METHOD AND SYSTEM FOR HIGH SPEED DEPLOYMENT MONITORING

Abstract: A method and system for measuring cable (16) tension or slackness when delivering or recovering a payload (22) in deep sea (12) applications is disclosed.

Description: PATENT APPLICATION TITLE: METHOD AND SYSTEM FOR HIGH SPEED DEPLOYMENT MONITORING INVENTOR: PETER MOLES FIELD OF THE INVENTION The field of this invention relates to method and system for monitoring cable tension or slackness when delivering or recovering payloads in deep sea applications. BACKGROUND OF THE INVENTION Frequently, loads have to be lowered from vessels to significant depths or use subsea. A typical example is the delivery of remotely operated vehicles in cages or other devices so that they can be launched down near the seabed at the wellhead. Frequently, the delivery time from the vessel to the seabed can last for several hours. In a desire to reduce that time, winches on delivery vessels are now designed to increase the payout rates of such loads. Conversely on recovery it is desirable to reduce the recovery time in the same manner. Due to the size and shape of the load, the surrounding water provides resistance to the descent of the load beyond a certain speed. The problem that arises is that on lowering if the lowering speed is too great, the cable develops slack and starts to loop. Subsequent huckling can result in damage to the cable. Another problem that can arise is that the cable wraps itself around a load because it is being paid out faster than the load is descending. The term "huckling", as used herein means to create a loop in a cable. Conversely, when raising the load, taking in cable at too high a rate can put undue stress in the cable and can cause it to snap. Accordingly, the object of this invention is to allow feedback to personnel on the vessel to inform them that such conditions are possible so that the speed of the hoisting equipment can be properly regulated to avoid them. Those and other objectives will become more readily apparent to one of ordinary skill in the art from a review of the description of the preferred embodiment below. SUMMARY OF THE INVENTION Feedback is provided in a hoisting system for delivery and recovery of loads from a surface vessel to the subsea location. A tension sensor is placed adjacent the load and sends a signal to the surface where the winch operator can react. Automation of the process is also envisioned. If the cable payout rates exceed the descent rate of the load, the sensor will indicate a reduction in tension, giving a signal to the personnel at the surface that the payout rate is too high. When recovering the load, the sensor measures directly the tension in the cable to prevent excessive recovery speeds. The present invention is directed toward a monitoring system for the deployment of loads subsea from the water surface. The invention comprises a cable and an apparatus capable of paying out or taking out the cable from the surface. The invention further comprises a sensor located or mounted on the cable and capable of measuring tension in the cable. DETAILED DESCRIPTION OF THE DRAWING Figure 1 is a side view of the system of the present invention showing the preferred location of the tension sensor. Figure 2 is a block diagram of the control system of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the Figure 1, a vessel 10 is shown floating in a body of water 12. It has an apparatus 14 which is able to take up and payout cable 16 over a boom 18. In a preferred embodiment the apparatus 14 is a winch mounted on the vessel. At the end region of cable 16 in the preferred embodiment, there is a tension sensor 20 which is located adjacent load 22, as shown in Figure 1. The tension sensor 20 is capable of measuring tension in the cable 16 at the load. In a preferred embodiment, the load 22 is connected adjacent one end of the cable 16. Shown in dashed lines as 24 in Figure 1 is a combination power/signal line that goes from the vessel 10 to the tension sensor 20. The power/signal line 24 can be included in the cable 16 or it can be a separate cable. It can also embody a processor 30 to automatically regulate the speed of winch 14 to control the tension in preset limits. In a preferred embodiment, the invention comprises a processor 30 to receive a measurement signal 32 from the sensor 20 and to use the signal to regulate take up or payment of the cable 16 by the apparatus 14, as shown in Figure 2. The processor is capable of sending a control signal 37 to the apparatus 14. In a preferred embodiment the invention further comprises a signal transmission system 34 coupled to receive a measurement signal from said sensor and capable of sending a signal indicative of measured tension 32 to the water surface, as shown in Figure 2. In a preferred embodiment, the processor 30 receives a signal from the sensor 20, via the signal transmission system 34. When the load 22 is lowered, the winch 14 pays out cable 16 at the selected rate. However, drag forces on the load 22 from the surrounding water can diminish its rate of descent. Accordingly, when the winch 14 pays out cable 16 at a faster rate than the descent rate of the load 22 in the water 12 there is a sensed decrease in tension at sensor 20. That measurement is communicated to the vessel 10 through the signal conductor 24 so that surface personnel know that an adjustment in the operating rate of the winch is required. This can also be done automatically with a processor. The most desirable location for the tension sensor 20 is as close as possible to the load 22. However, it can be positioned further away without departing from the spirit of the invention. On descent of the load 22 the position of the tension sensor 20 adjacent the load 22 will provide for the earliest detection of any slack in the cable 16. Putting it higher makes the location less than optimal, however it is still serviceable for some feedback for slackness in the cable upon descent of load 22. When the load 22 is being raised, the entire cable 16 is in tension. If the winch 14 is operated at too high a speed, the surrounding water 12 provides a drag force on the load 22 which can increase the tension in the cable 16. In this application the location of the tension sensor 20 is less critical. If the cable 16 is being taken up at too high a rate, the sensed tension will rise at sensor 20 and a signal will be provided through lines 24 to the surface personnel on the vessel 10 to decrease the speed of winch 14 to avoid snapping the cable 16 due to over stress. Those skilled in the art will appreciate that what has been described above is the preferred embodiment and minor changes and modifications to the described preferred embodiment can be made within the scope of the invention which is limited by the claims below.

Claims: WHAT IS CLAIMED IS: 1. A monitoring system for deployment of loads subsea from the water surface comprising: a. a cable; b. a floating apparatus capable of paying out or taking up said cable from the surface; and c. a sensor on said cable and capable of measuring tension in said cable. 2. The system of claim 1, wherein said sensor is located adjacent said load. 3. The system of claim 2, wherein said load is connected adjacent one end of said cable. 4. The system of claim 3, wherein said apparatus is a winch mounted on a vessel. 5. The system of claim 4, further comprising a signal transmission system coupled to receive a measurement signal from said sensor and capable of sending a signal indicative 1 of measured tension to the water surface. 6. The system of claim 5, further comprising a processor to receive a signal from said signal transmission system and use said signal to regulate takeup or payout of said cable. 7. The system of claim 1, further comprising a load connected to said cable. 8. A method of delivering a load subsea comprising: a. securing the load to a cable connected to a winch mounted on a floating surface vessel; and b. regulating the cable payout rate while lowering the load through a liquid to maintain a predetermined tension on the cable. 9. The method of claim 8, further comprising locating the sensor near the load. 10. The method of claim 9, further comprising sending a signal to the water surface in real time as to the measured tension by said sensor. 11. The method of claim 10, further comprising using a processor to regulate cable rate to control measured tension within desired limits. 12. A monitoring system for deploying loads subsea from the water surface comprising; a. a cable; b. a sensor connected to said cable such that it can measure stress in said cable, said sensor being capable of transmitting a signal indicative of measured stress; c. a processor capable of receiving an input signal from said sensor processing said input signal and transmitting a control signal; and d. a cable payout apparatus connected to said cable, such that it can payout or take up said cable, said apparatus further being coupled to receive a control signal from said processor, said control signal being capable of regulating the cable take up or payout by said apparatus. 13. The system of claim 12, further comprising a load connected to said cable. 14. The system of claim 12, further comprising a signal transmission system capable of receiving a signal indicative of stress from said sensor and transmitting said signal to said processor. 15. The system of claim 12, wherein said apparatus is a winch.

Inventors: MOLES PETER, MOLES, PETER
Applicants: OCEANEERING INT INC, OCEANEERING INTERNATIONAL, INC.
Application year: 2001
Main classification: G08B21
IPC codes: B66C13