Propulsion Machinery

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Power Sources.
^ Pre-Mechanization – Human (Poles & Paddles) & Wind (Sails).
^ External Combustion – Steam Engines (Wood, Coal, Bunker Fuel, Nuclear-Powered, etc).
^ ^ Boilers (Tube, etc).
^ ^ Reciprocating Piston Steam Engines: Expansion (Single, Double, Triple, etc).
^ ^ Steam Turbines.
^ Internal Combustion – Spark Ignition & Compression Ignition.
^ ^ Reciprocating Piston Engines – 2 & 4-Stroke Cycle. Duty Ratings.
^ ^ ^ Mechanical: Cylinder Block, Pistons, Rods, Crankshaft, Valve Train, Heads, etc.
^ ^ ^ Lubrication: Splash, Forced, etc.
^ ^ ^ Fuel: Spark Ignition (Gasoline, LPG & Natural Gas) , Compression Ignition (Diesel), etc.
^ ^ ^ Electrical: Cranking, Charging, Ignition, etc.
^ ^ ^ Cooling: Air, Water (Raw & Fresh), etc.
^ ^ ^ Exhaust: Dry, Wet, etc.
^ ^ ^ Directory of Engine Brands & Mfrs with Links to Model Pages, Specs, Manuals, etc.
^ ^ Rotary Engines.
^ ^ Gas Turbines (Kerosene, Jet Fuel).
^ ^ Jet Engines (Kerosene, Jet Fuel).
^ ^ Rocket Engines.
^ Electric Motors with Gensets, Fuel Cells, Batteries, Wind Generators, Solar Panels, etc.
Power Transmission (Drive Train).
^ Inboards, Outboards, IOs, Z-Drives, L-Drives, Pods, Water Jet Drives, etc.
^ Paddle Wheels.
^ Screws (Propellers)
Control Systems.
Impact Damage.
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Marine propulsion machinery is the mechanical system used to generate thrust to move a boat or ship across water. While paddles and sails are still used to propel some smaller boats, most modern ships are propelled by mechanical systems consisting of an engine turning a propeller via a non-shifting “Direct Drive” or a shifting “Marine Gear” that includes either the “In-Out Gear” providing forward and neutral, or the “Reversing Gear” providing forward, neutral, and reverse. Inboards (IB) include “Straight” Drives and “V” Drives. Inboard-Outboards (IO) include “Outdrives” of which most are “Stern Drives”. Other Drives include Outboards (OB), “Z” Drives, “L” Drives, Pod Drives, Hydraulic Drives, Electric Drives, and Hybrid Drives. Any of the drives may include a “Reduction Gear”. “Direct Drives” often connect the engine to a “Variable Pitch” propeller that provides forward, neutral, reverse, and feathering by controlling the blade angle.

SS Ukkopekka's triple expansion steam engine. GNU Wikipedia

SS Ukkopekka’s triple expansion steam engine. GNU Wikipedia

Steam engines were the first mechanical engines used in marine propulsion, but have mostly been replaced by more efficient internal combustion, reciprocating piston, 2-stroke or 4-stroke cycle petroleum fueled engines. Nuclear reactors producing steam that spin turbines are mostly limited to warships and icebreakers, as safety concerns have repressed attempts to utilize them to power commercial vessels. Battery powered electric motors have been used on submarines and electric boats and hold some promise in providing energy-efficient propulsion. Recent development in liquified natural gas (LNG) fueled engines are gaining recognition for their low emissions and cost advantages.

1 – External Combustion
1.1 – Steam
1.1.1 – Reciprocating Piston
1.1.2 – Turbine
1.1 – Fuel
1.1.1 – Wood
1.1.2 – Coal
1.1.3 – Oil
1.1.4 – Nuclear
2 – Internal Combustion
2.1 – Reciprocating Piston
2.1.1 – Cycles – 2-Stroke Cycle – 4-Stroke Cycle
2.1.2 – Ignition Source – Spark Ignition – Make & Break – High Tension with Spark Plugs – Compression Ignition – Diesel – Semi-Diesel – Hot Bulb
2.1.3 – Fuel (Heavy to Light) – Bunker – Diesel – BioDiesel – Kerosene – Gasoline/Petrol – Alcohol (Ethanol, Methanol) – Vapor – Gas, Coal (CO) – Gas, Production – Liquid Petroleum Gas (LPG: Propane, Butane, etc)) – Natural Gas (NG) – Compressed Natural Gas (CNG) – Methane
2.2 – Rotary
3 – Electric
3.1 – Battery
3.2 – Fuel Cell

Power sources


Until the application of the coal-fired steam engine to ships in the early 19th century, animal and human labor, wind and/or currents were used to assist watercraft propulsion. Merchant ships predominantly used sail, but during periods when naval warfare depended on ships closing to ram or to fight hand-to-hand, galley were preferred for their maneuverability and speed. The Greek navies that fought in the Peloponnesian War used triremes, as did the Romans at the Battle of Actium. The development of naval gunnery from the 16th century onward meant that maneuverability took second place to broadside weight; this led to the dominance of the sail-powered warship over the following three centuries.

In modern times, human propulsion is found mainly on small boats or as auxiliary propulsion on sailboats. Human propulsion includes the push pole, oars, paddles and pedals turning a wheel or propeller.

Propulsion by sail generally consists of a sail hoisted on an erect mast, supported by stays, and controlled by lines made of rope. Sails were the dominant form of commercial propulsion until the late nineteenth century, and continued to be used well into the twentieth century on routes where wind was assured and coal was not available, such as in the South American nitrate trade. Sails are now generally used for recreation and racing, although experimental sail systems, such as the kites/royals, turbosails, rotorsails, wingsails, windmills and SkySails’s own kite buoy-system have been used on larger modern vessels for fuel savings.

External Combustion


– Steam Engines (Wood, Coal, Bunker Fuel, Nuclear-Powered, etc)




(Tube, etc)

Reciprocating Piston Steam Engines

Single Expansion, Multiple Expansion (Double, Triple, etc)

The development of piston-engined steamships was a complex process. Early steamships were fueled by wood, later ones by coal or fuel oil. Early ships used stern or side paddle wheels, while later ones used screw propellers.

The first commercial success accrued to Robert Fulton’s North River Steamboat (often called Clermont) in US in 1807, followed in Europe by the 45-foot Comet of 1812. Steam propulsion progressed considerably over the rest of the 19th century. Notable developments include the steam surface condenser, which eliminated the use of sea water in the ship’s boilers. This permitted higher steam pressures, and thus the use of higher efficiency multiple expansion (compound) engines. As the means of transmitting the engine’s power, paddle wheels gave way to more efficient screw propellers.

Steam turbines

Steam turbines were fueled by coal or, later, fuel oil or nuclear power. The marine steam turbine developed by Sir Charles Algernon Parsons raised the power-to-weight ratio. He achieved publicity by demonstrating it unofficially in the 100-foot Turbinia at the Spithead Naval Review in 1897. This facilitated a generation of high-speed liners in the first half of the 20th century, and rendered the reciprocating steam engine obsolete; first in warships, and later in merchant vessels.

In the early 20th century, heavy fuel oil came into more general use and began to replace coal as the fuel of choice in steamships. Its great advantages were convenience, reduced manpower by removal of the need for trimmers and stokers, and reduced space needed for fuel bunkers.

In the second half of the 20th century, rising fuel costs almost led to the demise of the steam turbine. Most new ships since around 1960 have been built with diesel engines. The last major passenger ship built with steam turbines was the Fairsky, launched in 1984. Similarly, many steam ships were re-engined to improve fuel efficiency. One high profile example was the 1968 built Queen Elizabeth 2 which had her steam turbines replaced with a diesel-electric propulsion plant in 1986.

Most new-build ships with steam turbines are specialist vessels such as nuclear-powered vessels, and certain merchant vessels (notably Liquefied Natural Gas (LNG) and coal carriers) where the cargo can be used as bunker fuel.


LNG carriers

New LNG carriers (a high growth area of shipping) continue to be built with steam turbines. The natural gas is stored in a liquid state in cryogenic vessels aboard these ships, and a small amount of ‘boil off’ gas is needed to maintain the pressure and temperature inside the vessels within operating limits. The ‘boil off’ gas provides the fuel for the ship’s boilers, which provide steam for the turbines, the simplest way to deal with the gas. Technology to operate internal combustion engines (modified marine two-stroke diesel engines) on this gas has improved, however, such engines are starting to appear in LNG carriers; with their greater thermal efficiency, less gas is burnt. Developments have also been made in the process of re-liquifying ‘boil off’ gas, letting it be returned to the cryogenic tanks. The financial returns on LNG are potentially greater than the cost of the marine-grade fuel oil burnt in conventional diesel engines, so the re-liquefaction process is starting to be used on diesel engine propelled LNG carriers. Another factor driving the change from turbines to diesel engines for LNG carriers is the shortage of steam turbine qualified seagoing engineers. With the lack of turbine powered ships in other shipping sectors, and the rapid rise in size of the worldwide LNG fleet, not enough have been trained to meet the demand. It may be that the days are numbered for marine steam turbine propulsion systems, even though all but sixteen of the orders for new LNG carriers at the end of 2004 were for steam turbine propelled ships.

Nuclear-powered steam turbines

In these vessels, the nuclear reactor heats water to create steam to drive the turbines. Due to low prices of diesel oil, nuclear propulsion is rare except in some Navy and specialist vessels such as icebreakers. In large aircraft carriers, the space formerly used for ship’s bunkerage could be used instead to bunker aviation fuel. In submarines, the ability to run submerged at high speed and in relative quiet for long periods holds obvious advantages. A few cruisers have also employed nuclear power; as of 2006, the only ones remaining in service are the Russian Kirov class. An example of a non-military ship with nuclear marine propulsion is the Arktika class icebreaker with 75,000 shaft horsepower (55,930 kW). Commercial experiments such as the NS Savannah have so far proved uneconomical compared with conventional propulsion.

In recent times, there is some renewed interest in commercial nuclear shipping. Nuclear-powered cargo ships could lower costs associated with carbon dioxide emissions and travel at higher cruise speeds than conventional diesel powered vessels.

Internal Combustion

– Spark Ignition (Gasoline & Natural Gas) , & Compression Ignition (Diesel)

Reciprocating Piston Engines

The vast majority of modern marine engines are of the Reciprocating Piston – Internal Combustion type with either Spark Ignition (burning what is commonly called Gasoline in the US) or Compression Ignition (burning what is commonly called Diesel in the US).

A modern diesel engine aboard a cargo ship
Most modern ships use a reciprocating diesel engine as their prime mover, due to their operating simplicity, robustness and fuel economy compared to most other prime mover mechanisms. The rotating crankshaft can be directly coupled to the propeller with slow speed engines, via a reduction gearbox for medium and high speed engines, or via an alternator and electric motor in diesel-electric vessels. The rotation of the crankshaft is connected to the camshaft or a hydraulic pump on an intelligent diesel.

The reciprocating marine diesel engine first came into use in 1903 when the diesel electric rivertanker Vandal was put into service by Branobel. Diesel engines soon offered greater efficiency than the steam turbine, but for many years had an inferior power-to-space ratio. The advent of turbocharging however hastened their adoption, by permitting greater power densities.

Diesel engines today are broadly classified according to:

  • Their operating cycle: two-stroke engine or four-stroke engine.
  • Their construction: crosshead, trunk, or opposed piston.
  • Their speed:
    • Slow speed: any engine with a maximum operating speed up to 300 revolutions per minute (rpm), although most large two-stroke slow speed diesel engines operate below 120 rpm. Some very long stroke engines have a maximum speed of around 80 rpm. The largest, most powerful engines in the world are slow speed, two stroke, crosshead diesels.
    • Medium speed: any engine with a maximum operating speed in the range 300-900 rpm. Many modern four-stroke medium speed diesel engines have a maximum operating speed of around 500 rpm.
    • High speed: any engine with a maximum operating speed above 900 rpm.

4-Stroke Marine Diesel Engine System
Most modern larger merchant ships use either slow speed, two stroke, crosshead engines, or medium speed, four stroke, trunk engines. Some smaller vessels may use high speed diesel engines.

The size of the different types of engines is an important factor in selecting what will be installed in a new ship. Slow speed two-stroke engines are much taller, but the footprint required is smaller than that needed for equivalently rated four-stroke medium speed diesel engines. As space above the waterline is at a premium in passenger ships and ferries (especially ones with a car deck), these ships tend to use multiple medium speed engines resulting in a longer, lower engine room than that needed for two-stroke diesel engines. Multiple engine installations also give redundancy in the event of mechanical failure of one or more engines, and the potential for greater efficiency over a wider range of operating conditions.


Duty Ratings for marine diesel engines are most often determined to establish how hard the engine is worked to provide a reasonable service life in years. A heavy duty commercial engine will therefore have a continuous…


High output engines with high horsepower ratings are therefore reserved for engines that are used very few hours per year (typically only a few hundred hours per year) and operated at full power only intermittently (typically  no more then one hour out of every eight hours) and the rest of the time operated at less then 80% power. DRAFT.


As modern ships’ propellers are at their most efficient at the operating speed of most slow speed diesel engines, ships with these engines do not generally need gearboxes. Usually such propulsion systems consist of either one or two propeller shafts each with its own direct drive engine. Ships propelled by medium or high speed diesel engines may have one or two (sometimes more) propellers, commonly with one or more engines driving each propeller shaft through a gearbox. Where more than one engine is geared to a single shaft, each engine will most likely drive through a clutch, allowing engines not being used to be disconnected from the gearbox while others keep running. This arrangement lets maintenance be carried out while under way, even far from port.

LNG Engines

Shipping companies are required to comply with the International Maritime Organization (IMO) and the International Convention for the Prevention of Pollution from Ships (MARPOL) emissions rules. Dual fuel engines are fueled by either marine grade diesel, heavy fuel oil, or liquefied natural gas (LNG). A Marine LNG Engine has multiple fuel options, allowing vessels to transit without relying on one type of fuel. Studies show that LNG is the most efficient of fuels, although limited access to LNG fueling stations limits the production of such engines. Vessels providing services in the LNG industry have been retrofitted with dual-fuel engines, and have been proved to be extremely effective. Benefits of dual-fuel engines include fuel and operational flexibility, high efficiency, low emissions, and operational cost advantages. Liquefied natural gas engines offer the marine transportation industry with an environmentally friendly alternative to provide power to vessels. In 2010, STX Finland and Viking Line signed an agreement to begin construction on what would be the largest environmentally friendly cruise ferry. Construction of NB 1376 will be completed in 2013. According to Viking Line, vessel NB 1376 will primarily be fueled by liquefied natural gas. Vessel NB 1376 nitrogen oxide emissions will be almost zero, and sulphur oxide emissions will be at least 80% below the International Maritime Organization’s (IMO) standards. Company profits from tax cuts and operational cost advantages has led to the gradual growth of LNG fuel use in engines.

The vast majority of modern marine engines are of the Reciprocating Piston – Internal Combustion type with either Spark Ignition (burning what is commonly called Gasoline in the US) or Compression Ignition (burning what is commonly called Diesel in the US).
Internal Combustion: Spark Ignited, Compresssion Ignited (Diesel).
^  Reciprocating Piston Engine Configurations: 2 & 4 Stroke Cycle. In-line and V, + 20 Others
See DIY: Engines for articles on Engine Refitting, Repowering, Selection, Installation, Maintanance, Troubleshooting, and Repair


See How Piston Skirt Length Affects Engine Service Life.

Crosshead Engine

Beam Engine




Engine Systems


Marinizing the Petrol (Gasoline) Engine

The Marine engine is not quite the same as your standard car engine. There are certain things that need to be done to make it safe to operate within the environment of a boats engine bay.
The most notable differences between a marine engine and an automotive engine are the electrical system, the cooling system, the exhaust system, and the fuel system. Additionally, items such as heads and cams are usually different.
Here we will just cover a few of the differences to give you a flavour of the modifications that are made to a car engine to marinise it (this is not intended to be an exhaustive list).
In a car any petrol or vapour leak quickly disperses through the bottom of the engine bay. In a boat, the sealed engine compartment does not afford the same luxury. Therefore the electrical system is modified to eliminate the possibility of sparks occurring within the system. Marine starters and alternators are modified so they won’t release sparks and ignite and gas vapour that may be in the engine compartment.
Marine carburettors are modified so they won’t flood outside the carburettor. If there is a problem or there is too much fuel in the carburettor, it will flood back into the engine.
On a boat there is a constant flow of new water sucked up from the lake or the ocean which circulates through the cooling system (raw water cooling). This type of system is extremely corrosive to the pump especially if the boat sees salt water. An automotive style pump, with its stamped steel impeller, would fail due to corrosion in a short time. Therefore a marine pump with a special ceramic seal, stainless steel backing plate, and a bronze impeller to resist corrosion is usually fitted. Two other areas of the cooling system that are also marinised are the head gasket and the core plugs (which should be brass instead of steel)
More from Watermota


^  Reciprocating Piston Engine Configurations: 2 & 4 Stroke Cycle. Aspiration: N & T.

^ ^ Stroke Ratio: Square, Oversquare and Undersquare Engines.

^ ^ Piston configurations. Crosshead Piston.

^ ^ Crankshaft Orientation: Horizontal (IBs) & Vertical (OBs)

^ ^ Crankshaft Configuration: CrossPlane.

^ ^ Connecting Rod Configuration: Crosshead.

^ ^ Cylinder Orientation: u… = Upright (Vertical). s… = Slanted (Inclined).
^ ^ ^ i… = Inverted. h… = Horizontal (Flat).
^ ^ Cylinder Configuration: …S = Single Cylinder. …T = Twin Cylinder. …I = In-Line. …V = V Pattern (eg V8, V6).
^ ^ ^ …W = W Pattern. …Y = Y Pattern. …X… = X Pattern. …+… = + Pattern. …D… = Delta (Δ).
^ ^ ^ …R,R2,R3,R4 = Radial (Single,Double,Triple,Quad Banks). …® = Radial Rotary.

Con Rods: Crosshead.

^ ^ Piston Orientation:
^ ^ ^ …o = Outward Facing Opposed Piston (eg Boxer, FlatFlat-six engine). …i = Inward Facing Opposed Piston (O-P).

^ ^ ^ Engines with Inherently weak “Bottom Ends”.

^ ^ ^ ^ ~Engine Hydrolocking

Engine Cylinder Block Deck: Open, Semi-Closed, Closed.

Valve Train: Ports, Sleeve Valves, Side Valves, OHV, OHC, DOHC

Engine Cylinder Head: Integral in Block, Flat Head, VIH,

…r = Rotary. …w = Wankel.


^  Pressurized: Partially, Fully


Fuel Fundamentals: HC+O=H2O+CO2 (Gasoline, Diesel, Natural Gas, CNG, LNG, LPG, Propane)
^ Alcohols and Ethers (MTBE).
^  Octane, Cetane
^ ^ Tetraethyllead (Wiki).

Ignition Source: Spark, Compression
Gasoline: Carburetion, Injection (Electronic)
^ ^ Troubleshooting MEFI.
^ ^ TechMate Marine Scan Tool.
^ ^ TechMate Pro Marine Scan Tool.
^ ^ MerCruiser Scan Tool.
^ ^ CodeMate Code Reader.
^ ^ DIACOM Marine PC Software.
^ ^ ^ Diacom Software Training Videos:
^ ^ ^ ^ 1 – How to install the Diacom program.
^ ^ ^ ^ 2 – An overview of key Diacom features.
^ ^ ^ ^ 3 – How to choose a sterndrive or inboard system type.
^ ^ ^ ^ 4 – How to choose a Mercury outboard system type.
^ ^ ^ ^ 5 – How to record engine data and email a data file.
^ ^ ^ ^ 6 – An in-depth look at Fault Codes on various ECM types.
^ ^ ^ ^ 7 – Downloading calibration files into ECMs (ECM reflashing).
^ ^ ^ ^ 8 – Diacom cable information and software updates.
^ ^ ^ ^ Behind the Scenes: See the hi-tech Diacom cable assembly process at our in-house design and manufacturing facility.
^ ^ ^ ^ Click here for videos on the Rinda Tech YouTube Channel.
^ ^ ^+
^ ^ ^+
Diesel: Mechanical Injection, Electronic Injection (Common Rail)
Control Systems (see Propulsion)

Marcel Borcila, B.A. from The Ohio State University
Answered Dec 27, 2017

Intercoolers and After-coolers are identical devices serving the same purpose. In general, an intercooler or aftercooler is said to be a Charge-Air Cooler. A Charge-Air Cooler is used to cool engine air after it has passed through a supercharger such as a turbocharger, but before it enters the engine.

There is some confusion in terminology between aftercooler, intercooler, and charge-air cooler. In the past, aircraft engines would run turbochargers in stages, where the first stage compressor would feed the inlet of the second stage compressor that would further compress the air before it enters the engine. Due to the extremely high pressures that would develop, an air cooler was positioned between the first and second stage compressors. That cooler was the “Intercooler”. Another cooler would be positioned after the second stage, which was the final compressor stage, and that was the “aftercooler”. An aftercooler was the cooler whose outlet fed the engine.

An intercooler is basically an air-to-air radiator. The hot air from the turbo enters at one end, and as cooled as it passes through the intercooler (much like the water in a car’s radiator) before entering the engine at a much lower temperature. This allows the engine to make full use of a simple principal of physics; cooler air is more dense than hotter air. This basically means that for a given volume (of our engine’s cylinder for example) we can get more oxygen into the same space when the air is denser – and more oxygen means better performance.

It is usually best to refer to these charged- air coolers using the same term as the device’s manufacture in order to avoid confusion.

From Quora



Cranking Circuits
^  Batteries
Charging Circuits
Instrumentation (see Propulsion)


Air Cooling
^  Air Only
^  Air & Water (w/Radiator)
Water Cooling
^  Raw Water Cooling (Seawater)
^  ^  Raw Water Pumps
^  ^  ^  Jabsco
^  ^  ^  Johnson
^  ^  ^  Sherwood
^  Fresh Water Cooling (w/Keel Cooler)
^  Hybrid Raw & Fresh Water Cooling (w/Heat Exchanger) where a Fresh Water Cooling side is cooled by a Raw Water Cooling side. This is the common arrangement in a modern vessel.


Dry Exhaust
Wet Exhaust
^ w/Water Separator


Hard Mounting (Solid)
Soft Mounting (Captive, Non-captive)

Rotary Engines

BiQuad (Pure Rotary where all moving masses rotate around fixed axis)

Wankel (Pseudo Rotory where the rotor rotates around the rotating  eccentric shaft giving it an unfixed axis)

Wankel Rotary Engine


Gas turbines

(Kerosene, Jet Fuel)

Many warships built since the 1960s have used gas turbines for propulsion, as have a few passenger ships, like the jetfoil. Gas turbines are commonly used in combination with other types of engine. Most recently, the Queen Mary 2 has had gas turbines installed in addition to diesel engines. Because of their poor thermal efficiency at low power (cruising) output, it is common for ships using them to have diesel engines for cruising, with gas turbines reserved for when higher speeds are needed however, in the case of passenger ships the main reason for installing gas turbines has been to allow a reduction of emissions in sensitive environmental areas or while in port.[5] Some warships, and a few modern cruise ships have also used steam turbines to improve the efficiency of their gas turbines in a combined cycle, where waste heat from a gas turbine exhaust is utilized to boil water and create steam for driving a steam turbine. In such combined cycles, thermal efficiency can be the same or slightly greater than that of diesel engines alone; however, the grade of fuel needed for these gas turbines is far more costly than that needed for the diesel engines, so the running costs are still higher.

Jet Engines

(Kerosene, Jet Fuel)

Rocket Engines

Electric with Gensets, Wind Generators, Batteries, Fuel Cells, Solar, etc



Paddle wheels

The paddle wheel is a large wheel, generally built of a steel framework, upon the outer edge of which are fitted numerous paddle blades (called floats or buckets). The bottom quarter or so of the wheel travels underwater. Rotation of the paddle wheel produces thrust, forward or backward as required. More advanced paddle wheel designs have featured featheringmethods that keep each paddle blade oriented closer to vertical while it is in the water; this increases efficiency. The upper part of a paddle wheel is normally enclosed in a paddlebox to minimise splashing.
Paddle wheels have been superseded by screws, which are a much more efficient form of propulsion. Nevertheless, paddle wheels have two advantages over screws, making them suitable for vessels in shallow rivers and constrained waters: first, they are less likely to be clogged by obstacles and debris; and secondly, when contra-rotating, they allow the vessel to spin around its own vertical axis. Some vessels had a single screw in addition to two paddle wheels, to gain the advantages of both types of propulsion.
From: Wikipedia


(Inboard, Outboard, IO, Z, L, Pod, Water Jet, etc)

Main article: Propeller
Marine propellers are also known as “screws”. There are many variations of marine screw systems, including twin, contra-rotating, controllable-pitch, and nozzle-style screws. While smaller vessels tend to have a single screw, even very large ships such as tankers, container ships and bulk carriers may have single screws for reasons of fuel efficiency. Other vessels may have twin, triple or quadruple screws. Power is transmitted from the engine to the screw by way of a propeller shaft, which may or may not be connected to a gearbox.


Fans (Airboats using aircraft-type propellers) (Hovercraft)

Water Jet Drives

Control Systems

Cable and Pulley






Electric / Electronic


Control Systems Manufacturers




Impact Damage



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FROM Donald: "This is an awesome website. I found the information that I needed right away from one of the over 20,000 free articles that you provide as a public service. I'm surprised that so much if this site is free. But I still signed up so I could access the thousands of expanded pages, interesting articles, and dozens of valuable programs! The member's library of books, magazines and videos that I can view online is really terrific! I understand that you and your staff are all unpaid volunteers. Please keep up the good work. And I commend you for your plans to add another 10,000 free informative articles over the next year. I'm thrilled to support you in this endeavor with my small membership donation. Thanks again for all your hard work."

FROM Huey: "I agree with my Uncle, I too have found the articles to be very enlightening. They say that it will take about 100,000 articles to cover the full scope that they have envisioned for the website. They have over 20,000 articles so far and that's doing pretty well, but it could take several years to get the rest. I also noticed that many of the Main Topic Pages and some of the article pages are still in the rough draft stage. I guess that they will fill in as they can get volunteers to work on them. But what I can't figure out is why anyone would spend the time writing informative in depth articles just to give away free to this website for publication? What's in it for them?"

FROM Dewey: "Well Huey, to me It looks like most of the articles on this website are written by very informed people, like boating instructors, boat designers, boat builders, riggers, electricians, fitters, marine repair technicians and marine surveyors. Writing such articles helps establish them as knowledgeable professionals. After all, this website was originally created by a school for marine technicians and marine surveyors. The website is growing in content every day. They even had to move to a bigger, more powerful server because the website's traffic has been growing exponentially."

FROM Louie: "I agree with everyone above. This site is quickly becoming the ultimate reference resource about every aspect of boats and ships for everyone from the beginning recreational boater to the seasoned professional mariner. I use the topic pages on the right sidebar to browse around the website. It's like a Junior Woodchucks' Guidebook for Boaters. Their Members' Library of over 300 popular and obscure books and over 200 magazine back issues that can be viewed online is fabulous. The Academy's magazine is especially informative. On top of that, there is the "Ask-An-Expert program for members where you can get an expert's answer to any of your boat questions. And a whole years membership is only $25. What a deal! I really love being part of this "Everything About Boats" community and help provide thousands of helpful articles free to the public. I think that I'll sit down right now and write an article about my experiences boating with my uncle."

FROM Scrooge: "You rave about this website like it was the best thing since sliced bread. Well, I think it stinks. Sure, it has a lot of good information for boaters, and they're adding more every day, but it will probably never be finished. Furthermore, I don't even own a boat. And I wouldn't have a boat even if someone gave me one. Boats are a waste of money and time and energy and money! They're just a hole in the water you pour money into. If you gave me a boat, I'd sell it quicker then you could say Baggywrinkle. Then I'd lock up the cash with all my other money so I could keep my eye on it and count it every day. Bah humbug."

FROM Daisy: "I'm just so glad that Donald got the boat so we and the boys could enjoy boating — together. And of course all of the girls, April, May, and June, love to be on the water too, especially when that is where the boys are. Oh poor Scrooge, boating is more fun then you could possibly imagine."

FROM Scrooge: "After seeing how much fun you all have on the water together, I regret that I didn't have that much fun when I was young. I've had a change of heart, and I'm giving each of you a Lifetime Academy Membership."

FROM Editor: "For those of you that have stayed with us this far, many thanks. You inspire us to keep working on this phenomenal website. We know that we have a lot more to do. Ultimately, we hope that we can help you enjoy the wonder filled world of boating as much as we do. We are all waiting to see what you have to say about this webpage article. Submit any comments via email To⇒ Comments♥ (Replace "♥" with "@"). Be sure to include this page's title in the subject line. Also, your corrections, updates, additions and suggestions are welcomed. Please submit them via email To: Editor♥ (Replace "♥" with "@"). It has been truly amazing to see what we have been able to accomplished when we've worked together. Thanks to all those that have donated their valuable time and energy, and a special THANK YOU to all that have supported this cause with their membership donations."