-20, 880 kW × 720 rpm, Pmax 160, FO 1356 g/kW/h-class consumption, 1000 kVA 60 Hz 440 V. Propeller beside it: 4-blade solid-skewed, 9658 mm diameter, 6776 mm pitch. Emergency set: 480 kW × 1800 rpm. When the examiner points at any one line, read maker, model, duty, speed and output in that order.