Improvements in the Blades of Screw Propellers for Steamships.
Year: 1897

page_text: Date of Application, 9th Mar., 1897-Accepted, 1st May, 1897
COMPLETE SPECIFICATION.
Improvements in the Blades of Screw Propellers for Steamships.
I, JAMES GLOVER of 2 Erskine Street, North Melbourne, County of Bourke,
Victoria. Australia, Engineer, 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 :-
At present there are certain disadvantages attendant on the working of screw
propellers of steamships.
These disadvantages are namely: (1), When air is carried downwardly from the
surface of the water by the revolution of the propeller a partial vacuum is created at
the forward or passive sides or faces of the propeller blades. (2), The loss of useful
effect of the slip which occurs in the working of screw propellers. (3), The vibration
which is invariably present whilst the propeller is working.
Now by the use of my present invention I overcome the foregoing disadvantages
and by so doing I effect a positive gain in the way of propulsive efficiency without
increasing the blade area and a lesser number of revolutions of the propeller are
required and a greater speed of the vessel can be attained with a quicker turning of
the vessel and lighter draught than are possible by the employment of any kind of
screw propeller.
I attain my object, firstly;-By making mid-width of a screw propeller blade a
curved aperture or a straight aperture commencing from about one third of the
length of said blade and terminating at about two-thirds of its length. Secondly
By setting back either the leading half portion or the following aft portion of the
active or driving face of the blade to the extent of the length or thereabouts of
the aforesaid aperture.
But in order that my invention may be better understood I will now refer to
the accompanying sheets of drawings in which similar letters of reference indicate
similar parts wherever they occur.
Figures 1 and 2 illustrate respectively the port side and aft elevations of a screw
propeller having my improved blades cast solid with the boss and the leading edges
cut away more than the after edges.
Figures 3, 4 and 5 represent sectional plans upon the lines (a), (b), (c), shewn in
Figure 2 of one of my propeller blades.
Figure 44 is a transverse section of a brace that serves for the purpose of
strengthening the blades of my large propellers.
Said Figures 1 to 5 represent what I term a coarse pitch screw propeller."
Figures 6 and 7 represent port side and aft elevations of a propeller having blades
made according to my invention and suitably attached to the boss.
Figures 8, 9 and 10 represent sections of Figure 7, taken upon the lines d, e, f,
respectively.
"
Figures 6, to 10 represent what I term a fine pitch propeller" having blades
made with my improvement.
The scale of Figures 1, 2, 6 and 7 is three quarters of one inch to the foot
and that of Figures 3, 4, 4, 5, 8, 9, and 10 is one and a half inches to the foot.
Figures 1 to 5 illustrate my screw propeller blades having a pitch of fifteen eights
of the diameter, being coarser than usual, and I purpose using this form of screw
propeller for large vessels.

page_text: The blades shewn in these figures are not only unsymmetrical in shape but are
made integral with the boss (A) but I wish it to be here understood that said blades
may be made separate as shewn in Figures 6 and 7 and may be secured in any
suitable manner to said boss (A), and, further, that neither the manner of securing
the blades nor the boss form any part of my present invention.
(C) is the curved aperture of each blade the leading half portion of which is what
I term "set back" from the helical to the said curved aperture (C) as indicated by
the deviation from the dotted face line (D) in Figure 5 which represents the contour
of the said helical line.
The area of the "set back" of the leading half portion (E) lies between or extends
from a point slightly beyond the two ends of the said curved aperture (C) and the
leading edge of the blade.
This "setting back" of the said leading half portion (E) will be further understood
upon reference to the upper blade of the screw propeller illustrated in Figure 2.
In this view the dotted line (F) extending from the edge (G) of the said curved
aperture (C) and running along the leading edge of the blade represents that portion
which is set back" as aforesaid from the helix or true screw, the greatest
set back" being along the edge (G') of the said curved aperture (C) as clearly
shewn in sectional Figures 3, 4, and 5, therefore, it will be now understood that there
is a gradual inclination from said edges (G) and (G') towards the helical shape which
commences at that part of the dotted line situated along the leading edge of
the blade.
(H) is a brace which serves to strengthen the leading and also the following half
portions of the blade.
Along the said carved aperture (C) there may be either one or two braces such
as (H) as shewn in Figures 1, 2, 6, and 7; they are cast with the blade as shown in
Figures 1 and 2 or they may be dispensed with when small screw propellers are
employed.
Now my invention may be partly modified when a screw propeller is required to
be used for small vessels. In this case I make screw propeller as illustrated in
Figures 6 to 10 having a blade made also with a mid-width aperture (J) and
this propeller as shewn has a pitch of nine eights of the diameter, being finer
than usual.
This modified form of blade for a screw propeller has the following or aft half
portion (K) of the blades set forward from the dotted helical line (L) to the straight
aperture (J), the deviation being from said dotted line (L) shewn on the right hand
blade of Figure 10.
"
The aforesaid portion (K) which is what I have hereinbefore termed "set forward'
is situated between the edges (G) and (G') of the before mentioned aperture (J)
and the rounded ends of said dotted line (F) and also the following or aft edge of
the blade.
This "setting forward" is similar in character to that described with reference to
the "setting_back" of the leading half portion (E) of coarse pitch screw propellers
as shewn in Figures 1 to 5.
I may here point out that the passive sides or forward faces of the blades shewn in
Figures 1 to 10 are convex shaped, that is to say, the forward surfaces of the metal
body of each blade is rounded off between the leading and the following edges of the
blades to the tip thereof and the edges of either the curved or straight apertures (C)
and (J) respectively.
I do not confine myself to any particular pitch or diameter of my propeller nor to
any kind of metal that may be employed in its construction.
In order that the action of the blades whilst in the water may be understood I shall
refer to Figures 1 and 2 only for the reason that a similar action takes place with the
blade shewn at Figures € and 7.
In the working of my propeller the following half portion of the blade will cause a
stratumn of water to rush through the curved aperture (C) in the direction shown by
dotted arrow Figure 5, thereby diminishing the partial vacuum which is generally
t

page_text: created at (M) Figure 5 and also lessening the resistance to the movement or turning
of that portion of the blade.
The motion of the water through the said curved aperture (C) is effected without
any shock or eddy on account of the leading portion (E) and the following half
portion respectively of each blade being so arranged as to cause only a slight change
in the direction of the water passing through. The water disposed of as aforesaid
is part of that just acted on by the said leading portion (E) of the blades and set in
motion aft so that it will be seen that the remaining part of the water coming
into contact with the following half portion of the blades will have an accelerated
motion imparted to it by reason of the said following half portion acting on water
which has not been previously in direct contact with the blades.
Having now particularly described and ascertained the nature of the said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is :-
:-
Firstly. A screw propeller blade made with a curved aperture (C) extending from
about one third to about two thirds of the length of said blade and having a forward
half portion (E) set back" from the helix and gradually commencing from the
dotted line (F) of the leading edge of said blade and terminating at the edges (G)
and (G) of the said aperture (C), as hereinbefore described and as illustrated in my
drawings.
Secondly. A screw propeller blade made with a straight aperture (J) extending
from about one third to about two thirds of the length of said blade and having a
following half portion (K) "set forward" from the helical line (L) and gradually
commencing from the following edge of the blade and terminating at the edges (G)
and (G) of the said aperture (J)" as hereinbefore described and as illustrated in
my drawings.