Starting thrusters when vessel is moving at a high speed


#41

Let’s do it all again …

You’re the pilot $$ of a small 4000TEU. The docking order is to go starboard side alongside with a large 30ft clearance forward from a concrete knuckle and 30ft clearance aft from the bow of a moored container vessel. There’s a sucking eddy current below that knuckle, generated by an ebbing facing tide. The wind is blowing gently at 25 kts on the starboard quarter. It is cold outside in the middle of that night. You have a bow thruster so the only z-drive tug is fast on the portside in front of the accommodation, on the parallel body so to be able to push or pull. On the final approach, you have a +10° angle bow in to the concrete berth, the bulbous bow close by. The thruster is full to port. The tug is pulling full backward parallel to the fore & aft line. The rudder is hard to port, the engine slow ahead, kicking sometimes to half. The bulbous bow is still creeping in a little too fast but way fast according to the master, due to the pushing current on the port bow and the wind on starboard quarter.

Question: Where is the Pivot Point ?
Answer: I have no F%&?%# clue whatsoever but what I can tell you is that the Pivot Point starts to stink !!! :smiley: :smiley: :smiley:


#42

[QUOTE=Topsail;132172]Let’s do it all again …

You’re the pilot $$ of a small 4000TEU. The docking order is to go starboard side alongside with a large 30ft clearance forward from a concrete knuckle and 30ft clearance aft from the bow of a moored container vessel. There’s a sucking eddy current below that knuckle, generated by an ebbing facing tide. The wind is blowing gently at 25 kts on the starboard quarter. It is cold outside in the middle of that night. You have a bow thruster so the only z-drive tug is fast on the portside in front of the accommodation, on the parallel body so to be able to push or pull. On the final approach, you have a +10° angle bow in to the concrete berth, the bulbous bow close by. The thruster is full to port. The tug is pulling full backward parallel to the fore & aft line. The rudder is hard to port, the engine slow ahead, kicking sometimes to half. The bulbous bow is still creeping in a little too fast but way fast according to the master, due to the pushing current on the port bow and the wind on starboard quarter.

Question: Where is the Pivot Point ?
Answer: I have no F%&?%# clue whatsoever but what I can tell you is that the Pivot Point starts to stink !!! :smiley: :smiley: :D[/QUOTE]

why not use that boat all the way aft on the transom so as to have brakes if needed and work against the ships wheel to adjust headway, and provide effort on/off the dock. despite what the tug master says there is room back there in this situation until you’re nearly in position. Benefits/disadvantages? Curious to hear what you think, pivot point aside.


#43

I know that these z-drive tugs can do miracles through high professionalism from their captain. Maybe I’m an old fashion pilot but when I feel that there is not enough room for the tug to perform adequately, I make him fast on the opposite parallel body. I don’t like the tug being squeezed or crunched … between the stern and the bulbous bow of a moored vessel, in a crowdy 30ft gap with headlines hanging over head, stern lines sneaking in the water and into the prop wash. When there’s all kind of room at the stern, I have no objection whatsoever. I then let the pleasure to the tug’s captain. Team work.

[QUOTE=z-drive;132176]why not use that boat all the way aft on the transom so as to have brakes if needed and work against the ships wheel to adjust headway, and provide effort on/off the dock. despite what the tug master says there is room back there in this situation until you’re nearly in position. Benefits/disadvantages? Curious to hear what you think, pivot point aside.[/QUOTE]


#44

[QUOTE=z-drive;132176]why not use that boat all the way aft on the transom so as to have brakes if needed and work against the ships wheel to adjust headway, and provide effort on/off the dock. despite what the tug master says there is room back there in this situation until you’re nearly in position. Benefits/disadvantages? Curious to hear what you think, pivot point aside.[/QUOTE]

In Europe the pilots put tugs center line almost 100%. In Japan very rarely in other Asian ports it varies. In U.S. sometimes but not often. Pilots that handle a lot of tankers one center line aft more often then non-tanker ports, probably because that’s what everyone is used to.

.In some European ports the work is in tight quarters and they keep working even with relativity high wind speed. I’ve gone through the locks in Bremerhaven which doesn’t have much clearance in 35 + kts sustained using three huge tugs, one fwd center line and two aft center line and the forth smaller one for good luck Depending which berth you use some turns are very tight plus for some berths you back thorough the locks because not much room to turn around inside.

If there is not room the tugs just slack their lines and move to the side the last bit pushing in.

For the ship’s crew, tugs on the side recessed bitts is a lot easier. Running lines with the tug fast on the center line is a hassle, especially aft with an inexperienced crew. Sometimes we need to let the tug go while mooring or have them help a bit.

Eastbound starting in the southern Mediterranean, Egypt through the Middle East ports, India, through China ship’s lines, bad pilots and inept tug assist becomes more likely
One exception being Singapore
.


#45

[QUOTE=Kennebec Captain;132171]Yes, but Topsail was not asked to show written proof that the forces would be strong enough to veer the ship the wrong way, only to explain the physics of the phenomena, which he did.[/QUOTE]

No, he did not.

He was asked to describe the physics whereby the “suction” force would exceed the thrust force. Since the suction is a resultant of the speed of the vessel and the speed of the column of water exiting the thruster, at some point, usually described as around 3 or 4 knots, the water flow in and out of the thruster is inadequate to produce useable thrust and the thruster becomes ineffective. No thrust, no suction.

He was asked to cite a study or even provide a valid incident report wherein the ship reacted in opposition to the thruster. Not just a case of thruster not providing enough thrust to achieve the desired result, or one of the cases where the pilot did not understand the consequences of his actions as shown in the drawings, but an actual case of the thruster causing the bow to move in the opposite direction than selected.

It is much more plausible that a pilot would blame the thruster or some mysterious force for his screwup than simply admit to screwing up and getting on with it. If a mysterious force existed that was capable of reversing the action of a bow thruster command, the literature would be filled with examples, the NTSB, MAIB, CTSB, IACS, USCG, underwriters, and a host of other marine investigative bodies would have files stuffed to overflowing with cases where this phenomenon lead to even the most minor casualty. Even the toyboat fraternity would be talking about it.

All the smoke and mirrors about pivot points is just simple obfuscation. The pivot point is where the ship yaws around the forces imposed. We are talking about the source and amount of one of those forces.


#46

[QUOTE=Topsail;132198]I know that these z-drive tugs can do miracles through high professionalism from their captain. Maybe I’m an old fashion pilot but when I feel that there is not enough room for the tug to perform adequately, I make him fast on the opposite parallel body. I don’t like the tug being squeezed or crunched … between the stern and the bulbous bow of a moored vessel, in a crowdy 30ft gap with headlines hanging over head, stern lines sneaking in the water and into the prop wash. When there’s all kind of room at the stern, I have no objection whatsoever. I then let the pleasure to the tug’s captain. Team work.[/QUOTE]

Yes, but you’re the pilot, I’m not, no doubt there. Just from experience once nearly abeam the spot (100+ feet) the tug would usually have shortened their line with their bow up against the corner of the transom if not a few feet off. With a good winch you can work even more miracles but no issue backing effectively to 45 tons or so here in my experience as a boat guy, within 10-15 seconds of winch action I could give you full power astern… and some ships %100 up against. If I will be backing all the way to the berth I’ll just keep the line shortened up to 50’ or so outboard the ship on approach.

One reason, as explained to me by the pilots I have worked with over the years is that some ships, particularly certain classes of post panamax containerships cannot get an astern bell until under a much higher threshold of headway than normal. The nature of the harbor and berths requires them to carry a good deal of headway near the berth, and without the tug to help slow down they cannot get that backing bell in time to slow down. Once they get that astern bell then the tug is occasionally moved to the quarter just aft of the house especially with a weak thruster.

[QUOTE=Kennebec Captain;132215]In Europe the pilots put tugs center line almost 100%. In Japan very rarely in other Asian ports it varies. In U.S. sometimes but not often. Pilots that handle a lot of tankers one center line aft more often then non-tanker ports, probably because that’s what everyone is used to.

.In some European ports the work is in tight quarters and they keep working even with relativity high wind speed. I’ve gone through the locks in Bremerhaven which doesn’t have much clearance in 35 + kts sustained using three huge tugs, one fwd center line and two aft center line and the forth smaller one for good luck Depending which berth you use some turns are very tight plus for some berths you back thorough the locks because not much room to turn around inside.

For the ship’s crew, tugs on the side recessed bitts is a lot easier. Running lines with the tug fast on the center line is a hassle, especially aft with an inexperienced crew. Sometimes we need to let the tug go while mooring or have them help a bit.

.[/QUOTE]

I have been fortunate to work in a few places where we would put the line on the center a fair bit, not always but often enough to understand some of the limitations and advantages, at least from the boat side of things. What you describe is about what I understand which is good to see from a boat guy’s perspective. As far as the line being in the way for the crew on deck mooring, we often will let go the tug’s line once spring lines are out, breasts if possible. Very rarely is the line kept until all lines are fast. 1 in 100 times this is an issue for us and we can keep pinning the ship to the dock. A ship like yours we use one method inbound, another method outbound, all depends move to move and berth to berth here.


#47

[QUOTE=Steamer;132217]No, he did not.

He was asked to describe the physics whereby the “suction” force would exceed the thrust force. Since the suction is a resultant of the speed of the vessel and the speed of the column of water exiting the thruster, at some point, usually described as around 3 or 4 knots, the water flow in and out of the thruster is inadequate to produce useable thrust and the thruster becomes ineffective. No thrust, no suction.

He was asked to cite a study or even provide a valid incident report wherein the ship reacted in opposition to the thruster. Not just a case of thruster not providing enough thrust to achieve the desired result, or one of the cases where the pilot did not understand the consequences of his actions as shown in the drawings, but an actual case of the thruster causing the bow to move in the opposite direction than selected.

It is much more plausible that a pilot would blame the thruster or some mysterious force for his screwup than simply admit to screwing up and getting on with it. If a mysterious force existed that was capable of reversing the action of a bow thruster command, the literature would be filled with examples, the NTSB, MAIB, CTSB, IACS, USCG, underwriters, and a host of other marine investigative bodies would have files stuffed to overflowing with cases where this phenomenon lead to even the most minor casualty. Even the toyboat fraternity would be talking about it.

All the smoke and mirrors about pivot points is just simple obfuscation. The pivot point is where the ship yaws around the forces imposed. We are talking about the source and amount of one of those forces.[/QUOTE]

The point about the bow thruster was brought up to illustrate that the forces involved may act in ways that are counter-intuitive.

In any case when moving ahead much more then a couple knots bow thruster are ineffective. Any incident that occurs at more then 3 or 4 kts the bow thruster is not going to be a factor. That’s why nobody talks about it aside from curiously sake.


#48

[QUOTE=z-drive;132227]
I have been fortunate to work in a few places where we would put the line on the center a fair bit, not always but often enough to understand some of the limitations and advantages, at least from the boat side of things. What you describe is about what I understand which is good to see from a boat guy’s perspective. As far as the line being in the way for the crew on deck mooring, we often will let go the tug’s line once spring lines are out, breasts if possible. Very rarely is the line kept until all lines are fast. 1 in 100 times this is an issue for us and we can keep pinning the ship to the dock. A ship like yours we use one method inbound, another method outbound, all depends move to move and berth to berth here.[/QUOTE]

An American ship / crew / pilot / tugs is as good as it gets.

From my point of view I prefer slow, dumb moorings where there is plenty of time and room to make up the tugs, get stopped and then push straight in. Then have the tugs hold me while we tie up.

In cases where more control is needed, less space, higher environmental forces and so on everyone is relying more upon the skills of the crews, the tug driver and the pilot, less opportunity to correct errors. In this case my situational awareness is more narrowly focused on clearance and my own crew, verifying orders are carried out and I have to depend more on the pilot to maintain awareness of what the tugs are doing. It’s good when it goes right.


#49

When I joined the pilotage, I was trained to maneuver such type of vessel to a certain berth configuration, in different weather or current conditions, in a safe and approved manner. When you pass your final pilotage exams, you will have to answered tricky questions and demonstrate in details your local maneuvering knowledge and persuade a jury that is not acquired in advance. Answers must reflect the Standardize or By The Book Approach. When you start your career, you will effectively maneuver by the book. You cannot take any chance. But after 10 years of honest practice, you will gain much more flexibility. You will then refine certain approaches, by keeping in mind that speed kills and the possibility to be blame if you go too far out of The Book Approach. My own goal is to keep the control and maneuver the vessel herself to the maximum of her capabilities. So if the tug’s line part, I can keep control without panic. To reduce to the very minimum out of control lag time like main engine reverse, change of tug location. Do it right first but be ready to consider a plan B or C. To rectify the natural tendency of the vessel instead of forcing her. To take advantage and work with the elements to their fullest extent. To keep it as simple as possible and reduce to the minimum rudder, engine, communications and tug orders. To first assure the safety of the vessel and fellow partners.


#50

You could make a tug up alongside too, oh wait people are afraid of doing that it seems nowadays


#51

When starting tunnel thruster at high speed. This is assuming the thruster prop blades may already be turning or wind milling. On AC drives, trying to increase frequency from zero hz upward on a motor that is already turning can cause an overload condition to the ac drive. Causing drive to trip out. Possibly damage to drive, blow a few fuse or trip breakers, etc.

Some drive manufacturer suggest a feature call “fly catching” where the drive algorithm scan the motor for motor frequency and try to meet the start up output frequency with motor frequency. Thus minimising overload condition. This is a tricky feature to master.


#52

This topic very interesting to me.
May I asking some questions here?

How many type of Thrusters designs?
As my experienced Tunnels thruster(electric motor and CPP) and Azimuth Thruster retractable type (speed below 3 knots).
How many type are not state here?
Please, give more info.

Why they cannot start thruster at more than 6 knots?

Are they automatic engage the clutch or drive gear when start thruster? (Cause the overload feedback to circuits breaker)

Are they always engaged the clutch all the time?
What is different between finished thruster at speed below 6 knots and keeping system running at speed more than 6 knots? (control at neutral position)


#53

Old thread.


#55

Would jet-type thrusters such as OmniThruster or that whatever-gill work better at higher speeds? Or the maneuvering mode of an air bubbling system?


#56

well… I thought the question was prompted because someone considered using tunnel thruster to avoid a collision… possible i suppose and if a collision were imminent i’d run the daylights out of it since it’s going to be spaghetti anyway right? as for P or S? after reading some of this i’d push P for Port because i doubt any court is going to be convinced which would of been the right way to move it… especially if Steamer and Topsail were on the court !!! I was more intrigued by ‘windmilling’ props as I knew some ships tied up in current where the prob would rotate. No big deal? well, these props were hooked to big motors with independent lube systems and if the shaft wasn’t locked bearings would suffer eventually.
AND WHY is our category now the fourth one down?


#57

Should read the manufacturers manual prior to use. Lot of useful information on how and when to use the thrusters. Tunnel thrusters are pretty much useless above 5 or 6 knots, lowering a drop down or swing down above stated speed you can damage the thruster, once it locks into the locking plate you can,increase speed


#58

Lateral Resistance vs. Peripatetic Pivot Point is a brand new finding.

Actually it has been known about for decades in Europe. It is taught in the simulators and the manned models at Warsash.

One of the earliest instances of this were the disastorous PROBO vessels of the eighties, a step too far:

"As designed and as built, the ships had a “barge shaped” hull form with a V section bow and a swim ended stern.

It was found that the hatches did not seal reliably; the ship "worked at sea more than the relatively rigid hatch covers.

In the case of the KSEC ships, the buyers also objected to the steering characteristics; if helm was applied at speed the ship pivoted round a point between No 1 and No 2 hatches, refused to answer counter helm and continued to turn until she had swung through more than 180 degrees and had lost steerage way.

Consequently the buyers rejected the ships. "