When ordering astern Captains say " she is right handed" but always as an afterthought “usually”
The only trick I developed was that get a swing initiated one way and when going astern it usually carried on that way. Note the use of the word usually.
The only the I can say with certainty is that if you come off the pitch too quickly you will lose all directional control. Then it takes forever and full power ahead to regain it.
As far as the tug coming ahead with angle looking astern on the starboard bow as shown in that photo, that will 100% impart an astern (and athwartships) vector on a ship if you don’t account for it in some other way. Whether or not the tug has a line up is immaterial to whether an astern vector is imparted in this situation (although a line will keep the tug from sliding if you ask for a lot of angle). As long as the bow pudding sticks and the tug doesn’t slide, it’s going to push the bow around AND push the ship astern, all other forces ignored. A line WILL however allow, up to a certain hull speed, the tug the ability to hold itself up on a 90 more easily and effectively with less effect on the ship. So if you want the tug to be on a perfect 90 all the time it’s best to have him in a line.
When you have the assist boat work no line, it has to lay alongside until you ask it to push. The ships hull speed, wash, and the strength and duration of ahead bell ordered largely determine if the assist boat will achieve or maintain a 90 degree angle before you stop it again, at which point with no line up, it must flop alongside again unless the ship is almost totally stopped. Caveat, under 2 knots some modern tugs (and tug operators) can keep up with you in a walk, some can’t.
Some pilots ask for angle on the assist boats they want headway or sternway to happen, and sometimes they get it when they aren’t asking for it, when the tug operator isn’t diligent about staying on a 90 to the keel. (Not the hullplate!) It often doesn’t take much angle at all for an ahead or astern vector to develop when an assist boat is not on a good 90. When they work the stern rake or bow flare it is quite common for them to be off a 90 and push the ship ahead or astern without meaning to. Pilots know this and prepare for it.
If this is the picture we are talking about, that seems pretty close to impact - at this point the ship is doing 5-6 kts. Whatever small astern vector the tug is imparting not being at the 90 not going to matter much.
with 20/20 hindsight - I may have had him go aft of amidships at try and get me into the bank instead of the bridge -
But in reality in real time - i think it is all over by this point.
The question to ask is how long had the tug been pushing on the shoulder at the angled aspect. The one photo that I posted is not instantaneous.
I have gone back and revisited Sal’s video and taken this screenshot. I would suggest as soon as the tug shifted to the shoulder, she commenced imparting sternway.
This particular CPP system, on failure, defaults to the current pitch setting…….it doesn’t change and we know that the Cuauhtemoc sped up significantly. Current and wind were not major contributors.
Backing at 5-6 knots, there is no way a conventional twin screw tug could have stayed in shape at a 90 (with or without a headline).
The only thing that might have kept the tug in shape at a 90 at 5-6 knots would be a headline, And most importantly, a quarter line. Then only until: the line parted, the bitt pulled off, or the tug rolled over.
With the sailing ship at full astern, pushing on the bow only turned the stern toward the bridge and shortened the time to impact.
If the tug had had a headline and quarter line, and if it had been backing, the tug might have turned the bow of the sailing vessel toward the bridge and the stern away from the bridge.
With the ship moving astern at 5-6 knots, the tug pushing (probably with somewhere between 20 to 45 degrees of right rudder, the port engine full ahead, and the starboard engine probably backing to try to stay in shape) the tug was probably not very effective in pushing the bow to port.
Under these dynamic conditions the tug would have been adding little or nothing to the ship’s sternway.
If the tug had had a head line up, the thing to do would be to back full on both engines with rudders midships and let the tug flop alongside to slow or stop the ships sternway.
Perhaps the tug backing on a headline might have stopped the ship, and/or turned the stern of the ship toward the opposite bank, or outbound channel.
European style of ship assist. Both tugs have headlines up to the bow and stern of the ship. They dock the ship on the towlines without pushing on the hull.
Actually, it is centrelead aft and bow to shoulder. The forward tug has “half beam” effect and can alter its aspect to work the pivot point plus impart headway. The centrelead aft tug is both the steering and braking tug.
The fact that they are either ASD, rotor or Voith is a moot point…..we used to work a twin screw, conventional Pirate Class tug on a headline constantly and it towed from the stern hook.
It is reasonably apparent from the grainy photos that the Cuauhtemoc does not have a centrelead forward lead, therefore, the shoulder lead was the best option.
I ask the question as to why there were not two tugs on this job. You speak of customs……. I suspect cost.
There is a great variability from one tug to the next on how well flanking rudders work.
If there are twin flanking rudders, similar in size to the main rudders, ahead of each nozzle, then yes, they do a pretty good job.
If there is only one flanking rudder ahead of the propeller, then they may, or may not, accomplish much. Some flanking rudders are also pathetically small.
I’ve been on otherwise well designed and proven boats, where we’ve taken the flanking rudders off because they didn’t do much of anything.
How flanking rudder would perform while being towed ahead at 5-6 knots, I don’t know.
I am aware that Europeans used to dock ships on the tow line (and tow hook) with single screw tugs. Those tugs had the tow hooks placed much further forward (almost longitudinally amidships) than is possible on the typical present day American tug. (No tow hooks on American tugs either).
They probably chose to use only one tug because that was all that was needed (absent a totally unexpected and very low probability full astern CPP failure). Cost was probably another factor.
It would not surprise me if this sailing always uses two tugs from now on.
The hooks on our conventional twin screw tugs were dispensed with when we went from ship’s lines to tug lines at which point a remotely controlled winch was fitted on the aft deck allied with a high rating fairlead. They were then fully superseded by tractor tugs.
It was interesting to see that, post 9/11, the relevant NY authorities put a minimum of two tugs on all vessels.
We operate a CPP vessel. At the beginning and end of each voyage she maneuvers close to a bridge that must open for her to pass. They don’t use pilots or tugs.
The officers’ SOP for maneuvering is this:
A CPP system has an emergency control panel in the engineroom. If wheelhouse control is lost the maneuvering officer informs the ER. The CE takes over directional control in the engineroom, communicating with the wheelhouse via radio.
If this doesn’t solve the directional control failure there is a hydraulic directional control valve in the system, exactly the same as found in hydraulic steering systems. The CE inserts a screwdriver in the correct port, switching over the CPP direction.
That gives three different ways of directional control with the CPP.
The first question, of course, is whether it works to begin with. SOP is to change directional pitch several times ahead and astern before casting off lines. Not one cycle but at least three.
In maneuvering in areas like this the anchor is always backed out of the hawse, with a trusted AB or the second mate standing by at the windlass ready to drop it.
The key, our officers stress, is to anticipate that CPP control in the wheelhouse will fail at a critical time, and to have the departure checklist reflect this by specifying that the engineers have tested the switchover of control to the engineroom before maneuvering in places that will have you end up in a YouTube video.
no other way. I will keep my fingers crossed for You . Be brave .
