Question about Cruise Ship's stabilizer technology

[CruisinOnWheels]

Last December we went on our first cruise...western caribbean itinerary on the Rhapsody of the seas (RCI, 70k tons, launched 1996).

 

We were surprised how much movement of the ship we felt (I even had to hold both wheels of my wheelchair strongly, to keep from being thrown against corridor walls, etc)...once we left Galveston all the way to Key West, and then halfway to Grand Cayman we had "high seas" 10'-14', due to a cold front that had come through... and the ship was tossed around pretty hard.

 

This year we are on the Freedom of the seas 9/23 (Miami, eastern caribbean itinerary) and wonder if the technology of the ship stabilizers, etc has improved dramatically since the late 1990's ship designs?

 

Both wife and I were terribly seasick for 2 plus days :(

 

I am sure, the cruise lines spend alot of money and time in making their ships as stable as possible, sea sick passengers won't gamble, drink...buy stuff etc.

 

Please.. anything you can share with us to alleviate some of our worries would be deeply appreciated!

[Spikesgirl]

I'm not sure I can give you great words of wisdom beacuse it's unlikley that anything can keep a ship entirely stable if the seas outside are acting up. We were on the Grand Princess and were amazed at how smooth it was as we usually sail on the smaller ships. Even with stabilizers, they tend to have more movement, but the navigator and captian will try their best to steer out of rought waters if they can.

 

I would invest in some seasickness meds and go with the hopes of calmer seas.

 

Have a good (and stable) cruise

 

Charlie

[blindrid]

I would invest in some seasickness meds and go with the hopes of calmer seas.

 

Have a good (and stable) cruise

 

Charlie

 

Ditto. We do and the motion really doesn't bother us anyway. Better safe than sorry.

[Capt_BJ]

Stab' systems work only on the rolling motion...and not all that well at that. They don't do diddly for pitch (raising the bow) .... that's what a bulbous bow tries to help but in the end it is a function of wave size versus the length and displacement of the ship and the way the ship meets the waves....

 

Given the freedom to do so, one can try to limit the ship's motion in extreme conditions by ballasting & changing course and speed .... but those factors don't play well for a cruise ship on a set schedule.

 

As a ship captain in 40+ foot seas in the Bearing Sea I often found myself virtually hove-to for days ... but that was not a 'bad thing' as hove-to we were on station and available for the call .....

 

If you go back to the 'DAWN' incident a few years ago .... had the master the option of turning the stern to the seas and riding down swell, or slowing to minimum steerage speed - the wave probably would not have broken over the bow and smashed the (poorly designed) patio windows. In my similar experiences I had to turn in these conditions because the bow gun needed protection - that was priority one....not getting the pass' home on time.

 

If the seas are 'right' the ship is GONNA move .... that's the nature of the environment. The smaller the ship - the more it is gonna move. A larger ship can control its movement more than a smaller one ... primarily by ballasting (changing its weight and draft) but only up to a point.

 

Won't help you but trust me - a really ruff day on a cruise ship has nothing on a fishing boat in Alaska..... I was on CROWN PRICESS when I believe I may have been the ONLY passanger up and about (and looking for a beer) due to rough seas as the pitch & roll were on the order of 8 degrees. On Alaskan patrols days of 15 to 20 degrees are common and not even considered the ruff stuff...our beds come with seat belts

[Scooter-n-GB]

Hi Capt BJ,

 

First, I want to say, great response!!

 

Just curious, have you any opinion on this?

 

What effect, on the vessels forward speed, would deployment of stabilizers have, all other factors being equal? Any thoughts, say for your average Post-Panamax size?

[kitty9]

Not to lessen your experience with the 10 to 14 ft seas, in the reality of the high seas, that height isn't all that uncommon. I've been on cruises where the seas were 45ft and higher with force 10 gale winds. Now, that was rough. A lot on how a ship handles the seas depends on a few factors. Small ships such as ones like Seabourn and Silversea, don't handle high seas very nicely. Ships with a shallow draft also tend to bounce more. I did a crossing on Crystal where for three days we had seas of 35 to 40 ft and most everyone barely felt it----you know it's rough when you see green water washing over the windows on deck 6---but it was a very smooth cruise. I did a cruise on the QM2, and even in 15 ft seas, the ship really rocked. Plus, there's a big difference between waves and swells. Waves don't seem to have that much of an effect on bouncy ships, but huge rolling swells make a big difference. For some reason, I've been finding that these really huge ships are rougher than your mid-size ships. Perhaps it's because they are now building them with drafts that are much more shallow than the mid-size ships. And, BTW, I'm disabled and walk with a cane, so I'm very aware of rough seas and how careful I have to walk. It's the cane in one hand and holding the railing in the hallway with the other.

[Amlee]

Last December we went on our first cruise...western caribbean itinerary on the Rhapsody of the seas (RCI, 70k tons, launched 1996).

 

We were surprised how much movement of the ship we felt (I even had to hold both wheels of my wheelchair strongly, to keep from being thrown against corridor walls, etc)...once we left Galveston all the way to Key West, and then halfway to Grand Cayman we had "high seas" 10'-14', due to a cold front that had come through... and the ship was tossed around pretty hard.

 

This year we are on the Freedom of the seas 9/23 (Miami, eastern caribbean itinerary) and wonder if the technology of the ship stabilizers, etc has improved dramatically since the late 1990's ship designs?

 

Both wife and I were terribly seasick for 2 plus days :(

 

I am sure, the cruise lines spend alot of money and time in making their ships as stable as possible, sea sick passengers won't gamble, drink...buy stuff etc.

 

Please.. anything you can share with us to alleviate some of our worries would be deeply appreciated!

 

Was this the first of Dec? If so, I know exactly what you are talking about. But I was on the Mariner, and I'm sad to say we were a rocking and a rolling also. The Mariner is a bigger ship than the one you were on. While the side to side wasn't bad, the forward to aft was awful!!

[PennyAgain]

I have traveled by ship both for my work and for pleasure. I have a lot of Viking in me and don't get seasick, but I have fallen down in rough conditions. I crosssed the North Atlantic twice in a ship of less than 5,000 tons.

 

As I get older I am more worried about falls and injuries. Any advice other than staying in bed when things get rough?

 

By contrast I was on the QE2 when they wet the table cloths and put the ropes up in the corridors, but I stayed put in my room as I didn't trust myself to walk around. A big ship can take a rough ride as well.

[Vampire Parrot]

As Captain BJ says (I love reading his posts... and I learn a lot from them), the stablizers only reduce roll, and at the optimum stablizer speed (which is typically about 19-20 knots on a ship which has a service speed of 22-24 knots), they reduce roll by about 85%.

 

However, stabilizers can increase the pitching motion. This is the motion of the bow moving up and down, which causes the ship to pivot around it's centre of gravity, thus causing the stern to also move up and down. (I'm usually in a stern cabin on the top accomodation deck so am rather familiar with pitching...)

 

To reduce this, the ship will then be steered so that it's not going directly into and thus up and down the swells, but instead will be about 15 degrees off the swells. The ship's speed may also be slightly reduced to ease the pitching motion.

 

The least motion is felt in a midship inside cabin on the lowest deck.

[hammybee]

It is my understanding stabilizers are useless in mitigating the pitch, dolphin like movement and help only with rolling movement, similar to what one experiences when stepping into a row boat.

 

 

It is also my understanding that stabilizers are usually shut down in rough seas in favor of speed.

 

And lastly, it is my understanding the reason why the mega ships might pitch more than a mid sized ship has all to do with speed.

 

I'd love to have confirmation or new information. Thank you.

[Capt_BJ]

Question was about a 'stabilizer system' for pitch ....

 

In order to stop or dampen motion you need to exert force on the axis. To control roll that usually means one fin on each side, starboard and port. To to this for pitch you'd need two systems - fore and aft....or in reality two sets of pitch control fins - one forward and one aft.

 

Would that work? Well I'm no naval architect and I have seen designs like this but let's also consider the lengths of the mass to be controlled. Or on other words to control roll you have a lever arm who's length is equal to the beam - or width of the ship while to control pitch you have to deal with lever arms the LENGTH of the ship. & It is not uncommon for the ship's bow to be at the TOP of a swell, while the stern is at the bottom..... beam is less that 100 feet and length is 800, 900, 1000???? it's physics baby :D

 

A couple of other factors to think about.....

 

Some stab systems are 'active' and some 'passive'

 

A passive system sticks a wing out in the water - the wing is hard to move up and down in the water and therefore buffers the rolling motion by simple resistance as the roll of the ship wants to move the wing up and down.

 

An active system has sensors that see which way the ship is rolling and then changes the pitch of a wing out the side to compensate.

 

An active system has many moving parts

 

A passive system is larger and probably has a retraction system so the ship can get alongside a pier....

 

next issue

 

 

40 foot seas are not always 40 foot seas..... The shape of swells in the Atlantic and the Pacific differ..... This is due in part to the distances. Across the Pacific vs across the Atlantic? The Atlantic is a bath tub! A 45 foot swell in the Pacific will have a much longer period....or, the slope angle will be less....so the ship rides up and down more gently, while 30 feet in the North Atlantic has a small period, aka a steep slope and seems like an E-Ticket ride..... 20 footers in the Atlantic can seem as severe as 40 footers in the Pacific

 

And don't believe what the stewards tell you the wave heights are....they say the USCG charge for medivacs too..... :rolleyes:

 

Last thought .... did you know that a ship under full sail rolls very little even in very rough seas? Why? (I've crossed the Atlantic twice on a square rigger .... I think I know from where I speak more than many....)

[DougYWG]

On the old Royal Princess, they told us that each stabiliser cost them half a knot. On a trans-At trip, that equated to a whole lot of diesel, I forget how much. So because of the drag, they tried not to use the stabilisers any more than they had to.

 

The old QEII was built to shuttle back and forth across the pond in all weathers. In contrast, the new cruise ships are very wide, flat-bottomed tubs that do better to avoid the weather.

[Gingee]

Does anyone have a picture of these stabilizers in force? Maybe that would help us all understand.

[hammybee]

And don't believe what the stewards tell you the wave heights are....they say the USCG charge for medivacs too..... :rolleyes:

 

Last thought .... did you know that a ship under full sail rolls very little even in very rough seas? Why? (I've crossed the Atlantic twice on a square rigger .... I think I know from where I speak more than many....)

 

Thanks Capt for responding and the extra 411 too.:)

 

P.S. I thought you were older and then checked your profile and saw you are a few years younger than I. I hate when this happens and it's happening with increasing frequency. So I corrected my perception, you are experienced.Thanks again.

[Capt_BJ]

7 year resurrection

 

today's winner!

 

but bonus points for reading back!

Edited September 14, 2014 by Capt_BJ

[chengkp75]

Let me weigh in here as well. I'm not real good with getting the multi-quotes into my posts, so I'll just answer some without quoting.

 

Everyone is correct that stabilizers (formally called roll stabilizers) only reduce rolling, not pitching. There is no system designed to reduce pitching, and I don't believe that a twin wing system would have enough force to dampen pitching.

 

Course change is the cruise ship's best option to reduce motion. As someone posted, heading into the seas at a slight angle will reduce pitching, but increase rolling, which is not only controllable with stabilizers, but much easier motion for passengers. Cruise ships carry very little ballast water (it costs money to carry sea water around), so changes in ballast conditions aren't a major option.

 

From Capt BJ's posts, I gather that he was either USCG or USN. He and I both know the Gulf of Alaska in winter, but for those without the seagoing experience, there is a world of difference between a military ship and a cruise ship in the way they handle seas. Warships tend to be narrow in relation to their length, and are what we call "very stiff" ships in stability terms. While cruise ships are also moderately stiff, they are also more beamy (wider in relation to length). In 15' seas (depending on wave period, heading, etc), the military ship may be physically lifting people off their feet and slamming them into the bulkheads, while a cruise ship is experiencing slightly uncomfortable rolls.

 

I'm not sure where kitty9 gets the idea that the larger ships are being built with a smaller draft than mid-size ships. The Allure (225k tons) has a draft of 9.3 meters, while the Jewel (90k tons) has a draft of 8.1 meters, and the Rhapsody (78k tons) has a draft of 7.9 meters. You are correct that smaller ships "bounce" more, but that is a factor of the weight of the ships, as a larger ship weighs more, and it requires more wave force to lift the heavier ship.

 

For those who mention Cunard ships (and I did an October crossing on the QEII), those ships are specifically designed for the sea conditions in the North Atlantic. Their hulls are designed to slice through the seas, rather than ride them, and are not configured to maximize passenger space, but to maximize efficiency.

 

I will differ with Capt about bulbous bows. These are designed to create a bow wave that results in "lift" like an airplane wing, to sort of lift the ship forward, increasing efficiency, and to counteract the tendency of ships to sail with the bows down. Most ships trim themselves to be flat or slightly down by the stern while in port, but once underway, the force of the propeller all the way aft tends to push the bow down, increasing drag. The bulb helps correct this.

 

Stabilizers will reduce speed, perhaps a half knot, or increase fuel consumption. Stabs will not be used in moderate conditions, but will be more frequently used the worse the weather gets. Shutting the stabs off in rough weather in favor of speed is counterintuitive. Rough weather is when you need the stabs, and you will tend to slow down in rough weather to try to match ship's speed to wave period to minimize "banging" into the seas (where the whole ship shudders).

 

Not that many passive wing stabilizers these days. If you are going to the expense of a retractable fin, you can go the few extra bucks for a roll sensing system. Another system used by ships is a roll stabilizing ballast tank. These are two tanks (one port and one stbd) that are connected together at the bottom. As the ship rolls, water tends to flow back and forth between the two tanks (like the water in the bottom of a rowboat). What these tanks do, is sense the roll, and will close off the tank vents, so that when the port tank rises (ship rolling to stbd), the closed vents will not allow the water to flow from the higher port tank (no air to fill the space behind the water) to the lower stbd tank. This keeps more weight on the high side, and acts to counteract the roll. Also, the system will open the vents to allow the water to flow, but out of sequence to the roll, so there is a dampening effect.

 

Stabilizers are wings, creating lift. So, yes, speed is very important, in fact most have a sensor that automatically retract them when the ship is under 5 knots (to keep the Captain from forgetting to retract them while docking), so if a ship is slowed due to weather, the stabs will also lose effectiveness even when still deployed. I'm not sure they will dampen rolling by 85%, that sounds like a manufacturer's claim, but they can be very effective in most conditions.

 

For the OP, stabilizer technology has not improved greatly in the past few years, but ship design and ship handling have made the newer ships have easier motion.

 

Here is a link to a photo of a stabilizer in drydock, that is rotated to a "lift" position. https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&docid=JCwDEQJyyoLuzM&tbnid=piueZsAxGefgmM:&ved=0CAcQjRw&url=https%3A%2F%2Fwww.flickr.com%2Fphotos%2Fprincesscruises%2F5684114321%2F&ei=Bm4VVMqqM8yVyASXkoGIAw&bvm=bv.75097201,d.aWw&psig=AFQjCNEZaHVoQpzsPWAuIV8RoCl1HhMvBw&ust=1410776940252164

 

Sorry for encyclopedic answer, and also for this going wide format, not sure why that happened.

[peety3]

Stab' systems work only on the rolling motion...and not all that well at that. They don't do diddly for pitch (raising the bow) .... that's what a bulbous bow tries to help but in the end it is a function of wave size versus the length and displacement of the ship and the way the ship meets the waves....

 

Not in any way saying that I don't believe you, but I've seen/heard/read in multiple places that a bulbous bow exists to improve efficiency of the ship moving through the water by changing the shape of the forward displacement forces. Odd to hear that it's intended to improve pitching reactions.

 

I'm not sure where kitty9 gets the idea that the larger ships are being built with a smaller draft than mid-size ships. The Allure (225k tons) has a draft of 9.3 meters, while the Jewel (90k tons) has a draft of 8.1 meters, and the Rhapsody (78k tons) has a draft of 7.9 meters.

Remember that most ships "weights" are published in Gross Register Tonnage, which has nothing to do with weight. It has to do with volume, though with a bazillion strange factors tossed in to "account" for different things. Consider it similar to when you attempt to ship a package by UPS and they tell you "this weighs 14 pounds but the dimensional weight is 42.7 pounds, so you owe us $197 dollars for a ground shipment to the next zip code." You'd be better off comparing displacements, which are unfortunately hard to research.

[chengkp75]

Not in any way saying that I don't believe you, but I've seen/heard/read in multiple places that a bulbous bow exists to improve efficiency of the ship moving through the water by changing the shape of the forward displacement forces. Odd to hear that it's intended to improve pitching reactions.

 

 

Remember that most ships "weights" are published in Gross Register Tonnage, which has nothing to do with weight. It has to do with volume, though with a bazillion strange factors tossed in to "account" for different things. Consider it similar to when you attempt to ship a package by UPS and they tell you "this weighs 14 pounds but the dimensional weight is 42.7 pounds, so you owe us $197 dollars for a ground shipment to the next zip code." You'd be better off comparing displacements, which are unfortunately hard to research.

 

Quite well aware of the definition of Gross Tonnage (GRT is an unused term since 1982). I was using the tonnage of the various ships to delineate size, not weight, as the poster had said that the new, larger ships had a smaller draft. And neither gross tonnage nor displacement have a direct relationship to draft, as you could make a barge with a huge waterplane area (very long and very wide), that has a large displacement and a large gross tonnage, but only drew 1 foot of draft (large exaggeration, as the dimensions would be huge and unseaworthy, but I make my point).

[bbwex]

Well CaptBJ and Chengkp75 have weighed in pretty well, and have given a good lesson. I would only add that in a situation involving pitching motion, the question starts to get very complicated. All of the factors mentioned already are part of the equation, but it also gets into the size of the seas, the frequency of the seas, the frequency of the seas in relation to the length of the ship, the speed of the ship and how the hull design handles different sea states, the location of the Center of Motion, etc., etc., etc. Add this to the points made by the two very good posters, and you start to get an idea of how difficult this really is.

 

Rolling motion, as pointed out, can only be controlled so much. The ocean is so big and my ship is so small! Newer ships with extremely high superstructures raise the Center of Motion higher and make the rolling motion that much harder to control. A less complicated matter, but still difficult considering the considerable forces involved.

[Baldmont]

Hi all,

 

Very interesting argument. i always read your posts with great admiration.

 

I also hear and read here that cruise ship doesn't like to use stabilizers to reduce fuel consumption, but in reality, 21th century gives us some advantages..a solution also for this I guess... Sailing on the web and found this http://www.pinfabb.com/content/pinfabb-eco.

 

Don't like to pay for comfort for nothing. Ocean is ocean, but technology should help us, we should envoj everybody to use and improve technology to improve people way of life, in this case, cruiser holidays.

 

Hello

Baldmont

[busmech]

You can feel the stabilizers at work. I was on the Queen Victoria in March and we skirted a cyclone by New Zealand and you can feel the ship roll then a sharp stop then the rool back to the other side. They usually keep the stabilizers retracted when sailing only when there is a lot of roll do they extend them. Also the QM2 has 4 stabilizers. But then she is ocean liner.

[chengkp75]

You can feel the stabilizers at work. I was on the Queen Victoria in March and we skirted a cyclone by New Zealand and you can feel the ship roll then a sharp stop then the rool back to the other side. They usually keep the stabilizers retracted when sailing only when there is a lot of roll do they extend them. Also the QM2 has 4 stabilizers. But then she is ocean liner.

 

Actually, if the stabilizers are working properly they will be exerting anti-rolling force all the way through the roll, not just at the peak, so you should not feel a "sharp stop" from the stabilizers.

 

I believe what you were feeling is caused by the high center of gravity of most cruise ships causing a large metacentric height, which causes the ship to roll sharply. The more the ship rolls, the greater this "righting arm" that tries to move the ship back upright becomes, until it overcomes the rolling force of the wind and seas, and the ship will roll back. But this great righting arm doesn't go away instantaneously, so there will be a snap at the end of the roll. You don't notice this snap because it is much less in conditions where you are rolling less, so the force is less.

 

I know of several ships that have two sets of stabilizers, so its not just ocean liners. It depends on the length of fin required, and the length of the watertight compartments in the engine room. If the designed fin length is longer than the distance between bulkheads in the engine room, they will go with two sets of shorter fins instead.

[dancinman66]

They won't always use the stabilizers due to additional fuel but modern stabilizers work before the ship starts moving as now instead of gyros use pressure sensors to start movement changes

 

Also the movement it controls is only rolling

Up and down forward and back us not changed from them

 

 

Sent from my iPhone using Forums

[sanmarcosman]

Actually, if the stabilizers are working properly they will be exerting anti-rolling force all the way through the roll, not just at the peak, so you should not feel a "sharp stop" from the stabilizers.

 

I believe what you were feeling is caused by the high center of gravity of most cruise ships causing a large metacentric height, which causes the ship to roll sharply. The more the ship rolls, the greater this "righting arm" that tries to move the ship back upright becomes, until it overcomes the rolling force of the wind and seas, and the ship will roll back. But this great righting arm doesn't go away instantaneously, so there will be a snap at the end of the roll. You don't notice this snap because it is much less in conditions where you are rolling less, so the force is less.

 

I know of several ships that have two sets of stabilizers, so its not just ocean liners. It depends on the length of fin required, and the length of the watertight compartments in the engine room. If the designed fin length is longer than the distance between bulkheads in the engine room, they will go with two sets of shorter fins instead.

You have great knowledge but I have yet to see you weigh in on the Carnival boards when people ask questions about the temperature in their cabins and the lack of a/c in the cabins. If you have weighed in, my apologies but I have not seen any posts by you on the matter. My understanding is the cabins are ventilated but are not individually climate controlled like the cabins were aboard s/s United States or similar. The next time on the Carnival boards when the issue comes up I hope you will share your knowledge with those who want to know. Many thanks!

[chengkp75]

You have great knowledge but I have yet to see you weigh in on the Carnival boards when people ask questions about the temperature in their cabins and the lack of a/c in the cabins. If you have weighed in, my apologies but I have not seen any posts by you on the matter. My understanding is the cabins are ventilated but are not individually climate controlled like the cabins were aboard s/s United States or similar. The next time on the Carnival boards when the issue comes up I hope you will share your knowledge with those who want to know. Many thanks!

 

I've commented on cabin A/C several times, I can't remember if I've posted on the current Carnival ones.

 

The A/C normally has 20% fresh make up air that is cooled in large air handling rooms by cooling coils that handle a whole section of cabins. This 20% make up air is balanced by 20% exhaust via the bathroom exhaust "fart fan". Most of the ships have some form of recirculation cooler where the cabin air is taken in by a small fan, passed over a chilled water cooling coil, and then returned to the cabin. This is what is typically controlled by the cabin thermostat.

 

All of the A/C onboard is done via chilled water, so the only refrigerant is in the engine room, where it chills fresh water to about 50*F. This water circulates around the ship to the air handler rooms and the individual cabin coolers.

 

So, the make up air temperature is controlled by a master thermostat, and doesn't change. Some older ships use these group chillers to provide all cooling for the rooms, and the "thermostat" is only a damper adjustment to allow more or less cool air.

 

I can't speak specifically for Carnival, or for any particular ship (though I have found A/C system specs for some ships with a lot of research), but it seems to me that system wide warm cabins means that either the chilled water temp is being maintained too high, or the air filters at the cooling coils are blocked. The rooms that have individual room coolers will also have filters, and this could cause poor performance.

 

Hotel industry standard for room temperature is 72-74*F, and the cruise lines stick pretty much to this as their standards as well. What that means is that if the cabin is within that range, they will not consider compensation, but if it is outside that range for more than a day, usually there will be some compensation.

 

Whether they are consciously increasing temperature, or whether it is a problem with the system that they haven't found yet, I can't say. I was embarrassed for about 3 cruises when we were continually getting air into the chilled water system, which would then vapor lock the chilled water system and stop cooling. It was finally found to be an air compressor in the engine room that had had a chilled water cooler added at a later date, that was leaking air into the system. We had the entire engine department working 24/7 for three weeks to find that one.