Poulsen Hybrid Monorotor
The Poulsen Hybrid Monorotor
A Novel Approach to Flettner Marine Propulsion
January 2012
Background
The Magnus effect defines thrust developed by spinning a cylinder in an air
stream and was first utilized for marine propulsion by Flettner in 1924.
The cylinders are rotated by auxiliary power and create thrust dependent on
the wind speed and direction relative to the course. Lately the concept has
gained new interest for supplementing the engine power in cargo ships with
the object of reducing fuel consumption and carbon emissions.
The E-ship, launched in 2010 by wind energy company Enercon has 4 rotors,
each 4 meters in diameter by 25 meters tall.
Photo: E-ship
At the present time two companies are proposing systems for installing
multiple Flettner rotors typically 4-5 meters in diameter onto bulk carriers and
other cargo vessels, claiming potential fuel savings in the order of 20% to
50%. The rotors being offered are telescoping or foldable in order to not
interfere with loading and unloading of cargo.
Photo: Magnuss
Photo: Windagain
The thrust developed by a Flettner rotor depends on its projected area, and
for example a 4 meter rotor about 25 meters tall may generate power in the
order of 400KW at 14 knots in a 10 m/s (20 knots) crosswind. With this kind of
rotors typically 4-6 systems are required per vessel in order to accomplish
projected savings.
Folding and telescoping collapsible rotors require modifications to vessels
such as wells for stowing them below deck when collapsed and local
strengthening of the deck structure and frames in order to safely absorb the
large thrust forces and bending moments developed during operation. The
collapsing mechanisms are expensive, add complexity and require special
maintenance. As a consequence the total cost of systems and labor and
downtime for installation as well as cost of use is high and increasing
relatively with the number of rotors in the system.
The Poulsen Hybrid Monorotor
The Monorotor offers a novel way of configuring and locating a Flettner
propulsion system which is low in cost and contains a minimum of moving
parts. It does not interfere with loading and discharging and is dimensioned,
so its height does not exceed the height of the standing rig. The system is not
collapsible but yet may be easily and momentarily secured in case of extreme
wind or excessive roll and pitch of the vessel in the sea.
A single rotor must have a large diameter in order to match the performance
of the multiple slim and tall rotors currently being proposed for cargo vessels.
Typically a monorotor for a Handysize vessel of 30,000 to 40,000 dwt will be
15 to 20 meters in diameter and 20-25 meters tall. A cylinder this large would
be a significant obstacle if placed on the main deck, besides obstructing the
view ahead from the bridge. As a consequence the Poulsen Monorotor is
mounted aft of the deck house and straddles the stern of the vessel with its
lower edge raised 3 or 4 meters above deck so as not to impede mooring
operations. An alternative solution suitable for very large vessels such as
VLCC tankers and 200,000 to 3000,000 dwt bulk carriers may feature a
second monorotor mounted above the focsle deck and straddling the bow.
Locating the second rotor at the extreme bow does not impede loading and
discharging and at the same time brings the blind sector as viewed from the
bridge within or close to the 5 degree angle specified by the IACS.
A Monorotor system comprising 1 or 2 large diameter rotors, each generating
the same amount of trust as 4 or 5 slim rotors of similar height combines the
following features:
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Is less complex and contains fewer moving parts. The cost per ton
thrust is reduced by over 50%.
The supporting structure may be designed more efficiently within the
ample space inside the rotor. Less reinforcement of the deck structure
is required since forces may be spread over a larger area. The main
support legs can be placed 10+ meters apart and in most cases
connected directly to the hull plating near the corners.
Interference with gear and daily operation of the vessel is minimized
because the rotor is elevated 3-4 meters above deck, also raising
system safety.
Rotational speed is reduced from 200-250 rpm to 40-60 rpm thus
extending bearing life and periods between scheduled maintenance.
Easy installation, possibly during scheduled maintenance, may
eliminate down time.
Calculated Performance: 16 meters diameter x 22 meters tall Monorotor
suited for a 30.000 – 40.000 dwt vessel. Cruise speed: 14 knots
Wind speed m/s 5 10 Knots 20 25 30 60 19.4 29.1 38.9 48.6 58.3 116
Rotor rpm 30 60 60 60 50 43 Thrust tons 6 24 40 51 52 51 Power KW 430 1700 2900 3700 3700 3650 HP 585 2300 3900 5000 5000 4900 9.7 15 d speed m/s
About 50 KW of electric power is required to spin the Flettner rotor.
Effect of Wind Direction
Wind angle
(degrees) 30 45 60 75 90 105 120 135 150 175 Power % 10 35 59 77 91 99 100 94 82 49 The rotor is designed to rotate at max 60 rpm. The table shows how the thrust
can be kept within the 55 ton design limit by adjusting the rotor rpm.
Thrust is monitored by strain gauges located on the main axle at the point of
max stress just below the lower radial bearing. A simple program can be
developed for adjusting rotor rpm within safe limits while maximizing thrust.
The program will also monitor wind speed and angle of roll in order to stop
and park the rotor in extreme weather.
When evaluating the performance of the rotor system it is important to keep in
mind that it contributes thrust and thus propulsion horsepower. On the other
hand, when calculating propulsion horsepower of a marine engine its rated
power must be adjusted for propeller efficiency (0.65-0.70). Thus, for example
2,000 Flettner horsepower equals about 2,900 engine brake horsepower.
System Cost and Benefits
The cost of the Model16/22 Monorotor is estimated at US$ 600,000 to
700,000 including installation. It is intended for a vessel of 35,000 to 40,000
tdw, but may be used on larger vessels as well and save the same amount of
fuel under similar conditions. The system weight is about 55 tons. Models
optimized for other sizes of vessels will become available as required.
The Monorotor may be retrofitted onto existing bulk carriers and tankers and
reduce fuel usage and carbon emissions during the life of the vessel up to 25
years from now.
Equally important, Monorotor systems may be designed into new builds and
include modifications in the superstructure etc. to improve efficiency. In many
cases new designs may also benefit from engine optimization. For example in
a Handysize vessel, due to the supplemental power generated it may be in
order to reduce the size of the main engine about 20% while saving some
$500,000 in cost and 50 tons of mass, approximately balancing out the cost
and weight of the Monorotor installation.
Also, dependent on the trade and length of the journey, it may be safe to
reduce the amount of bunkers carried by up to 50 tons.
The importance of any system for harvesting sustainable energy aboard an
oceangoing vessel depends on world market fuel prices, and unfortunately
these are expected to keep increasing, perhaps in all future. In today's market
when shipping companies are struggling to break even, 20-30% fuel savings
may well change the entire dynamics of the game.
Proposal, 2 Rotor Retrofit, VLCC Tanker
Comparison: 16/22 Monorotor / 2.1 MW Wind Turbine
Flettner rotors harvest sustainable energy from the wind so it is relevant to
compare their performance with that of land-based and off-shore wind
turbines. However, for an economical comparison it is important to consider
the different venues and values per KW hour of energy produced.
A marine engine consumes 170g of heavy fuel per shaft KWh at a cost of
$0.14 based on currently $800/ton. However, due to propeller loss only 70%
of the shaft power is available for moving the vessel so the true cost of
propulsion is $0.20 per Kwh, and realistically this value can be applied to
energy from wind power harvested on a vessel at sea. Moreover this energy
does not need to be converted to electricity and can be utilized at any time
without transmission losses. For comparison, in land based wind energy
systems the alternative source is coal fired or hydro electric power plants,
where energy is generally rated not above $0.05/KWh at the plant, so in most
venues this value must be applied to wind power as well.
16/22 Monorotor on Handysize vessel
Rated output at 15m/s (29 knots)wind @14 knots.
2,500 KW
Estimated average output while at sea
1000 KW
Power lines and transformers
none
Transmission losses
none
Wind quality,
Ocean
Estimated cost, installed
$600-700,000
Weight of system, (steel 45%, aluminum 55%)
55 tons
Installation downtime at yard.
< one week
Value generated.1000 KW 200 days at sea at $0.15/KWh $720,000/year
Time to recover investment
less than1year
Reduced CO2 emissions
2,700 tons/year
2.1 MW General Electric Wind Turbine
Rated output
Estimated average output
Infrastructure required. Service roads etc.
Trunk power line, transformer
Transmission lines
Transmission losses
Wind quality.
Cost
Weight of turbine (steel 90%, fiberglass 10%)
Value generated, 800 KW 800h/year at $0.05/KWh
Time to recover investment
Reduced CO2 emissions
2,100 KW
800 KW
yes
yes
yes
yes
Inland or seashore
$2,000,000
280 tons
$320,000/year
>6 years
3,600 tons/year
The Poulsen Hybrid Monorotor
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May be easily retrofitted onto existing vessels with minimal changes.
May be incorporated in new builds in the design stage.
Does not impede loading and unloading or mooring and anchoring.
Does not impede view from the bridge.
Is reliable and easily maintained. Minimum of moving parts.
Does not require additional or specialized crew to operate.
Saves 20-35% on fuel consumption dependent on wind conditions.
The investment is recovered in 1 year or less.
Many factors over and above the wind conditions may affect the actual
efficiency, and it really does not make sense to announce potential percent
fuel savings with this or any other wind propulsion system. Rather than
physical efficiency of the energy conversion, the overriding factors must be
return on investment, reliability, and ease of installation. The above
calculations are believed to be conservative but actual performance can only
be determined through sea trials with a full size prototype.
January, 2012
Patents Pending.