The
KAPPEL propeller is a new, innovative propulsor with higher efficiency than a
conventional state-of-the-art propeller. Whereas traditional ship propellers
have blades modelled on the basis of helical surfaces, the KAPPEL propeller has
modified blade tips smoothly curved to the suction side of the blade. There is a
parallel development within aircraft design where many modern aircraft, from
high-performance jet liners to sophisticated gliders, have similar modifications
of the wing tips in the form of winglets. These are separate lifting surfaces
attached more or less perpendicular to the wings on the wing tips. Numerical
methods, as well as experiments, show that the effect of winglets is to increase
the lift-drag ratio of the wing.
Aircraft
have relatively well-defined design conditions such as climb, cruise and
descent. The flow to the propeller is more complicated since the propeller works
in the flow abaft the ship hull. This is in particular the case for single screw
ships. At each revolution a section of a propeller blade will experience a
highly varying inflow. This means that the pressure on the hull varies in time,
giving rise to noise and vibrations in the ship. The pressure variation is
exacerbated by cavitation, a phenomenon that occurs when the suction of the
propeller locally evaporates the water.
One of
the challenges of the KAPPEL propeller design was the optimization of the
propeller with respect to efficiency. When modifying the geometry of the blade
tip, relative to a conventional propeller, it was of paramount importance that
the beneficial effects of the modified blade loading were annulled by the
detrimental influence of friction on the relatively larger blade area in the tip
region. This optimization was made on the basis of numerical fluid dynamics by
which the flow field around the propeller was computed and hence the performance
of the propeller. The calculations were complemented with model experiments.
Further model tests were necessary to examine the interaction between ship hull
and propeller, in particular the extent and time history of cavitation and the
pressure field on the ship hull. On the basis of a vast number of calculations
and comprehensive model testing, a design was developed for a 35.000 dwt product
carrier.
A
full-scale KAPPEL propeller for this ship was manufactured. It was tested at sea
immediately after tests with the conventional propeller originally designed for
the ship. Both sea trials took place in April, off the coast of Portugal, in
good weather and under comparable conditions. The results confirmed the model
test predictions that the improvement in efficiency of 4 per cent aimed at was
achieved. Furthermore, the pressure pulse level was slightly lower with the
KAPPEL propeller than with the state-of-the-art comparator propeller.
Coulombi Egg tanker design
The
Coulombi Egg is an alternative to double hull design for tankers. It is based on
having a series of centre and wing tanks, divided by horizontal
bulkheads. Upper wing tanks form ballast tanks which act as emergency receiver
tanks for cargo should the lower tanks be fractured.
The design uses
hydrostatic loading principles, so that if a lower side hull is breached the
pressure from outside would be greater than that from the oil inside so seawater
would flow in, pushing the oil upwards through non-return valves into the
ballast tanks. The side ballast tanks also act as crumple zones in the case of a
side-impact collision to absorb the impact and prevent any damage to cargo
tanks. In addition, if a lower cargo hull is breached and cargo pushed into
ballast tanks, the tanker would list away from the damaged side, thereby
assisting refloating in the case of a grounding without oil spill.
The MEPC approved the Coulombi Egg Tanker Design
after several years of evaluation to determine if its design principles afford
an equivalent level of oil outflow protection relative to a double hull tanker
in the event of collision or stranding. As shown in the
illustrations below, the design combines principles of hydrostatic loading
and the 'mid-deck' design. The cofferdam (3%B located between 25%D and 35%D)
together with the 45° sloping bulkhead and horizontal partition
afford improved resistance to impact loads in the event of a side collision than
a double hull tanker. Additionally, the partial transverse bulkhead (to be
located at mid-length of the lower side cargo tank) decreases or virtually
eliminates the sloshing action of incoming seawater and thereby reduces oil
outflow from the undamaged side of the tank in the event of a collision.
The Sub-Committee
considered the Coulombi Egg tanker design and agreed that it fulfilled the
requirements for oil outflow calculations and therefore should be considered an
alternative design under MARPOL regulation 1/13F(5). Regulation 13F makes double
hulls and bottoms mandatory for new tankers, but allows for alternative designs
to be accepted as long as they provide at least the same level of protection.
The most logical
reason to use Coulombi Egg tanker design is costs. The Coulombi
Egg tanker in effect costs less to build and maintain than, its Double
Hull counterpart, there is less structure giving a weight saving, even if
the deck and keel plates are thicker than Double Hull, fewer penetrations
of stiffeners, less welding and a 70% reduction in surface area in the ballast
spaces.
The United States has
reserved its position on MARPOL Regulations 1/13F and 13G and at present the
Coulombi Egg design has not been found acceptable by the United States as
equivalent to or exceeding the double hull design.
Improvement in the reduction of noise on Cruise Ships
A system has been developed to reduce the noise produced by propellers and
pod drives, in both passenger ships and luxury motor yachts. The system is based
on an old principle, releasing compressed air in front of the propellers through
nozzles, producing air bubbles, which in turn absorb the noise produced by the
propellers. The first success was booked in the eighties when the system
was introduced and tested on the motor yacht "ABDUL AZIZ". From then until now
no real development had taken place until Holland America Line's new building
"OOSTERDAM" adopted the idea with success, now 2 further ships have been
complimented with the system namely the "ZUIDERDAM" and the "WESTERDAM".
Carnival Cruises has decided to take the design on board for all forth
coming new buildings.
The system can also be fitted to existing cruise ships, it is cost
effective in comparison to other means of noise reduction from propellers such
as floating floors and visco-elastic coatings.
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