Model Boat Mayhem
Mess Deck: General Section => Tugs and Towing => Topic started by: 6705russell on July 26, 2010, 08:56:00 pm
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This is a good site to show how these units work, if you download from the link at the bottom it lets you control....
http://www.voithturbo.com/vt_en_pua_marine_vspropeller.htm
Russ
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I realise Voith are much more manoeuvrable but HP for HP I wonder what the efficiency difference between Propeller and Voith drive is?
(ie. how do the bollard pulls compare?)
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%)....here is a simplified gearbox efficiency table & we see a typical input power to output power is in the 83>88% band
http://www.controleng.ca/SSHelp1033/source/GearboxEfficiencyVsRpm.htm
If we consider the geometry of a Voith Schneider drive, we could again simplistically accept that they would fall into a similar efficiency % band
Interestingly....a simplistic mathmetical model of a convential rotating engine & direct drive via a prop shaft & bearings would only offer a few % points better or say 88>92% over the former
From this....... >>:-( ...the only real advantage of the costly & complex Voith Schneider drive is in their inherent steerability ........ O0 ....Derek
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I was simply going to say it was a matter of how much horse power was put behind the drive.
Both types of drives, VS, and Z drives can put up bollard pulls of 65 tons or more.
O0
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%)....here is a simplified gearbox efficiency table & we see a typical input power to output power is in the 83>88% band
http://www.controleng.ca/SSHelp1033/source/GearboxEfficiencyVsRpm.htm
If we consider the geometry of a Voith Schneider drive, we could again simplistically accept that they would fall into a similar efficiency % band
Interestingly....a simplistic mathmetical model of a convential rotating engine & direct drive via a prop shaft & bearings would only offer a few % points better or say 88>92% over the former
From this....... >>:-( ...the only real advantage of the costly & complex Voith Schneider drive is in their inherent steerability ........ O0 ....Derek
I believe that Voiths above all else can alter speed and direction near instantaneously. A Voith tug can keep its engines at full throttle while 'idling' the props and instantly engage them in any direction.
Conventional props are still the most efficient for any sort of distance towing.
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Having been on both Voith Schneider and conventional tugs there are several main differences.
The Voith units are less efficient at steaming as there is considerably more drag and the sculling motion is not as efficient through the water.
The depth of the units also give the tug a harsh pendulum effect which makes them very uncomfortable. They recover very quickly.
Most Tractor tugs will be used astern as the Voith units are positioned 1/3 of the length from the bow, this produces a wash that will reduce the tugs efficiency against a ships hull.
The Voith are far more maneuverable but at a cost. The units are more expensive to buy and maintain over their lifetime.
This is why Azimuth powered tugs have become by far the most popular - cost.
Small harbour tugs suffer from excessive draught so cannot operate in shallow waters.
I have been aboard when the Voith unit picked up a cable from the seabed - not nice!!!
The Voith Schneider units were developed for maneuverability and are very good at that, but there is a heavy cost associated with them compared to Azimuth so owners taking the cheaper route.
Bob