Improvements in and relating to the Ascertainment of the Stabilities and Displacements of Ships, or other Floating Structures or Bodies.
Year: 1893

page_text: Date of Application, 8th July, 1893
Complete Specification Left, 7th Apr., 1894-Accepted, 7th July, 1894
PROVISIONATI DI MUITIATIO
Improvements in and relating to the Ascertainment of the Stabilities
and Displacements of Ships, or other Floating Structures or
Bodies.
1 EDWIN WILLIAM DE RUSETT of Warden House, Tynemouth, in the County
of Northumberland M.I.C.E. and M.I.N.A. Naval Architect do hereby declare
the nature of this invention to be as follows:-
The objects of this invention are
(1.) To ascertain, by experiment, in a tank, or any suitable vessel the curves of
stability of ships, or other floating bodies, by models, instead of by laborious and
protracted calculations such as are now generally employed.
(2.) To ascertain, by experiments with models, instead of, or in addition to, the
calculations usually employed, the variations of displacement of ships, or other
bodies, accompanying given variations of draught; or to find the draught, at
various trims, when displacement is given.
The means by which I obtain the object (1) are angular measurements of the
model's inclination while in the water under various dispositions of lading, and or
with one or more compartments more or less filled with water, such measurements
being effected by moving weights, which may be in suspension from one or more
circular hoops, discs, or curvilinear arcs, or may be in other manner so arranged
that their common centre of gravity coincides absolutely, or very nearly, with the
given centre of gravity of the ship, or other floating body, when free and at rest:
or in free motion.
The apparatus may be wholly or partially floating without any attachment to
the tank; or it may be partially attached; and the whole or part of the suspended
weights may be either immersed or not immersed in the water, or may be wholly
or partially within or without the model.
The angles of heel which the model assumes under varied dispositions of the
inclining weights, can be read off a graduated scale which may be marked on a
hoop, or arc, attached to the model, or on a vertical scale adjustable to any height,
or on any suitable part of the apparatus.
By the methods, any or all of them, above described the transverse, or
longitudinal, or oblique stability of a ship, or floating body, can be readily
ascertained, and graphically described by curves, automatically or not automatically
drawn, and much tedious labor of calculation now involved in obtaining such curves
can be dispensed with.
The means by which I obtain the object (2) are, first, a graduated lever,
sustaining the model itself, and or its ballast, and or other components of displace-
ment at one side of the fulcrum, and an adjustable weight or weights for counterpoise
on the other side of the fulcrum, where two weights preferably (but not necessarily
two, as one would serve) may be employed, one of them acting as a counterpoise
of the weights not associated with nor included in the displacement, but used say
for stability or other experiments; the other being used to find or check the
displacement.
The weights associated with and including the model on the one side of the
fulcrum may in their aggregate be in excess of the displacement weight due to
the required draught, and one of the counterpoising weights, on the lever above
referred to, will in that case, when the model &c. are immersed, betray, by its
compensating position on the graduated scale beam, the exact measure of the
excess above mentioned, which excess being deducted from the total weight of the

page_text: model and its associated weights, leaves, as remainder, the true displacement
weight; it being understood that, in the process of experimental counter balancing,
the model is immersed to the required draught, which can be done by the displace-
ment meter proper, which includes either (1st) a graduated lever and other
appliances associated with it for raising or lowering the model and the lever itself
together, as required in each case; or (2nd) instead of a lever, a spring may be
used, from which the model with its displacement weights and inclining weights
and apparatus are suspended, the spring itself being also suspended over a pulley,
or other suitable fixed support, by a cord attached to a windlass, or other suitable
arrangement, by which the spring &c. can be raised or lowered at pleasure. The
tank is partially filled with water. The spring is then lowered with the model &c.
depending from it, until say a pointer on the under side, or edge, of the inclining
hoop encircling the model, or upon any other selected point of the suspended
apparatus, first touches water. Then a sliding vertical scale which measures the
stretch of the spring is set with its zero against an index pointer attached to the
suspended model, or to other suitable part of the apparatus. Then more water is
admitted into the tank until the model is immersed to the given water line (as may
be indicated by adjustable water-line-pointers attached to the model) when the
index pointer, rising with the model as the spring contracts, will indicate on the
scale the true displacement weight of the immersed portion of the model and
accessories and, on deducting the previously known displacement of the immersed
accessories, the true nett displacement of the model at the given load line is arrived
at. Or the process may be reversed by first immersing the model &c. .to the
required water line, setting the zero of the scale to the pointer, and drawing off
the water to the lowest immersed part of model, and or accessories, the pointer
indicating the displacement as the spring yields to the weight. Relatively stiff
springs may, if desired, be used, with enlarging index. Or the immersed accessories
may be made of any suitable material having a specific gravity = 1, in which case
no deduction from the indexed displacement need be made. The apparatus for the
obtaining of stability curves may, in whole or in part, be also used for obtaining
displacement curves and vice versa; or separate and distinct apparatuses for the
two processes may be employed by suitable mechanical or other means similar to
those above referred to.
This invention is applicable to ascertaining the stability of a ship or other
floating body, either in still water, or among waves.
EDWIN WILLIAM DE RUSETT.
COMPLETE SPECIFICATION.
Improvements in and relating to the Ascertainment of the Stabilities
and Displacements of Ships, or other Floating Structures or
Bodies.
I EDWIN WILLIAM DE RUSETT of Warden House, Tynemouth, in the County
of Northumberland, Naval Architect do bereby 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 objects of this invention are
(1.) To ascertain, by experiment, in a tank, or in any suitable receptacle, the
curves of stability of ships, or other floating bodies, by models; instead of by
laborious and protracted calculations such as are now generally employed.
(2.) To ascertain, by experiments with models, instead of, or in addition to,
the calculations usually employed, the variations of displacement of ships, or
other bodies, accompanying given variations of draught; or to find the draught
at various trims, when displacement is given; or to find both draught and
displacement when both are unknown.

page_text: The means by which I obtain object (1) are angular measurements of the model's
inclination while floating under various dispositions of lading, as effected by
moving weights, which may be in suspension from one or more hoops or discs,
or arcs; or may be in other manner so arranged that the vertical plane of their
common centre of gravity coincides with the vertical plane of the ship's or other
model's centre of gravity when it is hanging, or floating, free & at rest.
The apparatus may be wholly, or partially, floating without any attachment
to the tank; or it may be partially attached; & the whole or part of the
suspended weights may be either immersed or not immersed in the fluid; & or may
be wholly or partially within or without the model.
The angles of heel which the model assumes under varied dispositions of the
inclining weights, can be read off a graduated scale, which may be marked on a
hoop, or arc, or other index table to be attached either to the model or to any
suitable part of the apparatus.
If the model is composed of removable sections; so that by removing any
section, or sections, the water may be admitted to replace same, then the floating
remainder of the model may carcen, & will show on the stability meter the reserve
of stability which the real ship would retain if that portion of her hull were stove
which corresponds with the removed section of the model.
By any or all of the methods above described, the transverse or longitudinal, or
oblique stability of a ship, or floating body, can be readily ascertained, & described
by numerals, or by curves of stability drawn either by hand, or by the apparatus
itself working automatically; & much labor of calculation now involved in obtaining
such curves can be dispensed with.
One of the above named methods of obtaining stability curves is shown more
particularly upon the drawing, Sheet 1, hereto annexed, Fig. 1, which may be
explained as follows ;-
The tank, T, has the ship model, M, suspended in the air above it. The model
is held within a hoop, H, by means of adjustable side screws, ss, & or top &
bottom screws, tt, the hoop being so adjusted that its centre coincides with the
given centre of gravity of the ship.
In order that the actual centre of gravity of the ship model may coincide with
the given centre of gravity, a weight W, Fig. 2, within the model is secured by
screws, passing through the model's deck, &, by their vertical motion,
permitting of raising or lowering the weight, W. The upper part of these f
screws is furnished with adjustable weights, a a, representing the total weight of
masts, funnels, & top hamper generally, & capable of adjustment, by check nuts
or otherwise, to the required common total height & leverage of same. These
screws are secured to two plates, pp, upon the model's deck which are made
to slide bowwards & sternwards by the screws y, g, & transversely by the
screws h, h; thus, by means of the vertical, fore & aft, & thwart ship adjust-
ments of the weight W, the centre of gravity of the model can be regulated to any
desired position.
This adjustment of the model's centre of gravity is effected, before immersing
the model, in the following manner. The given centre of gravity being marked on
both sides of the model, she is placed in the hoop, H, so that its side screws ss
& top & bottom screws tt, converge towards that centre. Then the hoop, H,
containing the model is placed edgewise on a smooth level table, & the screws ff
are adjusted till they have brought the weight, W, into such a position that the
hoop (whose double rim is broad enough to keep it upright) will stand indifferently
on any point of its circumference without tending to revolve. Or the centre of
gravity can be adjusted by slinging the model in the hoop H, from the pulley K,
& adjusting the weight W till K stands indifferently in any position without
tending to revolve.
When the centre of gravity of model has thus been adjusted, the model, remaining
inclosed within the hoop H is suspended by a loop of flexible cord attached to the
underside of the two scale pans J, J; the hoop H being grooved, or double

page_text: grooved, at its edge to receive this loop. The two equal weights I, I, are likewise
suspended from the hoop, H, by a loop of flexible cord resting in the same, or a
companion, groove at the top of the hoop, i.e. at its upper half. The two scale
pans, J, J, are slung by a loop of flexible cord passing over the grooved pulley, K,
which has a frictionless axle bearing on the edges of supporting pulleys, l, l
working on a frame suspended from the knife edge resting on the short arm of the
lever, L. For obtaining stability curves this lever, L, is clamped by the screw m,
to the lever frame N; so that no motion of L takes place when it is being used
simply as a fixed support during the inclining experiments by which stability curves
are obtained. The pulley K has its outer edge graduated in degrees, & an index
pointer, O, attached to the frame of the pulleys 1, 1, can be adjusted so as always to
point for nice adjustment to zero.
At the beginning of the inclining experiment the scale pans, J, J are loaded
with known weights so that perfect equipoise is established, the zero degree of the
graduated edge of K being at that position to which the index, O, points. Then
the tank is filled with water, by means of a tap or otherwise, so that the ship model
is immersed to her given load line; or if the tank is previously filled with water,
the lever L, with the scale pans, hoop & model suspended on it, can be lowered till
the model is immersed to her given load line.
This lowering can be effected by means of the adjusting nut, Q, on the frame, N,
which is supported by the standard, S.
When the model is thus floating in steady equipoise without any angle of heel,
she can be induced to assume any desired angle of heel, by taking weights out of
one of the scale pans & placing them in the other. The amount of weight thus
transferred to effect, by means of the known constant leverage of the K & H pulleys,
any given angle of heel gives the operator the correct measure of stability for that
angle; & by ascertaining in like manner the correct measure of stability for other
angles of heel, & plotting the results to a scale, the required curve of stability is
produced.
By working always with models to the same scale, the tiny weights used in the
scale pan can be inscribed in tons & cwts., as in terms of the full sized ship; so
avoiding the necessity of reduction by calculation.
The curves thus obtained are curves of transverse static stability; or transverse
stability in still water.
For obtaining curves of oblique static stability, the hoop, H, is adjusted at the
required skew, & the process is otherwise the same as for obtaining curves of
transverse stability.
For obtaining curves of longitudinal static stability (from which the longi-
tudinal meta-centre may be found) the ship model is turned about, so as to
bring its fore & aft longitudinal axis in the plane of rotation of the pulley K.
The hoop H is dispensed with, & the scale pans J J are connected with the
model's deck by short stiff rods adjustable by screws to the exact lengths
desired. The effect of removing weight from one scale pan & placing it in the
other is to put one of these rods in tension & the other in compression, inducing
the change of trim which will be exactly indicated in angular measure on the
K graduations by the pointer O.
Or, by another method, longitudinal stability may be measured by a lever,
suspended from the lever L, from the ends of which scale pans with stiff rods,
fastened to ship's deck as above described, may depend, a reading are for angles
being also furnished.
Or, by still another method, a weight or weights may be suspended from the
lever L, & moved along the same, so as to produce, by means of the apparatus
shown on Fig. 1 (or by any similar means) the required depression, elevation, or
alteration of trim.
Thus, by the behaviour of model when weights are so shifted on lever L, the
effect of filling or emptying any ballast tank or tanks, or of a fore & aft shift of
cargo, in changing the trim can be read off upon the instrument very exactly, by

page_text: means of the displacement & draught scales, in a manner similar to that hereinafter
detailed in reference to the method of ascertaining the displacement & draught in
their varying mutual relations.
The above described method, or set of methods, of operating the invention, will
serve merely as illustrating the application of the invention to the attainment of
its objects. Many other alternative methods of applying the invention are
practicable; though the methods above referred to are preferable.
For examples of other practicable methods, the following may be mentioned :-
Stability curves may be obtained by suspending, as per Fig. 3, the loaded scale
pans, J, J, from the hoop, H, in the same manner & instead of the weights I, I ;.
& not using K &c., the model, M, floating inclosed within the hoop, H, without.
being suspended from the lever. Then, the edge of hoop, H, being graduated,.
the angles of inclination, produced by changing the weights from one pan to the
other, can be read off the water line; or by a fixed pointer. In this method,.
the total weight sustained by the water must equal the given displacement of the
ship.
Or, as another example, the scale pans can be employed as per Fig. 4, in which.
method they are kept out of the water, for better handling; the immersed
weights, I, I, being retained to give the displacement draught to the model.
The curves of stability obtained by any of the methods of this invention are
such as express the measure of the ship's static stability, from minimum to maximum
value, port & or starboard, skews, or longitudinal.
The same apparatus, or parts or modifications of it, may also be employed to.
obtain angles of roll among waves of any given periods & heights, which waves.
may be artifically produced in the tank. In this class of experiment the free
model may be fitted with a light mast having a small mirror fixed to it, which.
mirror, by reflecting a beam of light on a graduated screen will show the maximum.
angle of roll due to a series of waves of any given period & height.
This angle of roll can be associated with the static stability curve obtained by
previous experiment. But the tank for such rolling experiments must of course.
be much larger than it need be for the static stability experiment.
The means by which I obtain object (2) are,
First; A graduated lever, sustaining the model itself, & its ballast & other
components of displacement & apparatus, at one side of the fulcrum, where several.
weights two preferably (but not necessarily two, as one might serve) may be.
employed, one of them acting as a counterpoise of the weights not associated with.
nor included in the displacement, but used say for stability experiments; the other
being used to find or check the displacement.
The weights associated with & including the model on the one side of fulcrum
being in their aggregate in excess of the model displacement weight due to the
required draught; one of the counterpoising weights on the lever above referred
to will, in that case, when the model &c. are immersed to the required draught,
betray by its compensating position on the graduated scale beam the exact measure
of the model displacement.
Immersion of the model can be effected by lowering the lever & the ship &c.
suspended therefrom; or by pouring water into the tank till it rises up to the
desired load line on the model.
Second As an alternative, springs may be applied either instead of or in
association with the lever & weights &c.
There are thus many optional & alternative details of application of this.
invention for finding draughts & displacements of ships & other Hoating bodies.
But as an illustration of one method (which is employed preferably to other
methods, though not to their exclusion) of obtaining by this invention the desired
particulars of a ship's displacement at any given draught & trim; or of the draught.
& trim of a ship at any given displacement; or of the draught & corresponding
displacement when neither is given, the following may be cited.
Referring to the drawing attached hereto, it will be seen that the weights R & r-

page_text: (Fig. 1) counter balance all weights otherwise unbalanced on the opposite side of
fulcrum. Always at the beginning of experiment, before the model is immersed,
the lever, L, stands dead level, pointing to zero on the graduated draught
quadrant, B, while stands on the minus (right hand) side of zero on lever scale.
This minus measurement of leverage is due to the displacement of I, 1, & of that
portion of the hoop, H, which has to be immersed. The lever scale is marked so
as to indicate the effect of the movement of along it, commencing zero & reading
towards the fulcrum in regularly increasing terms of tons of the full sized ship, it
being understood that these figures apply to models of one scale only; so that, if
models of a different scale be experimented on, a coefficient of scale correction
must be applied. By employing R, on tare & tret principle, to balance a large
portion of the total weight involved, the scale of graduations is larger than it
would be if R were not used.
No sooner does the model begin to enter the water than the water begins to
relieve the short arm of the lever, L, of part of its load, & the long arm
accordingly droops, & thus reveals on the graduated quadrant, B, the exact draught
of the model, on an enlarged scale, figured in terms of feet & inches of the full
sized ship.
When the model has thus settled to its displacement draught, the " is moved by
hand along the lever L to some position nearer the fulcrum (as indicated by dotted
lines on Fig. 1.) until the lever points again to zero on the quadrant B.
Then the will be standing on that part of the graduated lever, L, which indicates
by its scale the displacement due to the draught realised.
Thus the operator first reads the draught from the scale on the quadrant B, &
then reads the displacement from the scale on lever L.
For more exact reading of results, the r, & also the pointer of lever L, are both
furnished with a suitable vernier scale which moves with them.
The infinitesimal error due to a rise of water level in the tank, due simply to the
immersion of the model, can be eliminated by an adjustable overflow pipe. This
would be necessary in very small tanks. In large tanks the error would be
negligible.
Although the drawing shows the water line up to the centre of hoop H, the
water line may be either at that or at a higher or lower level.
Having now particularly described & ascertained the nature of my said inven-
tion, & in what manner the same is to be performed, I declare that what I
claim is :-
1st. The employment of floating models & apparatus in whole or in part sub-
stantially as above described for the purposes of obtaining curves of static & rolling
stability of ships & other floating bodies.
2nd. The employment of floating models & apparatus, in whole or in part, sub-
stantially as above described, for the purposes of obtaining curves of displacement
of ships & other floating bodies.
3rd. The employment of floating models & apparatus, in whole or in part, sub-
stantially as above described, for the purposes of ascertaining by experiment both
the draught & displacement of any given ship, or other floating body, when neither
draught nor displacement is known.
4th. The employment of floating models made in removable parts or sections,
together with apparatus in whole or in part, substantially as above described to
ascertain by experiment the effect of the bilging of any compartment, or com-
partments, of a given ship, on her stability, trim, & flotation.
FRANK CAWS,
Agent for Edwin W. De Rusett.