USEFUL CONVERSION FACTORS
AND TABLES


METRIC UNITS

QUANTITY UNIT SYMBOL
Length metre m
Mass kilogram kg
Time second s
Electric current ampere A
Thermodynamic temperature kelvin K
Luminous intensity candela cd
Amount of substance only used in physical chemistry mole mol
Force newton N
Energy joule J
Frequency hertz Hz
Pressyre and Stress pascal Pa
Power watt W
Quantity of electricity coulomb C
Electric potential volt V
Electric capacitance Farad F
Electric resistance ohm W
Electric conductance siemens S
Magnetic flux weber Wb
Inductance henry H
Luminous flux lumen lm
Illuminance lux lx

UNITS AND CONVERSION FACTORS
PRESSURE/DEPTH CALCULATONS

1 ft of water
=
 Pressure of 0.434lb/sq in
1 m of water
=
 Pressure of 1.43lb/sq in
2.31ft of water
=
 Pressure of 1 lb/sq in
34 ft of water
=
 1 atmosphere (14.7lb/sq in)
Pressure in atmosphere
=
 0.068 x pressure in lb/sq in
One cu ft of water
=
 62.39 lb
One cu ft of salt water
=
 64 lb (or 1/35th ton)

TEMPERATURE - FAHRENHEIT TO CELCIUS (CENTIGRADE)

° F ° C ° F ° C ° F ° C
212 100 100 37.7 45 7.2
200 93.3 95 35.0 40 4.4
190 87.7 90 32.2 35 1.7
180 82.2 85 29.4 32 0.0
170 76.6 80 26.7 30 -1.1
160 71.1 75 23.9 25 -3.9
150 65.5 70 21.1 20 -6.7
140 60.0 65 18.3 15 -9.4
130 54.4 60 15.6 10 -12.2
120 48.8 55 12.8 5 -15.0
110 43.3 50 10.0 0 -17.7

CONVERSION FACTORS AND TABLES

To Convert To Multiply To Convert To Multiply
AREAS POWERS
sq in to sq mm 645.16   horsepower to kW 0.7457
sq in to sq cm 6.4516   hp to metric hp 1.014
sq ft to sq m 0.0929   metric hp to kW 0.735
sq yd to sq m 0.8361   kW to hp 1.341
acres to sq m 4046.86   metric hp tp hp 0.9862
acres to sq yd 4840   kW to metric hp 1.359
sq mm to sq in 0.00155   FORCE  
sq m to sq ft 10.76   1 bf to N 4.4482
sq m to sq yd 1.196   kgf to N 9.8066
sq m to acres 0.000247   N to 1bf 0.2248
sq yd to acres 0.0002   N to kgf 0.101972
         
PRESSURES MASS
lb/sq in to kg/sq m 0.0703   oz to grams 28.35
lb/sq ft to kg/sq m 4.88   lb to kg 0.4536
lb/sq in to ft of water 2.31   tons to tonnes (1000kg) 1.016
lb/sq in to atmospheres 0.068   tons to short (US) tons 1.12
kg/sq cm to lb/sq in 14.22   grams to oz 0.0353
kg/sq m to lb/sq ft 0.205   kg to lb 2.205
ft of water to lb/sq in 0.433   tonnes to tons (2240 lb) 0.9842
atmospheres to lb/sq in 14.7   short (US) tons to tons 0.893
         
To Convert To Multiply To Convert To Multiply
SPEEDS DISTANCES
ft/sec to m/sec 0.3048   in to mm 25.4
ft/sec to knots 0.592   in to cm 2.54
ft/sec to miles/hr 0.682   ft to m 0.3048
ft/m to m/sec 0.0051   yd to m 0.914
knots to miles/hr 1.1515   fathomes to m 1.8288
miles/hr to km/hr 1.6093   statute miles to km 1.609
knots to km/hr 1.852   naut miles to statute 1.1515
m/sec to ft/sec 3.281   mm to in 0.0394
knots to ft/sec 1.689   cm to in 0.394
miles/hr to ft/sec 1.467   m to ft 3.2808
m/sec to ft/min 196.8   m to yd 1.094
miles/hr to knots 0.868   m to fathoms 0.5468
km/hr to miles/hr 0.6214   kn to statute 0.6215
km/hr to knots 0.54   statute miles to naut 0.8684
         
VOLUMES TORQUE
cu in to cu cm 16.387   lbft to Nm 1.3558
cu ft to cu m 0.0283   kgf m to Nm 9.8066
cu ft to galls 6.25   lbf ft to kgf m 0.1383
cu ft to litres 28.33   Nm to lbf ft 0.7376
pints to litres 0.568   Nm to kgf m 0.102
galls to litres 4.546   kgf m to lbf ft 7.233
Imp galls to US galls 1.2      
US barrels to cu m 0.16      
cu cm to cu in 0.061      
cu m to cu ft 35.31      
galls to cu ft 0.16      
litres to cu ft 0.035      
litres to pints 1.76      
litres to galls 0.22      
US galls to Imp galls 0.833      

WINCH CALCULATIONS

Winch horsepower can be approximated by the following formula:

HP = (L) (S)
(E) (33,000)

Where HP is the horsepower

L is the load (pounds)
S is the cable speed (feet/minute)
E is the overall drive efficiency

As cable builds up on a drum the radius changes thereby altering the speed and horse power for a constant load and RPM drive system. Therefore, the conditions of which load and speed are specified must be defined. It is common practice to specify conditions at mid drum unless other consideratons dominate in which case they should be used as design criteria.

Drive efficiencies vary greatly on the type of drive, as a guide:

Electric Drive worm gears TYP 60 - 75%
Electric Drive Bevel Box TYP 85 - 95%
Electro Hydraulic TYP 60% - 70%
Diesel Hydraulic TYP 60 - 70%

Exact figures depend on individual designs but duty factor and heat dissipation have a large impact on winch capability.

The following formula gives a close approximation of the length of wire rope that can be spooled onto a drum:

 

L
=
w x h
--------
(Dd + h)
4 Dd 2
Where:
L = the length of line which will fit drum (feet)
h = height of wire rope on drum when full (in)
Dd = diameter of drum (in)
w = width of the drum (in)
D = diameter of wire rope (in)