2. General Background In the production of hydrocarbons offshore, a variety of services are required. These services include laying pipeline on the sea floor and the installation of structures and equipment used in the drilling and production of hydrocarbons.

The means used to lay pipeline depends upon a variety of factors such as water depth and pipe diameter. Directing the pipeline into the water at an angle nearly vertical to the water surface is typically used in deep water. This is generally referred to as J-Lay. Directing the pipeline into the water at a relatively shallow angle is typically used in shallow water. This is generally referred to as S-Lay. Each method uses different equipment to accomplish the task. J-Lay may use a near vertical support and stinger. In S-Lay, the pipe may be unwound from a reel as it is laid or pipe joints may be welded together on the laying vessel during the laying operation. Installing equipment and structures requires the use of lowering equipment such as cranes capable of handling the weight of the equipment.

Having one vessel capable of performing each operation is expensive as this can result in a vessel remaining idle when the specific operation that it is dedicated is not required. Also, current vessels dedicated to specific tasks are only capable of speeds at six to seven knots.

The current state of the art leaves a need for vessels that have multiple use capability and greater speed.

SUMMARY OF THE INVENTION The invention addresses the above need. What is provided is a multi-use construction vessel designed to receive a variety of float-on modules that accommodate project specialty equipment and still allow the mother vessel to operate in the traditional construction mode. The vessel may be formed as a new construction or by converting an existing vessel. The vessel is provided with a lowered center section between the bow and stern. The center section is adapted to receive and secure float-on modules containing the equipment required for the desired operation. The center section may also be provided with a moon pool for laying pipeline directly through the vessel.

The vessel is ballasted to position the center section below the water line so that the float-on modules may be installed or removed. The stern section of the vessel includes a derrick crane for normal construction lifts, moving pipe, and equipment on the center section as necessary.

BRIEF DESCRIPTION OF THE DRAWINGS For a further understanding of the nature and objects of the present invention reference should be made to the following description, taken in conjunction with the accompanying drawing in which like parts are given like reference numerals, and wherein : Fig. 1 is an elevation view of the vessel of the invention.

Fig. 2 is an elevation view that illustrates the vessel ballasted in position to received float-on modules.

Fig. 3 is an elevation view illustrating float-on modules positioned over the mid-ship deck of the vessel.

Fig. 4 is an elevation view illustrating the vessel ballasted up with the float-on modules received on the mid-ship deck.

Fig. 5-9 are enlarged detail views of a docking probe and docking port and illustrate the connection sequence.

Fig. 10 is a plan view of the invention set up reels for laying pipeline.

Fig. 11 is an elevation view of the invention set up with J-Lay equipment.

Fig. 12 is a plan of the invention as set up in Fig. 11.

Fig. 13 is an elevation view of the invention set up with S-Lay equipment Fig. 14 is a plan view of the invention as set up in Fig.

13.

Fig. 15 is an elevation view of the invention set up with lowering equipment.

Fig. 16 is a plan view of the invention as set up in Fig.

15.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, it is seen in Fig. 1 that the invention is generally indicated by the numeral 10. The multi- use construction vessel 10 is generally comprised of a buoyant, self-propelled ship 12. For the sake of clarity, the forward house is not shown in Fig. 1-4.

The mid-ship deck 14 is lower than the fore and aft decks 16,18. It is preferable that the mid-ship deck 14 provide approximately forty feet of depth from the bottom of the ship to the deck. The mid-ship deck 14 is provided with a plurality of docking ports 20.

The ship is provided with several thrusters. Tunnel thrusters 22 are positioned near the bow. Full three hundred sixty degree rotating, retracting, thrusters 24 are positioned forward just aft of the fore deck 16. Full three hundred sixty degree rotating, retracting, thrusters 26 are positioned aft at the forward end of the aft deck 18. Standard ship-type controllable-pitch propellers 28 with rudders are provided at the stern. Although not shown, it is preferable two each of thrusters 24 and 26 be provided and spaced across the hull. It is preferable that the propellers 28 be in tunnels with balanced rudders.

The ship 12 may be built as a new construction or by converting an existing oil tanker. For the type of work envisioned, the preferred ship size for conversion is approximately eight hundred to nine hundred feet long, one hundred fifty to one hundred seventy feet wide, and seventy to eighty feet deep at the fore and aft decks. Existing oil tankers fit within these parameters and thus conversion will save time and money over new construction.

To convert an oil tanker, the aft portion of the ship that houses all machinery and accommodations are removed to obtain a "barge shape"approximately five hundred sixty feet long with the bow remaining. The mid-ship deck is cut out and lowered to reduce its overall depth to approximately forty feet, with a length of approximately three hundred feet. A derrick crane is mounted on the remaining aft deck 18. The fore deck 16 is modified to become the forecastle deck to accept crew accommodations and a heli-deck.

In operation, the ship 12 is ballasted to lower the mid- ship deck 14 approximately ten feet below the water surface as shown in Fig. 2. One or more float-on modules 30 are floated above the mid-ship deck 14 and positioned to align docking probes 32 with the docking ports 20. The ship 12 is then de- ballasted to raise the mid-ship deck 14 into contact with the float-on modules 30 such that the docking probes 32 are received in the docking ports 30.

Fig. 5 illustrates the initial position of the module 30 over the deck 14. It can be seen that the docking probe 32 is at first retracted position in the module 30. Fig. 6 illustrates the docking probe 32 moving to its second extended position toward the docking port 20. Fig. 7 illustrates the docking probe 32 being received in the docking port 20 during the initial de-ballasting of the ship. Fig. 8 illustrates the docking probe 32 fully inserted and extended into the docking port 20. The locking dogs 34 provided on the docking probe 32 are moved to their second extended position and received in complementary recessed grooves 36 in the docking port 20 to lock the module 30 in position. As indicated by the water line, Fig.

9 illustrates the vessel after it has been de-ballasted and is at the normal operating draft.

Fig. 3 and 4 illustrate the presence of pipe reels 38 on the modules 30. However, as seen in Fig. 10-16, the modules 30 may be used for a variety of equipment for different operations. It is also seen in these Figures that a derrick crane 44 is provided on the aft deck 18. Fig. 10 is a plan view of the vessel with the modules having pipe reels 38 as seen in Fig. 3 and 4. Fig. 11 and 12 illustrate modules 30 with equipment 40 for laying pipeline in the J-Lay mode through a moon pool 42. Laying pipeline in the J-Lay mode may also be accomplished over the side of the vessel. Fig. 13 and 14 illustrate modules 30 with equipment 46 for laying pipeline in the S-Lay mode. Fig. 15 and 16 illustrate modules 30 with equipment for lowering equipment to the sea floor.

Because many varying and differing embodiments may be made within the scope of the inventive concept herein taught and because many modifications may be made in the embodiment herein detailed in accordance with the descriptive requirement of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.