[0001] The present invention relates to a deck construction for marine tankers of the kind
which have no centreline bulkhead and which are fitted with at least one tank which
is defined by shell plating, transverse bulkheads, and deck structure in accordance
with the preamble of Claim 1.
[0002] There are two known kinds of tanker construction, by which is meant essentially marine
vessels for transporting mainly liquid products and/or crude oil but which may also
transport so-called pourable cargoes, e.g. seed. The first of these vessel types includes
marine vessels which are fitted with one or more centreline bulkheads and transverse
frames, in order to provide the strength or rigidity required. With the other vessel
type, the requisite rigidity is obtained by fitting the vessels with twin bottoms
and twin hulls and by installing deck frames across the deck. This type of vessel
will often require the provision of a centreline bulkhead for strength purposes. The
advantage of this latter vessel construction over the former is that the inner surfaces
of the tanks are smooth and therewith easy to clean, present a smaller surface area
to be painted, and greatly facilitate emptying of the tanks. One serious drawback
with this type of vessel, however, is the heavy weight of steel involved, which can
be far greater than the steel weight of the first type of vessel. A further drawback
is found in the presence of on-deck frames, which restrict access in the fore-and-aft
directions.
[0003] Still another drawback with known tanker constructions, particularly broad-beam tankers,
resides in the powerful stresses to which corners and junctions in the shell plating
and deck in particular are subjected when the vessel is at sea, these stresses being
due to hammering of the liquid against the structure, and also in the fact that the
tank must be dimensioned in correspondence with a dimension-determining roll angle.
[0004] The main object of the invention is therefore to provide a deck construction which
will firstly permit greater tank volumes to be obtained at a given hull width, secondly
results in a vessel of lighter construction, and thirdly eliminate the aforesaid drawbacks
of known marine vessel constructions.
[0005] This object is realized completely by means of the invention defined in the claims
and described hereinafter with reference to the accompanying drawing, in which
Figure 1 is a cross-sectional view of a marine vessel fitted with a deck construction
according to the invention and
Figure 2 is a cross-sectional view according to Figure 1 illustrating rolling of the
vessel in correspondence with a calculated maximum rolling angle, the dimension-determining
roll angle, and a section through a conventional tanker at the same angle of roll.
[0006] Figure 1 is a cross-sectional view of a tanker fitted with one or more transverse
tanks 1, each tank being defined by two transverse bulkheads 4 which are mutually
spaced in the fore-and-aft direction of the vessel and which are joined to the shell
plating 2 and to the bottom 3 of the vessel. Since the illustrated vessel has no fore-and-aft
bulkhead, the width of tank 1 will correspond to the width between the hull sides
2. Adjoining the hull sides 2 is a deck construction comprising a beam 5 which is
arranged in a vertical plane through the centreline of the vessel and which, e.g.,
may have the form of a box-beam. The beam 5 is joined to the transverse bulkheads
and also to inclined deck portions 6,7, which slope downwardly away from the beam
to the hull sides 2 and are connected thereto. The tank 1 of the illustrated embodiment
will therefore be defined by the hull sides or shell platings 2, the bottom 3, two
mutually sequential transverse bulkheads 4 and the deck construction comprising the
beam 5 and the sloping deck portions 6 and 7. The beam 5 is placed at
a level which is located far above the position 8 at which the deck joins the sides
of the hull or the shell plating 2. Consequently, when using a deck construction according
to the invention on a given hull there is obtained the advantage of a considerable
increase in tank volume, as will be seen immediately from Figure 2, which illustrates
on the right a hull provided with a conventional deck structure and on the left a
hull of the same width as the former hull but fitted with a deck constructed in accordance
with the invention. Naturally, it is assumed that the transverse hulls are located
at the same distance apart in both cases.
[0007] The inventive deck construction also affords other advantages, which will be made
apparent in the following. Normally, the rolling angle of a tanker lies between 20-30°,
although other rolling angles may be selected. The rolling angle forms a dimensioning
parameter when determining the dimensions of the vessel. The angle V₁ between respective
deck portions 6,7 and a horizontal plane through other points on the hull sides 2
is so selected in dependence on the chosen maximum rolling angle V₂ between the centreline
plane CL of the vessel and a vertical plane as to obtain the greatest possible increase
in cargo volume while decreasing the head or pressure height in the dimensioning roll
position (the angle V₂) of the vessel. By head or pressure height is meant the distance,
in the rolling position of the vessel, between the highest level N₁ of the liquid
or the pourable cargo and the level N₂ of the joints in the tank 1 to be dimensioned.
Because the beam 5 is located at a more elevated position than the conventionally
constructed deck 9, Figure 2, the rigidity or stiffness of the total ship's beam will
increase considerably, which in turn enables the height of the hull sides 2 to be
decreased without reducing the tank volume in comparison with the tank volume of a
conventional construction. Thus, Figure 2 illustrates a section which has lower hull
sides 2 than the conventional construction shown to the right of the Figure. A vessel
which is fitted with a deck constructed according to the invention will be lighter
in weight, since the hull sides can be made shorter in height and because the transverse
frames 10 required in conventional constructions are not required in the inventive
construction. Furthermore, the smaller deck portions 6 and 7 can be given a very light
construction, due to the short distance between the beam 5 and the location 8 at which
the deck portions are connected to the hull sides or shell plating. Because the hull
sides can be made shorter in height, the aforesaid pressure height can be decreased,
this pressure height, or head, being designated H₁ in Figure 2 for a vessel according
to the invention and H₂ for a conventional vessel. In the Figure 2 embodiment the
cross-sectional area of the tank in the vessel fitted with a deck structure according
to the invention is greater than the cross-sectional area of the tank of the conventional
vessel, with both vessels having the same width, i.e. a greater tank volume is obtained
despite a decrease in the height of the hull sides and despite a smaller pressure
height or head. Naturally, this decrease in pressure heights will also result in less
stresses on the hull and deck. Stresses caused by hammering of the cargo, as mentioned
in the introduction, are greatly reduced in a deck construction according to the invention,
since angles of the order of 90° or thereabove are completely lacking in the construction
according to the invention, wherewith it is also possible to reduce the dimensions
of the plating. In the case of the preferred embodiment, the angle V₁ is selected
so that when the vessel rolls to the maximum dimensioning roll angle V₂, the uppermost
deck portion 7 in Figure 1 will lie at least approximately in the horizontal plane.
[0008] Although the inventive deck construction has been described with reference to a hull
fitted with double bo ttoms and double shell plating, it will be understood
that the invention can also be applied to other types of hull.
[0009] The described and illustrated embodiment has been chosen solely by way of an example,
and modifications are possible within the scope of the claims. For example, the angle
V₁ can be increased to at least 30° even when the dimensioning roll angle is about
25°. In this case the tank, or tanks, is (are) particularly suited for transporting
grain or cereal products, which have an angle of repose of about 30°. The cargo space
is therewith self-stowing. When the vessel rolls to the maximum roll angle, the deck
portions will not lie fully horizontally, but will approach an essentially horizontal
position.
[0010] When the beam 5 has the form of a box-beam, preferably a fully closed box-beam, the
beam can be used advantageously as a tunnel system through which conduits, pipes etc.
can be passed, therewith relieving the deck portions 6 and 7 of such conduits to a
great extent. When the beam 5 comprises a box-beam, reinforcements can be arranged
in the interior of the beam. The upper surface of the box-beam is preferably smooth,
so as to facilitate access, and the undersurface of the beam which forms part of the
tank wall will also be completely smooth.
1. A deck construction for marine tankers of the kind which have no centreline bulkhead
and which are provided with at least one tank (1) defined by shell plating (2), transverse
bulkheads (4) and a deck structure (5,6,7), said deck structure comprising a central
part (5) having arranged on both sides thereof inclined deck portions (6,7) which
adjoin the hull of the tanker, the inclined deck portions being so formed that when
the tanker rolls to the dimensioning rolling angle the highest of the two inclined
deck portions will take an at least approximately horizontal position, characterized
in that said central part forms the primary strength part of the deck structure and
has the form of a beam (5) which extends along the fore-and-aft centreline (CL) of
the tanker and which is carried by the transverse bulkheads (4).
2. A deck structure according to Claim 1, characterized in that the beam is a box-beam.
3. A deck structure according to Claim 1 or 2, characterized in that the box-beam
(5) has a smooth upper surface and a smooth undersurface; and in that reinforcements
are arranged in the interior of the beam.
4. A deck structure according to Claim 3, characterized in that the box-beam is fully
closed and forms a tunnel system.
