Glossary

About:

Last update:	16 Jan 2001

Scope:		This page is a collection terms and definitions used
		for scuba, submarines, and general naval usage.
Index:

Glossary:

A:

B:
B		See "Center of Bouyancy".

Bends           See "Decompression Sickness".

Bow		Front of ship.

C:

Center of Bouyancy (B)
		Is the geometrical center of the underwater volume
		and the point through which the total force due to
		bouyancy may be considered to act vertically upwards.

Center of Gravity (G)
		Is the point in a body in which the total weight
		of the body may be considered to be acting 
		vertically downward.

D:

Decompression Sickness
                Decompression Sickness or bends occurs when nitrogen
                bubbles come out of solution in your blood stream
                or body tissues. The nigrogen goes into solution by
                breathing compressed air at a greater pressure than
                at see level. While breathing this air, nitrogen is
                absorbed by your body. If too much nitrogen is
                absorbed or if you return to sea level pressure air
                too fast, you get bends.
                Scuba divers and owners of ambient pressure 
                submersibles need to watch out for the bends by using
                dive tables and non-decompression dive profiles.

Density		Is a mass per unit volume (kg/m^3) or (lb/ft^3).
			Fresh Water	62.3164 lb/ft^3 at 20 degrees C
			Sea Water      ~64      lb/ft^3 

Displacement	The amount of water an object displaces or moves
		out of the way when put into that water. If the 
		object floats the the amount of water displaced
		weighs the same as the object. 
		Displacement = volume displace x density of water
						 displaced

Dive Tables     Charts or tables that show the safe level of nitrogen
                absorbtion of a human body graphed at a function of
                time and depth.

E:

F:

G:

G		See "Center of Gravity".

H:

I:

J:

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K:

Kort Nozzles
		A specialised ducted propellor system. 
		The duct helps to derive more 
		thrust then a open propellor in 
		two ways. First, the duct inside 
		diameter at the contriction 
		is very close the propellor tips. This 
		cuts down on energy loss from 
		turbulant vortexes coming off
		the tips of the propellor. Second 
		the duct cross section is shaped like
		an air foil. The water flow from 
		the propellor moving through the 
		duct generates thrust due to 
		the shape of the duct. Water is forced 
		through the contriction at high 
		pressure which creates thrust as it
		flows to the less contricted exhaust opening.

L:

M:

Main Ballast Tank or MBT
                Is a ballast tank that gives extra bouyancy when
                it is blown dry or reduces bouyancy when flooded 
                with water. Even though called the "main" ballast
                tank it may not be the only one. You may have two
                saddle tanks or a tank in the bow and stern of your
                submersible. In typical usage a MBT is either fully
                flooded or blown dry. There is no attempt in trying
                to keep its volume constant since most MBT are open
                at the bottom to the surrounding water pressure and
                would require some kind of continuous feedback loop
                to keep its level constant.

Manifold	A group of valves. Like high pressure manifold or
		air manifold.

Moment		Moment or "lever arm" is the product of a force
		and the distance the force is applied perpendicularly
		to the arm.

N:

Negative Bouyancy
		When the weight of the water displaced by an
		object is less than the weight of the object
		the then object is negatively bouyant. In
		other words it sinks.

Nuetral Bouyancy
		When the weight of the water displaced by an
		object is the same as the weight of the 
		object the the object is nuetrally bouyant.
		In other words it floats, or is suspended,
		at a point between the surface of the water
		and the bottom of the container or ocean
		bottom.

O:

P:

Port		Left side of ship.

Positive Bouyancy	
		When the weight of the water displaced by an
		object is more than the weight of the
		object then the object is positively bouyant.
		In other words the object floats.

Pressure	Is the thrust or force per unit area. Stated in
		PSI (Pounds per Square Inch) or kg/m^2.

Q:

R:

Relative Density (R.D.)
		Is the density of an object compared to the 
		density of fresh water. 

		R.D.= Density of object / Density of fresh water
		
		Density of fresh water = 1 g/cm^3

Reserve Bouyancy	
		Is the water tight volume of a boat or ship that
		is above the waterline.

S:

Starboard	Right side of ship.

Stern		Back of ship.

T:

U:

V:

Variable Ballast Tank or VBT
                Is a ballast tank whose volume is adjusted to give
                a selectable amount of bouyancy. A VBT is used to
                fine tune the bouyancy of a submersible so it is
                neutrally bouyant. Typically a VBT has three valves.
                One to let water in, one to let air out, and one
                to let air in. In usage you open the water valve to
                allow water in. Then you slowly open the air outlet
                valve to allow the air holding water out of the VBT
                out. If too much water is let in by letting out to
                much air you can add more air with the air inlet
                valve. Once neutral bouyancy is obtained close all
                the valves.

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W:

Waterline	Is where the water meets the hull of a vessal when
		it floating or positively bouyant.
		

X:

Y:

Z: