Comment by Casseres | Hacker News Reader

Comment by Casseres | Hacker News Reader

Parent Full thread

Former ship engineer here.

I only worked with Diesel, not HFOs.

Due to the rocking of the ship, it's hard to get an accurate reading of the fuel in the tanks. Fuel is transferred from storage tanks to a day tank, and a fuel meter can be used for that, but that only tells you how much you transferred, not how much you consumed. Unless you always fill the day tank to the exact same level (remember, hard to measure at sea) and at the same time each day, you won't know exactly how much was burned in a 24 hour period. And of course fuel consumption changes based on the ships speed.

This is a good, short explanation on how we measure tanks on ships: http://benvalle.com/Level.html

Edit: there is probably a lot of money to be made if someone can come up with a very accurate tank measuring method. I've seen some tanks use ultrasound to detect the level in a sounding tube, but sometimes those can be distorted if the "liquid" sticks to the sensor. Maybe some kind of 3d mapping? However not all tanks have an unabstructed free surface in order to prevent the free surface effect from capsizing the ship: https://en.wikipedia.org/wiki/Free_surface_effect

2nd edit: Maybe not, since measuring at sea isn't as important as measuring in port when the ship is not rocking and the products are being transferred to/from ship. I'll leave the first edit since it might be interesting to people.

> Due to the rocking of the ship, it's hard to get an accurate reading of the fuel in the tanks.

Would it not be possible to install a flow rate monitor between the engine and the day tank? If so it would be possible to estimate with okay precision flue usage for any given time period.

I Apologize for the naive question, because I imagine there's a reason it isn't done already.

Yes, and that is probably part of the "new technologies allow more accurate readings."

I've only been on one ship built in the last decade that had that, and you could read the number on a computer screen. (FYI, the computer systems and automation on ships are a joke, if you can do it better than the current companies, you could make some money. Also, tangentially related to why we'll never have fully-automated ships. Stuff breaks, and ships lose money every day they're in port for repairs.)

However not all fuel that goes to the engine ends up being burned. Fuel is always being pumped through the fuel line at a high pressure, and only a fraction of that is burned when the cam system actuates the injectors to inject fuel into the engine cylinders. The rest of the fuel is returned to the tank.

As for the ship I was on that had a more accurate measurement, I don't know exactly what was measured. I can only speculate it was the fuel in minus the fuel out.

Just to add on to your very good point, the reason these ships aren't (always) equipped with flow meters is also that they're quite expensive. My last vessel had one,the one before relied on tank soundings and what we know about consumption.

I was involved in a project that measured the fuel consumption of 1-2MW diesel gensets a couple of years back. It is not that hard...

Why would we need to know how much was burned in a 24 hour period?

For the purposes of this article, it would be sufficient to measure how much fuel you transferred during a calendar year, and that's about as much as you consumed. The particular level of the day tank can be ignored as it won't even make a 1% difference to the total amount

We need that info for the day's run. Many figures on ships are calculated daily. Distance, fuel use, lube oil consumption, fresh water, etc. This is mostly from tradition, because it's quite easy to compute the vessel's position at noon using celestial means.

Given that we can record how much fuel was put in, and how fast the motor was spinning at each point in time, why can't you model how much fuel is left in the tank? Is fuel consumption-to-motor-use very variable?

As for being variable, probably not outside of the margin-of-error. If the ship was full of goods, then it would be heavier, and would sit lower in the water adding more resistance to forward motion. So the weight would have an effect, but whether it's noticeable outside the errors introduced when measuring, I don't know.

It's up to the Chief Engineer if he/she wants to use an Excel spreadsheet to track fuel consumption (and most probably do). As for tracking it based on weight, maybe some chiefs do that, but I imagine it's not worth it for most.

I wasn't a chief, so I don't know what their responsibilities are in regards to fuel consumption. But I imagine they would have to give estimates of future fuel needs to the company based on the ship's schedule.

Absolutely, Chief is in charge of bunker planning. Fuel consumption must be tracked anyway because the charterer needs the consumption figures. After all, he's the one paying. The Excel spreadsheet definitely is a thing.

Reply on news.ycombinator.com