For narrow passages, the exact compass bearing of the channel is known. The ship’s compasses ought to be checked thoroughly before approach. In approaching the channel, there will usually be what are called leading lines or lights above or behind the channel. These are two lights placed in a line so that as long as the two marks are one over the top of the other you know for sure the boat is on the right line and as long as you keep your ship pointed at the marks you know you’re heading in the exact right direction.
Once you’re on the right line headed in the exact right direction it’s only a matter of keeping your exact course, which can be maintained by an experienced helmsman.
For large ships two local Greek pilots are needed, relegating the captain to the role of a somewhat anxious bystander. One of the pilots takes the wheel, while the other runs from port to starboard calling instructions and communicates with the tug in front.
The speed in the canal seems to be 4 knots, 5 max. There must be a bank cushion effect at both sides but I have no idea how this will affect the steering.
If that’s the Corinth Canal, I took my 35m sailing ship through in 1992. No pilot, but there was a pilot on the cruise ship astern of me. I was half a mile ahead and doing about 5-6 knots and was instructed by him to go faster presumably for the cruise ship to get the self centring canal effect. I got up to about 8 knots. I got no such effect in a much smaller ship and just steered to stay in the middle.
I suppose that’s caused by the banking cushion effect.
Just the terminology I was trained with. Same thing, I suspect.
An interesting behavior I was unaware of; I needed some brainwork…
On a ship advancing along a nearby bank, her bow is pushed away from the bank, while the stern is pushed to the bank; the lateral forces being increased with speed, and lowered with increased distance to the bank.
In an almost perfect straight canal, with a rectangular cross-section and similar banks, as the Corinth Canal seems to be:
The bow is pushed away from both banks and finds a stable equilibrium on the centerline of the canal.
The stern is in an unstable equilibrium on the canal’s centerline. As soon as a slight movement out of the centerline begins, the stern is pushed towards the nearer bank. A self-reinforcing movement, until the stern hits the bank.
The tied up tug on the bow seems not to really tow the ship, but only corrects lateral movements of the bow, due to small disparities between the two banks.
The ship’s rudder does the crucial work, with reinforced forces from the propeller wash.
The slightest stern walk must immediately be corrected.
Could my understanding be close to reality?
Passage here is similar to entering a set of locks. Typically courses are not steered instead the pilot will control the bow using the tug while rudder commands will be used to keep the stern off the wall.
Not quite as I understand it. And, as I said, I had to steer as my ship was too small to create the self centring canal effect (which we were taught in naval navigation but never got to see - until this).
You seem to understand that the ship’s bow will be pushed off each bank thus centring the ship.
Along each side the pressure is low as water speed is increased (as it does under the keel as well causing squat). There’s equal suction along the length of both sides. A pressure wave builds at the stern as well when water speed slows.
All pressures tend to centre the ship in a tightly constrained canal as long as the speed is maintained. My understanding is that the rudder should be kept amidships or minimal movement only. The canal guides the ship and the water pressures and suctions keep the ship in the middle and clear of both sides.
The pilots would be experienced as to these effects and know what speed produces the ideal effects for different ships. I suspect the tug is essential to guiding the bow into the canal and to simply maintain tension during transit to be instantly ready to tow the ship and maintain essential speed in case of main propulsion failure.
My knowledge is largely theoretical (from my training) and from a quick verbal briefing by the pilot in the ship following me. He needed to go faster, or was going at his desired speed and needed me to keep my distance ahead.
The big difference is that sufficient, constant speed is maintained in the canal, but locks require slow speed and stopping.
Like here?? Tight fit and no reliance on speed, or pressure zone by any name:
Netherlands-flagged, 2010 built, motortanker ‘VINOTRA 10’, 11.571 DWT, beam 22,8 meters, entering Hansweert Locks with 24,0 meters beam, from Antwerp, destination Rotterdam. Photo : Alexander Hoogstrate. ©
In the video the tug can be seen adjusting the bow position, one side then the other.
What ever forces are requiring adjustment forward are going to exist aft as well. You almost said the same thing here:
the rudder should be kept amidships or minimal movement only.
When an adjustment is required to the stern it’s minimal as you’ve said. A typically rudder command would be stbd (port) five or ten, held for a few seconds then back to amidships.
Slowing down and stopping is controlled by the tug made up center line aft.
Done the same way leaving the locks when the ship is accelerating.
That is 0,6 m free at each side. The cruise ship in the Corinth canal has 0.7 m at some points. The problem with the latter is that when it touches the rocky wall it will result in some real damage to the ship. I would be surprised if the insurers would be willing to pay for such damage.
With that beam this motor tanker would not fit in the canal which is 21.4 m wide at the base.
The canal has been closed to maritime traffic since January 2021 due to damage caused by landslides, making the passage dangerous. Maintenance and repairs are currently underway however no date has yet been given as to when it will be back up and running.
The initial inspections are expected to be completed in September. Then the construction for the project will go up for bid, and the preliminary works on the sides of the canal will begin subsequently.
Look at the entrance to that lock, it’s shaped like a giant funnel. The barge could just lay the bow against the lee side then slide ahead - or various versions of that.
Good view of the turbulences on both sides of the hull caused by the water pushed away by the displacement of the ship. I see a row of red objects at both sides (fenders ?) up the the beginning of the canal.
Looks like they are using a tug both forward and aft. I didn’t see a view aft in the video in the OP but seems likely, or at least possible they were using a tug aft that time as well.
I don’t recall off hand seeing a ship assist job like this with a single tug forward, usually if there is a single tug it’s aft.
They aren’t fenders. They are lights lower down the cliff face for night transits. You can see the red light of the closest one reflected in the water directly below it.
I don’t think the craft aft is a tug attached to the ship. It’s small and too far back. I’ve done a quick look at online images of ships in the canal and only one passenger ship used a tug aft out of many examples. The towing tug is always connected by two lines - one to each side of the bow of the ship such that they are as far apart as possible and any steering the tug does by moving left or right is immediately effective. Quite large cargo ships in the images have no tugs.
The image’s pixels are too few to see details.
The ‘after tug’ may look like the ‘front one’… or not!
Couldn’t it be a tug on a very long line for an emergency stop of the ship?
Far behind the troubled waters off the ship’s stern; where the water volume of the ship’s displacement must invade the centerline waters?
A not thread related equipment of the canal is interesting:
On both entries to the canal are ’submersible road bridges’ at street level.
The permitted air draft is 0.5 meter, not enough for the children’s inflatable beach flamingos.
When ships or boats need to pass, the bridges are lowered into the water, to guarantee the water depth of 8 meters.