# How fast an ocean liner could we build today? **URL:** \ **Category:** Factual Questions\ **Created:** [February 7, 2010, 5:11pm UTC](https://boards.straightdope.com/t/how-fast-an-ocean-liner-could-we-build-today/528039 "2010-02-07T17:11:52Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [February 8, 2010, 11:22pm UTC](https://boards.straightdope.com/t/how-fast-an-ocean-liner-could-we-build-today/528039/21 "2010-02-08T23:22:31Z")
> [@Kevbo](#): > > What are the possibilities of an ocean going hydrofoil? > > 30 years ago when I was in Cozumel, they had a wicked big hydrofoil ferry making the run between there and Cancun. Maybe half as big as a smallish cruise ship of that era (I saw them together) Could go for a Ground Effect Vehicle. While they get out of the realm of ships they are, technically, classified as a ship. The Soviets built one called the [Ekranoplan (aka Caspian Sea Monster)](http://2.bp.blogspot.com/_uzL7ZJ5iv9g/SN-LVQ5_j2I/AAAAAAAAA58/ccZ-G6Thkjs/s1600/Ekranoplan.jpg). At 540 tons it was pretty big and had a cruise speed of something like 350 mph (I think). Boeing has been talking about building a true monster GEV. [The Pelican](http://www.boeing.com/news/frontiers/archive/2002/september/i_pw.html) would have a wingspan of 500 feet and be able to carry 1400 tons of cargo! Doubt it will ever see the light of day but who knows? ---
**Author:** ![Icerigger](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/icerigger/32/432_2.png) [@Icerigger](https://boards.straightdope.com/u/Icerigger)\ **Post date:** [February 9, 2010, 12:05am UTC](https://boards.straightdope.com/t/how-fast-an-ocean-liner-could-we-build-today/528039/22 "2010-02-09T00:05:39Z")
Wow, only the Russians would build a monster like that! ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [February 9, 2010, 1:31am UTC](https://boards.straightdope.com/t/how-fast-an-ocean-liner-could-we-build-today/528039/23 "2010-02-09T01:31:47Z")
> [@Whack-a-Mole](#): > > I think we could build it today if someone really wanted to. They have gun stabilizers on tanks that hold the gun rock steady while the tank is bouncing all over the place. I see no reason this couldn’t be done on the ship as you describe. I disagree. Who can build it… now? Please advise. Some entity can launch into a feasibility study, design, engineering, etc. ---
**Author:** ![Daylate](https://avatars.discourse-cdn.com/v4/letter/d/9dc877/32.png) [@Daylate](https://boards.straightdope.com/u/Daylate)\ **Post date:** [February 9, 2010, 2:23am UTC](https://boards.straightdope.com/t/how-fast-an-ocean-liner-could-we-build-today/528039/24 "2010-02-09T02:23:37Z")
Alert - technical stuff follows: The formula I’ve read in all sources that touch on this is that the theoretical maximum speed of a displacement hull, in knots, is 1.34 times the square root of the waterline length in feet. This would give the max speed of a 900’ ship to be 40.2 knots, which sounds about right. Increasing the power above this would result in the ship just sort of squatting down, generating huge waves, and going little if any faster. One thing - the power necessary to get the last few knots is very large. I have also read about the speed of those old four stacker WWI destroyers. They had four fire rooms, and could run with one or all of these in operation. With two of the fire rooms on line, the ship could do 26 knots. With all four of them on line, they would make 32 knots. So that last 6 knots took almost a doubling of power. ---
**Author:** ![Snnipe\_70E](https://avatars.discourse-cdn.com/v4/letter/s/b5a626/32.png) [@Snnipe\_70E](https://boards.straightdope.com/u/Snnipe_70E)\ **Post date:** [February 9, 2010, 4:49am UTC](https://boards.straightdope.com/t/how-fast-an-ocean-liner-could-we-build-today/528039/25 "2010-02-09T04:49:12Z")
I do not remember the formula. But at the maritime academy the deckies were discussing speed vs hp. The factors are lenght:hull beam(one of them was to the third power). Baised on the formula the training ship max speed was 16 knotts and requires 6,000 hp. To get it up to 16.5 knotts would require something like 100,000 hp. ---
**Author:** ![Declan](https://avatars.discourse-cdn.com/v4/letter/d/ecae2f/32.png) [@Declan](https://boards.straightdope.com/u/Declan)\ **Post date:** [February 9, 2010, 6:30am UTC](https://boards.straightdope.com/t/how-fast-an-ocean-liner-could-we-build-today/528039/26 "2010-02-09T06:30:44Z")
> [@Sam\_Stone](#): > > Even modern warships aren’t much faster, because of the limit of the displacement hull design. A nuclear powered aircraft carrier like the Enterprise might be able to do about 35-40 knots flat out, but that’s about it. Actually they can go quite a bit faster than that, what the actual top end speed of a nimitz class is , I dont think they want to know. The above is based on a real set of circumstances, in which a carrier was ordered to procede to Bangladesh back in 1970 or so , for humanitarian relief. Declan ---
**Author:** ![KellyM](https://avatars.discourse-cdn.com/v4/letter/k/57b2e6/32.png) [@KellyM](https://boards.straightdope.com/u/KellyM)\ **Post date:** [February 9, 2010, 7:14am UTC](https://boards.straightdope.com/t/how-fast-an-ocean-liner-could-we-build-today/528039/27 "2010-02-09T07:14:13Z")
> [@Sam\_Stone](#): > > A nuclear powered aircraft carrier like the Enterprise might be able to do about 35-40 knots flat out, but that’s about it. Flank speed on _Nimitz_-class carriers is classified, but it’s estimated to be well in excess of 40 knots and possibly as high as 50, at least in short bursts. The Navy only admits to “30+ knots”. The _USS Carl Vinson_ (CVN 70, a _Nimitz_-class supercarrier) was ordered to flank speed for its diversion to Port au Prince; I imagine someone has added the data point for that journey to the database for estimates of the top speed of Nimitz-class carriers. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [February 9, 2010, 12:49pm UTC](https://boards.straightdope.com/t/how-fast-an-ocean-liner-could-we-build-today/528039/28 "2010-02-09T12:49:09Z")
> [@Philster](#): > > I disagree. > > Who can build it… now? Please advise. > > Some entity can launch into a feasibility study, design, engineering, etc. I assume your issue is with a stabilized platform. You can see in [this video](http://www.youtube.com/watch?v=cye86-9Abtk) of the Leopard tank its gun stabilization in action (can see it in the first 15 seconds of video…watch the gun stay stable despite the tank under it bouncing a great deal). They do the same for naval guns. So, clearly they can build stabilizers for this. Why would a platform be any problem? ---
**Author:** ![MarcusF](https://avatars.discourse-cdn.com/v4/letter/m/67e7ee/32.png) [@MarcusF](https://boards.straightdope.com/u/MarcusF)\ **Post date:** [February 9, 2010, 1:22pm UTC](https://boards.straightdope.com/t/how-fast-an-ocean-liner-could-we-build-today/528039/29 "2010-02-09T13:22:19Z")
> [@Philster](#): > > Since we are stuck with “Ocean Liners” as part of our requirements, we have to assume we are talking about cruise ships. Ocean liners and cruise ships are not the same in design concept. An ocean liner is built much stonger as it is designed to keep going through an Atlantic storm - the cruise ship just stays in port if dirty weather is on the way. As noted you don’t want people to spill their drinks or stop going to the casino! The [_Queen Mary 2_](http://en.wikipedia.org/wiki/RMS_Queen_Mary_2) is a liner, designed to cross the Atlantic regularly so has a different hull shape and a speed of up to 30 knots. The [\*Freedom of the Seas \*](http://en.wikipedia.org/wiki/MS_Freedom_of_the_Seas) - that overtook the QM2 as the biggest passenger ship - is definitely a cruise ship with a normal top speed of around 22 knots. ---
**Author:** ![MarcusF](https://avatars.discourse-cdn.com/v4/letter/m/67e7ee/32.png) [@MarcusF](https://boards.straightdope.com/u/MarcusF)\ **Post date:** [February 9, 2010, 1:29pm UTC](https://boards.straightdope.com/t/how-fast-an-ocean-liner-could-we-build-today/528039/30 "2010-02-09T13:29:39Z")
> [@Whack-a-Mole](#): > > I assume your issue is with a stabilized platform. > > You can see in [this video](http://www.youtube.com/watch?v=cye86-9Abtk) of the Leopard tank its gun stabilization in action (can see it in the first 15 seconds of video…watch the gun stay stable despite the tank under it bouncing a great deal). > > They do the same for naval guns. > > So, clearly they can build stabilizers for this. Why would a platform be any problem? I think the point is that there is one hell of a difference between stabilising a gun - max weight a few tons, probably a lot less - and stabilising the entire passenger space of a large ship. No idea of the precise split but the QM2 is 148500 gross tons. Assume only a 1/5 of this is the passenger compartments, gyms, restaurants, swimming pools, etc. (I am sure it is more an a 1/5 but just say) we still have to stabilize a 29000 ton mass! Not the same problem as a tank gun. ---
**Author:** ![jjimm](https://avatars.discourse-cdn.com/v4/letter/j/ba8739/32.png) [@jjimm](https://boards.straightdope.com/u/jjimm)\ **Post date:** [February 9, 2010, 2:11pm UTC](https://boards.straightdope.com/t/how-fast-an-ocean-liner-could-we-build-today/528039/31 "2010-02-09T14:11:43Z")
[Not the size of a cruise ship](http://en.wikipedia.org/wiki/File:20090411-TurboJET_Barca.jpg), but the [TurboJET](http://en.wikipedia.org/wiki/TurboJET) hydrofoil planing craft that ply the Pearl River Delta between Hong Kong and Macau are quite large (e.g. “27.8m length, 303 tonnes, 260 passengers”) and travel at 45 knots. They do go “whackata whackata whackata” as they cut through the waves, but the ride is pretty smooth regardless, and it’s cool when they bank round corners. Not sure how they’d be in deep ocean swells though. ---
**Author:** ![Elendil\_s\_Heir](https://avatars.discourse-cdn.com/v4/letter/e/7cd45c/32.png) [@Elendil\_s\_Heir](https://boards.straightdope.com/u/Elendil_s_Heir)\ **Post date:** [February 9, 2010, 2:22pm UTC](https://boards.straightdope.com/t/how-fast-an-ocean-liner-could-we-build-today/528039/32 "2010-02-09T14:22:17Z")
> [@gotpasswords](#): > > The hull design efforts for cruise ships today is focused on a smooth, stable ride. When you’re spending about $1,500-2,000 a person to go nowhere fast, you don’t really care how fast the ship can go - you just care that you get to Aruba and Half Moon Cay, or wherever it is the travel agent said you were going to, and that the ship doesn’t list so badly that you spill a drink… Perhaps more to the point, passengers don’t want to be seasick. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [February 9, 2010, 2:47pm UTC](https://boards.straightdope.com/t/how-fast-an-ocean-liner-could-we-build-today/528039/33 "2010-02-09T14:47:00Z")
> [@MarcusF](#): > > I think the point is that there is one hell of a difference between stabilising a gun - max weight a few tons, probably a lot less - and stabilising the entire passenger space of a large ship. No idea of the precise split but the QM2 is 148500 gross tons. Assume only a 1/5 of this is the passenger compartments, gyms, restaurants, swimming pools, etc. (I am sure it is more an a 1/5 but just say) we still have to stabilize a 29000 ton mass! Not the same problem as a tank gun. I agree it’s not the same problem, however, it’s worth noting that the mass of the object is a factor that would assist in stabilising it (per Newton’s first law of motion - things tend to stay the way they are, big things even more so). The really big problem here is the engineering of making it possible for the passenger space to _be_ stabilised - i.e. building a monumentally huge gimballed box, installing it inside the ship with enough elbow room to maintain its orientation as the ship pitches, rolls and yaws, and making it possible to move people and supplies etc between the stabilised and non-stabilised sections of the ship. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [February 9, 2010, 2:49pm UTC](https://boards.straightdope.com/t/how-fast-an-ocean-liner-could-we-build-today/528039/34 "2010-02-09T14:49:04Z")
> [@MarcusF](#): > > The [_Queen Mary 2_](http://en.wikipedia.org/wiki/RMS_Queen_Mary_2) is a liner, designed to cross the Atlantic regularly so has a different hull shape and a speed of up to 30 knots. The [\*Freedom of the Seas \*](http://en.wikipedia.org/wiki/MS_Freedom_of_the_Seas) - that overtook the QM2 as the biggest passenger ship - is definitely a cruise ship with a normal top speed of around 22 knots. Well, he mentioned a passenger area on a catamaran that is (presumably) a lot smaller than the Queen Mary II. That said the tech clearly exists and I think the rest is just an engineering problem. For the Queen Mary II you’d just needs lots and lots of hydraulics. As a practical matter I do not see it. Such a thing would have to be prohibitively expensive I’d think not to mention all the space the stabilizers would take up. Still, there is an easier way. Modern cruise ships [do have stabilizers on them](http://www.eurodamnews.com/2008/04/24/views-from-the-underbelly/). Basically wings that extend underwater and adjust to stop the roll on the ship. My parents were on such a ship and said while going through 12 foot seas the water in their glasses at dinner did not move. There are of course limits to how much motion any stabilizer can compensate for but apparently the modern cruise ships with stabilizers do very well at being steady in fairly rough seas. ---
**Author:** ![Clothahump](https://avatars.discourse-cdn.com/v4/letter/c/51bf81/32.png) [@Clothahump](https://boards.straightdope.com/u/Clothahump)\ **Post date:** [February 9, 2010, 11:09pm UTC](https://boards.straightdope.com/t/how-fast-an-ocean-liner-could-we-build-today/528039/35 "2010-02-09T23:09:37Z")
> [@handsomeharry](#): > > Hey! Let me do it! Sounds like fun!😃 > Is there anything I need to know? > > hh Don’t get near [the air intake](http://www.youtube.com/watch?v=GF3Iz7b95-8&NR=1). ---
**Author:** ![Sailboat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sailboat/32/461_2.png) [@Sailboat](https://boards.straightdope.com/u/Sailboat)\ **Post date:** [February 10, 2010, 1:19am UTC](https://boards.straightdope.com/t/how-fast-an-ocean-liner-could-we-build-today/528039/36 "2010-02-10T01:19:40Z")
It’s worth noting when talking about a supercarrier’s top speed that traveling at very high speeds will damage the props through cavitation. The propellers move through the water at high enough speed to leave tiny air cavities on their (trailing, I think?) edges, and the cavities collapse, causing tiny shocks that pit and erode the metal. Submarines can evade this damage if they go deep enough that water pressure prevents the cavities from forming (deeper=higher speed before cavitation). Cavitation also makes noise, which another reason why submarines are concerned about it. You run a _Nimitz_ at its classified top speed when the purpose is important enough to justify later prop replacement, not all the time. ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [February 10, 2010, 2:45am UTC](https://boards.straightdope.com/t/how-fast-an-ocean-liner-could-we-build-today/528039/37 "2010-02-10T02:45:08Z")
> [@MarcusF](#): > > No idea of the precise split but the QM2 is 148500 gross tons. Assume only a 1/5 of this is the passenger compartments, gyms, restaurants, swimming pools, etc. (I am sure it is more an a 1/5 but just say) we still have to stabilize a 29000 ton mass! Not the same problem as a tank gun. I really need to save the next few sentences somewhere so I can cut and paste them as a matter of course into every single thread concerning ships as a matter of course: it’s an issue that comes up pretty much every damn time. Gross registered tonnage is a measurement of volume not mass. The mass of a vessel is its displacement tonnage. The QM2’s displacement tonnage is according to Wikipedia approximately 76,000 tonnes. So your 1/5 would be 15,200. Which means your point is still utterly valid, but anyway, carry on. > [@Mangetout](#): > > The really big problem here is the engineering of making it possible for the passenger space to _be_ stabilised - i.e. building a monumentally huge gimballed box, installing it inside the ship with enough elbow room to maintain its orientation as the ship pitches, rolls and yaws, and making it possible to move people and supplies etc between the stabilised and non-stabilised sections of the ship. It’s not that easy. The vessel also goes up and down vertically also. Which is one of the worst forms of motion for seasickness in my experience. Admittedly this is going to be a much smaller effect on the QM2 than on a yacht. > [@Sailboat](#): > > It’s worth noting when talking about a supercarrier’s top speed that traveling at very high speeds will damage the props through cavitation. The propellers move through the water at high enough speed to leave tiny air cavities on their (trailing, I think?) edges, and the cavities collapse, causing tiny shocks that pit and erode the metal. I am not sure about this at all. Cavitation is a function of prop shape, and prop placement. IME adjustment of skew, pitch and rake of the prop used, and ensuring there is nothing forward of the prop causing turbulence, can usually stop cavitation. There are speedboats that can run a prop orders of magnitude faster than the prop on a large vessel without damage. I think you are confusing what occurs when something goes at a speed beyond the limits of standard operating speed, and what is possible. I don’t know that much about it though, so I could be wrong. ---
**Author:** ![Sailboat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sailboat/32/461_2.png) [@Sailboat](https://boards.straightdope.com/u/Sailboat)\ **Post date:** [February 10, 2010, 3:47am UTC](https://boards.straightdope.com/t/how-fast-an-ocean-liner-could-we-build-today/528039/38 "2010-02-10T03:47:57Z")
> [@Princhester](#): > > Cavitation is a function of prop shape, and prop placement. IME adjustment of skew, pitch and rake of the prop used, and ensuring there is nothing forward of the prop causing turbulence, can usually stop cavitation. There are speedboats that can run a prop orders of magnitude faster than the prop on a large vessel without damage. I think you are confusing what occurs when something goes at a speed beyond the limits of standard operating speed, and what is possible. I don’t know that much about it though, so I could be wrong. [Here’s](http://en.wikipedia.org/wiki/Propeller) what Wikipedia says. It doesn’t say how common or expensive [supercavitating propellers](http://en.wikipedia.org/wiki/Supercavitating_propeller) are, nor does it explicitly say there’s no damage. However, aside from those quibbles, looks like you are right about (some) speedboat props. Looks like my understanding is (roughly) correct for “subcavitating” propellers. ---
**Author:** ![pancakes3](https://avatars.discourse-cdn.com/v4/letter/p/ba9def/32.png) [@pancakes3](https://boards.straightdope.com/u/pancakes3)\ **Post date:** [February 10, 2010, 4:13am UTC](https://boards.straightdope.com/t/how-fast-an-ocean-liner-could-we-build-today/528039/39 "2010-02-10T04:13:52Z")
> [@robby](#): > > I am not a marine engineer, but I was in the U.S. Navy. > > There are a few things that can be done to speed up ships that haven’t been mentioned. Most of these aren’t really applicable to something the size of a cruise ship, though. > > One is to use … i just wanted to add that they could also change the material. aluminum is a lot less dense than steel - less boat in the water - less displacement. that’s what the brits tried for some their warships, but the flip side of the coin is that aluminum is essentially tissue paper in war terms. the result is the infamous faulkland sinking. cite? my college chemistry teacher. i never bothered to factcheck. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [February 10, 2010, 4:29am UTC](https://boards.straightdope.com/t/how-fast-an-ocean-liner-could-we-build-today/528039/40 "2010-02-10T04:29:10Z")
> [@pancakes3](#): > > i just wanted to add that they could also change the material. aluminum is a lot less dense than steel - less boat in the water - less displacement. > > that’s what the brits tried for some their warships, but the flip side of the coin is that aluminum is essentially tissue paper in war terms. the result is the infamous faulkland sinking. To be fair are any warships seriously armored anymore? The days of the insanely armored battlewagons are long gone. Thought in the modern era with over the horizon targeting and accurate missiles and all that they opt for killing the other guy first rather than surviving getting hit. To be sure, by their nature and size and metal composition they have some toughness but nothing like WWII standards I think. [Previous page](https://boards.straightdope.com/t/how-fast-an-ocean-liner-could-we-build-today/528039.md?page=1) [Next page](https://boards.straightdope.com/t/how-fast-an-ocean-liner-could-we-build-today/528039.md?page=3)