[tawm]

It is common practice to let vessels drift freely if no anchorage is available (congestion, depth of water) or if there's no intention to anchor the vessel. If the orders for the vessel weren't clear, it's very much possible that it was drifting a few miles off the Chinese coast.

[freddie_mercury]

The linked article includes a chart showing the vessels movements mapped down to every few minutes. Looking at that picture it is hard to imagine its path is caused by drifting. It is clearly moving in a circle. You can't tell from the static map in the article but if you check other marine vessel tracking websites you can see that it is moving in a counterclockwise circle at a fairly steady rate.

I suppose that could be caused by an anchor and drifting but it seems more likely to me (as an uninformed idiot, though I've been in anchored boats before and don't remember them moving in circles because of it) that it is under power (albeit not very much).

[theresistor]

Swinging about an anchor under the force of wind or currents would tend to make a circular arc.

[dmurray]

Normally back and forth on the downwind or down-current side of the circle, though. The chart shows it completing several circles.

[windows_tips]

The chart shows most of the data points on a small portion of the arc.

[theresistor]

Reversals are completely normal for cyclic tidal currents or sea breeze / land breeze cycles.

[poooogles]

Same for tides.

[dghughes]

Huge heavy ships need many kilometers to stop and then to get back up to speed more time and burn lots of fuel. If there was a possibility the ship was going to be allowed to dock in a certain window of time it would make sense to just keep sailing.

I see it like big rig trucks who don't want to stop at stop signs since the need a lot of energy and rowing through gears to get back up to speed.

Just my wild Saturday morning pre-coffee theory.

[EdwardDiego]

> Looking at that picture it is hard to imagine its path is caused by drifting. It is clearly moving in a circle

Eddies are a thing.

https://oceanservice.noaa.gov/facts/eddy.html

[duxup]

Considering how long it can take to get the engines started up on a big ship... drifting aimlessly seems a bit risky.

[rnd90]

Actually you would be surprised.

You can keep a ships main engines at various notice levels. For example:

Immediate Notice - Engines should be ready to start immediately from the bridge when required.

5 Minutes Notice - Usually

- Indicator cocks are open. - Fuel pumps are on. - Lube oil pumps are on.

Starting sequence : - Turn the engines on compressed air - Close indicator cocks - Engines ready to start

30 Minutes Notice - Usually - Indicator cocks are open - Fuel pumps are off - Lube oil pumps are off

Start sequence: - Start Lube oil pumps - Turn engines on turning gear for 10 minutes - Turn engines on compressed air - Turn fuels pumps on - Close indicator cocks - Engine ready to go

2 Hours:

You can do minor maintenance on the engines. For example, swapping out injectors. Engines are warm. Starting sequence is similar to the 30 minute starting sequence.

24 Hours:

Some larger maintenance can be done. Like changing a cylinder head.

48 Hours:

Engines can be completely cool. Jacket water drained. Usually for major maintenance. Like changing a cylinder liner.

These timings can vary between ships/companies. But generally they operate with similar ideas.

Source: I was a marine engineering officer working at sea for 5 years.

[duxup]

On a big freight ship like that do they usually operate at the shorter notice levels if they're not doing anything? That wouldn't seem to save a great deal.

I saw an old documentary following a big cargo ship who was anchored with others waiting to get in to the suez.

Another ship broke free of its anchor and was having trouble starting their engines and were drifting toward the ship in the documentary.

The captain was doing the math on how quickly they could start their engines to try to get out of the way and it would have to be an emergency start that they thought might result in damage.... particularly upsetting as this was their first voyage on a new ship, new engines... they didn't want to start them.

[camtarn]

Great comment! As always, delighted to find a variety of experience on HN.

[jacquesm]

Engine operation is independent of propulsion. You can have the engine idling and the screw in neutral.

[rnd90]

You can, but it's not always that simple :)

Some ships have a direct drive. So the moment the engines start, the prop shaft is turning. These ships will control thrust via Controlled Pitch Propellers. Basically the pitch of the propeller blades are controlled hydraulically and the steeper the pitch, the more the blades cut through the water and the more thrust generated. CPP systems allow ships to use shaft generators for electrical power at sea. The engine's revs are constant (to keep the electrical frequency the same) and power is changed via setting the propellers pitch.

Some ships have drive trains which let you clutch engines in and out, but you wouldn't run them for long periods of time de-clutched.

The engines do not like being run at an idle load for long periods of time (whether direct drive or clutched), you get loads of crud building up as they don't properly warm up. Also you are burning fuel and increasing their hours (planned maintenance is usually based around running hours). So you wouldn't generally drift and idle. You would shut the engines down and keep them on immediate notice.

A lot of modern ships are diesel electric. So the props are driven by large electric motors. So in this case, you can stop and start propulsion instantly (as long as you have enough generators running and connected to the switchboard)

[jacquesm]

I think 'screw in neutral' adequately addresses variable pitch screws.

The proper term in windmills and airplanes is 'feathered', I don't know what to call that state in a boat.

[fiter]

Is feathered the same? It seems like a feathered propeller is pitched with the blades flat surfaces oriented parallel to the forward direction, but on a CPP you'd set the flat surfaces of the blades oriented perpendicular to the forward direction to reduce the load on the spinning engine.

[jacquesm]

In a plane (where you are minimizing drag when an engine is out) you would put the blades such that the prop presents the minimum surface to the airstream, in a windmill you have a choice, you can put the blade in 'neutral' by picking one of two 90 degree offset orientations, one parallel to the apparent wind, one perpendicular to it. In either case the blades won't turn.

For safety purposes 'coarse' is not always the best position because if the wind is heavy enough it will have a lot of torque to work with, 'flat' is much easier to hold down with a brake.