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Old 19-06-2017, 05:40   #1
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Ship Turning Circle Diameter

Elsewhere on a different thread a commentor stated with regard to large cargo ships that "their rate of turn is usually between 1 and 3 degrees per minute".

This is simply not true.

While the distances are large compared to what we encounter maneuvering yachts, the speeds are fast, so all things are relative. A large cargo ship traveling at 25 knots can alter course 90 degrees in about two minutes during which time it might travel close to a mile. Depending on a number of variables including load and size of the rudder this time can be more or less.

Turning circle diameter for a Container ship

No, I haven't ever driven a ship but I provide diagrams, photos, and a video of an Arleigh Burke Class destroyer making a tight turn for your reference. As expected the destroyer is much more maneuverable than a cargo ship. In the video the destroyer can be seen completing the intitial 90 course alteration in about 15 seconds.

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Old 19-06-2017, 05:45   #2
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Re: Ship Turning Circle Diameter

Comparing an Arleigh-Burke destroyer to a loaded cargo ship is an exercise in futility.
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Old 19-06-2017, 06:34   #3
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Re: Ship Turning Circle Diameter

for reference, update, possible correction
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The red X on this plot was the initial navy report time of the incident. But the Japanese are now saying (after I guess looking at the ship logs) that they believe the initial collision was actually at the black X.

The 90 degree starboard turn there was their attempt to maneuver/avoid the collision.

Then the long dog leg was the ship getting its act together and returning to see if they could offer any help.

So related to this thread . . . you can see two turns on this track - the pretty sharp 90 degree starboard emergency one, and then slower end of dog legs one.
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Old 19-06-2017, 06:40   #4
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Re: Ship Turning Circle Diameter

https://www.nytimes.com/2017/06/18/w...T.nav=top-news
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Old 19-06-2017, 06:56   #5
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Re: Ship Turning Circle Diameter

Quote:
Originally Posted by Delancey View Post
Elsewhere on a different thread a commentor stated with regard to large cargo ships that "their rate of turn is usually between 1 and 3 degrees per minute".

This is simply not true.

While the distances are large compared to what we encounter maneuvering yachts, the speeds are fast, so all things are relative. A large cargo ship traveling at 25 knots can alter course 90 degrees in about two minutes during which time it might travel close to a mile. Depending on a number of variables including load and size of the rudder this time can be more or less.

Turning circle diameter for a Container ship

No, I haven't ever driven a ship but I provide diagrams, photos, and a video of an Arleigh Burke Class destroyer making a tight turn for your reference. As expected the destroyer is much more maneuverable than a cargo ship. In the video the destroyer can be seen completing the intitial 90 course alteration in about 15 seconds.

Thank you for posting this.

People have the most remarkable misconceptions about the maneuverability of ships, and these misconceptions lead to huge errors in understanding collision avoidance.

According to Tupper & Rawson, Basic Ship Theory, typical rates of turn for merchant vessels are 0.5 to 1.0 degrees per second, whereas 1.5 degrees per second can be expected in some kinds of ships, and some naval vessels achieve 3 degrees per second. These are PER SECOND.

So a 90 degree turn should take no more than 3 minutes, and might be much less.

The EFFECT of a turn is multiplied by speed. So a ship travelling at 15 knots and turning at 0.5 or 1.0 degrees per second, will have great power to avoid some obstacle -- that is, to create a safe CPA out of a 0 CPA -- much greater than a sailboat travelling at 5 or 6 knots except at the very shortest of distances.
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Old 19-06-2017, 07:01   #6
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Re: Ship Turning Circle Diameter

We used to do man overboard drills on the tankers I sailed on. At normal speed of 15-16 knots the ship could do a u-turn to a reciprocal coarse in 2-3 ship lengths. The problem was being afraid to put the rudder hard over at full speed as the forces on the rudder were tremendous. When I had to test steering gear prior to arrival we would only turn the rudder 10 degrees port and starboard, this was during testing of the astern turbine or reversing the main engine if diesel. Think of a rudder the size of the proverbial barn door.
When I sailed on UNREP tankers the tincans would be lined up like cars at the gas station to take on fuel. They would come in for a quick squirt of DFM and a pallet of groceries and be gone in under 10 minutes as the next one in line moved into position to take it's place. They would move out so fast some times throwing a rooster tail and heeling over so far it looked like they would lay over on their side.
This was always entertaining to us. Once a destroyer came in so fast the momentum carried it right on past our stb side and they lost their place in line and the next one in line snuck in and took it's place.
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Old 19-06-2017, 07:12   #7
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Re: Ship Turning Circle Diameter

But which track is this? Of the navy ship or of the cargo one?

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Old 19-06-2017, 08:01   #8
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Re: Ship Turning Circle Diameter

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Originally Posted by barnakiel View Post
But which track is this? Of the navy ship or of the cargo one?

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Cargo ship.
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Old 19-06-2017, 08:08   #9
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Re: Ship Turning Circle Diameter

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Originally Posted by Aaron42 View Post
Comparing an Arleigh-Burke destroyer to a loaded cargo ship is an exercise in futility.
You're missing the point. This collision should have never happened.
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Old 19-06-2017, 10:57   #10
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Re: Ship Turning Circle Diameter

If you refer back to the Melbourne/Voyager report ( linked in the other thread ) you will see that even though still some distance from the Carrier when the bridge team on Voyager realized it was all turning to custard it was already to late and any action by either or both ships was going to be futile.

One thing to consider is the time and distance from the 'wheel over' point until the ship actually starts to turn... and as the 'pivot point' is typically 2/3rds from frd the stern is going to kick out...i.e. you alter to starboard the stern is going to move to port of the original line of advance.

Moving right along... my first day job as junior of two watchkeepers 51 years ago was on a 37,000 grt 23 knot passenger liner..... you never used more than 5* of rudder at sea speed due to the effect on passengers ( in the scuppers with broken bits ) and the catering staff ( all their - broken - china in the scuppers along with the passengers).

My last day job was on an 18,000grt 18 knot ro-ro with twin Becker rudders https://itstillruns.com/use-becker-rudder-11404350.html
and there you never used more than 2 or 3 degrees of rudder... much more and you would be dealing with a major cargo shift ( ro-ro includes trailers and stuff).. and the caterers.

So yes many big ships can turn very rapidly if they need to...
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Old 20-06-2017, 07:51   #11
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Re: Ship Turning Circle Diameter

So, what happened to the AIS trail of the other one? The navy one? Using AIS is below their honour?

Just askin'. I remember sailing in Australia where their navy ship slipped by on a moonless night, NO AIS on either.

Another one came dangerously close (less than 1 cable) 'just to have a look at you' in international waters, shading ALL wind from our wee sailing craft. Top professionalism again. Aus navy again.

Navy can be cocksure to the point of collapse.

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Old 20-06-2017, 11:34   #12
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Re: Ship Turning Circle Diameter

"You're missing the point. This collision should have never happened."
What else is new? Wasn't it just five years ago that a USN minesweeper ran so hard aground in a protected area that it finally had to be cut up and lifted out a year later?
When and if the Nooze ever bothers with the followup after the formal enquiries, I'd give you odds that:
1) There's a lot of background clutter (shore lights, etc.) in the area, to confuse watchkeepers
2) The USN vessel may have been playing black-out exercises and not showing normal running lights
3) Watchkeepers on both vessels were inexperienced or distracted

All the usual things that lead to collisions at sea.

I'd expect the container ship to be "dead at the switch", i.e. they're often not the most critically attentive mariners. But the USN? In this day and age, they damn well should have been paying attention to anything entering their security perimeter, no matter what kind of games they were engaged in.

On turning circles: I once had the chance to take a shift on the helm of a converted 110' water lighter that was being used as a research vessel. "Wheeee!" You could spin the wheel full cycle from left full rudder to right, and still count thirty seconds before the bow even began to move across. And then of course, once it got moving...No brakes, either!

For what it was, it had been built well enough, originally. But big cargo ships and container ships aren't built for combat maneuvers. No one really wants or needs them to do ballet, much less water polo. Doesn't really matter, these incidents all come back to the story of "We're a lighthouse and we advise YOU to change course."
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Old 20-06-2017, 14:26   #13
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Re: Ship Turning Circle Diameter

Quote:
Originally Posted by Delancey View Post
You're missing the point. This collision should have never happened.
No car should ever crash. No plane should ever fall out of the sky. No train should ever jump the tracks, etc.

The actual point is that ship happens.

But, NOBODY yet knows why this happened. That will take an investigation to figure out not keyboard cowboys.

Until then it's all opinion and make believe.
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Old 20-06-2017, 15:04   #14
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Re: Ship Turning Circle Diameter

"ship happens."
Strange, but sailors have a very similar saying.(G)

SOMEONE out there knows very well how this happened. Whether it was a lookout on the destroyer, who knows s/he fell asleep, or a radar officer who was afraid to interrupt whoever was on the helm, or a Philippino merchant sailor, whose family were taken captive by Jihadis, so he had no choice but to ram the first USN vessel he saw. Be creative, pick any one.

Someone knows. They're probably very scared and upset right now and not talking. And no one else is going to comment until the courts of enquiry have finished their processes.

Apparently nothing is happening until the Japanese coast guard and the USN decide who has jurisdiction. The USN, because it is their vessel. Or the Japanese, because it is their sovereign waters.
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Old 20-06-2017, 15:08   #15
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Re: Ship Turning Circle Diameter

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Originally Posted by hellosailor View Post

Apparently nothing is happening until the Japanese coast guard and the USN decide who has jurisdiction. The USN, because it is their vessel. Or the Japanese, because it is their sovereign waters.
That is certainly one of the reasons I had in mind.
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