Marine propulsion in modern marine engineering is a flourishing technology. There are many ways to generate thrust in order to move a ship (or boat) through the water. These types of marine propulsion systems available vary from the archaic steam engines to reciprocating diesel engines. With the technology burst in the last decade, engineers have focused on creating efficient, economical, and environmentally friendly propulsion systems. This essay will explore the phenomenon of the evolution of the marine propulsion unit and the future of this vital system.
One of the first engines used in marine propulsion was steam. These early engines were replaced by the more lucrative and efficient diesel engines, gas turbines, nuclear reactors, and electronic motors. The ease of operation of the diesel engine (in combination with the turbo charger) makes it the primary mover for most modern day ships. They provide the most simplistic, continuous, and economical option for the majority of companies. Slow speed engines allow for an efficient operation of the propeller at operating speed. These tend to not need gearboxes, it has a direct drive engine.
The medium to high speed engine ships utilize reduction gears which enable a wide range of speeds. Also, by using multiple engines to drive the propulsion system, maintenance and repairs can be made while running out to sea. The Navy utilizes gas turbines and nuclear reactors to drive their ships and submarines. Turbines are usually coupled with other engines due to their inefficiency (mainly thermal inefficiency) at idle or low speeds. These reduce emissions, but due to the need for a combination of engines or a combined gas turbine cycle are not as cost effective as the diesel.
Nuclear reactor propulsion has been primarily used in Navy ships. A nuclear reaction is created and sustained. The heat created by the reaction is used to create steam and fed to a turbine which, in turn, drives the propulsion shaft. Nuclear reactor propulsion is not very efficient for the average ship owner since the technical and economic factors do not outweigh the elimination of fuel oil. Another comparable and ever evolving type of propulsion is diesel-electric motor propulsion which provide energy efficiency. It utilizes the diesel as a generator and the electric motor as the propulsion drive. All of these propulsion systems have served the industry well.
These engines reduce the overall weight of the vessel, reduce maintenance costs, increase operating speeds, and create a better overall performance level. Alcatraz Cruises just installed one of these Tier II standard propulsion systems last summer (2011) on their vessel, the Clipper. Due to stricter EPA standards, emissions are on their last leg and most companies will not install any engine that is not up to the Tier II emissions standards. With the progression of time comes change.
Thankfully for the maritime industry, that means technologically advanced toys that happen to be able to drive tugs, ships, and Navy cruisers. “Go Green” has been the mantra of many and has driven innovators to go beyond and above to create the quiet, sleek, efficient, and environmentally friendly systems we are getting a taste of now. One of the systems that has been a long time in development is an engine that can operate on LNG. Liquefied natural gas is one of the most efficient fuels available at this time. It is a cleaner fuel that has low emissions and operational flexibility.
An example of this fuel at work is the STX Finland and Viking Line (2010); they have proposed to create a line of ferries that reduce emissions up to 90%, 80% below IMO standards. This project is projected to finish next year (2013). Though the technology behind this isn’t initially financially favorable, the environmental gain is impressive. This year (next month to be exact-May 2012) will see the first LNG coaster fish feeder). The 2200T capacity, M/S Hoydal will operate off of the Norwegian coast. Rolls Royce has engineered the Bergen C25:33L6P engine (1,650 kW) that powers it.
This engine is one of the most technologically advanced engines on the market. It is very efficient and economically friendly. LNG fueling is hard to come by, so a 3,200 ft3 LNG tank will be provided on board. The reduced fuel costs and tax cuts will balance out the initial cost of the LNG installation. Water jets create propulsion from the reaction when water is forced in an aft direction (in regards to the forward facing direction of the vessel). Water enters the jet intake on the bottom of the boat, the pumping unit (impellor and stator) increases the head of the flow and is discharged through the transom (nozzle) at a high velocity.
The force exerted behind the vessel creates an equal and opposite reaction; the thrust of the reaction is transferred to the hull which propels the ship forward. Rolls Royce has been a leading developer in marine propulsion systems. They have created the Kamewa waterjet. This jet has great top speeds and fuel economy. The jets can develop power over 24 megawatts with an input power of 50 megawatts. The mechanical layout has been created into a series of elements with the inlet duct integrated into the hull.
The thrust bearing incorporates PTFE thrust pads and dynamic positioning of the impellor (supported by a downstream bearing). The mix flow pump has an efficiency of over 90%. The thrust and vibration developed by the resistance to propulsion is negated by the thrust block in the hull of the ship. Due to the many advances in the design of this propulsion system, it can even enable the vessel to crab sideways (depending on vessel size). Another propulsion system is the azimuth thruster, normally called the Z-Drive. Though more commonly found on tugs & barges, coasters, and ferries, some tankers and cargo ships utilize this system.
This system was founded in the 1950’s, but has been revitalized with modern technology. The Z-drive pod can rotate a complete 360? through the connection of the driving energy to the thruster device by the rotary motion created by the formation of two right angle turns. It uses a conventional shrouded screw that pivots. This propulsion system eliminates the need for a traditional propeller. Marine propulsion has always been an important aspect of the industry. More efficient, economical, and (in recent years) environmentally friendly is the current drive for our systems.
The diesel electric engine, LNG compatible engine, water jet systems, and thrusters are the way of the future of propulsion. References: ?Rolls Royce. “Kamewa SL-Series Waterjets”. 2012. < http://www. rolls-royce. com/marine/products/propulsors/waterjets/kamewa_sl/index. jsp> ? Intellijet Marine, Inc. High Tech Water Tech Jet for Energy Conservation”. 200-2012. . ? Keith Henderson. “World’s First LNG Coaster Nears Completion”. Maritime Propulsion. April 17, 2012. ?SwanJet. “How Does the Jet Propulsion System Work”. 2008. http://www. swanjet. com/howjetunitswork. html ? Wikipedia. “Kamewa Waterjets”.