Method of Dynamic Positioning of a Vessel

Abstract

A method of dynamic positioning of a vessel (16, 32), wherein a positioning system controls at least one positioning machinery (18), and where two or more buoys (1), each comprising at least one positioning machinery (18), are coupled to the vessel (16, 32).

Description

The following describes a non-limiting example of a preferred method illustrated in the accompanying drawings, in which:

FIG. 1 shows a vessel equipped with two buoys according to the invention;

FIG. 2 is a section taken along I-I in FIG. 1, on a larger scale;

FIG. 3 is a plan view of a buoy; and

FIG. 4 shows two buoys connected to a semi submersible platform.

In the drawings, reference number 1 denotes a buoy comprising machinery housing 2, a flat coupling portion 4 projecting sideways from the machinery housing 2 and two vertical columns 6 projecting upwards from the machinery housing 2.

The machinery housing 2 and the coupling portion 4 are submerged when the buoy 1 is in the operative position, while the columns 6 protrude, at least partly, above the sea level 8.

The upward facing side of the coupling portion 4, which is equipped with ballast tanks 10, is fitted with a flexible friction material 12. Surrounding the friction material 12 is a seal 14 arranged to sealingly abut the bottom of a vessel 16 when the buoy 1 is coupled to the vessel 16.

In the machinery housing 2 there is arranged positioning machinery in the form of two positioning thrusters 18 that may be rotated about their own vertical axes. Each thruster comprises a submerged angular gear 20 with a propeller 22 driven by an electric motor 24. A generator 26 placed on the deck of the vessel 16 delivers energy to the motor 24 via a cable 28.

The machinery housing 2 holds ballast pumps (not shown) and also the necessary piping and valves (not shown).

The columns 6 have fenders 30 facing the coupling portion 4. The upper portion of the columns 6 is always located above the surface 8 of the sea, and therefore the columns 6 constitute a connection from the surface down to the machinery housing 2, for access and conveyance of the cable 28 plus control cables and pipe connections (not shown).

The positioning machinery 18 of the buoy 1 is controlled in a manner that is known per se, by a control system for dynamic positioning (not shown).

In order to couple the buoy 1 to the vessel 16, the buoy 1 is lowered into the sea by regulating the ballast, among other things in the ballast tanks 10, until the coupling portion 4 is somewhat deeper in the sea than the bottom of the vessel 16.

The buoy 1 is then moved in towards the vessel 16, preferably until the fenders 30 stops against the vessel 16. Pumping out ballast raises the buoy 1 until the friction material 12 stops against the bottom of the vessel 16. Pumping out additional ballast from the buoy 1 increases the contact pressure between the friction material 12 and the bottom of the vessel.

The seal 14 that sealingly abuts the bottom of the vessel 16 prevents inflow of water to the friction material 12 when water is drained from the space between the coupling portion and the bottom of the vessel 16.

FIG. 4 shows two buoys coupled to a semi submersible platform 32.

Claims

1. A method of dynamic positioning of a vessel (16, 32), wherein a positioning system controls at least one positioning machinery (18), characterized in that two or more buoys (1), each comprising at least one positioning machinery (18), are coupled to the vessel (16, 32), and thereby arranged to keep the vessel (16, 32) in a directional orientation.

2. A method in accordance with claim 1, characterized in that the buoy (1) is attached to the vessel (16, 32) by means of buoyancy.

3. A method in accordance with claim 2, characterized in that a friction material (12) is placed between the buoy (1) and the vessel (16).

4. A method in accordance with claim 3, characterized in that water present by the friction material (12) is drained.