566
Molesworth's pocket-book
Screw Propellers.
RULE FOIl THE SPEED OK SCREWS.
V = Velocity in knots per hour.
v — Velocity in miles per hour.
P — Pitch of screw in feet.
R — Number of revolutions per minute.
t,_101 v v-ti pj
K - “p“ ‘ ioi ’ R
88 v PR r> _ 88 ü
K “ ' V ~ 88 ’ P R ‘
This is exclusive of the slip, which varies fiom
10 to 30 per cent.
Pbopobtions of Screw Propellers.
PITCH OF SCREW.
The pitch of screws varies with the ratio of the
circle described by the screw to the uiidaliip section.
FOR TWO-BLADED SCREWS.
2
1-47
Ratio of screw’s disc
to midship section
being 1 to .. ..
Ratio of pitch to the
diameter of screw
is 1 to __________
For four-blade<l screws multiply the ratio of the pitch to
the diameter as given above by 1 • 35.
Length of screw = -J th diameter of screw.
Multipliers for ascertaining the Stowage of Tallow,
Waste, Oil, am> Coal, in Coal-bunkers and Tanks
for Steam Vessels:—
Tallow 59 lbs. in a cubic foot.
Waste 11 „ „
Oil 6'23 gallons in a cubic foot.
•Coal 45 cubic l'e< t to a ton as stowed in coal-bunkers.
* Navy allowance : a ton may be stowed into a siara of 4CJ cube feet.