METHOD AND DEVICE FOR CONNECTING A TANKER AT SEA

This invention relates to a method for connecting a tanker at sea. More particularly, it relates to a method for connecting a tanker to a loading facility at sea, in which, after having positioned itself at the loading facility, the tanker is connected to a loading hose for fluid to be transferred from the loading facility to the tanker. The stern of the tanker is turned towards the loading facility, the tanker being provided at its stern with propulsion machinery which is steer- able in the horizontal plane, after which the loading hose is connected to a cargo manifold located at the stern of the tanker.

So-called buoy loading of tankers at sea is used to a considerable extent, for example for loading crude oil from some fields in the North Sea. The offshore loading facility may include, for example, a loading buoy or a production ship, often referred to as an FPSO (Floating Production, Storage and Offloading) vessel.

Several solutions have been developed, some of which include mooring of the tanker and connection to a submerged buoy, whereas, in other solutions, it may be unnecessary to moor the tanker.

Gradually, so-called bow loading has come into relatively wide use. The method involves that the tanker to be loaded

moves its bow up to the loading facility. A loading hose is then passed from the loading facility and connected to the cargo manifold of the tanker, which is at the bow of the tanker. During the loading the tanker is held in position by means of the propulsion machinery of the tanker and relatively powerful thrusters at the bow of the tanker.

However, loading of this kind is relatively vulnerable to weather, as forces from waves and wind acting on the bow of the tanker must be balanced by sufficient force from the thrusters to hold the bow of the tanker in a substantially fixed position relative to the loading facility. Especially in the wintertime it happens that loading must be put off because the effect of the thrusters is not sufficient to ensure that the bow of the tanker will stay in the right position during the loading.

Besides, bow manifolds are relatively highly exposed to sea spray and, thereby, icing in wintertime. This may entail considerable extra work before loading can be started.

The invention has for its object to remedy or reduce at least one of the drawbacks of the prior art .

The object is achieved according to the invention through the features which are specified in the description below and in the claims that follow.

A method in accordance with the invention for the connection of a tanker to a loading facility at sea, in which, after having positioned itself at the loading facility, the tanker is connected to a loading hose for fluid to be transferred from the loading facility to the tanker, is characterized by the stern of the ship being turned towards the loading facil- ity, the tanker being provided, at its stern, with propulsion machinery which is steerable in the horizontal plane, and the

loading hose then being connected to a cargo manifold which is located at the stern of the tanker.

With advantage, the tanker is provided with so-called dynamic positioning, in which a control system calculates, by means 5 of external navigation signals, any current deviation from a desired position, the control system seeking to reduce the deviation by means of the steering and propulsion machinery of the tanker.

Preferably, the propulsion machinery, which is steerable ino the horizontal plane, includes at least two propellers which are arranged to be pivoted in the horizontal plane. The propulsion machinery of tankers of this kind has substantially greater efficiency than what could possibly be transmitted via thrusters at the bow. s Thus, matters are well arranged for the tanker to be held in position by means of the positioning system's control of the power and relative direction of the propulsion machinery, while the stern of the tanker is connected to the loading facility. This is also the case in considerably worse weathero conditions than those under which it is possible to load when the bow of a tanker is to be held in a particular position.

Preferably, the cargo manifold, which is at the stern of the tanker, is set back somewhat on the poop of the tanker, in order for any leakage at the manifold connection to be cap-5 tured and directed to a collecting tank.

The loading hose may be formed by known loading hose arrangements and is not limited to a loading hose which is reeled up, in its inactive position, at the loading facility.

The cargo manifold, which is located at the poop, is wello protected from sea spray and icing during the sailing to the

loading device, which simplifies to a substantial degree the connecting work in cold periods and in northern waters.

In what follows, there is described a non-limiting example of a preferred method and embodiment which are visualized in the accompanying drawings, in which:

Figure 1 shows schematically a side view of a tanker which is connected to a production ship; and

Figure 2 shows schematically a plan view of the tanker and production ship of figure 1.

In the drawings the reference numeral 1 indicates a tanker, for example a so-called "shuttle tanker" which is used for transporting crude oil from sea-based production sites to inshore receiving facilities. The tanker 1 is connected to a loading facility 2 in the form of a production ship by means of a loading hose 4. The loading hose 4 is formed by, for example, a flexible hose which is reeled up, in its inactive position, on a drum 6 on the production ship 2.

At its free end portion, the loading hose 4 is provided with a connection 8 which complementarily fits a cargo manifold 10 in a manifold housing 12 on the poop 14 of the tanker 1.

The propulsion machinery 16 of the tanker 1 includes two propulsion propellers 18 steerable in the horizontal plane, which are placed at the stern 20 of the ship 1. In figure 2 the propulsion propellers 18 take different directions rela- tive to the longitudinal axis of the tanker 1. This indicates that the direction and thrust of the propulsion propellers 18 are controlled to keep the stern 20 of the tanker 1 in a desired position relative to the production ship 2.

In the main, the bow 22 of the tanker 1 may be allowed to

turn according to the wind and weather. If necessary, the thrusters 24 of the tanker 1 are used to maintain the direction of the tanker 1.

When a tanker 1 is to connect to a production ship 2, alter- natively another loading facility, not shown, the stern 20 of the tanker 1 is turned towards the production ship 2, the tanker 1 being moved to an appropriate distance from the production ship 2.

The stern 20 of the tanker 1 is stabilized in this position as explained above .

A line, not shown, is shot across from the production vessel 2, whereby the loading hose 4 is gradually pulled across and connected to the cargo manifold 10 on the poop 14, after which loading of the tanker 1 may take place .

When the loading is finished, the loading hose 4 is disconnected from the cargo manifold 10 and pulled back onto the production ship 2. The tanker 1 then sails to its destination.