Voith Schneider Propeller

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The Voith Schneider Propeller (VSP), also known as a cycloidal drive (CD) is a specialized marine propulsion system (MPS). It is highly maneuverable, being able to change the direction of its thrust almost instantaneously. It is widely used on tugs and ferries; but in recent years, it has also been used in offshore vessels, like Platform Supply Vessels, or even in Offshore Accommodation Vessels. Therefore, it is assumed that it could also be a good propulsion system for a structure for colonizing the ocean.

The advantages that the VSP presents for a seastead can be summarized in these points:

  • The very rapid and precise thrust variation according to cartesian coordinates makes the VSP an ideal propulsion system for efficient dynamic positioning even in extremely rough weather conditions, something of a great help if a solution similar to an MOB (Mobile Offshore Base) is adopted for the seastead.
  • Redundancy of the entire propulsion system, which guarantees full control of the vessel even with only one power train in operation. In a structure accommodating so many residents, like a seastead, this is very important; the same redundancy is desirable in cruise vessels and offshore accommodation vessels.
  • It offers additional roll stabilization, which reduces the roll motion of the seastead (ship shaped) while it is stationary, avoiding the installation of an additional anti-rolling system (like active tanks). It implies that a VSP is a cheaper option compared to a solution of thrusters + active anti-rolling system.
  • The compact design and installation procedure makes the VSP suitable not only for traditional steel vessels but also for concrete barges, although use in concrete barges has not been tried before. The only difference in installation in comparison to a steel vessel is that the steel well flange would be bolted or attached in a different way to the concrete, instead of being welded directly to the hull.

These advantages results in a better solution when compared to traditional thrusters, if the dynamic positioning system is used instead of mooring system for keeping the position of the seastead in the middle of the ocean.

One of the offshore flotel vessels designed in the recent years, the Edda Accommodation, incorporates this propulsion system, precisely due to the advantages listed above.

One of the main reasons that explain why the VSP is being used in offshore vessels is the special features of the Voith-Schneider Propeller that allow very effective roll stabilization. Very rapid thrust variation and generation of very high moments makes it possible to use the VSP for efficient reduction of the ship’s rolling motion, in particular when the ship is stationary or during slow motion along the longitudinal axis, where other systems are limited. This additional function has been proven by Voith in theoretical computations with the University of Hamburg-Harburg, during model tank tests and full scale measurements in the North Sea.

References and more info at http://www.voithturbo.com/vt_en_pua_marine_vspropeller.htm

5 comments

  1. Carl Pålsson 10:05 pm

    Very interesting.

    Although I suspect the Voith-Schneider drives are only needed for very precise positioning with a walkway connecting to another platform.

    For positioning of a single vessel some distance away from the next one, I think something like Azipods will be cheaper. Not that I know what the VS propellers cost (or their propulsive efficiency), but they must have a lot more moving parts than the average azimuth thruster.

    600 beds, and something like 15000kW of propulsion units. Sounds like big energy bills and capital costs just for the pleasure of walking to the neighboring seastead. Place seasteads farther apart and you’ll only need a fraction of that.

    But it’s still interesting. Does anyone know how efficient the VS drives are compared to a propeller?

  2. Miguel Lamas 12:07 pm

    The main advantage of  the VSP compared to Azipods is:

    It offers additional roll stabilization, which reduces the roll motion of the seastead (ship shaped) while it is stationary, avoiding the installation of an additional anti-rolling system (like active tanks). It implies that a VSP is a cheaper option compared to a solution of thrusters + active anti-rolling system.

    The installation of an anti-rolling system could cost as much as 1 million of Euros. If we want to avoid the roll motion on a ship or barge, it is requested the installation of such a system. But with VSP it seams that it is not required, as per info from Voith-Turbo, due to its feature in roll stabilization.

    Regarding the power of propulsion units installed on the Edda Accommodation, it should be noted that it is the power required to achieve a speed of 13 knots. If we use the VSP only for keeping the position, the power would be much lower.

     

  3. Carl Pålsson 10:37 pm

    It offers additional roll stabilization, which reduces the roll motion of the seastead (ship shaped) while it is stationary, avoiding the installation of an additional anti-rolling system (like active tanks). It implies that a VSP is a cheaper option compared to a solution of thrusters + active anti-rolling system.

    Hmm.. we would need the total operating costs of the VSP system, Azipods, alternate roll-control system and so on to before we know what is cheapest, right?

    I’m thinking a couple of Azipods with variable pitch propeller blades would be just as fast as the VSP in changing the direction of the thrust. Variable pitch could make the complexity rival that of the VSP though, so that might not be much better. We need prices.

    What sort of alternative anti-rolling system are you thinking about? Stabilizer fins like on cruise ships only work at speed I would think.

    Regarding the power of propulsion units installed on the Edda Accommodation, it should be noted that it is the power required to achieve a speed of 13 knots. If we use the VSP only for keeping the position, the power would be much lower.

    Wouldn’t this also mean we could only keep position in a lot calmer seas. The Edda info says 5 meter waves (presumably with the gangway connected to another platform).

  4. admiral doty 7:19 am
    These propellors would be great for station keeping for a floating breakwater. We had a discussion on this a while back in relation to Vince Cate’s Tension Ring House Design and other floating breakwaters. The system can be modularly expanded to add additional servo-controlled sails and prop blades as the circular or hexagonal breakwater expands.
     
     
     
    Cycloidal Drive – Voith Schneider Propellor and sails

    A ring of cycloidal sails around the top of the ring and cycloidal propellor blades underneath could provide wind propulsion from any direction.  The rings spins from the sails changing angles to catch the wind while the prop blades change angle to provide thrust in the desired direction.

    http://en.wikipedia.org/wiki/Voith_Schneider_Propeller

     

    cycloidal drive: interesting

    For Vince’s circle tension house, the foamed concrete island, or some other lighter-than water structures that are extremely shallow in draft, (hexagonl lash barges, "Spiral Island"-like structures) I can imagine that instead of a few hydrofoils on a shaft, a setup where a chain- or track-driven set of hydrofoils that encircles the entire structure would be possible.

    larger propulsion surface = lower power, higher efficiency

    Yes, the idea is to have the sails and blades along the perimeter.  A larger propulsion surface reduces the velocity required and corresponding drag for a given amount of thrust.  This is similar in principle to a larger diameter fan requiring less power to move the same amount of air, or a larger diameter rotor requiring less power to produce the same amount of lift in a helicopter. If the breakwater ring spins then there is no need for the tracked drive train. The tracked drive train would make sense for a large solid structure like a barge.

    Capturing waves breaking on a sloped surface and channeling the water to produce thrust and run high volume, low head vane avial turbines to produce power may also be an option.

     

    Another good thing about this is, for a powered solution, the engine can be anywhere. The problem of vectoring thrust pretty much goes away. For redundancy, two engines could be located on opposite side of the structure and either balance the load or one can be a smaller engine kept in reserve for emergencies (this is a cost savings). Locating close to the edge makes it easier to service and fuel these engines.

  5. Miguel Lamas 10:05 am

     

    Stabilizer fins are used in navy and cruise vessels, as these type of vessels are most of the time sailing at a fixed speed. In offshore vessels, normally working at low speeds or even stationary, an active tank stabilizing system is used if we want to avoid the roll motion. The installation of such a system is quite complicate. According one of the manufactures of the system, the benefits of this system are:

      • Delivers 40-50 per cent roll reduction.

      • Efficiency is independent of ship speed. 

      • Improved ship performance and passenger comfort. 

      • Immediate response to any change in roll motion. 

    A good study can be donwloaded here: antirolling

    For me it is a surprise that Voith Schneider Propellers can act as an anti-roll system. I have not found such feature in any other propeller or thruster like Azipods. That is perhaps because the blades in VSP are positioned in a very different way than in the rest of propeller sytems.

    Regading power required in Dynamic Positioning, it is quite lower than at transit speed. It depends not only on waves, but also in wind and current forces. But as speed increases, power required increases in a cubic form. Holtrop methodology explains quite good this speed dependence through Froude number. Calculation of power for DP is quite different as it does not depends on ship speed.

    In next blog posts we will try to study this.

     

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