Pushing Boundaries

There’s No Replacement For Steam Displacement

Yesterday, we all stood in awe at the big engine. However, it’s too…modern. So, I am making up for it today with this big engine. Oh, and it belonged to the RMS Titanic.

The steam ship had been around since the 1770s, and the idea had been around for a hundred years more. Like any technology it improved over time. In the world of shipping, improvement usually means bigger.

This meant trans-ocean shipping was now faster, more economical, and, in the case of passenger liners, more luxurious. People of means were clamoring for the chance to sail the open waters without sails. The more people you could put on a ship, and the more amenities you could offer, meant more dollars or sterling pounds in the ship owner’s pocket.

The pinnacle of early 1900s luxury liners was the RMS Titanic. She was the biggest ocean liner built to that point. She was also one of the most powerful.

She had two four-cylinder reciprocating triple-expansion steam engines, like the one above. Each engine was capable of making 15,000 hp for the two outboard wing propellers at 75 revolutions per minute. She also had a low-pressure steam turbine, fairly new technology at the time, that made 16,000 hp and drove the center screw. She was supposed to have three steam turbines, but the ship builder was unable to get the Admiralty to help with their expertise. Probably because Cunard was using them for their big ocean liners.

This was enough to propel the Titanic at a cruise speed of 21 knots, slightly slower than the big Cunard ships, but still respectable for such a large ship. With all three engines pumping out their maximum of about 59,000 shaft horsepower, the luxurious floating entertainment vessel could do 23 knots.

These engines were fired by steam from 29 boilers fired by 159 coal furnaces.

[Image Credit: rmstitanicremembered.com]

  • The Professor

    Looking at this beast, it appears to have some common points with your last post. It looks like the crank and con rods connect to a crosshead, and then the pistons connect to that. Is that right or am I seeing things?

    • Most steam engines are double acting: steam is alternatively admitted at the top (like an IC engine) and the bottom of the cylinder. As a result, the piston rod travels through a seal and can not be hinged to the piston. Similar construction is used for hydraulic cylinders used, among other things, on construction equipment.
      A double acting engine produces two power pulses per cylinder per revolution of the crankshaft. A two cylinder, double acting, steam engine is self-starting and reversible.

      • What he said.

        Also, I forgot to mention that the two outboard steam engines had a high pressure cylinder, an intermediate pressure cylinder, and two low pressure cylinders. The steam from the boilers came in as a high pressure and entered the HP cylinder, forcing it down and then traveling to the IP cylinder (slightly larger bore) forcing it down then on to the LP cylinders, forcing them down. So, rather than have an "intake manifold" like on an IC engine, the steam is travelling through passages opened and closed by the cylinders themselves.

        • The Professor

          Dealing with engines of this size, and with steam engine in particular, requires a very different way of thinking as opposed to 'normal' sized engines. It's not just 'normal sized' scaled up. I guess that's part of what makes them so interesting.

          • Absolutely. They're like a different beast altogether.

    • Most steam engines are double acting: steam is alternatively admitted at the top (like an IC engine) and the bottom of the cylinder. As a result, the piston rod travels through a seal and can not be hinged to the piston. Similar construction is used for hydraulic cylinders used, among other things, on construction equipment.

  • P161911

    Torque specs?
    I know that steam engines make HUGE amounts of torque. The Doble steam cars only had about 150HP, but 1000+ ft./lbs. of torque.

    • Using Torque=(5252*hp)/RPM I get 1050400 pound-foot for the two outboard engines. The inboard turbine made 509284 lb-ft. Note, the center turbine turned at 165 rpm. Also, it was non-reversible.

      • P161911

        Over 1 million ft. lbs. of torque sounds more like what it would take to move a huge ship. 59,000 HP, just seemed too low. That only about 8 Top Fuel dragsters or 59 Veyrons.

        • tonyola

          Very low revolutions per minute will do that.

        • Oh, that's each outboard engine! Altogether, the Titanic made 2.5 million torques!

    • tonyola

      The Doble engines, like all steam engines, made near-maximum torque at 0 rpm, unlike gasoline engines. However, the engines did not rev highly, which explains the fairly low HP numbers. At 75 mph, the Doble engines were only turning around 900 rpm.

      • The Professor

        I've seen the same sort of operation as the Doble in some steam locomotives, although don't ask which ones (it's been a log time). Did Doble get the idea from the locomotives or vice-versa?

        • Steam engines are usually directly connected to whatever device they are powering (wheels for locomotives and cars, propellers for boats and planes. Yes, planes, look it up).
          On many locomotives, the entire drive train is right out in the open. It was done to ease maintenance and also provided more space for large cylinders. On steam cars, the engine (usually two double acting cylinders) was located at the back, driving the outer casing of the differential. On some vehicles, a single gear reduction was present between the engine and the wheels. I'm not very familiar with steam cars, but special purpose locomotives, such as the Shay, gearing allowed event higher torque at the wheels. They were primarily used on Logging operations were high pulling power on steep grades was more important than speed. More info here: http://www.gearedsteam.com/ WARNING: that site may reduce your productivity.

          • (click)…

            Aw damnit. (click, click, click, click)

          • The Professor

            I've seen one of those Willamette's before, somewhere in Oregon. Damn, it's been too long, I can't remember where. I do remember those odd drive mechanisms though.

          • There goes my day.

  • The Professor

    I found a nice picture of boilers used in the Cunard liner Campania, that are probably similar to the Titanic's:

    <img src="
    http://img.photobucket.com/albums/1003/PeterS/Campaniaboilers1024x682.jpg&quot; width="500" border="2" style="border:2px solid black;" alt=" " />

    From PracticalMachinist.com

  • Sonny

    i do believe that the titanic had no reverse gear or am i wrong and why was there three propellers on the rear end and the

    mid drive prop not driven for reverse having said that, mid prop was always in neutral and if they had designed the mid prop's

    shaft driven to be reverse with 2 cylinders driving the mid prop and the 3 cylinders on the left the other 3 cylinders on the right

    it would have been a inline double three on the sides and a extra inline 2 you wouldn't have the ship always going forward

    and when the man controlling the huge ship could of had mid prop reverse and neutral for turning and 6 cylinder shutoff

    for safety. that would have been better and the .Royal Mail Ship. wouldn't have sank into the bottom of the sea.