P&O and Mallorca - repercussions of weather elsewhere

[Kelpie]

Am I right in thinking that many ports now require ships to hook up to mains power (I know it isn't a 13amp plug ) and stop their engines to reduce pollution?

If so, starting up is going to take a bit longer than a few seconds preheat and turn the key, so engines may not be available in time.

I'm no expert but I'm pretty confident that on ships of this size, propulsion and electrical power are handled by different engines.
They don't have one big engine and an enormous 1-2-both switch in there.

 

[Tranona]

The drive is electric through pods. It is actually one big hotel with a diesel generator to power everything.

 

[dunedin]

I'm no expert but I'm pretty confident that on ships of this size, propulsion and electrical power are handled by different engines.
They don't have one big engine and an enormous 1-2-both switch in there.

I am also no expert …. but thought most cruise ships have such huge “hotel” power demands that they have lots of large generators running 24x7 and the propulsion is electric (in principle like a diesel electric train, but MUCH bigger and very different drive mechanisms).
The people with real knowledge will be along shortly.

The talk of using tugs in strong winds is fine up to a point - but over a certain point I don’t think they have enough grip in the water to make enough difference. A much smaller ship broke free in the Clyde in a severe storm and I think they could only stabilise it slightly with tugs and took more than a day and abated winds before the tugs could push it back to windward onto the berth.

 

[RunAgroundHard]

The vessel will have 4 to 8 diesel generators. There will be a power management system that brings on line engines as required, automatically. Likely there will be a degree of redundancy for steering and propulsion, typically arranged either in 4 engine rooms with two engines each, or 3 engine rooms with 2 engines each. The vessel likely can function fully with any engine room shut down, for whatever reason. Likely no rudders just azimuthal, variable speed thrusters. Variable pitch tends not to get used these days. The thrusters likely are variable frequency drives, powered by a pair of engines and electric motors. There will be separate bus ties for each engine, thruster set, configured to operate with open or closed bus ie one big ring main, or individual ring main per thruster or thruster pairs. Going in a straight line, all breakers will be closed, all engines operating at the best fuel consumption, some shut down. If current or wind gets up, the PMS will decide which engines to start. When in a critical manoeuvre, or some failure risk, the breakers are open, isolating each set of motors from each other. There will be no separate hotel power system, just less engines running.

 

[AntarcticPilot]

The vessel will have 4 to 8 diesel generators. There will be a power management system that brings on line engines as required, automatically. Likely there will be a degree of redundancy for steering and propulsion, typically arranged either in 4 engine rooms with two engines each, or 3 engine rooms with 2 engines each. The vessel likely can function fully with any engine room shut down, for whatever reason. Likely no rudders just azimuthal, variable speed thrusters. Variable pitch tends not to get used these days. The thrusters likely are variable frequency drives, powered by a pair of engines and electric motors. There will be separate bus ties for each engine, thruster set, configured to operate with open or closed bus ie one big ring main, or individual ring main per thruster or thruster pairs. Going in a straight line, all breakers will be closed, all engines operating at the best fuel consumption, some shut down. If current or wind gets up, the PMS will decide which engines to start. When in a critical manoeuvre, or some failure risk, the breakers are open, isolating each set of motors from each other. There will be no separate hotel power system, just less engines running.

A friend of mine was appointed as Third Officer of a Cruise ship last year - she's in the throes of exams for Second Officer. All her cadet time was on freighters; she was "fortunate"(!) to be at sea when Covid struck, so did a LOT of sea time in a relatively short period because she couldn't get off the ship! But when appointed to the Cruise ship, she had to be qualified for the use of Thruster pods (also emergency crowd management - I think firing pistols as in Titanic is regarded as unacceptable these days!), and for some reason (I think she needed help with some English) I saw some of the material. Operating with thrusters is NOT like the bow thrusters many yachts have! All sorts of minute detail about does and don'ts; I won't try and give detail as I'd either get it wrong or be teaching Granny to suck eggs, but there are MANY scenarios where doing it wrong can damage the thrusters or the ship. But the point is that operating thrusters isn't as straightforward as we amateurs might think.

 

[Bodach na mara]

Regarding shore power for cruise ships I read recently that the port of Southampton has only 2 shore power delivery systems, each of which is powered from a sub station on the grid. But such is the demand that only one sub station may be active at any time. As I understand that it means that only one ship in the port can have shore power at a time.

 

[Neeves]

Dyneema mooring lines? Surely not. I was once rafted on by a Dutch boat that used a retired dyneema halyard as springs. In very settled conditions we were together for less than an hour before I gave in and relocated for fear my cleats were going to part company from the deck.

Nylon, or elastic mooring lines are now commonly, or exclusively, banned. Men have been killed when they fail.

As far as I am aware all mooring lines (there might be exceptions) are dyneeema. The idea is to keep the vessel stationary. If there was any elasticity the shore facilities, as simple as gang planks, would be moving back and forwards. I assume there is a system to account for large tides. I have wondered who makes the mooring line splices, which seem quite short, and are any of the splices tested. In the current case, and those previous, the actual failure of the mooring lines is not defined, does the splice fail or do the lines snap


In terms of drives - there are changes to come - many ports will or are going to ban use of 'diesel' engines, think Venice, Barcelona and all of Norway, and a green alternative will need to be introduced ...... quickly. One redeeming feature of very large cruise ships is that they are now so large the ports that they can actually visit is restricted - they are simply too big.

Jonathan

 

[RunAgroundHard]

This is a thruster (I have never heard them called pods on a drillship or semi submersibles). My eye level is at the line of anodes. They stick out under the hull. They are removed in water, by divers. In the hull there is a vertical shaft tunnel that rises above the water line, and three rams that pull the thruster up into the seal area. Once the bolts are released the hydraucls lower the thruster and then a rigging arrangement is used to move them sideways and onto barge. A domed cap is then fitted inside to seal the hull again. The seal is about a 1" diameter elastomer O ring. This is one of 6 x 5,500 kW, Rolls Royce thrusters, powered by 6 x 8000kW engines connected to 6 x 7400kW generators. The prop shaft is fitted where the red cap is, and is directly coupled to the electric motor. Each side of the red cap are the hydraulic motors that rotate the thruster. I may be wrong, but only one hydraulic motor is required to rotate the thruster, which is required for the redundancy classification by the vessel certifying authority.

 

[Bodach na mara]

In reply to Neeves, there is no such thing as an inelastic material other than a plastic one. Think of Hooke's law and Young's modulus. Materials are classified as inelastic if they permanently distort under load.

 

[Stemar]

In a strictly scientific sense, that's true, but in a practical sense, it's reasonable to think of nylon laid rope as elastic (low modulus of elasticity) and Dyneema (high modulus) as inelastic.

I get why you don't want elastic ropes on a big ship, and why I absolutely want them on my boat. My lines are very strong in relation to the mass of my boat - one is strong enough to lift her, but no rope is strong in relation to the mass of a big ship. Out of interest, where's the changeover point?

 

[Neeves]

Mooring line breakage on large commercial ships is not uncommon. For those that are interested this is a short description of how 300+m ship might be moored and the mooring lines used.

The article describes how one line failed, causing injury, and why.

https://safety4sea.com/cm-case-study-mooring-line-failure-onboard/

The article is not long.


On a separate note I had thought, expected, that if the P&O ship Britannia broke its moorings, so all lines failed, then yachts moored or anchored nearby, plus or minus 20nm, would have suffered a rash of incidents. Oddly there have been no reports.

Jonathan

 

[Clancy Moped]

Mooring line breakage on large commercial ships is not uncommon. For those that are interested this is a short description of how 300+m ship might be moored and the mooring lines used.

The article describes how one line failed, causing injury, and why.

https://safety4sea.com/cm-case-study-mooring-line-failure-onboard/

The article is not long.


On a separate note I had thought, expected, that if the P&O ship Britannia broke its moorings, so all lines failed, then yachts moored or anchored nearby, plus or minus 20nm, would have suffered a rash of incidents. Oddly there have been no reports.

Jonathan

Photo gallery: The storm that battered Mallorca on Sunday

 

[Clancy Moped]

This weekend is going to be another grim one.

​

 

[Stemar]

On a separate note I had thought, expected, that if the P&O ship Britannia broke its moorings, so all lines failed, then yachts moored or anchored nearby, plus or minus 20nm, would have suffered a rash of incidents. Oddly there have been no reports.

Jonathan

Could it be because smaller vessels' lines are very strong in relation to the weight and windage of the boat? Having said that, Clancy's photo gallery does show a few boat having a seriously bad day.

Most lines used for mooring yachts have a breaking strain close to or above the weight of the boat, the ones in the article you linked to said the lines had a breaking strain of 137 tonnes for a ship weighing, maybe 100,000 tones. I know windage is more important than weight, but the Britannia has a HUGE windage for its weight. which isn't inconsiderable at nearly 120,000 tones

Also, while I appreciate the dangers of low modulus lines when they do break, a high modulus line is subjected to more stress when the ship surges and jerks the line.

 

[Neeves]

Could it be because smaller vessels' lines are very strong in relation to the weight and windage of the boat? Having said that, Clancy's photo gallery does show a few boat having a seriously bad day.

Most lines used for mooring yachts have a breaking strain close to or above the weight of the boat, the ones in the article you linked to said the lines had a breaking strain of 137 tonnes for a ship weighing, maybe 100,000 tones. I know windage is more important than weight, but the Britannia has a HUGE windage for its weight. which isn't inconsiderable at nearly 120,000 tones

Also, while I appreciate the dangers of low modulus lines when they do break, a high modulus line is subjected to more stress when the ship surges and jerks the line.

The windage of a cruise whip is not much different to that of a full container ship or a car/vehicle carrier. Cruise ships are not 'that' different. Commercial docks tend to be less exposed (piles of containers, big warehouses) than some facilities used by cruise ships and maybe cruise ships are thus more prone - though google searches do indicate line failure occurs on ships other than cruise ships.

I have been told, anecdotally, the American navy bans the use of nylon as mooring lines. This is an ambiguous statement - they have different ships of very different sizes and the ban, if its true, may refer to specific circumstances.

The lines in the article are, or were, 137t and the specific ship carried and used 22 of them (still not quite enough to lift it ). But if you were to replace those lines with nylon, also of 137t, the ability to handle the nylon lines would be 'difficult' as they would be huge. Making the end splice would be a real challenge. You cannot double up on lines on commercial ships as the don't have the equipment to handle, say, 44, lines simultaneously.

I might be simple but I did not quite understand the failure mechanism described in the article. They mentioned evidence of fusion in the individual strands but did not define whether this occurred in a previous 'event' or was a result of the line failing. I was interested that they identified 'kinks' in the strands that seriously reduced strength - this might occur in any rope (using the same base cordage) - and ropes we use?

If you do a google search and broaden the parameters it seems mooring lines , or failure of, has caught the attention of authorities and they appear to be looking at the practice a lot more seriously than in the past - part motivated by the use of newer cordage (I assume dyneema). Interesting guy the article I linked to indicted that the injuries sustained were as a result of whiplash - despite the minimal amount of elasticity.

Jonathan

 

[Stemar]

On that mooring plane you've got 2 or 3 lines for each mooring point. It's only going to take a slight difference of tension to make one of those lines take almost all the strain that should be shared by, say, the 3 stern lines. In this case though, it seems the line broke at well under its design strength.

In the case of the Britannia, assuming I've got the maths right, which is by no means certain, 30 knots gives a pressure of around 17.6kg/sq m. The ship's 330m long and has about 60m air draft, fudging to allow for funnels and stuff, call it 300 x 50. That's a force of 264 tonnes, which shouldn't be anywhere near enough to break the lines, but double the sustained wind in a gust, and you've got 17.6kg/sq m, over 1000 tonnes across the ship, which is getting near the load needed to break the lines. Add a bit of unequal tension and a bit of surge causing the lines to snub, and bang! No wonder big ships prefer to sit out a storm at sea.

 

[AntarcticPilot]

On that mooring plane you've got 2 or 3 lines for each mooring point. It's only going to take a slight difference of tension to make one of those lines take almost all the strain that should be shared by, say, the 3 stern lines. In this case though, it seems the line broke at well under its design strength.

In the case of the Britannia, assuming I've got the maths right, which is by no means certain, 30 knots gives a pressure of around 17.6kg/sq m. The ship's 330m long and has about 60m air draft, fudging to allow for funnels and stuff, call it 300 x 50. That's a force of 264 tonnes, which shouldn't be anywhere near enough to break the lines, but double the sustained wind in a gust, and you've got 17.6kg/sq m, over 1000 tonnes across the ship, which is getting near the load needed to break the lines. Add a bit of unequal tension and a bit of surge causing the lines to snub, and bang! No wonder big ships prefer to sit out a storm at sea.

Also, the relationship between wind pressure and wind speed is non-linear, so doubling the wind speed will more than double the force.

 

[Stemar]

Yes, IIRC, it goes up with the square of the windspeed.

 

[boomerangben]

Aren’t mooring lines like this on constant tension windlasses?

 

[AntarcticPilot]

Yes, IIRC, it goes up with the square of the windspeed.

I thought so too, but wasn't certain so I didn't say!