^ Ship Propeller – Image Courtesy of Eastimages at ShutterStock.com
A Step in the Right Direction
In recently concluded sea trials off the coast of China, MAN Diesel & Turbo made Alpha Kappel Fixed Pitch Propeller (FPP) successfully demonstrated its worth aboard the Elsabeth C.
Another recent development is that MAN Diesel & Turbo has changed its recommended range of Light Running Margin (LRM) and incorporated the change in this latest FPP. Sufficient LRM ensures enough propulsive power for the vessel to deal with challenging weather and shallow water.
Elsabeth C is a 58,500dwt Supramax bulk carrier and is the first in a series of eight ships. The FPP was also successful aboard the Mirela, the sister ship of Elsabeth C. Lemissoler Navigation Co. Ltd. owns these vessels through its affiliate company Frontmarine Co. Ltd.
This FPP helps improve fuel efficiency and lower emissions. Through its VibraSafe concept, the FPP minimizes hazardous vibrations. Plus the FPP offers exceptional reliability and the choice of using biodegradable lubricants.
Augsburg, Germany-based MAN Diesel & Turbo is a global leader in large-diameter diesel engines and turbo machinery for marine and stationary applications. The company also makes propellers, large gas and steam turbines, chemical reactors, compressors, and gas engines.
What the Alpha Kappel FPP Offers & Why?
MAN Diesel & Turbo’s fresh generation of Fixed Pitch Propellers (FPPs) come with the following distinctive features:
- lowest total ownership cost
- high fuel economy
- incredible efficiency
- great reliability
- least noise and vibration
The company offers a whole range of FPPs from 4MW to 40MW for diverse propulsion plants such as geared four-stroke medium-speed, diesel-mechanical two-stroke direct-coupled low-speed, and diesel electric.
Through its Computerized Optimization of Propulsion Systems (COPS), the company pre-optimizes hydrodynamic and mechanical considerations while also integrating statistical data.
During the trials, both vessels used an average 23mtns fuel a day when sailing at around 14.2knots in ballast conditions. When examined for the Crash Stop Test, the Elsabeth C recorded no noise or vibration.
Very small Light Running Margins (LRM) are a problem for bulk carriers. With this in mind, MAN Diesel & Turbo introduced 4-10% LRMs on all its FPPs and two stroke engines.
That apart, the company kept the propeller layout 3-4% higher for these bulk carriers in order to ensure safety, efficiency, reliability, and maneuverability at all times.
These FPPs have lowest EEDI to EEOI ratio thereby boosting environment-friendly performance to new heights:
- EEDI is the Energy Efficiency Design Index that stipulates a minimum energy efficiency level per capacity mile such as a ton mile
- EEOI is Energy Efficiency Operational Indicator used to measure a ship’s operational fuel efficiency and estimate the effect of operational changes
The stern tube lubrication systems of these FPPs can use biodegradable as well as ordinary mineral oils. And you can change from one oil type to the other without changing any component.
Crash Stop Test & Light Running Margins (LRM)
Also called the Crash Astern Maneuver, the Crash Stop Test / Maneuver examines a vessel for engine operation and propeller reversal. Here the stopping distance depends on the ratio of astern power to ship displacement.
In this test, the vessel is loaded / ballasted to obtain a predetermined draft (draught) and the propulsion system is set full astern at some fraction of the Maximum Continuous Rating (MCR). The helm is put hard-over to either port or starboard.
Differential GPS continuously records the position, speed, and heading of the vessel. The vessel is then brought to a stop while noting the final time to stop, drift, track line, and advance.
MCR is the maximum power an engine can produce when running continuously within safety limits. Ships usually operate at the Nominal Continuous Rating (NCR) that is 85% of the Contractual Output. The Contractual Output is 90% of the MCR. This makes NCR 76.5% of MCR.
Drift is the distance a ship travels perpendicular to its original course. It indicates the effect of winds and currents on ship movement. Advance is the distance the vessel travels along its original course.
MAN Diesel & Turbo recently changed its recommendation for the optimum range of LRM values. Earlier they proposed a 3-7% LRM, now they suggest 4-10%.
Technically, LCM is the margin between the Light Propeller Curve and the Engine Layout Curve measured horizontally at the SMCR point of the engine. SMCR stands for Specified Maximum Continuous Rating i.e. specified MCR.
Adequate LRM ensures that the engine generates enough power when the ship:
- sails in rough weather and / or in shallow water
- requires maneuvering
- has fouled propeller(s) and hull
Ships designed with ample LRM:
- maintain safe and sufficient speed in heavy weather even with a fouled hull
- accelerate for efficient and safe maneuvering
- rapidly pass over a barred speed range
Considering how sophisticated the involved technical details are, an exhaustive treatment is in order:
Higher Efficiency: Designed and tested using a combination of experience-based knowledge and cutting edge techniques, the Alpha Kappel FPP hikes efficiency by up to 6% while slashing cavitation, pressure impulses, noise, and vibration.
Towards this end, designers adopted a holistic approach and:
- reduced drag by streamlining the hub shape and by reducing the hub size
- customized the propeller design to individual ships and the wake field
- energy-optimized the area ratio, skew, number of blades, and rake
For complete hydrodynamic integration, designers will optimize the propeller and its layout with the ship’s hull as well as the flow-affecting devices placed upstream and downstream of the propeller.
Low Vibrations: MAN Diesel and Turbo follows a comprehensive approach through its VibraSafe concept to curtail potentially disastrous vibrations to a bare minimum.
The company has gone to great lengths to ensure that every part fits in with other parts in order to create a minimum-vibration assembly. In order to achieve this, designers have:
- optimized the number of propeller blades and erratic firing sequences of two-stroke engines while synchronizing the propeller with the firing order
- modified the main engine tuning or shaft line dimensions to trim down torsional and axial vibrations
- selected an appropriate layout for the shaft line and its bearings
Axial vibrations can cause the failure of thrust bearings particularly in 4-5-cylinder main engine driven propulsion plants. Whirling vibrations can degrade stern tube seals and shaft bearings in twin screw vessels that employ longer and more slender shafts.
Fuel Savings and Low Noise: A combination of several factors lower fuel use by as much as 10% as well as noise levels. These include:
- minimum flow over the tip of the propeller where low and high pressure flow come together and cut down propulsion efficiency
- larger diameters with low speed and lesser number of blades
- longer strokes
- reduced pressure impulses and lesser clearances to ship’s hulls enable use of large-diameter propellers
Reliability: Designers have gone for a sturdy design to ensure reliability. Considerations include:
- compliance with IACS and FSICR Ice Class notations
- 30-year design life after factoring in external and internal loads as well as fatigue
- least number of components
- sufficient design margins
- devised for low material stresses during normal operations and extreme loads
- low bearing loads and small hub sizes
- G-CuAl10Ni propeller material
- balanced pitch distribution
- single reliable and strong hydraulically tightened nut for the propeller-shaft press-fit structure
- service and inspection friendly
Sometimes while focusing on the details, we tend to lose sight of the larger goals. MAN Diesel & Turbo has successfully and seamlessly negotiated this pitfall and delivered a stellar product.
For a roundup of more such cutting edge developments in the maritime industry, visit our blog. Contact Kemplon Engineering for exceptional marine fabrication services, marine pipe fitting, and large scale custom metal fabrication.