A good read: A Master’s Guide to Berthing - 2nd Edition
Many berthing accidents occur because the speed of approach is too high. The master should advise the pilot of the ship’s stopping distance and general manoeuvring characteristics, giving particular emphasis to speed, corresponding engine revolutions and to the critical range. When close to a dock, speed should be the minimum necessary to maintain control. Masters should plan ahead with the pilot on if, and how many, tugs are to be to be used.
Control while slowing
It can be difficult to reduce speed and maintain control. This is because reduction in propeller speed reduces water flow over the rudder and the rudder becomes less effective. The normal procedure for stopping is to put engines astern. However, when a propeller rotates astern, water ow over the rudder is broken and the ship will be less responsive to the helm. In addition, there is the disruptive effect of transverse thrust.
One unknown factor here from the master’s point of view is the tugs.
I recall going inside the locks at Zeebrugge a few years back when high-horsepower tugs started getting more common. After we cleared the locks the pilot goosed it and kept it up till fairly close to the dock. Twice I mentioned to the pilot about our speed as it seemed a little too fast to me. Second time he tells me “Don’t worry captain, the tug is 8000 hp, it will stop us”
Sure enough that tug, which as made up center line aft stopped us quicker then I’d ever seen before. We got stopped with room to spare.
Pusan tends to be a fast port in general wrt pilotage. They might have failed to adequately adjust for these much larger ship.
“Are you in a hurry captain?” That’s what the pilot asks when they board. Or so I’ve been told.
If the error in speeds was plotted would it be a Rayleigh distribution?
Say 1 is the perfect speed and navigators want to err on the side of safety by this graph the number of ships coming in twice too fast is more than zero. In practice the x-axis would have to be adjusted but the general shape of the curve seems right.
Rayleigh distribution is familiar to mariners from the distribution of wave heights.
Not arguing here, but intuition of the Mate/Master standing the watch is the cornerstone of safe navigation…if in doubt you must act. Drilled into us since day one. One could argue that if you think you may be going too fast, you are, since Safe Speed is up to the interpretation of the operator who considers all prevailing circumstances and conditions.
A piece of advice was given to me by a pilot a lifetime ago, about making landings:
If it’s a difficult landing, make it twice. First, make it a considerable distance from the dock. Say, 200-feet. Same orientation as you would at the dock. With this “landing" you test everything: astern propulsion, thrusters, etc. You orientate your mind to the effect of wind and current. Then you turn around and make the actual landing, which he specified as always being parallel to the dock but several yards from it.
With modifications, we do this for the first of the many landings in a given voyage. For some reason the first landing after an ocean crossing tends to be the one that goes wrong, and needs the most care.
When I read about the Milano Bridge incident, I wondered if the procedure above is a local harbor practice, or is it followed in other places?
Another example of the limits of intuition is entering a set of locks with the max allowable beam, for example the original locks at Panama and elsewhere.
Unless the captain is familiar; based on distance to the gates ahead and the vessel speed when entering the locks it’s going to seem too fast. It’s going to seem that a big backing bell is going to be needed to avoid catastrophe. However because the water in the locks is being forced out (and the locomotives) the ship is usually stopped without using an astern bell at all.
Of course, but what principle is at play here? Maintain safety margins and reserve capacity.
In actual port operations if two 8000 hp tugs are used to pull a ship off the dock it can be expected the operation is going to go quicker then if a single 1000 hp tug is used. Quicker ops but higher safety margins.