This page contains a Flash digital edition of a book.
Feature 1 | GEARS AND PROPELLERS


with the same rudder blade but without bulb and twist. Compared to more simple standard


type rudder the efficiency gain can be as big as 6%-9%. Faster and slenderer single- screw vessels can have an efficiency gain of 2%-5% and twin screw vessels 1%-3%. The efficiency gain originates from


energy recovered from the water behind the hull and propeller. This is the reason for lower figures for slender singles- screw and twin-screw vessels.


Manoeuvring The manoeuvrability at low speed of the IPMS has been investigated and verified by means of measurements in model scale. Rudder forces were measured at bollard pull condition in the towing tank with the propeller and rudder mounted on a hull dummy. From these measurements sets of lift


and drag curves has been produced, which show that the maximum side force of the IPMS is increased by 15% compared to the conventional alternative.


Cavitation tests and CFD Since the rudder bulb follows the rudder during steering it will leave its protected and optimal position behind the hubcap and be exposed to the propeller slipstream. The exposed leading edge of the bulb, which causes an edge exposed to high water velocities, was expected to be an area where cavitation could initiate. Therefore the risk for cavitation on the bulb leading edge as well as on the rudder blade surface has been carefully investigated in cavitation tests and CFD calculations. Several cavitation


tests have


been performed in the Rolls-Royce hydrodynamic research centre large cavitation tunnel with the IPMS operating behind a hull dummy of a single screw vessel. Both cavitation observations as well as propeller and rudder force measurements were performed. A range of ship speeds (13knots-19.6knots) and propeller loadings were tested for a number of rudder angles between ±6 deg, which covers the typical range of rudder angles used at transit speed. In order to verify the cavitation test


32 Today Effi ciency history comparing a propeller, against a propeller, a rudder, and a hull.


and to gain further understanding of the flow around the IPMS, CFD analysis was carried out. Both propeller and rudder was modelled but the effect of the hull wake was neglected. The efficiency gain of the IPMS


compared to a conventional rudder predicted by CFD was compared to model self-propulsion test results, and showed good agreement.


Fuel cost savings A payback time less than two years has been the target during the development of the IPMS. This should include all extra investment costs compared to the same propeller and rudder but without bulb, twisted leading edge and hubcap as well as any extra model test costs for comparing and verifying the efficiency gain of the concept.


Summary The last years raised fuel prices have increased the markets focus on fuel economy and propulsive efficiency. This has driven the development of an IPMS that combines a number of separately well-known energy saving devices. The propulsion system consists of a


twisted full-spade rudder with bulb, a hubcap and an adapted propeller design. The rudder bulb is fixed welded on to the rudder blade and moves with the rudder and the hubcap is mount as a fairing cover outside of the existing standard hub rotating with the propeller. The IPMS is mechanical simple


and robust due to few movable parts and the installation is not much more complicated than for a conventional rudder and propeller. Largest efficiency gains are seen


on blunt single-screw vessels with a high block coefficient for which the efficiency gain can be in the range of 4%-6%. Also on slenderer single-screw and twin-screw vessels a significant efficiency gain is seen even if it is smaller than on blunt single-screw vessels. Propeller and rudder should be designed together as one integrated system instead of two different products. The propeller design should be designed with respect to the twisted rudder with bulb and the rudder should be adapted to the velocity and swirl distribution in the propeller slipstream. The result is improved efficiency and a higher potential of the propeller design giving improved possibilities to reduce propeller pulses, vibrations and noise levels. The twisted rudder improves not only


the propulsive efficiency but also the low speed manoeuvrability by giving 15% increased maximum side force. Also the manoeuvrability at transit speed is improved compared to the conventional rudder giving reduced movements of the rudder. The simple mechanical design of the IPMS gives low investments cost resulting in short payback time. SBI


*This paper was first presented at the


Marine Propulsion Conference held in London, in March 2008.


Ship & Boat International September/October 2008 Time  Propeller alone


 Propeller+Rudder+Hul Max


Potential Max


Efficiency


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68