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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.

 

 


An Internet Guide to Engineering

 

  

 

 

 

 


 


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