GB2356174A

GB2356174A - Drag reduction plate for ships

Info

Publication number: GB2356174A
Application number: GB9926792A
Authority: GB
Inventors: Frode Hauken; Nils Arnfinn Vika
Original assignee: Stolt Comex Seaway Ltd; Stolt Offshore Ltd
Current assignee: Stolt Comex Seaway Ltd; Stolt Offshore Ltd
Priority date: 1999-11-13
Filing date: 1999-11-13
Publication date: 2001-05-16
Also published as: GB9926792D0

Abstract

A transverse plate member 20 is attached to but spaced from the bottom of a ship's hull 10 and aligned parallel or at a small angle to the ship's bottom so as to alter the water flow over the hull to reduce the ship's resistance to motion as it passes trough the water. The plate member may be foil shaped and mounted at a forward edge of an opening in the ship's hull bottom, such as a moonpool 11. The plate member may be set at a rearwardly opening angle of 5{, spaced from the hull by two longitudinally extending webs 40 and may extend across the full width of the opening or 50% of the hull width. At least two plate members may be arranged laterally or longitudinally spaced on the hull bottom.

Description

2356174 Drag Reduction Device For Shim The present invention relates to a

drag reduction device for a ship During the design of a ship every effort is made to produce an efficient rsed shape that will offer the least resistance to motion through the water thereby enhancing the speed of the ship and reducing the power requirement and therefore the fuel consumption.

In order to produce a practical working ship various openings must be cut into the hull for such purposes as transverse tunnel thrusters and cooling water intakes. Ships intended for the offshore industry may have wells or "moonpools" through which equipment or diving bells may be deployed, or through which drilling may take place in addition to the more usual openings.

Each of these openings exerts additional drag which may effect a greater or lesser reduction in speed depending on the size and form of the opening and its position on the hull. For instance a group of three tunnel thrusters installed in the bow of a ship of about 100m length may well reduce the speed by 2 knots or more depending upon the exact design of the openings, while an 8m x 8m moonpool fitted amidships on the same size of ship may reduce the speed by I to 2 knots if well designed, or as much as 6 knots if badly designed although it is unlikely that such a design would be allowed to remain without modification.

It is the principal object of the present invention to obviate or mitigate these disadvantages and in so doing provide a drag reduction in a ship.

According to the present invention a ship has a transverse plate member attached to but separated from the bottom of the ship's hull and aligned parallel or at a small angle to the ship's bottom so as to alter the water flow over the hull as the ship passes through the water and thereby reduce the ship's resistance to motion.

2 The plate member may be of foil shape. A transverse tubular member may be situated near the aft edge of the plate member.

The plate member may be situated at or near the forward edge of an opening e.g. a moonpool opening in the hull of the ship, and preferably the plate member extends over substantially the full width of the opening. It will be understood however that the transverse plate member, or more than one of them, could be present on a substantially "bare" hull.

It is found that when such a ship now embodying the present invention is taken to sea, that the ship's speed will be approximately the same as its premodification speed, indicating that if the opening had not been installed then the speed would have been above that of the bare hull prior to the modifications; a gain of about one to two Imots. It is believed therefore that the transverse plate of the present invention can be applied with benefit to a substantially "bare" hull of a ship.

It is also believed that such a plate can counteract the "Coanda" effect whereby the water might well up into a moonpool having a curved transition to the ship's bottom.

Embodiments of the present invention will now be described by of example with reference to the accompanying drawings wherein:

Fig. 1 shows a side view and inset detail of an off-shore off service ship fitted with a transverse plate member in accordance with the present invention; Fig. 2 shows schematically a bottom view of the ship of Fig 1; Fig. 3 shows to a larger scale a side view of one embodiment of the transverse plate member suitable for use in the ship of Fig. 1 and located at the forward edge of a moonpool of the ship, i.e.

per section A-A of Fig. 2; 3 Fig. 4 shows a similar view for an alternative form of transverse plate member; Fig. 5 shows yet a further embodiment of the transverse plate member; and Fig. 6 shows in side view, a transverse plate member generally as shown in Fig. 3 but fitted in a ship generally with a bare-hull and not specifically associated with a moonpool opening.

Referring to Figs 1 and 2, an off-shore service ship 10 has a moonpool defmed by an opening 1 through the bottom of the ship 10, the moonpool 11 being located in a mid-section 10M of the ship's hull. In accordance with the present invention, a transverse plate member 20 constituting a depressor is located on the bottom surface of the ship's hull, and specifically in this example, so as to be positioned at the forward edge or comer 30 of the moonpool's bottom opening in the hull.

Fig 3 shows a suitable form of plate member 20 and in this example the plate member 20 is in the form of a flat plate 20A. The plate 20A is carried by two or more support plates 40 secured to the hull so that plate 20A is separated by a small amount from the hull bottom and so that it extends parallel with or at a small angle a to the hull bottom. The plate 20A can have a portion extending forward of the leading wall 1 1A of the moonpool 11 with a tail portion below the opening 11. The angle a can lie in the range 0 101, with 5' preferred. A transverse tubular member 50 carried by the support plates 40 so as to be located adjacent the rear edge of the plate 20A provides for a further spoiling effect on the waterflow passing between the hull and the plate 20A.

The plate member 20 of Fig. 4 is similar to that of Fig 3 but dispenses with the tubular member 50. The Fig 5 arrangement is similar to that of Fig 4 except that in this case a foil section depressor member 20B is employed in place of the plate 20A. The foil member 20B has a flat top surface 60 parallel with the hull bottom with a curved bottom surface facing downwardly.

4 The depressor member 20 need not be associated with a bottom opening in the hull, and in this case can be arranged as shown in Fig 6. The plate member 20 of Fig 6 similar to that of Fig 4 can be placed at any appropriate 5 position on the hull bottom, for example, in the midsection 10M of the ship. The present invention therefore is applicable to ships with "bare" hulls i.e. hulls without any substantial openings such as moonpools. It will be appreciated that more than a single transverse member 20 could be provided on the ship's bottom.

The extent of the depressor plate or other member in the fore-aft direction of the ship in the above may for example be 0.5m, particularly in an 80m hull. A range of 0.2m to 2m may be envisaged in general.

The extent of the plate member in the direction transverse to the hull substantially, to the width of the hull bottom, or to the width of a feature such as a moonpool or drive tube which the depressor is associated. Individual depressors may be spaced across the width of the ship's bottom, and further depressors may be spaced along its length-

Claims

Claims 1. A ship having a transverse plate member attached to but

separated from the bottom of a the ship's hull and aligned parallel or at a small 5 angle to the ship's bottom so as to alter the water flow over the hull as the ship passes through the water and thereby reduce the ship's resistance to motion.
2. A ship as claimed in claim 1, wherein the plate member is of foil shape.
3. A ship as claimed in claim 1 or 2, wherein a transverse tubular member is situated near the aft edge of the plate member.
4. A ship as claimed in any preceding claim, wherein the plate member is separated from the hull by at least two webs extending longitudinally on the hull.
5. A ship as claimed in any preceding claim, wherein the plate member is set with a rearwardly opening angle to the ship's hull in the range 00 to 100.
6. A ship as claimed in claim 5, wherein said rearwardly opening angle is about 50.
7. A ship as claimed in any preceding claim, wherein the plate member extends over more than 50% of the hull width.
8. A ship as claimed in any preceding claim including an opening on the hull bottom, for example as formed by a moonpool or other wen, said plate member being situated at or near a forward edge of said opening.
9. A ship as claimed in claim 8, wherein the plate member extends over substantially the full width of the opening.
10. A ship as claimed in any preceding claim, wherein at least two of said plate members are arranged laterally spaced on said hull.

6
11. A ship as claimed in any preceding claim, wherein at least two of said plate members are arranged longitudinally spaced on said hull.
12. A ship substantially as hereinbefore described with reference to one as illustrated in the accompanying drawings.