How fast can a liner go


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Feb 13, 2004
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How fast can a 1000 ft liner travel? If equipped with some form of nuclear power, could a ship this size approach 70 knots? or more?
 
Jan 21, 2003
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Hate to say it little over 70 mph is a little intense for a liner to go and the least to say dangerous. I know 1000 foot freights on the lake can reach up to 16 knots or more.
 
Jul 9, 2000
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>>If equipped with some form of nuclear power, could a ship this size approach 70 knots? or more?<<

While this may be doable with some of the more exotic hull forms, I don't think you're going to see it with a 1000 foot anything in the forseeable future. Nuclear power isn't quite the supercharged magic bullet that a lot of people think it is. It's not the Starship Enterprise producing a stream of plasma which fires up the warp coils. What you do with nuclear power is use highly enriched uranium in a sealed vessel to put a lot of heat into water which is circulated through a closed system to a heat exchanger. The heat exchanger transfers that heat into water in an "open" system which flashes into steam, the steam of which is in turn used to spin the turbines.

In other words, a nuclear plant is really little more then a fancy way to make steam, and a steamship is going to have all the strengths and limitations that come with whatever hull form it's pushing through the sea. It's biggest single advantage is that it can produce power consistantly for years, even decades, befor the core is sufficiently spent that it has to be replaced.
 
Jul 11, 2001
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Evan, Try looking into the SS.United States. I'm not sure the exact length, but its' turbines could keep her humming along at 40+ knots.
 
Feb 13, 2004
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Thanks! So basically the United States was pushing the limits for speed and a liner that size couldn't travel much over 40 knots?
 
Jul 9, 2000
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>>Thanks! So basically the United States was pushing the limits for speed and a liner that size couldn't travel much over 40 knots?<<

That's about the size of it. The sort of hull used imposes some very definate limits on what could be accomplished with it and that's due to the problems you run into with hydrodynamics. A really large monohull won't be good for much beyond 44 -45 knots no matter how powerful the plant because the water resistance increases with speed. Eventually you get to a point that even if you double the power available, you'll only get a knot or two more.
 

Jack Devine

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Jan 23, 2004
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I understand that the current USS Enterprise was originally built with eight (!) reactors, one for each boiler that it replaced. With all eight teakettles online, the ship could be driven fast enough to risk damaging the hull from the pounding and stress. I don't know what speed was finally reached, but it probably was not much beyond 45 knots, if any more than that. As Michael said, water resistance increases with speed, and eventually you just can't push the water out of the way any faster.
 
Oct 28, 2000
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Broadly speaking, there are two types of hulls: displacement and planing. Ocean liners are displacement vessels, meaning they do not rise up and ride on top of the water as planing hulls do. The top speed of displacement vessels is limited by their waterline lengths, while planing hulls have only horsepower as a practial limitation.

The theoretical maximum speed (in knots) of a displacement vessel is called "hull speed." The rule-of-thumb for determining this on smaller vessels is 1.35 times the square root of the waterline length. Using this formula Titanic works out to have about a 40 knot hull speed.

That 1.35 is known as the "speed length ratio." Whenever it reaches 2, by definition the vessel is operating in the planing mode. To get "on plane" it is necessary to make the water break cleanly away from the stern of the vessel. This is why fast powerboats have a sharp "corner" where the transom meets the bottom. Titanic had a "fair" run aft with no such sharp discontinuity. Titanic's stern was intended to be efficient at displacment speeds.

It takes very little horsepower to get even a huge ocean liner moving. But, speed is expensive. Look at the size, complexity, and coal hunger of Titanic's plant just to get 22 knots.

Lots of other factors limit a large ship's speed well before it reaches hull speed. One is just the frictional resistance of the water passing against the skin of the vessel. Another is the resistance caused by the waves the ship creates as it moves through the water. And, eddy making resistance caused by things like Titanic's outboard wing propeller supports can also cause resistance.

--David G. Brown
 
Jul 9, 2000
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>>I understand that the current USS Enterprise was originally built with eight (!) reactors, one for each boiler that it replaced.<<

She still has them too. Eight reactors feeding 32 heat exchangers if I recall correctly. I seriously doubt the Enterprise ever made 45 knots, though 'tween the decks, there was always the "Golly-Gee-Whiz-Willikers-Wow" jabberjawing that had her doing something a little short of lightspeed.

The thing with a nuclear powered vessel is that any ship so powered can do her best speed for months, even years on end, until the core in the reactor is spent to levels that are no longer useful. That's why a nuclear powered vessel is often held to have virtually magical attributes when in reality, it's really no more then a steamship that has a fancy and long lasting way to boil the water.
 

Jack Devine

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Michael, you're absolutely right. It's funny how we perceive "nuclear powered" as just short of Star Trek, yet it's simply another way to make steam. It's ironic that we also seem to perceive steam engines as quaint and outmoded, pretty to see at the county fair but otherwise not very useful. (I suppose you could make quite a scene at the county fair if you brought a small reactor to power the steam tractor!)

David, thank you for the detailed post. I've noticed that quite a few merchant vessels and warships have a blunt square stern, apparently for functional reasons. Does this create any drag penalty compared to a narrowed stern?
 
Jun 10, 2004
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Nuclear plant provide the distinct advantage of rendering a large warship independent of fuel supply. This is pertinent if a great warship like an aircraft carrier is to be on station for months in a politically fractious zone. Until quite recently, I don't think you could develop sufficient power with diesel engines to drive an aircraft carrier, so that left steam turbines, which give you great power, but guzzle oil like there's no tomorrow.
Just recently very large (100,000hp) diesel engines have become available. Three such engines would drive even the biggest warship quite economically, so maybe the need for nuclear is not quite so great now. Motor ships have vast range due to the very high thermal efficiency of diesel engines. Even during WW2, the German navy developed an ocean-going U-boat that could motor around the world without refuelling (on paper, on operations it could not do that). One such sub made it to Japan and back during the war.
 
Oct 28, 2000
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Jack -- regarding sterns...aahh!

Now, as to boats...look at any high-speed powerboat and you'll notice a flat transom that meets the bottom at a sharp angle. This sharp change helps the water break free of the bottom at planing speeds. In fact, you can't really get a boat to plane off without that sharp, virtually 90-degree angle.

At slow speeds things are different. Yes, the broad flat transom creates drag. That is, it creates drag if it is immersed in the water. For maximum efficiency you need a "run" aft that allows the hull to break free without creating drag-inducing burbles in the water.

The large ships that I've seen tend to have a smooth run aft under water, then a flat billboard of a transom above. This reduces drag while allowing the more economical slab wall construction of the transom. There is no overhanging counter as it is relatively more expensive to build and does not add greatly to the paying cargo capacity.

Good design in anything, but most especially ships and boats, should be "eye sweet." It should be pleasant on the eyes. This modern chopped-off look is an abomination in the sight of God or anyone else who happens to be looking. But, it's cheap which means it follows the "golden rule" -- he who has the gold, rules.

The eliptical stern of Titanic was not the result of a higher sense of aesthetic values. It combined the necessary run aft with a protected area for the quadrant of the steering gear. In other words, form followed function. Still, the design office at H&W achieved the goal of "eye sweetness" through the use of a decorative knuckle under the poop, the correct choice of ellipse, etc. None of this made the ship a whit faster, burn less fuel, or carry more passengers. Today, the extra cost of beauty would not be a design consideration.

-- David G. Brown
 

Jack Devine

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Interesting, thanks for explaining the gawdawful looking sterns of so many modern container ships. "Abomination" is right, these ships don't look like they have an actual stern, it's just the point where they stopped building.
 

Noel F. Jones

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The counter stern loses function with increasing size. Its classic function was to maintain seakeeping by enabling the vessel to counter(?) potentially dangerous following seas.

Very pertinent with such as a tea clipper running down the easting in the Southern Ocean but in the case of the Olympics etc. the counter stern was little other than an aesthetic and anachronistic embellishment.

Also, the larger the vessel the greater the unsupported weight, giving rise to an unnecessary sheer force and bending moment at the after extremity.

Noel
 
Jul 9, 2000
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>>Three such engines would drive even the biggest warship quite economically, so maybe the need for nuclear is not quite so great now.<<

I don't know about that. Nuclear power has quite a number of tactical advantages which are useful for a warship, not the least of which is endurance measured in years rather then in miles. The cores used on modern submarines are designed to last for the projected 30 year lifespan of the vessel and the cores of a nuclear carrier are disigned now...so I've been given to understand...to last for up to half a century, thus eliminating the need to recore the reactors.

The problems are that the system is so bloody expensive, requires numerous safety devices to prevent a reactor breach in the event of an accident, are weight intensive because of all the sheilding required, and present a signifigent problem for disposal after the cores are spent or the ship is too old to be useful. They cores can be recycled to get some useful material, but that only goes so far, and the waste that's left over will be dangerously radioactive for centuries to come.

The reactor sections of U.S. Navy ships that are being scrapped at the Puget Sound Naval Shipyard are cut out almost in their entirity for burial at the Hanford Facility. They're too hot to handle otherwise.
 
Oct 28, 2000
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Noel -- never saw the obvious relationship of counter to counter before. Thanks for the tip. I'll be looking for the etymology of that.

--David G. Brown
 
Feb 7, 2005
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For what it's worth..."Origins of Sea Terms" by Rogers says that the origin is uncertain, but may be from the French term "contre arcasse", the curve of the stern. As far as function, "The Oxford Companion to Ships and the Sea" by Kemp states that tugs are always built with a counter to "keep their towing hawsers, when they fall into the water, clear of the propellers." Perhaps there was a similar reason for larger ships involving lines, either for docking or towing (?).

Denise
 

Noel F. Jones

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"As far as function, "The Oxford Companion to Ships and the Sea" by Kemp states that tugs are always built with a counter to "keep their towing hawsers, when they fall into the water, clear of the propellers.""

Sounds like another flight of fancy to me (vide 'the devil and the deep blue sea' rubbish).

I would have thought tugs were designed so that the counter would combine with the significant tumble-home of the bulwark down aft to put the protective belting (chafing strake, on the knuckle) outermost on the hull and thus duly protective of it.

Counter sterns, in their day, must have been a menace to attending tugs - at risk of getting under the counter during manoeuvreing.

Noel
 
Oct 28, 2000
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On older tugs that I've seen the tiller is a quadrant mounted above deck and pointing aft. It swings an arc that describes the tugboat's rounded stern. Steering is accomplished by chain and cable from the wheel to the quadrant. The total of this design provides a steering system in sight for easy maintenance and repair. And, the resulting counter protects the propeller and rudder from errant barges, etc.

Noel's comments about the counter providing a place for the protective belting are valid. So, the counter design on a vintage tugboat was not only pretty, but also an elegant combination of form and function.

Once a rope gets into the water, it has an unerring desire to tangle in a propeller. This is true without regard to the design of the stern of the boat. Only good seamanship on the part of the deck crew prevents the problem. You learn pretty quickly never to trail lines from a powerboat.

The counters of large ships may have knocked down a few of the old "stovepipe" smokestacks on steam tugs. However, the real problem in tugging around big ships is being "tripped," or rolled over by the strain of your own tow line. If the hawser comes at right angles to the tug's keel, the strain is upsetting. Tugs have been known to roll so quickly that men in the open on deck were trapped beneath them and killed.

Titanic's stern was an enlargement of the same design used on sailing vessels. As Noel pointed out, it was designed to lift the stern in a following sea. Being "pooped" by a wave (a following sea breaking onto the fantail) was a real threat to windwagons. In fact, on the Cape Horn route steering was reportedly more dangerous than climbing in the rigging for this reason.

-- David G. Brown
 
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