Improvements in or relating to the Construction of Ships.
Year: 1899

page_text: Date of Application, 16th Aug., 1899-Accepted, 16th Aug., 1900
COMPLETE SPECIFICATION.
Improvements in or relating to the Construction of Ships.
I, CHARLES DAVID DOXFORD, Ship Builder, of Pallion, Sunderland, in the
County of Durham, 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:
This invention relates to the construction of ships.
Certain of the regulations of the Board of Trade prescribe for ships a propor-
tion of reserve buoyancy which bears a greater ratio to the cubic capacity of
the holds in large than in small vessels, whilst the Classification Societies' regu-
lations and certain well-understood constructional considerations enable the depth
of double bottom or of the "floor plates" to be proportionately less in large
than in small vessels. It will be found that from these circumstances the cubic
capacity of holds per ton of deadweight cargo increases with the size of the ship,
so that the larger vessels are handicapped commercially by excessive measure-
ment tonnage and waste space, except when carrying the light kinds of cargoes.
The principal object of the present invention is to construct the double bottom
or ballast tank in such a manner that the depth thereof may readily and inex-
pensively be adjusted in the design of the vessel, to enable a deadweight capacity
best suited for a given trade to be allotted to the vessel whilst the measure-
ment capacity shall be no more than is sufficient to take the full deadweight
cargo of an assumed character without waste of space, i.e. so that the measurement
tonnage can be brought into close agreement with the dead-weight tonnage in
all sizes of vessels for the selected trade.
This improvement would render profitable the use in the dead-weight trades
for instance, of larger vessels than those which are at present economically
employed therein because they happen to possess an appropriate ratio of measure-
ment to dead-weight tonnage.
"
If in ships of normal types the depth of double bottom or depth of "floor
plates were increased, the depth, total weight and extra cost, of the keel,
keelsons and some of the other longitudinals, and in particular of the numerous
and closely-spaced floor plates" would need adjustment correspondingly (as
may be seen upon consideration of Figures 1 to 5 of the accompanying drawings
hereinafter again referred to) and therefore the commercial efficiency of such
vessels would be reduced by reason of their increased first cost.
According to the present invention the depth of double bottom can be increased
in such a manner that no waste space will be provided in the holds, whilst
increased water-ballast space will be provided in the double bottom and not
be counted against the ship in the reckoning of her measurement tonnage;
further the necessity for high tank-holds for water-ballast, with their attendant
disadvantages of excessive tonnage measurement and risk of damage to cargo
is abolished. That this adjustment of the depth of double bottom or ballast tank
may be obtainable economically and without any increase in the depth of the
keel, keelsons and other longitudinals or of the "floor plates," there is employed
according to this invention a columnar construction between the inside of the

page_text: skin plating and the underside of the tank tops or inner bottom. This columnar
construction possesses the additional advantage of affording great facility for
examination and repair of the bottoms.
In the accompanying drawings
Figures 1, 2, 3, 4 and 5 illustrate vertical transverse sections of half-breadths
of the bottoms of the normal types of steel ship. For each ship in which the
construction at alternate frames differs, two sections taken near alternate frames
and bracketed together are shown in the figure allotted to it.
Figures 6, 7, 8 and 9 illustrate a columnar construction of ship's bottom
according to the present invention.
Figure 6 being a transverse vertical section of the bottom.
Figure 7 being a sectional part' plan on the line 7-7 of Figure 6.
Figure Sa longitudinal section on the line 8-8 of Figure 6.
Figure 9 an enlarged perspective of a short length of the keel and of the parts
in immediate connection therewith.
Figure 10 a section on the line 10-10 of Figure 6, and
Figure 11 is a view similar to Figure 6, showing an alternative columnar con-
struction of ship's bottom according to this invention; in this instance the inner
bottom is neither flat for its whole width nor cambered slightly, but is inclined
upward from a flat central portion towards each wing; in this figure a chain line
indicates that the inner bottom may instead be sloped from the midship line
downward to each wing.
Like letters indicate like parts throughout the drawings.
With reference first to Figures 1 to 5 it will be seen that if the normal types
of construction which they illustrate be adhered to, any increase in the dimen-
sion "d" would involve an increase in the depth of each keel A, keelson B,
or related longitudinal, and of the floor plates" C or brackets D, for the
dimensions of these members when they are combined in the manner illustrated
must maintain a relationship to the dimension d" which is approximately
constant, because of mechanical considerations and of the Classification. Societies'
rules evolved therefrom.
"
Alternatively a reference to Figures 6, 7, 8, 9 and 10 will show a vessel in
which the dimension "d" is much greater, proportionately, than in the examples
illustrated in Figures 1 to 5, but in which despite the increase of that dimension
the depth, total weight and cost of the keel, keelsons and other longitudinals is
reduced instead of increased, and in which moreover "floor plates are dispensed
with. From Figure 6 it will be seen that the main frames E of the vessel
are carried from the centre line up in the bilge to the height of the top T¹ of
the tank T. They are fitted on the centre line with a moderately deep keel A
and at approximately equal distances from the centre line with smaller inter-
costal keelsons B, thus making the construction of the outer bottom F complete
in itself and similar to the construction of the sides of ordinary vessels; the inner
bottom or tank top T is constructed, in the vessel illustrated in Figures 6
to 10, like a deck, upon beams G extending from side to side of the ship, and
with a centre intercostal girder H and side intercostal girders J, corresponding
respectively with the keel A and keelsons B of the outer bottom; the construc-
tion of the inner bottom like that of the outer bottom is complete in itself.
The columnar construction herein before referred to connects the inner and
outer bottoms T₁ and F rigidly, plate columns or struts K (of cruciform cross-
section, see Figures 7 and 9, in the example illustrated) extending between the
inner and outer bottoms and firmly connecting them, being attached to the longi-
tudinals A, B, H and J, and to the transverse members E and G, a novel double
bottom possessing great longitudinal and transverse stiffness being thus arrived
at. In this type of construction, an increase or diminution of the dimension "d"
affects only a small amount of the material in the double bottom, that is to say
the material in a portion of the length of the columns or struts K.
The use above indicated of columns or struts of any convenient transverse

page_text: section, instead of deep longitudinal and transverse plate or continuous girders
upon the inside of the outer bottom of a vessel, for the purpose of obtaining
increased water ballast space in the bottom, is an important feature of this
invention and they are applicable to vessels having various constructions of
inner and outer bottoms not necessarily those illustrated by way of example in
Figure 6. For instance in the construction illustrated by Figure 11, columus
or struts K are shown firmly connecting the outer bottom with an inner bottom
or tank top T which is inclined upwards towards the wings from a flat central
portion. The slope of the tank top T or inner bottom may alternatively be from
the centre downwards towards each wing in the manner indicated by the chain
line in Figure 11. It is evident that the depth of double bottom could be
adjusted to the hold capacity in both the examples for which Figure 11 serves
(these being convenient constructions for ships which are to be discharged by
grabs) without involving alteration of the kind hereinbefore explained in the
depth of keel, keelsons and other longitudinals or of the "Hoor plates"; it
therefore follows that the advantages of this invention are not limited to ships
in which the inner and outer bottoms are approximately flat.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, 1 declare that what
I claim is:-
1. In a ship a double bottom or tank of a construction enabling
depth of double bottom to be adjusted to the hold capacity without involving
alteration of the nature hereinbefore explained in the depth of keel, keelsons
and other longitudinals or of the "floor plates."
2. In a ship a double bottom or tank which includes a columnar construction
enabling depth of double bottom to be adjusted to the hold capacity without involv-
ing alteration of the nature hereinbefore explained in the depth of keel, keelsons
and other longitudinals or of the "floor plates."
3. In a ship the combination with a double bottom or tank which includes a
complete deck, of columns or struts between that deck and the outer bottom, the
construction enabling depth of double bottom to be adjusted to the hold capacity
without involving alteration of the nature herein before explained in the depth of
keel, keelsons and other longitudinals or of the "floor plates."
4. In a ship a double bottom substantially such as is hereinbefore described
with reference to Figures 6, 7, 8, 9 and 10 of the accompanying drawings.
Dated this 16th day of August 1899.
BOULT & WADE,
Agents for the Applicant.