Air Pump
Do NOT confuse with a Locomotive Air Pump, used to power the brakes! An Air Pump on a steam launch is used to remove water from the condenser, while at the same time createing a vacuum. This has the benefit of adding a further 14psi (on a good day) to the total pressure differential of the engine, while making use of more heat from the steam (more Enthalpy). The increase in power from the heat removed from the steam is significantly greater than the power required to drive the pump in the first place.

Ball Valve
Ball valves are valves with a physical ball in the centre of them. The balls have a hole thorugh them which rotates through 90 degrees to either allow or stop substances flowing through. Because of the design, a ball valve does not require great effort to open or close the ball regardless of the pressure within or across the valve. Ball valves can be gas rated, steam rated and pressure rated. One important fact is that some ball valves, although they may have a 22mm input and output, may only have a small hole through the ball, and as such can be very restrictive if the wrong type is used.

Bar (Pressure)
Bar is the name for Pressure mearurement. Originally from acient Greece, it has no specific relation to any other measurement in use today, however 1 Bar is almost exactly 1 Atmosphere in pressure (given average atmospheric pressure). 1 Bar = 100,000 Pascals. 1 Bar = 14.5 PSI. 1 Bar = 1.0197 kg/cm squared. Bar is often used in Hydraulic pressures because these tend to be very high, and it would be daft to have a pressure gauge saying 100,000,000 Pascals when 10,000 Bar can be used.

A Barometer is a device used for measuring atmospheric pressure relative to a vacuum. Two typical designs are a Mercury Barometer (See Inches of Hg) and a Vacuum Diaphgram Barometer. Both use the presense of a vacuum to measure the air pressure. The air pressure causes water to boil at 100°C at sea level, and nearly 70°C on Everest.

BDC (Bottom Dead Centre)
Usually speaking of an engine, the Bottom Dead Centre is the point where the piston is at the very bottom and the crank webb for that piston is in line with the con rod. Because BDC on the crank is very hard to measure using piston height, BDC and TDC are often marked on the flywheel or other noticable part of the engine if they are required for setting the engine up. Most small boat engines are not too critical on the valve timings.

A Belt is a loop of flexible material used to transmit power through rotating pulleys. They work very much like a Chain except not all belts have teeth. Early belts were flat leather joined by metal clankers, which make a clanking noise every time they hit a pulley. Modern belts are all sorts of shapes but mostly V, Poly-V and timing belts are often a form of D shape on the teeth. Timing belts shouldn't slip, V belts can slip.

BHP (Brake Horse Power)
Brake Horse Power is the power being fed in to a brake connected to an engine, usually as either heat or pulling force. The heat required to raise a the brake by a certain ammount in a given time can be uased to calculate the power required to do so. Likewise the pulling force is used to work out the engine's torque, multiplied by the speed at the time to give the power. This method is crude but gives a good indication of the power of the engine. It can give a higher than normal reading sometimes due to the losses in the drive train not being taken into account.

Bore (Measurement)
The Bore of a cylinder is it's diameter.

A chain is a string of metal, often a short section connecing another short section and so on. Chains are used to hold heavy items to things, like an anchor to the anchor winch where rope simply isn't strong enough. Chain can also be used to transmit power just like a belt, only instead of pulleys they use sprockets. These sprockets are wheels with teeth on which the chain connects to. Because of this a drive chain ratio is set bt the number of teeth on the sprockets.

Compound (Engine)
The word Compound means to combine so as to form a whole. A Compound engine combines two cylinders of different pressures to one crank shaft. Steam enteres the HP and exhausts into the LP before exiting the engine. This uses the steam twice to allow the steam to expand further, reduce in temperature and thus allow more heat energy to be transferred into turning the engine. This has the advantage of much higher efficiency compared to a simple or twin-hi engine at the cost of more complexity to build.

Crankshaft (Engine)
The Crankshaft is the part of the engine that rotates. The output shaft of the engine is the crank shaft, the crank being the large U shaped part in the middle which the conrod connects to. Early cranks were wrought iron bend into shape with a large hammer and generally not very good. Later when machines became better, crankshafts were cast iron. Today any method can be used, including glue, shrink-fit, vacuum braze, pin, machine from solid, shrink fit solid webbs.

Crank Pin Bearing (Engine)
Known as the "Big End" in the motor trade, the crank pin bearing is the big bearing at the end of the con rod connected to the crank. Typically larger than most other bearings, the crank pin bearing takes all the force of the piston pushing, the force of the conrod spinning round and the fact its turning on the crank pin.

Crank Webb (Engine)
The Crank Webbs are the sides of the U shaped part on a crankshaft They connect the crank pin to the crank shaft and often have balance weights fitted to the opposite end. The connections between the crank webbs and the shaft are considered to be the main weak point of any crankshaft Generally speaking the easier the crankshaft design, the weaker the crank webb.

Crosshead (Engine)
The Crosshead is the part of an engine that connects the piston shaft to he conrod. It allows the linear oscillating piston shaft (moving up and down) to connect to the angular oscillating con rod, the other end of which spins round on the crankshaft. The Crosshead also connects to the Crosshead Guides to steady the crosshead and to bear the sideways force exerted onto the crosshead. Car engines do not use crossheads, the conrod connects direct to the piston.

Crosshead Guides (Engine)
Crosshead Guides keep the crosshead moving in line with the piston shaft and bear the sideways force exerted onto the crosshead from the con rod as the piston tried to pull the conrod in line with its self if the piston is pulling or to push the conrod out of the engine if pushing. The force exerted onto most crosshead guide designs is always in one direction for ahead and the reverse direction for astern, thus most boat engines are designed to be used in one direction most of the time.

Displacement (Engine, Pump)
Displacement is how much volume is taken up by the movement of the machinery. For instance a pump with 4" bore and 3" stroke has a displacement of 37.7 cubic inch. This is calculated by 4" bore = Pi x r squared = 3.142 x (2" x 2") = 12.56" square surface area. Multiply that by the stroke 3" = 37.7 cubic inch. Displacement is not to be confused with the volume of the cylinder, as there is always some clearance space top and bottom, not to mention the valve ports.

Dry Steam
Dry steam is essentially Wet Steam, that is steam which is at the temperature of which water boils at the given pressure, or just slightly colder, and contains little droplets of water, but with the water droplets removed.

The term Engine means to convert energy into a mechanical force. With steamboat engines this is specifically meaning pressure and temperature into a rotational force. A basic steamboat engine uses steam pressure to push a piston up and down causing a crank shaft to rotate. The steam is shut-off part way down the piston's travel and the steam then expands and cools. This then uses the energy stored in the heat of the steam to power the engine, and so the heat of the steam is as important as the pressure. Common types of engine are Simple, Twin-Hi, Compound, Triple and Uniflow.

Fire Tube (Boilers)
This is a type of boiler. Here the fire / hot gasses flow through tubes surrounded by water. Most Locomotives and old style mill boilers operate like this. They typically hold a lot of water compared to a water tube, but are very stable pressure wise as the mass of water takes a long time to change temperature. Also see Water Tube boilers.

Flywheel (Engine)
A Flywheel is a wheel fitted to the crankshaft of an engine. Its design is engine specific but the principle is to carry momentum so allow smooth running of the engine. Angular momentum is generated by a mass rotating round a point (the point being the crankshaft). The larger the mass, the further from the point and the fasterit turns all add to the momentum. On a Simple engine, there is a point around TDC and BDC where the steam cannot push the piston up or down. At this point the flywheel pushes the crankshaft round. It slows down while doing this, only to speed up on the power stroke. The more momentum the flywheel has the less it slows down and the smoother the engine runs.

A Gasket is used to seal two mating surfaces, generally making them steam tight. They allow this steam-tight seal between two surfaces that are not absolutely true or machined 100% flat as this is nearly impossible to achieve. One of the best gasket material for steam is asbestos, though it can't be used now. Modern gasket paper is made of fibrous material usually with graphite. Blown gaskets are always an issue, though an emergency tube of instant gasket should be carried at all times. Otherwise, use your breakfast cereal box.

Gate Valve
A gate valve is a basic type of valve where a flat gate slides down to close the valve. These are identified by the rectangular top of the valve before the packing gland. These valves are rarely rated for steam or any real pressure. They are good for your house central heating system and low pressure water shut-off only.

A Gland is a seal, usually around a shaft. This shaft may be a valve shaft, piston shaft, rudder shaft etc. The shaft may be turning, sliding or both. The type of gland depends on what it has to seal. A valve gland may need to be steam tight. Rudder shaft only needs to be water tight at no real pressure. A steam tight gland usually comprises of graphite string packing, cut into three circles, pushed snugly into the gland housing and pushed down with the gland nut. Other glands may be a simple O ring, a rubber sleeve etc. It should be noted that the prop shaft water tight seal is called a Stuffing Box, not a gland though it does the same job. Glands should also not be confused with Seals (e.g. oil seal).

HP (Horse Power)
Stands for Horse Power. Defined as a foot-pound-second unit of power. Originally it meant the useable power you can get from 1 horse. In electric motor terms, it is equivelant to 745.7 Watts, or in other words the power required to move 550 foot-pounds in 1 second (every second you can move 550 pounds in weight 1 foot).

HP (High Pressure)
Also stands for High Pressure. Typically used to describe the High Pressure cylinder of an engine.

ID (Measurement)
ID means Internal Diameter. I.e. if a cylinder has a bore of 4", its ID is 4".

Inches of Hg (Mercury)
Inches of Hg (Mercury) are used when measuring a vacuum. When condensing steam, a vacuum can be formed and this is typically measured in Inches of Hg. This comes about by having a 31" tube of Mercury sealed at one end. You tip the tube upside down into a bowl and allow the weight of the Mercury to create a vacuum in the top. 1 Atmosphere (on a good day) = 29.9 inches of Hg. On a bad day with low pressure (i.e. rain storms) this can drop to 28" Hg.

Laymens (Term)
When you are asked to explain something in "Laymans' Terms" you are being asked to explain something in a really simple way and dumb it down. E.g. instead of explaining in detail how a steam engine works, you would simply say steam goes in, and it turns round. This misses out on much detail, but it is often necessary with technology to do so for people to understand who do not originate from an engineering background.

LBS (Pressure)
Alternative name for PSI. Stand for LB (pounds) per S (square inch).

LOA (Measurement)
Length Over All. Meaning the total length of the boat from the very forward part of the bow to the very rear part of the stern, includes any hand rails, flag poles etc.

LP (Engine related)
Stands for Low Pressure. Typically used to describe the Low Pressure cylinder of an engine.

LWL (Measurement)
Length Water Line. This is the legnth of the boat on the water line.

Pascal (Pa)
Pascal (Pa) is a unit of pressure named after Blaise Pascal, the eminent French mathematician, physicist, and philosopher noted for his experiments with a barometer, an instrument to measure air pressure. Pascals are rarely used in steam as their units are too small. Inches of Water are more common when dealing with tiny pressures.

PSI (Pressure)
This stands for Pounds per Square Inch and is a measurement of pressure. Imagine you weigh 150 pounds, and you stood on a 1" square block of wood, the force exerted on to the ground would be 150 psi. This is the same force the average steam boat runs at. Imagine the end plate of a boiler running at 150 psi is 8" diameter, that is 50 square inches. At 150 psi, 7500 pounds (3.4 tonnes) is trying to push that plate out. 14.5 psi = 1 Bar.

Pump (Machinery)
A pump transfers material from one place to another. In steamboating terms, it usually means a Feed pump which transfers water into the boiler, or an Air pump which removes the condensate out of the condenser, or a bilge pump which removes water from the bottom of the boat.

The term Ratio means a comparison from one to the other. E.g. if you had a pulley on an engine turning at 100rpm and another pulley on a prop shaft turning at 50rpm, the ratio would be 2:1, that being 2 turns on the engine = 1 turn on the prop shaft. Or it could be written as 1:0.5 as the engine speed is often seen to be a multiple of 1 and all other ratios are worked out from this. If you had a sprocket and chain drive with 90 teeth on the driving sprocket and 30 teeth on the driven sprocket, the driven sprocket would turn 3 times faster than the driving sprocket, giving a ratio of 1:3. Ratio's have no units.

SHP (Shaft Horse Power)
Shaft Horse Power. This is the power going through a drive shaft. This is often measured by the ammount of torque twisting the shaft multiplied by the speed the shaft is turning at. This gives an indication of the power going into the propeller, while Brake Horse Power does not always include all the losses along the system. Shaft Horse Power gives a more realistic figure for the power that can be given by an engine.

Simple Engine
A Simple Engine is the most basic type of engine. It has 1 cylinder and usually 1 valve. Steam pushes the piston up (or down) only once before it is exhausted. These engine are very simply to build and maintain. They are not very efficient, but on a small steam boat there is no great ecconomic advantage of having other types of engine.

Steam is the gaseous form of water. It can be categorised in to four types; Wet Steam, Dry Steam, Superheated Steam and Water Vapour. Steam has both Pressure and Temperature. These two are very closely linked, to the point where the pressure of wet steam is directly linked to its temperature. Steam Tables are used to calculate the temperature compared to the pressure. The usefull part of steam is the heat it contains as there is little power in the pressure, although if there was no pressure there would be no temperature to be used.

Stern Tube (Propeller Shaft)
See Stuffing Box.

Stroke (Engine)
The Stroke of an engine is the distange the piston moves up and down. E.g. a stroke of 4" means the piston moves 4" down to BDC from TDC. The Crankshaft will have a throw of 2" from the shaft centre to the crank pin centre.

Stuffing Box - Stern Tube (Propeller Shaft)
The Stuffing Box, also known as the Stern Tube, is the water tight seal on the boat hull that allows the propeller shaft to pass through. Traditionally this was a box stuffed with very greasy rope to hold the water back. In modern times the stern tube is more like a gland with a proper sealing compound and often includes a bearing. They still require plenty of grease.

Suction (Pressure)
The idea of suction is wrong from the very start, to suck water into a pipe you imply the water is stuck together pulling its self along, which it doesn't. The term suction is only used as a laymens term so as to not over complicate the terminology. In reality, when you "suck" water into a pipe, you are in fact removing water, or air, from one end of the pipe and the resulting lowered pressure inside the pipe causes a pressure difference with the outside of the pipe (the atmosphere) and it is the atmosphere pushing the water into the open end of the pipe. This is also the same for a Vacuum; you can't have a vacuum as it implies that you have a nothing, you simply have less pressure than outside.

Superheated Steam
This is steam which has been heated above the temperature at which water boils at the given pressure. As heat contains a lot of energy, the more heat you can put in to steam, the more heat can be used by the engine.

TDC (Top Dead Centre)
Usually speaking of an engine, the Top Dead Centre is the point where the piston is at the very top and the crank webb for that piston is in line with the con rod. Because TDC on the crank is very hard to measure using piston height, TDC and BDC are often marked on the flywheel or other noticable part of the engine if they are required for setting the engine up. Most small boat engines are not too critical on the valve timings.

Triple Expansion (Engine)
A Triple Expansion engine has three cylinders. The steam enters the HP first, exhausting into the IP and then the LP. This re-uses the steam twice before it exits the engine. Benefits are a huge gain in efficiency and smoothness of running. Disadvantages are increase in technicality of the engine and a larger engine per power output. Generally a larger/heavier engine is not a big issue on a boat or ship. The increasing cylinder capacity is usually exponential, following the steam expansion graphs. This allows each cylinder to produce roughly the same power to spread the load. As the steam expands it cools, the more it cools the more heat energy you get out of the engine. See Enthalpy.

Twin-Hi (Engine)
A Twin-Hi enigne is like two Simple engines bolted together, usually with the cranks 90 degrees apart. Typically these engines will start from any crank position because if one piston is at TDC or BDC the other one is id-way through its stroke. Although not very efficient they are very powerful for their size and are very responsive to their controls. Ideal for short bursts of lots of power like on the Umpire boat Consuta.

A valve is a device which controls something. In our case it is normally steam, water, oil or gas. The most basic type of valve simply turns a ball with a hole in the middle through 90 degrees, so that in one posision water, steam etc flowing through a pipe into the valve can flow through the hole and out the other side. In the other postion, the substance is blocked by the ball and can go no further. Valves come in many different types, the common types being a Ball valve, Globe valve, Gate valve, Check valve, Flap valve, Cock and Needle valve.

A Vacuum is the generic name given to any pressure lower than Atmospheric pressure. I.e. lower than 14.7psi compared to an absolue vacuum. Vacuums is measured in Inches of Mercury ("Hg). That is, if had a glass tube, typically 32 inches long, sat in a bucket of Mercury, and at the top of the tube applied your vacuum, the level of vacuum is how many inches the Mercury can be sucked-up. 31"Hg being classed as an absolue vacuum. Of course you cannot "suck" a liquid, the Atmospheric Pressure pushes the Mercury up the pipe to fill the space left by the absence of air. For this same reason, there is no such thing as a Vacuum, it is simply a lower than atmospheric pressure (which changes, 980 to 1050 millibars or so). For this reason, your standard pressure gauge can never be correct. The only way for a pressure gauge to read correct would be to place it in an absolute vacuum, and remove 14.7 psi to every reading. Another feature of a Vacuum is that water will boil at 25C with a 29"Hg vacuum. When nearing 31"Hg, water will boil at near freezing point. It is therefore impossible to create a perfect vacuum with any water present - it turns to steam!

Water Tube (Boilers)
This is a type of boiler where the water is inside tubes and the fire / hot gasses flow around the outside of the tubes. Modern day coal and gas power stations use these. They can be designed to run at much higher pressures than fire tube boilers, but your typical steam boat doesn't take advantage of this feature. They can be harder to fire as they generally hold less water, meaning the pressure can rise and fall quickly.

Wet Steam
This is your normal type of steam. Wet Steam is steam that is at the temperature of which water boils at the given pressure, or just slightly colder, and contains little droplets of water due to the steam condensing as it cools. This steam is good for self-lubricating engines.