A New or Improved Instrument for Determining the Initial Stability of Ships or other Vessels.
Year: 1894

page_text: Date of Application, 8th June, 1894
Complete Specification Left, 7th Mar., 1895-Accepted, 13th Apr., 1895
PROVISIONAL SPECIFICATION.
A New or Improved Instrument for Determining the Initial
Stability of Ships or other Vessels.
I GEORGE JOHNSTONE, of 50, George Street, Edinburgh, Master Mariner, do
hereby declare the nature of this invention to be as follows:-
My invention relates to a new or improved instrument for determining the
initial stability of ships or other vessels, and has for its object to provide means
for finding the true distance between the meta-centre and the centre of gravity
of a vessel, when in or near the upright position, while the cargo is being taken
on board such vessel or after the latter is fully laden, for the purpose of
enabling the person responsible for the correct loading of such vessel, to
immediately detect any tendency there may be toward instability, or excessive
stability, and to regulate the stowage accordingly.
In carrying my invention into practice I provide a metal frame of the desired
size, to the lower part of which is secured longitudinally, a glass or other tube,
bent to represent the true are of a circle, to the given radius.
This tube contains a colored liquid and an air-bubble, and above the said tube,
tangential to it and secured to the aforesaid frame, is a scale of inclining moments
in foot tons,
Upon the upper portion of the frame and parallel with the scale of
inclining moments, I provide two other scales, the upper one being a scale of
"meta-centric " heigbts in feet, and decimals of a foot, and computed to the
same radius as the tube, while the bottom one is a scale of displacement
in tons.
Between the upper and the lower scale, a metal bar is fitted, which can be
inoved across the face of the instrument at will, such bar having a slot extending
its full length, in which slot a stud moves up or down as required.
Upon the lower part of the frame and at a point equidistant from the sides, is
secured the lower end of a pointer, the upper end being made so as to be capable
of moving freely across the face of the instrument.
The instrument is intended to be placed in the captain's cabin, the chart-room,
or in any other convenient place or position on board a vessel, and the meta-centric
height, for determining the initial stability of such vessel, is obtained in the
following manner.
Assuming that the vessel is floating freely in still water, and the displacement
corresponding to the mean draught has been carefully obtained from the displace-
ment scale; that such vessel is upright or nearly so; that her bilges are dry and
the ballast tanks, if empty, have been drained dry, or if full, pressed up, and that
all moveable weights are secured, and all persons on board the vessel that are not
required for moving the weights are caused to remain stationary during the
operation of finding the meta-centre heights of the vessel.
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1
The instrument is then placed in position-the air bubble contained in the tube
pointing to zero on the scale-then let W be auу known weight moved across the
deck through a known distance d (equal to) inclining moment (equal to)
W. x d foot tons, and this moment causes the vessel to incline through an angle e.
Place the pointer of the instrument to the vessel's displacement on the scale
of displacements, and the bar to the inclining moment on the scale of moments,

page_text: and move the stud down until it touches the side of the pointer, and then
clamp it.
.
The bar is now moved across the face of the instrument until its edge is
coincident with a line passing over the centre of the bubble in the tube aforesaid-
and the pointer brought into contact with the stud in the said bar-whereupon
the pointer will point to the true meta-centric height on the meta-centric scale.
Dated this 8th day of June 1894.
HUGHES, SON & Co.,
38, Chancery Lane, London, Agents for the Applicant.
A New or Improved Instrument for Determining the Initial
Stability of Ships or other Vessels.
I GEORGE JOHNSTONE of 50 George Street, Edinburgh, Master Mariner, 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 :-
•
My invention relates to a new or improved instrument for determining the initial
stability of ships or other vessels, and has for its object to provide means for
finding the true distance between the meta-centre and the centre of gravity of a
vessel when in or near the upright position, while the cargo is being taken on board,
or after the vessel is fully laden, for the purpose of enabling the person responsible
for the correct loading to immediately detect any tendency there may be toward
instability, or excessive stability, and to regulate the stowage accordingly. I am
aware that the stability of vessels has been and is now tested by moving a known
weight or weights through a known distance and measuring the angle of inclination
by plumb-bobs or pendulums, and also by use of a tank or tanks of known capacity,
but in accordance with this invention I construct an instrument forming a stability
indicator from which (the displacement and inclining moment being known) the
true initial stability of. the ship or other vessel may be easily read without the
calculations and measurements hitherto necessitated.
And in order that this my invention may be fully understood and readily carried
into effect will describe same with reference to the accompanying drawing which
represents in front elevational view an instrument for determining the initial
stability of ships constructed in accordance therewith.
a a is a metal frame to the lower part of which is attached a metal strip a' upon
which is marked a scale d of inclining moments in foot tons. To this metal stripa
and below the scule d aforesaid, is secured longitudinally a glass or other tube b
bent to represent the true arc of a circle, of a given radius.
This tube 6 contains a liquid (preferably coloured) and an air bubble marked c.
Lines d' radiate from a common centre towards the lower edge of this scale.
The same radius as that to which the glass tube is formed will give the common
'centre from which the lines d' radiate as aforesaid. The inclining moment is
.ascertained as follows:-Let W represent a known weight which is moved across
the deck a given distance D then W x D equals the inclining moment, and
this moment causes the vessel to incline through a certain angle and the method of
.measuring this angle of deflection of the vessel from the upright position by means
of the divisions and radial lines on the scale d in conjunction with the glass tube b
containing the colored liquid and air bulb, é will hereinafter appear. Upon th
upper portion of the frame a and parallel with the scale of inclining moments d
I provide two other scales e, f, the upper one e being a scale of meta-centric
heights in feet and decimals of a foot computed to the same radius as. tube b
as the

page_text: and with an inclining moment equal to one tenth of the displacement, while the lower
scale fis a scale of displacements in tons. These scales are graduated to tenths
and twentieths of an inch.
Between the scales e, f, and the scale of inclining moments is fitted a metal
bar 9 which 1 term a reducing scale and this is intended to be used when inclining
moments are employed other than those to which the meta-centric scale e has been
computed. This bar y must always be perpendicular to the scales of displacements
and moments as shewn, and is provided with a sloth extending nearly its full
length. In this slot his fitted a small stud i with a triangular.head k.
This stud i can be moved freely the full length of the slot h and be clamped in
any intermediate position by screwing up the nut 1. The bar g is capable of a
transverse movement across the face of the instrument and to this end is fitted
at either end to the sliding blocks m suitably grooved or shaped to slide or
run upon the inner edges of the upper and lower horizontal portions of the
frame a a.
To the lower part of the frame a and at a point equidistant from the sides is
pivotted at n the lower end of a pointer o, the upper end of which is free to move
across the face of the instrument. This pointer o can be clamped in any desired
position by tightening up the nut p on stud 9 which moves in the slot r formed in
the arc s fixed to the upper part of the frame a.
When performing the inclining experiment for the purpose of obtaining the
meta-centric height in accordance with this invention it is essential that the
following particulars should be observed: (1) That the vessel is floating freely in
still water (2) that the vessel is upright or nearly so (3) that the bilges are dry,
and if fitted with.ballast tanks they should, if empty, be drained dry, or if full they
should be pressed up, (4) that all movable weights are secured, and that all persons
on board other than those required for moving the weights be made to remain
stationary during the inclining operation, (5) that the displacement corresponding
to the mean draft of water at the time be carefully taken from the vessel's displace-
ment scale, (6) that the instrument be secured in any convenient place on board
ship say in the captain's cabin, the chart room or other suitable place or position,
and that the air bubble c contained in the glass tube be brought to coincide with
the zero lines on the scale of inclining moments d. Then to determine the initial
stability of the vessel proceed as follows:-
A known weight or weights is or are caused to be moved across the deck a
certain number of feet, then as the vessel inclines the air bubble c in the tube
moves to the high side, and after a short time will come to a state of rest or nearly
so and the vessel will again be in equilibrium. Now move the pointer o across the
face of the instrument to the vessel's displacement on the scale of displacements f
and there clamp it by screwing up the nut p. Then bring the edge of the reducing
scale to coincide with the inclining moment on the scale of moments, and clamp
it in that position and move the stud in the slot h until the triangular head k rests
lightly against the edge of the pointer and there clamp it by turning the screw 7.
Then move the reducing scale across until its edge coincides with the radial
line that points to the centre of the air bubble c in the tube b, and bring
the pointer o again in contact with the triangular head when said pointer o
will then point to the true meta-centric height on the meta-centric scale e.
с
As an example I will assume a vessel to have a displacement of say 3000 tons
and that a known weight of say 15 tons is moved across the deck a distance
of 18 feet, giving the ship an inclination sufficient to bring the air bubble c into
the position shewn in dotted lines on the drawing. Then 15 tons × 18 feet
gives an inclining moment of 270 foot tons. Set the reducing scale g with its edge
to the figure 270 on the inclining moment scale d, and the pointer 。 with its
edge against the 3000 upon the displacement scale f, then adjust the stud / so
that the triangular head lightly touches the edge of pointer o and the point
of contact will be where shewn in the drawing marked z. Then move the
reducing scale until its edge coincides with the radial line d' that points to

page_text: 1
the centre of the bubble c and bring the pointer o again in contact with the
triangular head all as shewn in dotted lines upon the drawing and the pointer o
then indicates upon the meta-centric scale the true distance between the
meta-centre and the centre of gravity of the vessel, in this instance 1 foot.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is:
1. The instrument for determining the initial stability of ships, substantially as
hereinbefore described and shewn in the accompanying drawing.
2. In instruments for determining the initial stability of ships the combination
and arrangement upon a suitable frame, of an inclining moment scale, a displace-
ment scale, a scale of meta-centric heights, and a reducing scale or sliding vertical
bar provided with an adjustable contact piece, with a glass tube containing liquid
and an air bubble, and a pivoted pointer all constructed and operating substantially
as and for the purpose hereinbefore described and shewn.
3. In instruments for determining the initial stability of ships the meta-centric
scale with meta-centric intervals thereon computed for a given radius, and for
inclining moments bearing a constant ratio to the displacements marked on the
scale of displacements, substantially as hereinbefore described and shewn.
4. In instruments for determining the initial stability of ships the scale of
inclining moments with lines radiating thereto from a common centre said common
centre being determined by the radius used in computing the values on the meta-
centric scale aforesaid substantially as shewn and described.
5. In instruments for determining the initial stability of ships the reducing scale
or vertical bar arranged with adjustable contact piece and constructed to slide across
the face of the instrument and to act in combination with the pointer in the manner
aforesaid for the purpose of enabling any inclining moment to be used less than the
moment used in computing the meta-centric intervals on the meta-centric scale
aforesaid substantially as shewn and described.
Dated this 7th day of March 1895.
HUGHES, SON & Co.,
38, Chancery Lane, W.C., Agents for the Applicant.