Improved Means of Preventing the Fouling of Screw Propellers.
Year: 1892

page_text: Date of Application, 19th Aug., 1892
Complete Specification Left. 18th Apr., 1893-Accepted, 2nd June, 1893
PROVISIONAL SPECIFICATION.
Improved Means of Preventing the Fouling of Screw Propellers.
I, FLORA THOMSON, of Londesborough Park Farm, Market Weighton, in the
County of York, do hereby declare the nature of this invention (a communication
to me by John Thomson Engineer of Steamship "Mongkut" of Hong Kong) to
be as follows:-
This invention has for its object to free screw propellers from ropes which may
become fouled therewith, which is particularly liable to happen if any rope be
trailing overboard when going astern, and it consists in providing means whereby
any rope which may become entangled with the propeller blades will be severed as
is carried round by the screw and so prevented from becoming coiled round the
shaft between the boss and the shaft bearing in the stern post.
it
To this end I mount around the shaft bearing in the stern post a casing or boss
constructed preferably in halves and provided, as represented in the accompanying
drawing, forming part of this Specification, with right and left handed cutters
whereby any rope carried round by the screw blades would be immediately caught
and severed in whichever direction the screw may be revolving.
Dated this 19th day of August 1892.
FLOKA THOMSON,
By A. M. & Wm. Clark,
53, Chancery Lane, London, Chartered Patent Agents.
COMPLETE SPECIFICATION.
Improved Means of Preventing the Fouling of Screw Propellers.
I, FLORA THOMSON of Londesborough Park Farm, Market Weighton; in the
County of York, do hereby declare the nature of this invention (a communication
to me by John Thomson, Engineer of Steamship Mongkut" of Hong-Kong) and
in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement:-
This invention has for its object to free screw-propellers from ropes which may
become fouled therewith, which is particularly liable to occur if any rope happen
to be trailing overboard at the moment when the vessel goes astern, and the inven-
tion consists in providing means whereby any rope which may become entangled
with the propeller blades will be severed as it is carried round and so prevented
from becoming coiled round the shaft between the boss and the shaft bearing in the
stern-post.
The invention is illustrated in the accompanying drawings, forming part of this
Specification, wherein
Figure 1 is a side elevation of a propeller and rope guard or cutter. Figure 2 a
longitudinal section thereof, and Figure 3 a cross-section of the propeller shaft,
shewing the rope guard in end elevation.
The same letters of reference indicate the same parts in all the figures.
To accomplish the object in view, I mount around the propeller shaft bearing A. in
the stern-post B a casing or boss C constructed preferably in halves bolted together
and provided, as represented in the drawings, with series of right and left-handed
cutters ccc whereby any rope carried round by the screw blades would be
immediately severed close up to the propeller, thus freeing the latter and this in
whichever direction the propeller may be revolving. It will be observed the
cutters on the one-half of the boss or casing C are right-handed and those on the

page_text: other half are left handed in direction, but I do not limit myself to this arrange-
ment as the right and left handed cutters might be alternated or otherwise arranged,
but the arrangement shewn is adopted for convenience of manufacture.
It is preferred to make the cutter boss of non-corrosive metal, ciz. nickel-steel.
It is preferably formed with a shoulder and three series of cutters as shewn, viz. a
series c on the shoulder presenting their cutting edges towards the propeller,
a series c¹ on the cylindrical portion of reduced diameter, and a series c³ on the end
face of this portion, immediately around the shaft, this series presenting their
cutting edges towards the boss of the propeller. It will be observed that the
cutting edges of the cutters c and care forwardly inclined and slightly curved in
the direction of their length, but they might be straight and either radial or
slightly tangential to the shaft, the object of curving them or placing them
tangentially being to facilitate the severance of the rope by producing a drawing
cut. For the same reason the cutters c', which project from the cylindrical portion
of reduced diameter, preferably have their cutting edges inclined at an angle to the
plane of the shaft and in order that they may act more efficiently they are
alternated in position with the cutters of the series c and c² whilst their cutting
edges are continued so as to project beyond the plane of the end face on which the
cutters are formed. I do not, however, limit myself to the particular arrange-
ment of the cutters, nor to the use of three series as described, since it will be
obvious that the cutters may be variously arranged upon the rear face of the shaft
bearing or of a casing covering the same, so as to catch and sever any rope which
the propeller may carry round with it and coil upon the shaft between the propeller
and its bearing.
The halves of the casing Care screwed or rivetted to the bearing boss B and are
provided with flanges united by bolts as shewn, whereby the whole is firmly secured
in position on the boss B.
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―
1. The application, to the bearing boss of a propeller shaft, of cutters adapted
to sever any rope which may happen to foul the propeller and the stern post
bearing.
2. The application, to the stern post bearing boss of a propeller shaft, of an
outer casing provided with right and left handed cutters adapted to sever any rope
which may happen to foul the propeller and stern post bearing.
3. The application, to the stern post bearing boss, of an outer casing provided
with three series of right and left handed cutters, substantially as and for the
purpose specified.