GB2114078A

GB2114078A - Underwater survey system

Info

Publication number: GB2114078A
Application number: GB08203227A
Authority: GB
Inventors: Peter Raymond Redshaw
Original assignee: FURNESS UNDERWATER ENGINEERING
Current assignee: FURNESS UNDERWATER ENGINEERING
Priority date: 1982-02-04
Filing date: 1982-02-04
Publication date: 1983-08-17

Abstract

An underwater pipeline or seabed can be surveyed using two remote vehicles towed by a craft (1), such as a surface ship. One of the vehicles (2) has negative buoyancy and is linked directly to the craft, for example by a tow-cable which extends in use at a small angle to the vertical. The other vehicle (3) is linked to the first vehicle, for example by a tow cable, so as to be towed behind same. <IMAGE>

Description

SPECIFICATION Underwater survey system This invention relates to an underwater survey system.

A range of systems is used for seabed surveying purposes, particularly for pipeline survey techniques in offshore industry. These systems involve the use of an operating platform which may be defined by a ship, a combination of a ship and a towed "fish", a small manned submersible (which can either be free swimming or tethered), or a remotely operated vehicle.

Ship platforms generally provide low resolution data. Towed fish can provide better data, although mainly in the form of low resolution, side-scan sonar data, and can gather this data at speeds up to approximately four knots. Manned sumbersibles and remotely operated vehicles can obtain visual, pipe profile, positional, pipe spanning, pipe burial and other data necessary for the monitoring of seabed pipelines both existing and p!anned, but this data is usually gathered at speeds of less than one knot.

The cost of gathering pipeline and other seabed data is generally very expensive, especially if the platform can only gather the data slowly.

An object of the present invention is to provide an underwater survey system which can be used to gather data of a high resolution at relatively high speeds, say, up to and in excess of 10 knots and which therefore may be particularly advantageous for use in offshore industry in deep water.

According to the invention therefore there is provided an underwater survey system comprising a water craft and two remote vehicles to be towed by the craft a first said vehicle having negative buoyancy and the second said vehicle being adapted to be towed via the intermediary of the first said vehicle.

The said craft may comprise a surface ship similar to but not limited to a supply boat. The towed vehicles may be of any suitable form.

The invention will now be described further by way of example only with reference to the accompanying drawing which is a diagrammatic representation of one form of a survey system according to the invention.

The survey system illustrated included a surface boat 1 and two towed remotely operated under water survey vehicles 2, 3. One vehicle 2 is connected at its front and by a suitable tow cable 4 to a hawser 5 or the like on the ship 1 , and the other vehicle 3 is connected by a suitable tow cable 6 at its front and to the rear end of the vehicle 2. The said first towed vehicle 2 has a high negative buoyancy which provides a 'dead weight' effect sufficient to keep the second towed vehicle 3 close to the ship 1. This is extremely important for obtaining accurate positional data and for keeping the second towed vehicle 2 which is the main platform for gathering data, accurately aligned with a pipeline or seabed to be surveyed.

The vehicles may be spaced by about 60 metres.

The first vehicle 2 will have a slow response time due to its high negative buoyancy and may rise approximately 1 5 to 30 metres above the seabed, although heights outside this range may also be used. A further feature of the high negative buoyancy is that when the ship 1 is underway, the angle 0 by which the tow linkage 4 departs from its static vercial disposition will remain small, and the high tension inthe towing cable 4 will minimise the dynamic vibration/oscillation of the towing cable and also in control/data cables connected between the ship and the vehicle 2.

The vehicle 2 may be used for initial low resolution data.

The vehicle 3 is towed by vehicle 2 and is in effect a flying fish which will have similar characteristics to a glider whilst remaining a remotely controlled vehicle.

With vehicle 3 towed by vehicle 2 and not directly by the ship, higher manoeuvrability and positional accuracy at high speeds can be obtained than is possibie with conventional towed fish.

The deeper the water the greater the "in-line" towing of vehicle 3 by vehicle 2 benefits the gathering of high resolution survey data.

The control of vehicle 3 can be by conventional means aided by additional forward gathering data techniques to ensure vehicle safety athigh forward speeds. Ultimately the ship will be controlled by data fed back from vehicle 3 in a closed loop system. Although vehicle 3 may have thrusters as in a conventional remotely operated vehicle, it can have roll pitch and yaw ability using flying surfaces as in an aircraft, and the vehicle 3 may have control instrumentarion similar to an automatic pilot in an aircraft.

Another advantage of the "in-line" tow is that vehicle 3 will retain manoeuvrability even in deeper water and at high speeds, whereas a standard towed fish or remotely operated vehicle is subject to very high surface cable drag. With the illustrated system, only vehicle 2 is subjected to this problem and this can be overcome by its negative buoyancy. Vehicle 2 isolates vehicle 3 from the problem of cable drag and ioading.

It is of course to be understood that the invention is not intended to be restricted to the details of the above embodiment which are described by way of example only.

1. An underwater survey system comprising 2 water craft and two remote vehicles to be towed by the craft a first said vehicle having negative buoyancy and the second said vehicle being adapted to be towed via the intermediary of the first said vehicle.

2. A system according to claim 1, wherein said water craft comprises a surface ship.

3. A system according to claim 1 or 2, wherein the said remote vehicles are remotely operated underwater survey vehicles.

4. A system according to any one of claims 1 to 3, wherein the said first vehicle is connected at its

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Underwater survey system This invention relates to an underwater survey system. A range of systems is used for seabed surveying purposes, particularly for pipeline survey techniques in offshore industry. These systems involve the use of an operating platform which may be defined by a ship, a combination of a ship and a towed "fish", a small manned submersible (which can either be free swimming or tethered), or a remotely operated vehicle. Ship platforms generally provide low resolution data. Towed fish can provide better data, although mainly in the form of low resolution, side-scan sonar data, and can gather this data at speeds up to approximately four knots. Manned sumbersibles and remotely operated vehicles can obtain visual, pipe profile, positional, pipe spanning, pipe burial and other data necessary for the monitoring of seabed pipelines both existing and p!anned, but this data is usually gathered at speeds of less than one knot. The cost of gathering pipeline and other seabed data is generally very expensive, especially if the platform can only gather the data slowly. An object of the present invention is to provide an underwater survey system which can be used to gather data of a high resolution at relatively high speeds, say, up to and in excess of 10 knots and which therefore may be particularly advantageous for use in offshore industry in deep water. According to the invention therefore there is provided an underwater survey system comprising a water craft and two remote vehicles to be towed by the craft a first said vehicle having negative buoyancy and the second said vehicle being adapted to be towed via the intermediary of the first said vehicle. The said craft may comprise a surface ship similar to but not limited to a supply boat. The towed vehicles may be of any suitable form. The invention will now be described further by way of example only with reference to the accompanying drawing which is a diagrammatic representation of one form of a survey system according to the invention. The survey system illustrated included a surface boat 1 and two towed remotely operated under water survey vehicles 2, 3. One vehicle 2 is connected at its front and by a suitable tow cable 4 to a hawser 5 or the like on the ship 1 , and the other vehicle 3 is connected by a suitable tow cable 6 at its front and to the rear end of the vehicle 2. The said first towed vehicle 2 has a high negative buoyancy which provides a 'dead weight' effect sufficient to keep the second towed vehicle 3 close to the ship 1. This is extremely important for obtaining accurate positional data and for keeping the second towed vehicle 2 which is the main platform for gathering data, accurately aligned with a pipeline or seabed to be surveyed. The vehicles may be spaced by about 60 metres. The first vehicle 2 will have a slow response time due to its high negative buoyancy and may rise approximately 1 5 to 30 metres above the seabed, although heights outside this range may also be used. A further feature of the high negative buoyancy is that when the ship 1 is underway, the angle 0 by which the tow linkage 4 departs from its static vercial disposition will remain small, and the high tension inthe towing cable 4 will minimise the dynamic vibration/oscillation of the towing cable and also in control/data cables connected between the ship and the vehicle 2. The vehicle 2 may be used for initial low resolution data. The vehicle 3 is towed by vehicle 2 and is in effect a flying fish which will have similar characteristics to a glider whilst remaining a remotely controlled vehicle. With vehicle 3 towed by vehicle 2 and not directly by the ship, higher manoeuvrability and positional accuracy at high speeds can be obtained than is possibie with conventional towed fish. The deeper the water the greater the "in-line" towing of vehicle 3 by vehicle 2 benefits the gathering of high resolution survey data. The control of vehicle 3 can be by conventional means aided by additional forward gathering data techniques to ensure vehicle safety athigh forward speeds. Ultimately the ship will be controlled by data fed back from vehicle 3 in a closed loop system. Although vehicle 3 may have thrusters as in a conventional remotely operated vehicle, it can have roll pitch and yaw ability using flying surfaces as in an aircraft, and the vehicle 3 may have control instrumentarion similar to an automatic pilot in an aircraft. Another advantage of the "in-line" tow is that vehicle 3 will retain manoeuvrability even in deeper water and at high speeds, whereas a standard towed fish or remotely operated vehicle is subject to very high surface cable drag. With the illustrated system, only vehicle 2 is subjected to this problem and this can be overcome by its negative buoyancy. Vehicle 2 isolates vehicle 3 from the problem of cable drag and ioading. It is of course to be understood that the invention is not intended to be restricted to the details of the above embodiment which are described by way of example only. CLAIMS

4. A system according to any one of claims 1 to 3, wherein the said first vehicle is connected at its front end by a tow cable to the said water craft and the second vehicle is connected by a tow cable at its front end to the rear end of the first vehicle.

5. A system according to claim 4, wherein the tow rope between the water craft and the said firsl vehicle is arranged to extend in use at a small angle to the vertical.

6. A system according to claim 1, substantially as hereinbefore described with reference to an as illustrated in the accompanying drawing.

7. A system according to any one of claims 1 to 6, when used to survey an underwater pipeline or seabed.