EP0687235B1

EP0687235B1 - Ship comprising a displacement central hull and two side hulls

Info

Publication number: EP0687235B1
Application number: EP94910084A
Authority: EP
Inventors: Jörgen HANSSON
Original assignee: WINTRIA AB
Current assignee: WINTRIA AB
Priority date: 1993-03-11
Filing date: 1994-03-11
Publication date: 1999-12-22
Anticipated expiration: 2014-03-11
Also published as: SE501457C2; NO953551L; NO953551D0; FI954253A; NO305159B1; WO1994020359A1; EP0687235A1; FI111616B; SE9300842D0; SE9300842L; AU6266394A; FI954253A0

Abstract

The present invention relates to a hull concept with a central main hull and two, on each side of the main hull, located side hulls. The invention is characterized in each hull (1, 2) having free-boards restricted in height and being broken through (4) along at least a portion of its length.

Description

The present invention relates to a hull concept with a central main hull and two, on each side of the main hull, located side hulls.
Ships, cargo, crew and passengers on board a ship at sea are each sensitive to certain kinds of movements and accelerating forces. E.g. there is a great risk of loosing the foothold at a rolling angle of 15° making the manual work out on e.g. open deck critical. An other critical limit is the horisontal acceleration of about 0,2 g where loose items on board on tables and shelves fall on the floor. At so small vertical g-stresses as 0,05 g the risk of seasick-ness is drastically increased.
Regarding cargo units and cargo carriers on board these will be exposed to mass forces during acceleration. These mass forces gives in turn rise to stresses in lashings and means for securing the cargo.
Generally it can be said regarding hull constructions when they are exposed to cyclic stesses that their lifetime are dependent on a correct dimensioning regarding the material fatigue. High quality and strong materials will not show to be of advantage if cyclic stress concentrations leading to high load/stress concentrations are allowed to exist. Sailing in heavy sea e.g the hull of a ship is exposed to big accelerating forces often leading to high stress concentrations independtly the hull being made very stiff or flexible. Thus what is restricting the lifetime of a ship is the fatigue stresses during use. In rough see these stresses may partly be derived to the cargo carried on board, but mainly from g-forces acting directely onto the hull. Thus it is desirable to design a hull of a vessel in such a way that so small g-forces as possible will act upon the hull of the vessel, especially during travel in heavy sea. Also travel in choppy sea great cyclic stresses can be transferred to the hull, which means that the design of the bow and its load carrying capacity is of outmost importance. Also the dispostion to roll is of importance regarding to expected stresses onto the cargo on board and onto the lashings of the cargo. The length-breadth ratio, kind of cargo, the position of the cargo within or onto the hull, kind of waters the ship is intended to visit, are all factors to observe in the search of an optimal design for each specific hull.
The main object of the present invention is to obtain a hull concept which is very advantageously when it comes to transfering acceleration forces onto the hull and also to the cargo, also at proportionately high speed in rough sea and in addition is less sensitive to rolling compared to conventional hull concepts. The favourable characteristics of the concept are also valid regarding the acceleration forces acting in the horisontal plane, which is essential regarding the safety and the comfort on board.
Yet an other object of the present invention is to obtain a hull concept allowing propelling in a high speed using modest power output.
The objects mentioned above are obtained by a hull concept having the characterizing clauses stated in the claims.
By using a trimaran concept, i. e. a central hull with side hulls, each hull having freeboards restricted in hight and being broken through along at least a portion of its length, the acceleration stresses transferred to the hull of the ship are decreased. This is obtained by having the waves "planed of' or "rolled over" the broken through portions of the hulls . Thus the main part of the waves will roll in beneath the space between deck, main hull and side hulls without executing any essential accelerating buoyancy. This is the case both in travelling with and towards the sea.
By having the main part of the buoyancy in the main hull at the same time as the front portions of the side hulls are located at the place for the waves of the bow from the main hull there are very favourable conditions to design the lines of the hull in an optimal way. By choosing the flare angle and the buoyancy of the bow of the main hull equipped with a bulb in a convenient way the trimaran will have a capacity to manage travel in heavy sea without the risk of the bow burrowing its way down in the sea. Though the buoyancy of the broken through main hull will be restricted its total buoyancy will be big thanks to the relatively long lever between the bow and the pitching axis of the ship.
By making the insides of the side hulls essentially straight and parallell to the length axis of the ship the interference beween the main hull and the side hulls will be smaller.
Thus the invention will allow the building of light hull for a trimaran creating very modest accelerations stresses during travel in rough sea.
The invention will now be described in connection to the enclosed drawings, wherein;
Fig. 1 is a schematic perspective view of the hull concept according to the present invention used at a container carrying ship with a length of 150 m and a breadth of 40 m,
Fig. 2 is a schematic sectional length view through the centre of the ship according to fig. 1 showing the basic form and location of the centre hull in regard to the loading deck,
Fig. 3 is a plan view showing the relative location of the centre hull and the side hulls and showing a bow wave from the centre hull,
Fig. 4 is a comparison of the horisontal and vertical acceleration forces at a conventional vessel and at a hull concept according to the present invention.
In fig. 1 is a schematic perspective view of the hull concept according to the present invention used at a container cargo ship with a length of 150 m and a breadth of 40 m. The centre hull 1 has been shown with a bulb 1a. As the centre hull the side hull 2 is broken through 4.
The broken through 3 of the centre hull 1 is best shown in fig. 2, in which this hull also is shown with a greater buoyancy at the front part, as the buoyancy of each side hull is displaced far behind the bow of the ship. This is shown more clear in fig. 3. In fig. 2 the hight H above the freeboard of the centre hull is shown, which in this case is about 4 m. Thus there will be lot of "emty space" beneath the loading deck, i.e. space for waves not being capable of transferring their kinetic energy to the ship.
In fig. 3 a plan view showing the relative location of the centre hull1 and the two side hulls 2a and 2b is shown. The side hulls 2 are so located relative the bow wave 5 that the bow of each side hull will be located behind the bow wave. This means that the side hulls 2 will be in a wave trough reducing the resistance of the side hulls during travel. Preferably the inner sides of the side hulls 2, i.e. the sides facing the centre hull are straight and the distance beween the side hull and the centre hull can be varied depending upon the form and the size of the hull.
In fig. 4a and 4b the distinction between the acceleration stresses acting onto load carried on board during travel in rough sea are shown, first onto a conventional ship at fig. 4a, and second, in fig. 4b, onto a ship with a trimaran hull concept according to the present invention.
The invention is not restricted to the embodiments described above, but modifications can be done within the scope of the appended claims.

Claims

A hull concept with a central main hull (1) and two, on each side of the main hull located, side hulls (2),
Characterized in that the free boards of the main hull (1) and the side hulls (2) are broken through (4) along an essiential part of their lengths so that waves can roll through the space formed between hulls and deck.
Concept according to claim 1, characterized in that the main hull (1) has about 50 - 85 % of the total buoyancy, while 50 - 15 % of the buoyancy are distributed on the two side hulls (2).