Milano Bridge allides with gantry crane in Busan today

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The two choices faced could be characterized as using speed to get away or slowing down and getting the ship under better control.

If they had chosen to slow down and get the ship under control with the tug assist then perhaps using the anchors would have been a good option. But it doesn’t look as if that was what they were trying to do.

Anchors wouldn’t have been my first choice either. With speed up around 8-9 knots approaching the turn into the basin (due to mechanical failure or whatever) I’d have been making that turn with the bow tug alongside facing forward and backing full. That would have made the turn tighter and kept them from setting down while slowing the ship down at the same time. The stern tug would have been in line backing hard too. But you can’t just do that and hope for the best. You have to make yourself do a loop of observe–orient–decide–act over and over again. Maybe the next time through the loop you see she is making the turn ok but still has too much speed so then you drop an anchor.

But I wasn’t there. Usually I wouldn’t second guess a pilot but in this case it’s almost like the pilot had a heart attack or something and wasn’t part of the picture.

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I agree on that approach. Most of the time I liked that bow tug up close.

The following is from the ‘Ship Maneuvering Technical Reference’.

Speed Control page 28, which is highly applicable in this case.

Incidents of failing to control a ship’s speed while entering harbour, with the vessel consequently colliding with the pier causing major damage to the pier, shore cranes, and the vessel itself, never cease.

Approximately 70% of incidents of damage to harbour facilities involve damage to piers and fenders, however most are due to mistakes in operation of the vessel.

Such mistakes in confined harbours with limited area available for maneuvering are due to the following:

(1) Inability to accurately determine the effects of external forces such as wind and tides.

(2) Mistakes in speed control and turning of the vessel while using engines and tugs.

IMG_5805

According to this table the Milano Bridge, which has a DWT of 146931 tons, needed 3 - 4 tugs. The engine power is sufficient: 38490 kW.

Also of interest is the item “Preventing Damage to Harbour Facilities” on pages 40 - 43. On page 49 it says:

It is necessary for the captain to plan the procedure for entry and exit in advance.

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That’s a good find.

My thinking here is this is more of a planning error than an error of execution. There are several factors here which may have put this shiphandling problem outside the pilots experience and seat of the pants intuition.

From my experience at least pilots in Pusan don’t do a real master/pilot exchange. Just sign the paper and get on with it.

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I counted only two tugs. If so that should have been indeed 3 or 4 with this kind of ship, lightly loaded and propeller partly out if the water. Normally speaking here the tug’s captain would use his ship transverse as a drogue chute to decelerate the ship. I don’t know how much bollard pull they have while going astern as can be seen on the videos.

How much power is being transferred given the propeller immersion?

Shown are submergence depths of / 0.0, 0.5, and 1.0. Here, h is the submergence depth from the free surface to the propeller shaft center and R is the radius of the propeller. With h/R 0.5 the propeller blade is half out of the water. We don’t know how much blade of the Milano Bridge is out of the water and that makes it hard to estimate the loss of thrust, but there is still a lot left.

It is interesting to read that a surface-piercing propeller is one of the most efficient propulsion systems for high-speed vessels. They can use a larger propeller size because it is not limited by the minimum blade tip clearance from the hull or the maximum vessel draft. Moreover, they can avoid cavitation damage because the propeller operates under ventilated conditions by drawing air from the free surface.

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Some good research here. I think the speed given is the maximum at landing on the wharf which is about a quarter of a knot. It sounds a bit too high for anything over 100,000 tonnes. I remember at Rotterdam back in the 70’s they had big dials on the Quay which gave the approach speed of the bow and stern as metres and decimal parts of metres per second.
The major ports in NZ equip the pilot with an electronic device that gives approach speeds and distance off independently of ship’s equipment and the display can be moved around the bridge wherever the pilot wants.

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I don’t know how to read that table. Presumably T is thrust and Q is torque. I don’t know what the n is.

If this table is applicable we could assume the Milano Bridge prop is about 1/4 out of the water what results does that give?

Google tells me that n is efficiency which is: Efficiency = 100% - Slip.

In this case it looks like its the third column divided by the forth column. ( 8th row: 0.259/0.314 = 0.824)

I think it is safe to interpolate this value which is half of the half blade distance, thus in between 1 and 0.789 which amounts to about 0.89 of thrust meaning that 89% of the full thrust is available at that moment.

The efficiency, generally indicated with the nabla sign η, is the quotient of thrust and torque.

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I was thinking that on the Milano the Bridge the blade was likely more than 1/4 out of the water so 1/4 would be h/R = 0.5.

From h/R = 1.0 at 2 rps thrust drops off from 0.944 to 0.789 which is -20.6%.

You mean that the interpolation is between .944, not 1, and 0.789. The remaining thrust is then a little bit less, about 87%.

I see now that the rpm of the ship is 76 and thus the rps 1.27. The slower the rpm or rps the more thrust so that is not a bad thing. Hard to tell the difference.

I’m saying that from looking at this:

image

That h/R = 0.5 or maybe less. Assume 0.5.

Don’t know what it’s called. The part fwd of the prop that holds the shaft can be seen:

image

MB closer to h/R = 0 than 0.5 possibly.

I don’t get it. Is the last photo of the Milano Bridge? Just dipping with the propeller blades in the water…

The top picture is the MB, the top of the shaft housing can be seen just above water level. It’s from the video taken by the crew member.

The photo of the ship with the blue paint is a photo of the same area but of some random ship.

A different somewhat crude approach. I measured on the photo the width of the ship. In my case it was 17.5 cm but that might be different on larger screens. Then I measured the top of the rudder to the waterline which was 1.2 cm. A bit difficult because of the wake. So the rudder and the prop as seen are 1.2/17.5 * 51 m ≈ 3.5 m above the waterline.

Normally the propeller’s tip is in line with the top of the rudder so then the part of the blade that is out of the water is also 3.5 m. For a ship of this size I estimated the propeller’s diameter at 9.6 m, could not find this value on the internet. Interpolating this as done earlier the efficiency is 84%, still not too bad considering.

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The 84 % assumes that efficient is max at h/R = 0. But the tip of the blade at the surface is not considered efficient. At least not in my experience.

We measured propeller immersion by the radius of the prop, not the diameter. The minimum required immersion was 0.7, that number being the distance the tip was submerged. For us it worked out to an aft draft of about 7.2 meters or thereabouts.

Using the h/R method minimum allowable submersion would be h/R = 1.35

I posted this before but here at the min drafts for the Panama Canal.

Here’s the min drafts for transit through the Panama Canal for a 200 meter ship.

Over 625′ (190.50 m) – 24′ (7.32 m) forward, 26′ (7.93 m) aft, TSW

We had a min draft fwd as well for bow thruster effectiveness.

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Company report that came with the chartlet noted 60% (looks like) immersion:

What went wrong screen shot