An Improved Cofferdam for use in the Repair of Screw Propellers.
Year: 1898

page_text: Date of Application, 1st Apr., 1898-Accepted, 25th June, 1898
COMPLETE SPECIFICATION.
An Improved Cofferdam for use in the Repair of Screw Propellers.
I, CARL AUGUST EICKE, of 37, Sielstrasse, Bremerhaven, in the Empire of
Germany, 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:-
The dry dock forming the subject matter of this invention has for its object
to dock separately, so as to be able to replace them, the vanes or wings of a
screw propeller so constructed that these vanes or wings can be screwed on and off
the same. Such a dock is designed to avoid the inconvenience adherent to similar
constructions heretofore devised such as for instance those forming the subject
matter of the German Imperial Patents Nos. 51426 and 80581. The first of these
patents discloses a construction of dock which is very awkward and inconvenient
and very heavy, being moreover cumbersome to handle and in many cases not
applicable to twin screw propellers; while that disclosed in the second patent,
which is theoretically a much superior construction, has the defect that it occupies
on board a considerable amount of useful space, while the workmen engaged
repairing this dock have to work in an atmosphere of compressed air, which in all
cases must have an injurious effect on the health of these workmen as experience
has fully demonstrated.
The present dock is comparatively light in weight, it can be stowed away on
board in spaces which are not suitable for other storing purposes, and its
manipulation is, according to circumstances, free from many difficulties.
The accompanying drawings show,the new dock constructed according to this
invention.
Figure 1 shows the rear end of a steamship equipped with a single screw pro-
peller which is docked according to this invention, Figure 2 shows an aft view of
the same steamer.
Figure 3 is a front view of the dock in situ.
Figure 4 is a plan view of this dock drawn to an enlarged scale for the sake of
clearness.
Figure 5 is a side view of a clamp or frame used in connection with the dock.
Figure 6 shows, to a still further enlarged scale, a partial sectional plan view
of the dock.
This figure is really a horizontal section of the dock on line 6-6 of Figure 3,
and is drawn to particularly illustrate the construction of the clamp or frame
shown in Figure 5, and the manner of fitting the same to the fixed part of the
dock surrounding the vane or wing which is being repaired.
When using the dock herein described and illustrated the screw propeller
must be so turned that the vane required to be repaired or replaced by another
assumes a vertical and lowermost position. A sack a is suspended over the propeller
from the top so as to entirely enclose the whole screw. This sack a should
consist of watertight strong material, and in order to be able to place it con-
veniently over the screw it is composed, like an ordinary pocket, of two parts which

page_text: are joined at the front as well as at the rear side by a hinge
piece or frame b, c.
Figure 6 shows the mode of fixing the two sack
halves to the hinged frame b, c; ordinary headed screws pass through this frame
and press by the aid of rails & the material firmly against b, c, along the length
of the hinged frame. The two portions of the frame are provided with notches e
and (Fig. 5) which allow the said frame to fit tightly around the propeller shaft.
In cases wherein the propeller shaft n is not arranged relatively to the rudder
post so as to turn therein the rear part b, c, may not require the notches e, f, in fact
the whole of that rear part may be entirely dispensed with. The docking sack in
such a case cannot be so conveniently handled for the purpose of removing the
horizontal vanes of the propeller. In the construction shown by way of example
the frame b has a forked shape, a projecting edge g on the part e engaging in this
fork and bearing tightly against an india rubber strip h in order to form a
tight joint. is the hinge which connects together the two parts b, c, of the
frame. When the sack a is placed over the screw, the front and rear parts of
the frame b, c, (Figure 1) must be held sufficiently far apart by cords or ropes;
while the open side of the sack which is obviously turned downwards must be
sufficiently stretched out. To be able to use the above dock it is obvious that the
water should be still or at least only slightly in motion, that is to say the ship
should either be anchored in a harbour or be in a smooth sea, and it is furthermore
necessary that the screw propeller should project out of the water or remain but
very little under the surface of the water; although the dock may still be utilized
when the screw is lying at a greater depth in the water so long as a prolongation
in the height of the sack is provided for by annexing an additional attachment
thereto.
It is not absolutely necessary that the screw propeller should project out of
the water or be only slightly immersed therein, in order to allow the work of
repair to be commenced as otherwise the dock for the propeller would have to be
unnecessarily large and heavy. When the sack a has been placed over the screw
until the notches or recesses c, f, of the hinged frame b, c, are at the same height as
the screw shaft, the two sides of the frame are closed and the sack is thus fixed
over the propeller, when the screw is turned through an angle of 180° so that the
damaged vane may come uppermost, the whole sack following this motion and
having its open side likewise brought uppermost. The sack is now opened to
such an extent as to be able to slip therein, along guides k formed on the outside
of the frame b, c, two plates or shells of sheet iron or other sufficiently stiff
material or metal. The vertical edges of the shells should have a suitable shape as
shown in Figure 6, in order to remain engaged within the grooves k. These shells
are, as shown in Figure 2, of such a height as to project outwardly over the
greatest periphery of the screw, so that they may thus safely project above the level
of the water in case the screw was situated or immersed slightly below such
water level.
Figure 1 shows the whole dock in longitudinal section, so that the dock shell
placed on the right side of the ship is that which is visible; the left sided shell
on the contrary cannot be seen. To facilitate the adjustment of these shells, each
shell may consist of several different parts which may be connected together
by screws or any other suitable means. In the drawings, each shell has been shown
as formed of one piece only for the sake of simplicity of manufacture. These
shells are supported by the lower ends of the guides or grooves k as well as by the
two horizontal propeller vanes or wings; although it is obvious that this latter mode
of support, i.e. on the vanes or wings is far from being indispensable. When the
dock has been brought to the position clearly shown in Figures 2 and 3 in the
manner herein before described and the upper edges of the sack have been secured
to the upper edges of the dock shells or side pieces in any suitable manner such
as for instance by means of hooks and eyes, the dock is then emptied by means of
a pump, to such an extent that the water left therein only reaches as high as the
propeller shaft. After having introduced a wooden grating inside the said dock

page_text: to prevent the tools such as spanners, hammers and the like required for use from
falling into the sack and perchance piercing the latter. The workmen employed
for the purpose of repairing or exchanging one of the vanes proceed to get inside
the dock from the top in order to loosen the vane which is to be replaced. When
this is done and the form of the aft part of the ship is such that the vane cannot
be removed right away from the dock, the latter is refilled with water when one
of the shells is taken out. The corresponding side of the sack a which adheres
tightly around the dock shell or side drops consequently so far down that the
vane can be readily taken out at the side, and replaced by another which is first
allowed to hang loosely on the boss or hub, when the released dock shell or side
is put back again in its place and the water is again pumped out of the dock as far
as the said boss or nave, whereupon the new vane is allowed to slide on its fixed
pins or screw bolts or rivets in order to be finally fixed in position. The wooden
grating is now removed from the dock and the two sides or shells are stored
away again on board; whereupon the propeller is turned again through an angle
of 180° so that the new vane may come downwards, when the frame b, c, is opened
and the whole dock sack is taken off the screw at the bottom and drawn
out of the water. In the parts where this sack is laid on the propeller vanes
it can be properly strengthened or stiffened if required.
It may be remarked, that during the loosening and screwing up of the vane or wing
the exhaust pipe of the pump must be left in the dock in order to be able to
constantly remove the water pressing in owing to the unavoidable leaks occurring
in the water tight making arrangement.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, I declare that what
I claim is:-
-
A dry dock for screw propellers, characterized by a sack or bag turned in a
downward direction, and suspended over the whole screw propeller when a vane or
wing requires repairing or renewing, this bag being made of any suitable water
tight material and being firmly closed upon the shaft of the propeller by means of
one or two pairs of frames b, c, the sack being subsequently brought with its
opening uppermost by turning the screw propeller through an angle of 180°, so
that after having introduced into the sack fixed dock plates, shells or sides l, a
space open at the top but closed on. all sides is formed around the vane which is to
be repaired and this space is pumped dry; the dock sides or shells being firmly
held against the frames b, c, by the aid of grooves k or in any other suitable manner.
Dated this 31st day of March 1898.
CRUIKSHANK & FAIRWEATHER,
Chartered Patent Agents,
62, Saint Vincent Street, Glasgow, Agents for the Applicant.