Improvements in and relating to the Propelling Gear of Shallow Draft Screw Vessels.
Year: 1898

page_text: Date of Application, 29th June, 1898-Accepted, 27th Aug.,
1898
COMPLETE SPECIFICATION.
Improvements in and relating to the Propelling Gear of Shallow
Draft Screw Vessels.
We, SIMPSON, STRICKLAND & COMPANY, LIMITED, of Dartmouth, South Devon,
Engineers and Yacht Builders, and WILLIAM CROSS, Member of the Institute of
Civil Engineers, of Dartmouth, South Devon, do hereby declare the nature of this
invention, and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement:―
Our invention relates to a novel arrangement of the propelling gear of shallow
draft screw vessels of the "screw-in-tunnel" type.
In such vessels the screw propeller is disposed in a tunnel or chamber formed
beneath the stern, and enclosed at its base by the water; before starting the main
engines the water but partly fills the tunnel or chamber and the screw is there-
fore only about half immersed, but after starting the engines the screw gradually
fills the tunnel with water and becomes wholly immersed, and it then acts in
the ordinary way.
Owing to the time taken in exhausting the air contained in the tunnel and
filling same properly with water there is always some delay at starting, and the
object of our invention is to obviate this delay by independently filling the tunnel
with water prior to starting the engines.
This we effect by providing air ejecting apparatus of suitable kind adapted to
be operated either by steam from the boiler or by any power available, or by
vacuum, so as to efficiently exhaust the air from the tunnel and enable same to
fill with water at any convenient time previous to the starting of the main engines.
The annexed drawing illustrates by way of example one arrangement for the
purpose, which consists in the provision of an ordinary air ejector. A represents
the after end of the vessel with the tunnel or chamber T beneath her stern and a
screw propeller S, which, as will be seen, is but half immersed below the normal
level W L of the water closing the base of the tunnel T. E represents the air
ejector which is fitted in convenient position within the vessel above and con-
nected with the tunnel T. It is supposed to be operated by steam from the
boiler led through the pipe P, and it is provided with a delivery valve D and an
air exhaust pipe 1" which is shown in the drawing as exhausting through the stern.
We do not confine ourselves to this or any specific arrangement of apparatus for
carrying out our invention, as there are many kinds of apparatus suitable for
exhausting the air from the tunnel T prior to starting the main engines which
may, with ease, be substituted; for example, we may connect the air space of the
tunnel direct by a valved pipe to the condenser of the engine (if used) or we may
employ an air-pump adapted for operation by hand or power.
Having now particularly described and ascertained the nature of our said inven-
tion, and in what manner the same is to be performed, we declare that what we
claim is:-
In shallow draft vessels of the "
screw-in-tunnel" type, the provision of air

page_text: ejecting apparatus such as above referred to, for use in connection with the
tunnel, for the purpose of exhausting air therefrom, and enabling same to be
filled with water previous to starting the main engines.
Dated this Twenty-ninth day of June 1890.
For the Applicants,
J. C. CHAPMAN,
Chartered Patent Agent, 70, Chancery Lane, London, W.C.