Ship Propulsion
Solutions, LLC

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Lexington, KY 40591-0148
USA

Phone No: +1.859.533.8848

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shippropulsionsolutions.com

SHIP ENERGY SAVING DEVICES

In the continuing effort to improve ship hydrodynamic efficiency, i.e. greater speed and/or less fuel consumed, several recent and innovative approaches have been put into practice. Some of these involve modifications of the hull upstream of the propeller, such as asymmetrical sterns or full or partial ducts. Some involve the propeller, such as putting fences on the blade tips or encasing the propeller in a duct. Others tackle the region downstream of the propeller, such as attachments to the hub or putting a bulb on the rudder. For example, an engine maker, had previously marketed a not-so-new concept, calling it the Propac Rudder and promising an optimistic 4 to 10% power reduction.

Stern-Appended Hydrodynamic Energy Saving Devices (SAHESD)

All of these approaches represent incremental gains in comparison to complex approaches such as counter-rotating propellers on a single shaft. In addition, some, such as an asymmetrical stern, can be only realistically installed when the ship is being built. Several incremental approaches can be cost-beneficially added in retro-fit situations. See References 1 and 2. Most importantly, because of their potentially-high cost-benefit, the following stern-appended hydrodynamic energy-saving devices (SAHESD) merit consideration for both newbuildings and retro-fit on existing ships:

Downstream of Propeller

• Propeller Cap Turbine (PCT)
• Costa Propulsive Bulb (CPB)
• Rudder Thrust Fin (RTF)

Upstream of Propeller

• Simplified Compensative Nozzle (SCN)
• Hydrodynamic Partition Plate (HPP)
• Fore-propeller Hydrodynamic Fin Sector (FPHFS)
• Thrust Shaft Bracket (TSB)

Evaluation of existing or planned vessels can be conducted for a nominal cost. More than 200 ships have had these energy saving devices designed by SPS’s partner, MARIC in Shanghai. A detailed reference list of installations is available. Recent installations by SPS’s predecessor company Global Marketing & Trading are listed under Installations and Results.

Because each one of these SAHESD's provides incremental savings, realistically in the range of 2 to 5 %, it is difficult to measure an individual device's contribution on ships in service. Note that ship designs usually allocate sea margins of 10 to 15 %, so finding, for example, a 4% improvement in service conditions requires precise long-term data. Therefore, combining several of these energy saving devices, especially before, at, and after the propeller, is the recommended approach in order to achieve a greater cumulative improvement which can be readily measured (potentially 7 to 10 %) , even on sea-trials for newbuildings. A successful combination has been the Propeller Cap Turbine (PCT), aft of the propeller, with the Simplified Compensative Nozzle (SCN), forward of the propeller for single screw vessels. (See Reference 5 for SCN applications.) For ships with twin screws utilizing hydrodynamic fins may be more cost-beneficial than nozzles when there are shaft brackets. To properly assess and design SAHESD's, technical information is needed about the ship. A form outlining the information required is provided under Engineering Input.

To illustrate the potential cost-benefit of SAHESD’s, the following table is based upon an assumed unit cost-reference of $6.00 per rated horsepower for manufacture and installation of an SAHESD. This ratio may be more or less depending upon ship size and type and specific SAHESD. Only from specific projects can accurate assessments be made. Also, fuel cost is taken at $500.00 per metric ton, which is current market value. (See Economic Incentives for a detailed Cost-Benefit nomograph.)

Based upon an energy saving rate of only 2% and minimal days at sea of 200 per year, an investment of $6 per installed horsepower achieves a payback period of less than one year even on the basis of the higher fuel efficiency of the propulsion motor. (See Economic Incentives for a nomograph of Payback Period.)

Depending upon freight markets, revenue gains from increases in ship speed over the life of the vessel (cargo deliverability) can result in cost-benefits that approach an order of magnitude greater then operational-cost reduction from fuel-savings because of reduced power. Market conditions will guide how SAHESD benefits will be taken - speed increase or fuel reduction. (See Economic Incentives for nomograph yielding Incremental Velocity Increase.)

Classification society and flag state regulatory approvals, if required, are assumed to be accomplished by the shipowner/operator, unless it is desired to have the designer/supplier obtain such approval, in which case the class fee, etc. would have to be added to the project price. Depending upon individual classification societies, certain devices only require inspection at installation.

Propeller Cap Turbine (PCT)

Because of its almost uniform effectiveness in both full-load and ballasted conditions, the propeller cap turbine (PCT) is generally the most cost-beneficial of the listed SAHESD’s. It is easily designed for retro-fit and the relatively low cost can be recovered quickly. (See Reference 3.) By installing a properly designed PCT, with varying pitch of air-foiled shaped blades integrally cast into the hub cap, energy from the rotating fluid coming off the propeller hub is recovered by these small shaped blades, and hence energy savings is achieved over a wide-operating range of ship speed and draft/trim conditions. A device similar to the PCT, but proven to be less-efficient and more-expensive in competition, is called the PBCF (Propeller Boss Cap Fin)which utilizes only flat plates. It has been installed on more than 600 ships in Japan with some ships having installed power over 40,000 horsepower and in sizes above 140,000 tons deadweight. (See Reference 4.) To properly design an efficient PCT, technical information is needed about the ship as listed under Engineering Input.

Because open-water propeller tests should be conducted to design the PCT, time to manufacture the PCT is about 5 months. Sea shipment from Shanghai to any location worldwide can be done in less than 6 weeks. In addition, air freight can be arranged as an alternative to sea transport in urgent delivery situations. Large units for 40,000 to 60,000 HP propellers weigh in the region of 2500kg and are somewhat less than one-third of the propeller diameter, or about 2.500 meters.

Because weight of the PCT represents only about 1 to 2% of the propeller weight and propeller torque is reduced about 3 to 5%, there appears to be only a very small influence of the PCT on engine RPM and shaft torsional vibration. However, for a reasonable fee, calculations can be provided, but has not been required by classification society in previous applications, to quantify the expected influence. Also note this torque reduction can provide a benefit to diesel propulsion engines that are operating in a heavily loaded condition.

Significant cost-benefit can be gained from application of the PCT to propellers on all type of ships: tankers, bulk carriers, and container ships. Even ships with controllable-pitch propellers have been fitted with PCT’s.

Simplified Compensative Nozzle (SCN)

Just as the PCT was evaluated in competition, the Simplified Compensative Nozzle (SCN) was shown to be more-efficient and less-expensive in direct competition with circular designed Wake Equalizing Duct (WED). The improved efficiency is achieved by re-shaping the nozzle to improve uniformity of wake flow into the propeller. This is accomplished by having a more vertical or cylindrical shape rather than remaining circular. Also the forming of the nozzle only requires rolling steel plates in a single direction, which reduces cost of fabrication.

Needless to say self-propelled model tests are used to determine optimum nozzle shape , size, and orientation. The reports in reference 5 provide details as to the design approach, as well as an extensive installation reference list.

To design an SCN installation, particular technical information is needed and is outlined under Engineering Input.

SPS and its partner MARIC are prepared to provide successfully engineered products to ship owners, shipbuilders and ship repairers at competitive prices with on time deliveries to any worldwide location.

Technical Reference Papers:

1. Energy-Saving Stern Forms and Stern appended Energy-Saving Devices, QIAN WENHAO (MARIC) the sixteenth Asian-Pacific Shipbuilding Experts Meeting 1992 Beijing Seminar.

2. The design and hydrodynamic efficiency of propulsion energy saving devices, Dr. Victor Mishkevich, SNAME, 1994 Ship Operations, Management and Economic Symposium, May 12, 1994.

3. A new simple practical energy saving technique - Propeller Cap Turbine (PCT), HUA HANJIN (MARIC) undated English translation.

4. Propeller Efficiency Enhanced by PBCF, Ouchi, Kawasaki, and Tamashima, 4th International Symposium of Marine Engineering, Kobe, October 1990.

5. Papers and Installation References for Simplified Compensative Nozzle (SCN).

6. Cost-Benefit Nomograph for Energy Saving Devices with results from installations.

7. Stolt-Nielsen assessment of Propeller Cap Turbine from service records.
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