Ship Design

[dreamerdick]

As a newbie at cruising I was curious about this post on another part of cruise critic:

 

" I wouldn't really fancy crossing the Atlantic on a ship that was built for the Caribbean - they have neither the speed nor the stability to cope with even slightly bad weather."

 

Why would any line (knowing that they have to reposition their ships thru the Atlantic and Pacific) design a ship that couldn't take the rough seas of either ocean?

 

Are ships actually designed to only sail the mostly calm seas of The Caribbean and others to handle the Atlantic or Pacific? If so, what is the difference - heavier steel in the hull? bow style? drive systems?

 

By the way - what ARE rough seas? 20 ft waves, 30 foot waves or ????

 

Thanks to all you pros out there for your comments.

[rain_bowbrite]

Most cruise ships are not built for transatlantic crossings. This doesn't mean that they aren't tough enough to withstand crossing it just means that when repositioning they can't go as fast as say the Queen Mary, which was specifically designed for transatlantic crossings.

 

I am not an engineer so I don't know the factors behind this. I am sure that someone on CC can tell you why. But what I do know it that there is nothing unsafe about doing a transatlantic crossing on a ship built for regular cruising.

 

Hope this helps.:confused:

[Cruzman]

The statement that you quoted is a misnomer at best. Back in the days when "cruise ships" were primarily used to transport passengers across the Atlantic or some other ocean, the ships hulls were designed for speed. Hulls were narrower and deeper in order to cut through the surf rather than climb and dip over and around the large waves. They were also designed so that areas normally outdoors and exposed to the elements, would be mostly enclosed. Todays ships use a lot of modern technology to accomplish all of the above without sacrificing the advantages that the older transatlantic ships had. Of course, very few, if any modern cruise ships can match the speeds of ships like the SS United States or the SS France, but they are nevertheless just as stable, if not moreso.

[1932Canal]

As a newbie at cruising I was curious about this post on another part of cruise critic:

 

" I wouldn't really fancy crossing the Atlantic on a ship that was built for the Caribbean - they have neither the speed nor the stability to cope with even slightly bad weather."

 

Why would any line (knowing that they have to reposition their ships thru the Atlantic and Pacific) design a ship that couldn't take the rough seas of either ocean?

 

Are ships actually designed to only sail the mostly calm seas of The Caribbean and others to handle the Atlantic or Pacific? If so, what is the difference - heavier steel in the hull? bow style? drive systems?

 

By the way - what ARE rough seas? 20 ft waves, 30 foot waves or ????

 

Thanks to all you pros out there for your comments.

 

All ships, whether Cruise ships or plain old cargo ships that are intended for Ocean passages have to meet the standards of the Classification Society that they subscribe to; ships sailing on Inland Waters (i.e. Great Lakes) have lesser standards to conform with. These standards are set by several Societies but are allied to Marine Insurance. (Note: whilst a particular 'country of registration' might have certain standards; or lack thereof; the Classification society rules predominate). This means that today's cruise ships are designed and built to sail anywhere in the world, or at least where the waters allow for a ship of their size. However, a cruise ship with high upper decks and lots of glass etc. requires caution when crossing an open stretch of ocean. Additionally, for the comfort of the passengers the Captain will most likely proceed at a reduced speed; that is not drive the ship through the seas. Most cruise ship have a designed cruising speed of 21/23 knots but on a transocean crossing are scheduled at an average speed of 18/20 knots.:p

Rough seas are a result of both the direction of the wind and the length of time it has been blowing in that direction. If you can see 'white caps', that is the tops of the waves breaking it is an indication of 'rough seas', but only if they are large 'white caps'. In certain areas of the ocean the ship experiences a lot of movement, not because of 'rough seas' but because of the seas/swells striking the shore and rebounding; e.g. the Bay of Biscay: West Coast of California.

[dreamerdick]

Very informative posts to a newcomer to sailing - thanks. The post mentioning maritime insurance made great sense as did its country of registry. I can see the difference between casual cruising and those liners whose job it is to ply the rough seas faster to get from point a to point b the quickest.

 

To a newbie, some of the newer vessels seem almost 'top heavy' but you really cant see just how much of the ship is down in the water nor what elaborate systems it has to stay more level in the water. Thanks to all of you who posted - any ship design engineers out there?

[1932Canal]

To a newbie, some of the newer vessels seem almost 'top heavy' but you really cant see just how much of the ship is down in the water nor what elaborate systems it has to stay more level in the water. Thanks to all of you who posted - any ship design engineers out there?

The correct term for a 'Designer of Ships' is "Naval Architect".

Whilst a Cruise Ship may appear 'top heavy' the Architect designs the ship to be otherwise, sometimes to the point where it is 'bottom heavy'. the difference shows up in the movement of the ship at sea; that is some ships have a 'Slow Roll' which is very comfortable to the persons onboard; but not all that stable, and some have a 'Fast Roll' but are, in effect very stable, but somewhat uncomfortable. All Cruise ships have 'Stabilisers' which minimise the roll and make it comfortable for passengers et al.

I am not a Naval Architect; just a retired Master Mariner who has been involved in the building of a couple of ships.:cool:

[dreamerdick]

If 1932 approximates your birth year then you must remember the television series "Victory At Sea". I was always amazed at the film intro to each sequence showing a destroyer plunging thru incredibly rough seas that looked higher than the ship. Camera angle probably had a lot to do with the 'look' of the footage but it sure was impressive to watch and not something I'd love to experience first hand. What is the most you are exposed to in an average cruise at sea? Will a ship continue thru 30 foot seas rather than go around or will it pull into safe harbor - is there a sailing guideline that companies use? I heard that one ship docked before a hurricane struck, disembarked it passengers ashore and went out and rode the storm out at sea to prevent damage at the pier and then came back for the passengers the next day and continued on its journey. So it appears that the companies really do care about your experiences aboard and will do what it takes to keep you comfortable and safe.

[1932Canal]

Deamerdick; you ask a lot of questions, all rolled up into one. First: The safest place for a ship during a storm is at sea well away from land; but it is also very uncomfortable for those onboard. If the ship is in the middle of the ocean it cannot easily reach a safe haven(harbour) so just has to ride out the storm.Yes! if an oncoming storm is forecast and the ship can put its passenger ashore it will do so for two reasons. One, the comfort of the passengers and two, to avoid claims for injuries- real or imagined- from the passengers.

1932 is not my birth year but relates to a physical entity close to where I live. I do remember 'Victory at Sea' (actually being shown on the local PBS station at the moment); you should understand that even the largest Naval Warship is quite small compared to present day Cruise ships. Destroyers were designed and built for speed and were often 'forced' through the seas to meet a war/battle need.

By-the-way, my experience is with Merchant ships and thus might not be totally correct for Warships.

[piper28]

To a newbie, some of the newer vessels seem almost 'top heavy' but you really cant see just how much of the ship is down in the water nor what elaborate systems it has to stay more level in the water. Thanks to all of you who posted - any ship design engineers out there?

 

Actually, you'd probably be surprised at how little is underwater. As an example, the Crown Princess, which is a pretty large ship, actually only has a draft (how far it sticks below water) of 26 feet. However, there is a LOT of weight down in that area. Even when they try to tip it over, there's enough weight down there to prevent that from happening :).

[1932Canal]

Actually, you'd probably be surprised at how little is underwater. As an example, the Crown Princess, which is a pretty large ship, actually only has a draft (how far it sticks below water) of 26 feet. However, there is a LOT of weight down in that area. Even when they try to tip it over, there's enough weight down there to prevent that from happening :).

Piper28 you are correct - I missed answering that part of the question. The Naval Architect in designing a ship has to always take into consideration the Stability and the Righting Lever (the forces to bring the ship back to the upright) but at the same time in order for a Cruise Ship to enter some of the ports he has to limit the draft; 26 feet is pretty well a standard for Cruise Ships; however, a large Cargo Vessel or Tanker can have much greater drafts but, obviously, limited to the ports that they can enter.

[Capt_BJ]

My experience is on .... "government vessels" .....

 

Ships which are operating within the limits defined by the naval architects will maintain stability in conditions the average person won't want to be on board for. War ships are built with huge righting moments and some can roll past 90 degrees and right themselves. Coast Guard surf rescue boats can be turned completely turtle, and will self right. Commercial vessels while not 'as much' still have a heck of alot. Loydd's coupled with SOLAS provides one heck of a set of rules that must be followed for a ship that plans to carry passagers on the ocean.

 

In a large vessel however a huge variable is the loading condition. The stability is tighly coupled to the distribution of weight on board ... and that changes constantly. Consumption of fuel is the largest factor but the entire liquid load is a concern. Fuel is typically stored low in the ship. Weight low in the ship is good. Burning fuel reduces low weight ... that's bad. It is offset by ballasting - taking on water to add weight. A ship is delivered with a 'liquid load plan'. It tell what order fuel tanks should be used and how to ballast as fuel is used. It is important and a daily - if not more often - function of the engineer and the master...is uder to be done by books and tables and now by fancy computers and sensors (until they break)

 

Weights that move are also bad - a cargo ship master is very familiar with this and the possibility of shifting cargo weights causing a capsize is real. Problem is liquid loads also cause shifting weight. A half empty fuel tank in a rolling ship equals a weight shifting as the ship rolls. This is called free surface effect which is bad. A tank that is 'topped off' or what's called 'pressed up' allows little room for the liquid to move and is good. A half empty tank is a shifting weight if the liquid sloshes from side to side. An empty tank has no shifting weight, but may also decrease the low weight and is therefore a negative influence on stability. And you don't want to fill an empty fuel tank with sea water because that's bad when you want to empty the water you must clean oil water mix - and water in fuel is bad when you refill the tank..... so many factors.....

 

So when faced with impending heavy seas:

 

a) check for possible weight shifts, including pressing up tanks if possible; ballast to get the ship at the intended draft - get weight low in the ship.

b) as stated - in hurricane conditions a ship is safer at sea .... you can get torn apart at a pier. It is best to run away from the storm - but if caught you want room to maneuver.

c) when the ride gets really really bad and the roll is threatening to tear stuff up - turn the bow into the wind and waves and try to find a speed where the ship will ride up and over the waves. {see DAWN 'rougue wave' report - exactly what was being done} The design of the bow is intended to allow the ship to ride up.....intended. Water exploding over the bow and crashing into the front of the superstructure is not unusual ... it takes seamanship to monitor the pitch of the ship versus the seas to avoid the bow commin down hard as the seas go up ... (but suggests windows facing forward should be minimized if the conditions are to be expected.... back to DAWN ...)

 

but wait - there's more - be careful that the wave period does not result in the bow and stern carried up by the seas as the swell drops away in the middle. In the extreme - this would cause the ship to break its back. Not a good thing.... you may need to angle the seas and adjust speed .... and of course everything is constantly changing...

 

Why not turn the stern to the sea?... well a following sea can have a negative impact on the seakeeping ability of the ship. Water past the rudder is what turns a ship. A following sea can reduce the flow across the rudder. And running "the wrong direction" is not as negative to what amounts to holding in one place by steering into the sea at just enough speed to control the bow. In the worst case a wave catches you from behind and you get 'pooped'....the rudder looses effect and out of control,the ship finds itself beam to the seas. Not good.

 

have been able to put all this into practice in the winter in the Bearing Sea - a real e-ticket ride when the lows come thru.

 

A ship - which is 'intact' and loaded in accordance with the designers instructions and handled prudently is not going to tip over ... It will roll much farther than you'd want to be on board for ... but will come back up. On the average cruise ship the disaster will come from all the improperly secured items inside LONG b4 the ship itself is in serious trouble. Furniture - pianos - bingo tables - bar stock - gift shops - all this stuff "getting under way" will cause a heck of a lot more problems than the actual rolling will.

 

just some highlights.....

[dreamerdick]

That sure was an interesting post, very informative and educational. Just a chuckle thinking what must go thru your mind as YOU cruise under another captain in stormy seas :-) I don't ever remember a cruise ship rolling over but I am sure there are passengers that were sure it was going to happen on several ships recently. I read that the draft of the QM2 was almost 33 feet compared to 26 feet on Princess ships and my guess is that in rough seas it seems more stable but may not actually be. Its just good to know that a lot of thought and formulas are applied to whatever ship you decide to travel on. My guess is that until you know your personal tolerance for rough seas, being lower down in the center of the ship with a handfull of Scopace is your best bet? I also assume that one acclimates to the motion of the seas after you take a half dozen or more cruises and you might never need medication. If you were in command of any ship for four years you probably have experienced much rougher seas than a passenger will ever face.

 

Sorry about having to be on land so much BJ - just cruise as often as you can :-)

[KreinKrunker]

but wait - there's more - be careful that the wave period does not result in the bow and stern carried up by the seas as the swell drops away in the middle. In the extreme - this would cause the ship to break its back. Not a good thing.....

Exactly one of the theories on the sinking the 729 foot 'Edmund Fitzgerald', November 10, 1975, in Lake Superior.

 

http://home.europa.com/~random7/fitz.htm#line

 

"The legend lives on from the Chippewa on down

of the big lake they call Gitche Gumee

Superior they said never gives up her dead

when the gales of november come early"

Gordon Lightfoot

[piper28]

I don't ever remember a cruise ship rolling over but I am sure there are passengers that were sure it was going to happen on several ships recently.

 

Yeah, when you start seeing pool water fall in front of you on your balcony, even knowing how much weight is down there doesn't get you over thinking that the horizon is just not where it's supposed to be :).

[Capt_BJ]

"My guess is that until you know your personal tolerance for rough seas, being lower down in the center of the ship with a handfull of Scopace is your best bet? I also assume that one acclimates to the motion of the seas after you take a half dozen or more cruises and you might never need medication."

 

Sea sickness is basically vertigo caused by one's reaction to the things happening in the inner ear. Some people 'never felt it' altho my theory there is any one who's "never been sea sick" just hasn't been in ruff enuf seas - yet...:p

 

Most will experience a day or so of discomfort and then they adjust to the strange impulses being sent from the balance circuits of the inner ear and until it gets 'really ruff', they are fine.

 

And then there are a small percentage that just can't adjust. These few are the chronic, who tend to also get air-sick and car sick. They just have inner ear issues and I've seen folks who couldn't even hadle the ship tied to the pier. A few sailors I experienced like that were encouraged to seek other careers. Altho every once and a while you see some one who's always sick, but loves the sea, so just carries a bucket or a plastic bag around all the time :eek:

 

Using 'scope (or a puppy patch as we call them) helps some get adjusted - but for some others they cause just as unpleas' side effects. Same with the various pills.

 

There is also a strong psych end to this. I've seen people cured by a round bandaide behind the ear - told it was a scope patch ... And there is sympathetic sea sickness - when 10 people around you turn green, well, some just love to follow the crowd :p

 

On a cruise a few years ago a PRINCESS vessel DW and I were on was heading north, east of the Bahama Bank. "The weater started getting rough....". The water all sloshed out of the pool and in the afternoon I seemed to be one of the few out and about. I found one open bar and was talking to the BT, sipping a Guiness and obsrving 'one hand for the ship rules' when a particularly strong swell slapped the bow and we lurched pretty good. I'd just asked BT how experienced he was with such seas, and he'd told me of his extensive experience...as the ship rolled maybe 5 degrees to port and every bottle and glass of his setup crashed to the deck..... Later that nite I awoke to the sounds of someone praying to the porc'lin gods and thought 'some one next door is having a rough nite due to the seas'; then I rolled over and realized I was alone in bed...:o

But a certain set of days, when my ship sat turned into the wind for 4 days in the Bearing enjoying 40+ I'll readily admit that I too was not very interested in the seafood fest offered by my cook!

[Capt_BJ]

some entertaining discussion of sea sickness

 

http://forums.military.com/eve/forums/a/tpc/f/415197802/m/4510041790001

 

beware of sodium chloride spice in the language

[Capt_BJ]

Exactly one of the theories on the sinking the 729 foot 'Edmund Fitzgerald', November 10, 1975, in Lake Superior.

 

http://home.europa.com/~random7/fitz.htm#line

 

"The legend lives on from the Chippewa on down

of the big lake they call Gitche Gumee

Superior they said never gives up her dead

when the gales of november come early"

Gordon Lightfoot

 

 

see http://www.uscg.mil/hq/g-m/moa/boards/edmundfitz.pdf

[dreamerdick]

This has proven to be a very interesting thread, thanks to everyone that shared their stories and the links to other sites. Think I'm gonna try a round band-aid first, sure is cheaper. The newer Scopace seem to have less side effects than the old Dramamine because of the lower doseage. I only remember being seasick once on the old South American cruise ship in the Great Lakes when it was busting thru twenty foot seas but I was only seven and had a cold at the time. I was never sick on a small boat in rough seas so I imagine that I will do just fine with the band aid and a ginger ale :-) If its all in the mind I should never have trouble :)