Year: 1885

page_text: I ALFRED JULIUS BOULT of 323 High Holborn, in the County of Middlesex,
Engineer, do hereby declare the nature of this invention (a communication from
Cyrus William Field, Junior residing at New York, United States of America) and
in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement :-
Briefly stated, this invention consists in mounting the screw in an extensible
manner wholly behind the rudder so that the screw can be projected backwardly
to operate in clear solid water aft of the rudder and stern; or on the other hand
can be retracted close to the stern as occassion requires, the screw being capable of
continuous rotation in either of said positions. By this means a much greater pro-
pelling effect may be secured when in open water, whereas when in port the screw
can be shifted to a safe position close to the stern. In order to properly accomplish
this purpose in connection with the shifting screw a peculiar form of rudder is
employed which consists of two leaves hinged respectively in recesses on either side
of the deadwood, and between which the screw-shaft passes and projects out through
and back of the stern-post to receive the screw.
In the drawings which accompany and form a part of this specification, Figure 1
is the side view of the stern of a vessel with this invention applied thereto.
Figure 2 is a sectional plan view taken on line x x Figure 1. Figure 3 is an end
view of the mechanism employed to extend the main shaft, being taken on line y y
Figure 2. Figure 4 is a view of the stern of the vessel showing both leaves of the
rudder extended.
In carrying out this invention it is preferable to employ a rudder which consists
of two leaves which are shewn in the drawings at a a¹. These leaves are hung in
the ordinary manner by pintle and brace hinges, but instead of being secured aft
of the rudder-post they are mounted in recesses formed in the deadwood just
forward of the rudder-post.
The rudders are controlled by the ordinary steering gear, which of course is
duplicated on account of their being two rudder-heads. The steering mechanism,
however, is not shown in the drawing, as it does not constitute part of this
invention.

page_text: In operation it will be understood that so long as both leaves of the rudder are
in the recesses formed for their reception, the pressure on each will be equal and
the vessel will be in a state of equilibrium as far as any effect from the rudders is
concerned, but if one of the leaves be turned out the pressure on that side will be
increased and the vessel will revolve around the centre of gravity. The rudder in
fact operates in precisely the same manner as the ordinary rudder except that two
leaves are employed each of which describes an arc of 90 degrees and together
make up an arc of 180 degrees.
By this arrangement of the rudder the propeller shaft can be extended directly
through the rudder-post and therefore support the screw in a position where it can
operate in clear solid water, away from the soapy, foamy water that is always
found in the immediate wake of a vessel.
The distance which the screw would advance in an unyielding substance during
a single revolution is called the pitch of the screw, and the difference between the
pitch and the actual advance made when the screw revolves in a yielding medium-
such as water-is called the slip.
Now it will be readily seen that the slip would be much less in what is called
"solid water than it would be in water filled with air bubbles, as the former would
be of greater specific gravity and therefore offer a much greater resistance to the
blades of the screw.
Within reasonable limits, the further the screw is from the rudder-post the
better the water for it to operate in, and in order to obtain the benefit arising
from operating the screw in water of greater specific gravity the main or
screw-shaft of this vessel is constructed so that it can be extended and retracted
at will.
The mechanism employed for extending the shaft, is seen in Figures 2 and 3.
A sleeve as 1 is keyed to that section of the shaft which is in direct conjunction
with the engine.
This sleeve is provided with a feather which rides in a groove formed along the
forward end of the rear section of the shaft. The rear section of the shaft, which is
shown in the drawing at 2, passes through one end of a sliding carriage 3 and is held
in its relative longitudinal position with said carriage by the collars 4 and 5. The
carriage 3 is supported by a bearing frame 6 and slides in ways formed therein.
Two pinions 7 and 8 which mesh together, are mounted on the frame 6 in
position to engage with the toothed racks 9, 10, formed on either side of the
carriage.
A hand-wheel 11 is secured to the shaft of one of the pinnions 7 or 8, and by
simply turning this wheel 11 the shaft 2 is extended or retracted.
It would not be advisable to mount the screw so that it would be always at a
considerable distance from the rudder-post, for it would then be liable to injury
when the vessel was in port or tied to the dock. Therefore the shaft is constructed
as described so that it may be extended when the vessel is under weigh and
returned to its normal position when the vessel is in port.
Figure 1 is, or may be assumed to represent, the stern of an ordinary screw-
propelled vessel, in which the space usually occupied by the screw between the
stern-post and rudder-post is utilized to form the recesses or pockets in which the
leaves of the rudder described are placed, the shaft being extended through this
space and through the rudder-post, and the screw placed entirely behind the
rudder and rudder-post, as illustrated.
I am aware that a rudder consisting of two leaves, one placed on each side of the
deadwood; is not new in itself, as such is shewn in United States patent 232651
and I am also aware that it is now new to mount a propeller on an extensible
shaft adapted to be projected from, and retracted towards, the stern, as this is
shewn in United States patent 20862, but in that case the screw works in an
aperture cut in the rudder and the rudder lies behind the screw, whereas in this
case the extensible screw-shaft and screw are completely back of the rudder, by
which means a greatly increased propelling effect from the screw is secured without

page_text: being impaired by the position of the rudder, whereas on the other hand the
rudders are not effected by the action of the screw.
Having now particularly described and ascertained the nature of this invention
and in what manner the same is to be performed as communicated to me by my
foreign correspondent I declare that what I claim is
1. In a screw propeller a shiftable screw mounted wholly behind the rudder,
with means for projecting the screw backwardly to operate in clear solid water aft
of the rudder, and for retracting the screw close to the stern, the screw being
capable of continuous rotation for propulsion in either of said positions, substan-
tially as herein set forth.
2. In a screw propeller a screw mounted on an extensible shaft and arranged to
operate in a position wholly behind the rudder, with a projecting and retracting
device to project the shaft and screw back into clear water aft of the rudder and
stern, and to retract the same toward the stern as occassion requires, the said shaft
and screw being capable of continuous revolution in either of said positions,
substantially as and for the purpose set forth.
3. The combination of a rudder composed of two rudder leaves mounted in the
deadwood or narrow part of the stern, with a longitudinally extensible or movable
screw-shaft passing out of the stern between said rudder leaves, a screw mounted
on the end of said shaft aft of the rudders and a shaft projecting and retracting
device for projecting the shaft into clear water aft of the stern and rudder and
retracting the same toward the stern and rudder substantially as herein shown and
described.
300-
ALFRED J. BOULT.