In this discussion things will probably heat up – like some engines do when their complicated cooling systems fail. Especially marine diesel engines are by far the most dirty and polluting parts of a boat, smoking, leaking and breaking down. Yet remarkably awesome inventions, despite their complexity, still manage to push us out of unpleasant situations, saving our ships and even ourselves, or simply just pushing us to the next harbour or anchorage.
So show some respect to the old lady sitting in the bottom of your dark moist boat, being pushed around by your stupid schedules or poor planning. She may create most of the drama on your trips, but that’s ok (that sounds so sexist that I (Leo) might need to change it – Pernille doesn’t approve).
Here I should probably add that combustion engines should no longer be ok, we should all be thinking and supporting non-greenhouse gas emitting alternatives in order to speed up the decarbonization process. But in parallel let’s also focus on minimising their impact and usage.


With diesel/casoline having such a high energy density and low price it’s arguably impossible to replace combustion engines and all their capabilities entirely at the given time, so what can be done?
- Maintenance and love. Keeping the lady in good shape (obviously), making sure she runs as smoothly as possible, will increase efficiency, reduce smoke (including pollutants) and oil consumption. Another important part seems to be running the engine on an ideal RPM, slow steaming. But although it’s fuel efficient, it might actually reduce or worsen your efficiency in the long term due to unburned fuel building up on your injectors and causing all sorts of trouble. Cruising at full speed is also far from being great, reaching hull speed or near hull speed, the rpm/speed curve becomes exponential and you consume a lot of fuel while only going slightly faster. So try to figure out what is your most ideal speed (easier said then done) that’s provides maximum fuel savings without compromising the engine. As you might happen to see us on the water we haven’t really nailed any of the above quite yet, but then again you might not even see us because of all that smoke. That’s the reason we try to skip right away to step 2 as fast as possible. Here we should add that the overall condition of the underwater parts and propeller have a huge impact on your good vessel’s hydrodynamics, thereby contributing to fuel efficiency, but that’s no news to anybody.
- Avoid the Engine. Da, obviously that’s why you have a sailboat. Good weather planning and some flexibility will get you sailing more and further. It also feels so much better completing a long or short trip entirely on sails. Don’t you admire sailors who even sail into the harbours or anchorages on sails? But who are we kidding, sometimes it just doesn’t work, or we simply have no patience, we just want to make it to that cold beer by sunset. But we can agree that that it’s probably one of the most effective ways to reduce our impact and emissions with only cost being our time and patience and perhaps that missed sunset beer/drink by the docks or anchorage.
- Upgrade your old lady, sometimes it’s just time to call it, all relationships don’t last forever, goodbyes are hard and expensive. But you might end up being happier after all. The good news are that once you are at this point there are actually some interesting, yet tricky options:
- You can go for another diesel engine, because you might need the range it provides, or because after all those years, you have received your imaginary boat engine mechanics degree. So there you are, looking for newer models or a used one. We have no clue, but we could imagine that over the years diesel engines have become, as all engines, more efficient and much more complex- good luck there.
- You can also go down a new road, try something new, go electric or hybrid. For most greenhouse gas emitting activities, green electricity/propulsion seems to be the most likely answer. It has its problems, but there are solutions. So as this topic is big we will make another post about electric propulsion.
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