For the seafarers, new stevedores, and general public (those that are interested at least) figuring out how many shifts to work a ship and how many cranes will be working per shift seems to be a mystery. We'll cover how a terminal makes the decisions of how many shifts are required to work a ship and how many cranes are required.
Move counts, averages, & productivity
One of the most important numbers that stevedores live by is their vessel productivity number. This number is how many container mover per hour they can perform. A move is taking a container from the ship to the dock or from the dock to the ship. For most ports, a standard move count to expect is 25 containers per hour per crane or gang, meaning every hour 25 containers will move off or on the ship.
As a gang works and ships sail, stevedore companies keep track of what the gangs and cranes were able to get accomplished in a certain amount of time. They average this out over a period of time across many ships, gangs, and seasons to determine their average number of moves they can expect. Stevedores also keep track of the lowest average and highest average for planning purposes (more of this later). These averages help stevedores keep enough cranes of the ship to finish them on time but not so gangs are without work.
There are two different move count averages, gross and net. A gross move count is purely the number of container moves performed per hour worked. Simply meaning if a crane performed 26 container moves in one hour and 26 container moves in another hour, the gross average would be 26 moves per hour.
Moves accomplished in a given time / Length of given time
The net move count is where things get change a little. Most terminals calculate their production hourly so they can anticipate what may get accomplished during the shift and what needs to be changes, as well as what they need to plan for the following shifts. Most hours, the crane works continuously with little or no interruptions. However, there are moments where the crane is not productive and terminal operators keep track of these non-productive times to calculate what is known as their "net move count". Let's say a crane breaks down for 30 minutes, between 0915 and 0945, and the crane operator is only able to accomplish 15 moves between the hours of 9am and 10am. The gross move count for the hour would be 15 moves but net net would be 30 moves. The net number is to determine the skill of the operator to determine how many moves can realistically be expected from an operator. Typically, only non-productive times (typically things outside of the terminals control) may be taken out to give an accurate net move count.
Moves accomplished in a given time / (Length of given time - non-productive down time)
Each terminals keeps a list of what they consider productive and not. To help keep math easier, terminals (and most of the maritime industry) keep track of time in tenths (0.1) of and hour - or six minute increments.
|Tenth of Hour||0.1||0.2||0.3||0.4||0.5||0.6||0.7||0.8||0.9||1.0|
|Minute of Hour||06||12||18||24||30||36||42||48||54||60|
Some terminals keep tabs on discharge vs load production and/or shift time productivity, where some just keep an overall number of terminal and crane productivity.
Looking at the ships move count
Now that the terminal knows what to expect per hour for a move count, they take a look at how many moves the ship will need to complete to sail. For this example, lets say the ship has 1250 moves to complete before they sail.
Moves are broken up into two categories, discharge and load. Discharge typically goes faster than loading because the crane operator only has to take the container off the ship and not carefully set the container down perfectly lined up with the container below it. For the example above, lets sat they re 643 containers/moves to discharge and 607 containers/moves to load for the total of 1250.
As we said earlier, some terminals keep a closer eye on discharge vs load production however, ships typically are relatively close to 50/50 discharge and load so utilizing an overall move count production figure to determine how many shifts and gangs they'll need. If there was a large difference between discharge numbers and load numbers then we'd think about looking more into the production difference in shifts but, for our purposes we'll stick with an overall move count average.
For the example of 1250 moves, we'll assume a gross average of 24.2 and net of 26.8. We'll need 2 shifts and 3 gangs on one shift and 4 on the other shift (total of 6 gangs) to complete this ship.
How did we get to that answer? The math is relatively simple:
Total move count / gross average = hours required
Hours required / shift length (typ. 8 hrs) = number of gangs required
1250 / 24.2 = 51.65 hours
51.65 hours / 8 hours = 6.45 gangs
Once we have the number of gangs required we can look at different gang scenarios. Let's say the ship is big enough and there is enough equipment on the terminals to operate with five cranes on the ship at a time, then there would be one shift with five gangs and another with two. Depending on how the equipment and ship layout is (combined with location of the container moves) will determine how many cranes you can have at one time.
If you notice there were 6.45 gangs required to complete the vessel assuming the move count average was achieved but the answer was seven gangs. Why would you order more gangs than required? As you can imagine, gangs/cranes are employed and paid for the entire shift, there are no partial shift gangs (there may be in theory but not in practice). If we only ordered six gangs and we achieved our average exactly, then we would be left with about 88 moves to complete but nobody to perform the work. Ensuring the work is complete requires an additional gang. This also provides an "out", which we'll cover in other posts, where if for whatever reason you fall below your average, there is enough people on the terminal to complete the work required in the timeframe the ship and shipping line needs the work performed. An extra gang covers you in the event something goes wrong, you have flexibility to get the work complete. An extra gang also gives you the ability to move containers around and refine your operational plan as needed.
There are some additional considerations that come into play like which shift type it is (first, second, or third shift), time of year, availability of labor (how many other ships are working that same shift), as well as time of year (vacations, holidays, etc.) where a terminal may decide to add more gangs or fewer.
Partial shifts are those where there is time at the start or end of the shift where no work if performed. This may occur for several reasons, the most common being waiting for the ship to arrive and be ready to work at the terminal, or there are no more containers to load or discharge. Terminal operators and ship lines typically do not voluntarily to run partial shifts. For both parties, partial shifts are expensive for no work performed.
Ships attempt to time their arrival (and be ready to work) at the start of a shift or even several hours before the shift. This eliminates the ship being billed for the terminal standing by with gangs ready to work and the terminal potentially being caught with more expense then they are billing for.
Terminals attempt to hire just enough gangs to keep the ship working up until the end of the shift for the same reason as above. If there is not enough containers for the terminal to move, then the ship is billed for the dead time as "no work provided", which is expensive as it is non-productive. Typically to avoid this, international shipping lines will request that the last X% of moves are empty containers, so the time is filled with productive moves (returning empty containers back home) and then the terminal cuts what ever is left at the end of the final shift as not to go into over time or bring in another shift.
The math behind determine how many shifts and gangs are required largely revolves around averages of recent ships and shifts hourly production figures. Subscribe to our posts to get more content like this delivered straight to your inbox.