and includes the spherical boss with gear inside it setting the blades
(see fig. 8), but consisting of a pinion fixed to each blade shank
geared to a bevelled segment, etc.
Joseph Maudslay claimed, in patent No. 646 of this year, to turn
round propeller blades by a lever on the side of the shank worked by
a link taken into a grooved sliding collar, etc. (See fig. 47.)

John Fisher proposed making blades with various openings through
them ; to form flanges or ridges at the back, and to enamel the
surface.
James M'Connell claimed, in patent No. 1775, to make screw
propeller shafts hollow or tubular, as is now always done for H.M.
Navy.
James Mackay proposed to shape the " deadwood " of the ship near
the screw into a cylindrical enlargement so as to cause the water to run
along without closing in and be again disturbed by the boss. This
idea was improved upon many years after by Sir John Thornycroft.
28 MARINE PROPELLERS.
a.d. 1854. — Eennie of London built a twin-screw steamer for the
Khedive of Egypt, 60 feet long, 6 feet beam, and 21 inches draught
of water. The screws were 24 inches diameter and made 310
revolutions per minute when the boat was travelling ten knots per
hour, driven by disc engines 13 inches in diameter supplied with
steam at 45 lbs. ; with 60 lbs. it was said that a speed of twelve
knots was attained. The following year a similar, but somewhat
larger, boat, 70 feet long and 7 5 feet beam, did ten knots at 260
revolutions and consumed 100 lbs. of coal per hour.
