What is the quietest, most efficient form of ship propulsion?

Discussion in 'Boat Design' started by JosephT, Feb 4, 2016.

  1. fredrosse
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    fredrosse USACE Steam

    Run Silent

    Submarines with electric propulsion are very quiet, at least if they are going slow. Nuclear subs tend to make more noise, running a big steam plant, along with a noisy gear reduction system to get the high RPM of a steam turbine down to a few hundred RPM needed at the prop. While working at Electric Boat (where subs are made) we were told that the Natalus (first nuclear sub) could be detected leaving England with noise sensors in the USA.

    A steam plant, with a slow turning direct drive engine, and a hand fired natural draft boiler, is probably a close second to battery-electric, and far less noise than any diesel-electric or other internal combustion engine drive system.
  2. daiquiri
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    daiquiri Engineering and Design

    Excellent points, thanks. I have forgotten to consider the vortex shedding in my comment about sailboats.
  3. Powerconversion
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    Powerconversion Junior Member

    Diesel electric using sterling engines could be quiet except the switching noise from frequency converters.
  4. JosephT
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    JosephT Senior Member

    I've done quite a bit of sailing. The whales we encountered followed us around at times and didn't seem to mind a bit about light turbulence generated by the hull & rudders.

    I do know the US Navy has taken a lot of heat for doing sonar testing. I think this study is targeted towards the main culprits (big ships that make loud noises).

    It would be interesting to know if there is an official engine + hull noise standard for ships these days (or at least one that meets the requirements of the study). As the fleets of global ships expand, so with the harassment of the whales and other sea life.
  5. fredrosse
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    fredrosse USACE Steam

    " Diesel electric using sterling engines could be quiet except ................"

    I do not understand, what is the meaning here. Diesels and Stirlings are far different machines, one is a well established technology, the other is still waiting to become practical.
  6. gonzo
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    gonzo Senior Member

  7. upchurchmr
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    upchurchmr Senior Member

    Nuc is not quietest.
    A battery powered diesel boat is quietest while on battery.
    Nuc's have lots of auxiliary equipment (generators/ pumps) required to operate which the battery powered boat does not.

    The noise radiated will also depend upon speed.
    A sub at 20 kts is a lot more noisy than at 2 kts, which is cruising speed, for that reason.

    Edit: I just saw similar posts, you beat me to it guys. :)
  8. Justaguy
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    Justaguy Junior Member

    Was looking for info on this a few months ago. Below are some things I found. Of course, I can't find the one that I think included natural sound. Due to the groovy music, you'll need to use your imagination about the quietness or lack of same:

    12m yacht:

    Cargo ships:

    Just for fun:
  9. portacruise
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    portacruise Senior Member

    The Gotland class is supposed to be the quietest sub, not counting what has been kept top secret. http://military.wikia.com/wiki/Gotland-class_submarine
    It uses both diesel and stirling to extend range as well as slow turning screws, and various other techniques for sound reduction.

  10. rubenova
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    rubenova Junior Member

    A nice, big Atlas-Imperial loafing along at a few hundred rpm. No reduction gear, a lovely steam engine like puffing exhaust note, a large prop with little cavitation...THEA FOSS introduced me to these engines, just wish I could get back aboard for a cruise.
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    FAST FRED Senior Member

    Being realistic the folks willing to pay for quiet are submarines and survey boats that want the best numbers by not scaring the denizens of the deep..

    There effort at QUIET! has been to install the engine on a frame that accepts the engine motor mounts and an extra set under the frame .

    Expensive , and mostly works best at a designed RPM , but very little engine and hull noise is put into the water.
  12. tom28571
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    tom28571 Senior Member


    Sounds reasonable to me. As for a quiet power source, Stirling engines are probably quieter than any internal combustion engine although any engine that pulses air makes noise.

    Much testing of effects of noise (especially pulsed sound) on ocean creatures has been done in the Bahamas "Tongue of the Ocean" by the US Navy AUTEC facility. Some data may be available.
  13. Angélique
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    Angélique aka Angel (only by name)

    Maybe the quietest, but it seems not to be the most efficient form of ship propulsion . . . .

    Magnetohydrodynamic drive
    The world's first working prototype using MHDs in 1991: Yamato 1

    TIME Technology: Run Silent, Run Electromagnetic (Note: need to subscribe for full story)

    P.S. - Popular Science, November 1992, page 80 - 85, Superconductivity Goes To Sea
    Popular Mechanics, August 1990, page 60 - 62, Jet Ships
    Skews.Me - Magnetohydrodynamics (MHD)
  14. fredrosse
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    fredrosse USACE Steam

    Heat Engines

    Some Background about Heat Engines:

    All heat engines operate between a "Hot" (High Temperature) heat source, and a "Cold" heat sink. The maximum theoretical efficiency of any heat engine was defined in the 1820s by Sadi Carnot, and is equal to:

    Carnot Efficiency = 1 - Tcold / Thot

    Where the temperatures here are on the absolute temperature scale. Degrees Rankine = (460 + F) in the English System of units, Degrees Kelvin = ( 273 + C ) in Metric.

    For heat engines we common folk use, the "Cold" temperature is something around ambient temperature, 100F = 560 Rankine, and the "Hot" temperature is limited by the metals we use for engines, something approximating 1000F = 1460 Rankine. Therefore you have a maximum efficiency of about:

    Carnot Efficiency = 1 - Tcold ) / Thot = 1 - 560 / 1660 = 0.61

    Actual efficiencies for real engines are lower, the current real maximum efficiencies in today's world run from about 40% to 55%.

    Taking an example for an engine with 45% efficiency (typical of Diesel Engines of today's world), 100 units of fuel energy are input, 45 units of output energy are produced at the shaft, and 55 units of "cycle reject heat" are dumped to the ambient surroundings. What goes in equals what comes out.

  15. fredrosse
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    fredrosse USACE Steam

    Gotland Class Submarines

    With reference to the previous post about "Heat Engines":

    The Gotland Class Submarines use a Stirling engine, where the heat input source is taken from ambient sea water, and the cold heat rejection is a vat of boiling liquid Oxygen, a very low temperature.

    This Stirling engine, where the "Hot" temperature is the ambient sea water temperature, about 70F (530 Rankine), and the cold sink temperature is boiling liquid Oxygen minus 362F (98 Rankine), the Carnot Efficiency looks much better:

    Carnot Efficiency = 1 - Tcold / Thot = 1 - 98 / 530 = 0.81

    I don't know the actual efficiency of the Stirling Engine used in these submarines, but the Stirling Cycle can approach Carnot efficiency, and if, for example this engine has an efficiency of say, 75%, then with 100 units of energy supplied from sea water, shaft output would be 75 units of energy, and reject heat energy is only 25 units of energy. The 25 units of energy boils away the stored liquid Oxygen and the process can continue as long as there is a storage of liquid Oxygen.

    The other main benefit here is the boiling Oxygen, when liquid Oxygen boils, it gives off gaseous Oxygen, which is very good for the crew on a submarine spending long periods submerged.

    While this arrangement is workable for a military submarine, with budgets so large that using liquid Oxygen might even be considered, it is totally unworkable in anything we might consider on the civilian side of propulsion.

    So the point here is, while an interesting technology, Stirling engines do not belong in this discussion in any reasonable way.
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