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

General propulsion question: What is the quietest, most efficient form of ship propulsion? Just read the story below and it's clear loud, noisy propulsion systems negatively impact killer whales and perhaps other sea life.

"...their echolocation abilities are greatly reduced by disturbing sounds made by vessels."

http://www.lighthousenewsdaily.com/ship-noises-severely-impact-killer-whale-populations/4288/

I do recall some electric drive systems by Siemens. Are they quieter than diesel or older fuel oil engines? Soundproofing around the engine compartment and in the lower hull seems like it would help too.

 

Sails.

 

LOL daiquiri you're quite clever. Excluding the stealth quietness of sails, what is the quietest propulsion system out there (e.g. with propeller). It would seem they would be in this order from quietest to loudest:

1. Total electric (no auxiliary generator). Granted there are not many of these out there in larger boats, but in theory they are quietest.

2. Generator + electric drive.
e.g. http://www.industry.siemens.com/verticals/global/en/marine/passenger_ships/propulsion/eco_prop/pages/default.aspx

3. Nuclear (don't really know how loud the tubines are, but they don't bang a lot like combustion engines.

4. A gasoiline engine (mainly used for smaller boats)

5. A pinging diesel that will make your ears bleed!

 

quiet means peaceful or silent ?, for men or for marine life?. Disturbances from the engine or propeller?

 

@ TANSL pure silence may be unattainable, so the quietest design for marine animals. Such a system would most likely achieve a quieter environment for man as well.

Is there anything that competes with the Siemens eco-prop? This 100HP engine from Elco looks interesting.

 

For a power source, Nuclear is quietest by a lot.

FWIW, radiated noise has nothing to do power sources and everything to do with implementation details. Sailboats are noisy compared to other things.

 

Ok, you've got my attention JH.
Could you elaborate on this, please?

 

Kites are the most quiet. Large ships are using them now. Also, they can be flown at great altitude making them silent.

 

I would have thought that whatever the means of propulsion, the speed played a critical role in how much noise is generated.

Do we know if it is any particular noise that is problematic? I'd guess that engine and prop created more problems than wake and bowwaves, but I'm guessing.

 

When I worked in offshore oil surveys, we towed arrays of air guns to make enough noise for the hydrophones to pick up echoes. The cable was one mile long with a hydrophone every 25 meters. The concussion was enough to lift the stern of a 185' tug every four seconds. Dolphins and porpoises would follow us routinely and didn't seem affected at all.

 

A bit like someone fired a shotgun close to your ear every four seconds...
It is very hard for me to believe they were not affected.

 

It seems incredible but, well, I was not there.

 

Cetaceans are most definitely affected by noises. They may not make their pain evident but they endure it without identifiable evidence.

Whether prop and engine noise is bothersome to them is not yet definitively determined. One would suppose not, judging by the frequency of dolphin play around powered vessels in motion. Supposing not is not a reliable indicator of whether we are causing distress to these marvelous creatures.

 

"Noise" in the water is nothing but a cyclic pressure disturbance over a relatively short time. What is "noisy" is large del P/del t in a frequency of interest which is above background noise. Tides, for most locations the largest del P, are not considered "noisy" because del P/del t is so small. Likewise, rain can be overwhelming to specific sensors, like your ears. The bow feather of a racing cat or the vortex shedding of a dagger board can be very "noisy" compared to a well designed submerged body of revolution.

They were probably eating the stunned fish.
Anyway, it is important to note what I mentioned about sensors above. A normal depth sounder would never "hear" an air gun and likewise the seismic array wouldn't "hear" the depth sounder. Most likely the dolphin's melon is too small to have significant del P/ del t from the pulse because of the cube law and the bubble oscillation frequency. Being right next to it when it goes off and catching the direct pulse is another matter, but they are smarter than that.

 

Do not anthropomorphize cetaceans; though they are smart and feel pain like any animal, they are evolved, like humans, elephants, and bats to sense specific frequencies. Given the energy in the pulse they are capable of producing, you would have to be almost within touching distance of one to be louder than their own pulse. That is not to say that close fish-finding sonars don't interfere with their hunting sonar, because that is what both are. Otherwise, just like we don't hear elephant and bats unless they are close, they really don't hear us unless we are very close.