Improved Instrument to be Used in Ascertaining the Metacentric Height and Trim of a Ship.
Year: 1895

page_text: Date of Application, 1st Apr., 1895-Accepted, 4th May, 1895
An
COMPLETE SPECIFICATION.
Improved Instrument to be Used in Ascertaining the
Metacentric Height and Trim of a Ship.
We, ARCHIBALD DENNY, of Leven Shipyard, Dumbarton, in the County of
Dumbarton, North Britain, Shipbuilder, and WILLIAM GRAY, of the same place,
Ship Draughtsman, 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 that is to say :-
Our said invention has for its object to facilitate and expedite the operations for
ascertaining the metacentric height and trim of a ship.
Our improved instrument is shown on an accompanying sheet of explanatory
rawings, Figure, 1, being a front elevation and Figure, 2, a vertical section as at
right angles to Figure, 1.
The instrument comprises a board, A, which when in use is placed with its
surface in a vertical plane and athwartship. At the upper part of the board, A,
there is placed a spirit level, B, one end of which is jointed on a pin fixed in the
board, the other end resting on the upper end of the spindle, C, of a screw
inicrometer, D. Below the spirit level, B, there is fixed on the board, A, a rect-
angular frame, E, made in one or two parts so as to form an undercut groove which
retains and guides a vertical scale, F, made with top and bottom_crossheads to
A straight
insure the scale being kept vertical when moved along the frame, E.
edge, G, is at one end of it jointed on a pin fixed in the board at the lower left-
hand corner just within the frame, E; and this straight edge, G, and the vertical
scale, F, are formed with slots for the purpose of their being connected by a pin, H.
Graduated scales are formed on the parts as shown in Figure, 1, namely on the
vertical scale, F, along a bottom horizontal line, and along the right-hand vertical
border this last graduation being continued along the top horizontal border.
In using the instrument, the board being fixed in position on the ship, the spirit
level is carefully set, and then a convenient known weight is shifted across the
deck through a distance, d. The spirit level is then again set and the amount of
adjustment required by the micrometer is noted, that is the difference between the
readings of the micrometer scale for the first and second setting. The scale, F, is
then set with its graduated edge at the point of the bottom horizontal scale
representing the micrometer adjustment for difference of level. From the displace-
inent scale of the ship take the displacement at the draught at which the ship is
floating at the time. Multiply the weight, w, shifted by the distance d through
which it is shifted and divide by the displacement, W; and set the straight edge, G,
with its upper edge to the point corresponding to the quotient of the calculation on
the vertical scale, F. The straight edge, G, will then indicate on the scale on the
right-hand vertical border or on the top border, what the metacentric height is.
By way of illustration inclined lines in Figure, 1, show different positions of the
straight edge, G, and the corresponding metacentric heights.
The level, B, and micrometer, D, may be used for ascertaining alterations in
the trim of a ship. For this purpose the board, A, should be placed against a
longitudinal bulkhead or in an equivalent manner. At the beginning of a voyage
the level should be carefully set and the micrometer marking noted. The draught
of the ship should also be noted at the same time. Afterwards any change of trim
during the voyage and due to consumption of coal, addition or removal of water
ballast or other alteration in the distribution of weights can be ascertained from

page_text: the differences in the micrometer markings. Thus the length of ship being L, and
that of the level, B, being then the change of trim will be equal to the adjustment
of the level ×
L
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
The improved instrument shown in the accompanying drawings and hereinbefore
described, to be used in ascertaining the metacentric height and trim of a ship.
Dated this Thirtieth day of March 1895.
EDMUND HUNT,
Applicants' Agent.