On large cargo ships (dry bulk carriers, or tankers) there are main and auxiliary engines. Auxiliary engines can be internal or external combustion (generators vs boilers) and generate electricity to power the ship's equipment (cargo pumps, cargo cranes and all other machinery).

I have read that tankers can have pumps that are powered by the main engine.

I have a number of questions about the engine usage related to powering equipment:

  1. Generally do ships have either boiler(s) or generator(s) as auxiliary engines, or could they have both for different purposes?
  2. Do newer ships more commonly use generators instead of boilers?
  3. Are larger equipment (cranes or cargo pumps) powered by the auxiliary engines or is it common to have these powered by the main engine?
  • $\begingroup$ What does your research show? This is something you can find out for any ship or tanker you are interested in. $\endgroup$
    – Solar Mike
    Feb 20, 2020 at 4:36
  • $\begingroup$ Hi Mike, unfortunately my research doesn't cover the questions I have. Which is why I reached out on this platform. The two first paragraphs are a brief summary of what my research did show. $\endgroup$ Feb 20, 2020 at 4:45
  • $\begingroup$ Mike, could you please share how I could find this out for any ship or tanker I am interested in? $\endgroup$ Feb 21, 2020 at 14:31

1 Answer 1


There is no one way to do things. Ship design is continually evolving.

In general, cargo ships are low and slow, as in powered by large 2-stroke diesel engines with big propellors and slow speeds. Higher speed vessels use smaller 4-stroke engines with smaller propellors and higher speeds.

Traditionally, propulsion has been diesel, but as ship sizes get larger, companies seek energy efficiency and specialiaty requirements (noise, passenger comfort, etc.), diesel-electric is being embraced (diesel to electrical propulsion).

We have two requirements: propulsion and auxiliary loads. Auxiliary powers everything else. Diesel-drives have diesel propulsion (2 or 4 stroke) and 4-stroke auxiliaries. Diesel-electric drives have 4-stroke gensets (diesel generator) generating AC power and large electric motors for propulsion.

Ships use 50Hz or 60Hz auxiliaries. A rough estimate would be 5% of propulsion power would power auxiliaries. A lot of energy goes up the stack. Heat exchangers recovery this heat to heat boilers, which can be used as required. In principle, this energy could be used to generate the electricity powering some or all of the power for the auxiliaries. The problem being synchronizing this power with 50Hz or 60Hz auxiliary diesel generated power.

  1. Yes to all possibilities.

  2. And this sort of answers this also. As ships get larger and IMO forces energy efficiency on ship owners, diesel-electric ships become the predominant choice.

  3. Again, this would be vessel specific, but most cargo pumps are electrical. Electrically driven pumps are easier to control, but diesel-engine pumps have more capacity, with one cavaet, they burn more fuel.

So FiFi monitors (long distance fire-fighting pumps putting out up to 2 tons/s - FiFi 3 = 9600 m3/hr @ 70m height) are typically main diesel-engine driven pumps. They put out enough water to drive ships backwards over 3 knots. In this case, it makes sense to use large capacity of the propulsion engines.

Cargo pumps are typically electrically driven, so the load can be provided by auxiliaries or even shore power (burn no fuel = cheaper electricity). This is more of an efficiency or scale issue. You can hammer a nail with a sled hammer, but you don't want to be holding the nail.

8-16 electrically driven cargo pumps vs 1 or 2 diesels running at low efficiencies. Diesels have the best fuel consumption around 75% to 85% of MCR (Manufacturers Continuous Rating). Power up auxiliaries and match load on auxiliaries to load required by pumps. Propulsion engines would be below 25% load.

  • $\begingroup$ Large Ship fuel is not the regular diesel one buys at the local garage or fuel station... it is a much heavier grade and needs preheating. $\endgroup$
    – Solar Mike
    Feb 21, 2020 at 6:16
  • $\begingroup$ @SolarMike AFAIK On the extreme, Heavy Fuel Oil (HFO), which is essentially crude is more solid than liquid. So it must be heated into a liquid for burning. NOx and EEDI regulations are putting pressure on all ships to burn cleaner fuels and less fuel to reduce emissions. MDO (Medium Diesel Oil) and HFO vary depending on the type of dinosaur they were made from, but there is greater variance in MDO over HFO, but I wouldn't say there was much difference between MDO and car diesel. $\endgroup$ Feb 21, 2020 at 13:12
  • $\begingroup$ Thanks for taking the time to respond. However I think my question is not clear or not relevant on this forum. I will delete the question and will try to find another medium to get help. $\endgroup$ Feb 21, 2020 at 14:24
  • $\begingroup$ Your question is too broad for this format, but I don't think it is irrelevant. Up to you if you delete the question. There is motion to close it, but not strong. $\endgroup$ Feb 21, 2020 at 14:34

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