GB2278446A

GB2278446A - Hull monitoring apparatus and method

Info

Publication number: GB2278446A
Application number: GB9310962A
Authority: GB
Inventors: Alan Thurston Ractliffe
Original assignee: SHIPBOARD INFORMATICS Ltd
Current assignee: SHIPBOARD INFORMATICS Ltd
Priority date: 1993-05-27
Filing date: 1993-05-27
Publication date: 1994-11-30
Also published as: GB9310962D0

Abstract

Apparatus for monitoring the effects of waves (3, 7) on structural stresses on the hull of a ship (4) is in the form of a number of pressure monitoring devices (5) mounted at a series of positions below the normal water-line on the outer surface of the hull, and a corresponding number of signal conductors (6) connecting the monitoring devices separately to a computer within the hull of the ship, whereby to monitor the wave pressure at each of the positions. The method entails frequently or continuously monitoring the signals from the pressure monitoring devices and calculating hull stress values from the signals. As shown the pressure sensors (5) are located below a bilge keel (8) for protection. <IMAGE>

Description

Hull monitoring Apparatus and Method.

The present invention is concerned with the monitoring of stresses in the structure of ships' hulls and comprises apparatus and a method for carrying out such monitoring.

It is a legal requirement under at least some jurisdictions that ships larger than a specified size should carry an on-board computer system to calculate hull bending moments resulting from the load distribution throughout the ship. As cargo and/or ballast are added to or removed from the ship, and as fuel is consumed, the load distribution changes and the bending moments along the length of the hull also change.

Even when the load carried by a ship is correctly distributed, undesirable high bending moments can arise as the pattern of waves encountered by the ship changes. For example, a high wave of which the length is of the same order as the length of the hull gives rise to relatively high bending stresses.

One approach which has been adopted to anticipate high bending stresses is to monitor longitudinal stresses in the deck of the ship. When dangerously high bending stresses are approached, the ship's captain can take remedial action, for example by altering the course or speed of the ship.

Systems relying upon direct measuring of longitudinal deck stress are indeed effective but they require the installation of long-line strain gauges upon the surface of the deck. Such gauges and the cables necessarily associated with the gauges not only obstruct the deck surface but are potentially hazardous for that reason.

It is an object of the present invention to provide an alternative method and apparatus for monitoring the effects of waves on structural stresses on the hull of a ship, by means of which some at least of the disadvantages of prior art deck-stress monitoring methods are reduced or eliminated.

The apparatus according to the present invention comprises a number of pressure monitoring devices mounted at a series of positions below the normal water-line on the outer surface of the hull of the ship, and a corresponding number of signal conductors connecting the monitoring devices separately to a computer within the hull of the ship, whereby to monitor the wave pressure at each of said positions.

The method according to the invention, for monitoring the effects of waves on structural stresses on the hull of a ship, comprises disposing a number of pressure monitoring devices at a series of positions below the normal water-line on the outer surface of the hull, providing a corresponding number of signal conductors to connect the monitoring devices separately to a common monitoring point within the hull, frequently or continuously monitoring at that point the signals from the pressure monitoring devices, and calculating hull stress values from said signals.

By means of the method and apparatus of the present invention, the wave pressure at the selected number of positions along the length of the hull can be monitored directly and from these values and details of the distribution of the load throughout the ship the hull bending moments can be calculated, without the necessity of obstructing the deck surface by installing long-line strain gauges upon it.

The pressure monitoring devices are of such a number and in such positions as to provide the optimum required information. They are preferably mounted symmetrically along the opposite sides of the hull, preferably close to the lowest level of the sides. It is preferred to provide from 5 to 20 such devices on each side, more preferably of the order of 10 or 12 per side. Advantageously, the devices are located at the foot of the bilge keel on each side of the hull, where they are less exposed to possible damage. They may take the form of conventional pressure transducers or any other form of pressure measuring gauge or device including, for example, devices employing pressure-sensitive materials.

It is emphasised that the pressure monitoring devices are mounted upon the outside of the hull and it is therefore not necessary to penetrate the hull at their points of mounting. The devices may be attached to the hull by means of a water-resistant adhesive, for example an epoxy resin, or by some means of reversible and/or renewable attachment, for example by a loop-and-pile fabric or by mechanical clips.

The signal conductors, for example electrical conductors or fibre-optic conductors, by means of which signals from the pressure monitoring devices are conveyed to a common monitoring point within the hull are also attached to the hull by means such as those discussed above. The conductors may be enclosed within one or more protective tubular conduits or they may be left exposed, in which case if desired the conductors may be of a reinforced or heavy-duty type. Such conduits may be watertight but need not be so.

The conductors may together form a bundle at their ends nearest to the common monitoring point and they are preferably led into the ship through a single hole in the hull or one in each side of the hull, preferably in the engine room, or via a hole in the superstructure above deck level. If the system is installed on an existing vessel, the conductors may advantageously be led in through an existing hole, in order to avoid the statutory need for authorisation when a new hole is made in the hull.

The monitoring of the signals from the individual pressure monitoring devices will normally be carried out by a suitable computer, for example that already installed to control load distribution. The computer preferably samples the signal from each device at a rate which is at least ten times the frequency of the highest-frequency sea waves likely to be encountered when the ship is operating.

Typically, the signals may be monitored at a frequency of the order of five times per second. Preferably the signals from all of the pressure devices are monitored as near to simultaneously as possible, so as to give as near as possible an indication of pressure distribution at a given instant. By combining that information with information relating to the distribution of weight along the length of the ship, which latter information will usually be already determined, the computer is able to calculate the total bending moment and shear force acting on the hull at any point along its length. The calculated figures may conveniently be presented as a running average value over a moving ten-minute or other interval, to equip the captain with the information required to anticipate the need to take corrective action, as by changing course or speed.

The invention will now be further described and illustrated with reference to the accompanying drawings, which show in diagrammatic form one preferred embodiment of the apparatus according to the invention and wherein: Fig.l is a longitudinal elevation of a ship incorporating the invention; and Fig.2 is a transverse sectional view of the ship of Fig.l.

In Fig.l, the line 3 represents a typical profile of a wave encountered in operation of a ship 4. In the wave position shown, the upthrust or buoyancy pressure of the ship is greater at its ends than in the middle of its length and this will produce an overall sagging moment at the middle of the hull length, which in turn gives rise to a compressive stress in the deck and a tensile stress at the bottom of the hull.

In the illustrated installation, a series of ten pressure transducers 5 are secured to the face of the hull along each side of its length. Each transducer 5 is separately electrically linked to a computer (not shown) within the ship by a conductor 6. The inset to Fig.l illustrates the connection of a single transducer to an associated conductor.

Fig.2 is a transverse sectional view within the region, of the middle of the length of the ship. A typical wave profile is shown at 7. As seen more clearly in the inset to Fig.2, each pressure transducer 5 and associated conductor 6 is, in the illustrated embodiment, located below the bilge keel 8 of the ship, where it is well protected against damage.

Claims

1. Apparatus for monitoring the effects of waves on structural stresses on the hull of a ship, which apparatus comprises a number of pressure monitoring devices mounted at a series of positions below the normal water-line on the outer surface of the hull of the ship, and a corresponding number of signal conductors connecting the monitoring devices separately to a computer within the hull of the ship, whereby to monitor the wave pressure at each of said positions.

2. Apparatus as claimed in Claim 1, wherein the monitoring devices are mounted symmetrically along the opposite sides of the hull of the ship.

3. Apparatus as claimed in Claim 2, comprising from 5 to 20 said monitoring devices on each side of the hull of the ship.

4. Apparatus as claimed in any of the preceding claims, wherein the pressure monitoring devices are located at the foot of the bilge keel of the ship.

5. Apparatus as claimed in any of the preceding claims, wherein the pressure monitoring devices are pressure transducers.

6. Apparatus as claimed in any of the preceding claims, wherein the pressure monitoring devices are attached to the hull by means of a water-resistant adhesive or by reversible and/or renewable attachment means.

7. Apparatus as claimed in any of the preceding claims, wherein the signal conductors are electrical conductors or fibre-optic conductors.

8. Apparatus as claimed in any of the preceding claims, wherein the signal conductors are attached to the hull by means of a water-resistant adhesive or by reversible and/or renewable attachment means.

9. Apparatus as claimed in any of the preceding claims, wherein the signal conductors are enclosed within one or more protective tubular conduits.

10. Apparatus as claimed in any of the preceding claims, wherein the signal conductors are together led into the ship through a single hole in the hull or one hole in each side of the hull, or via a hole in the superstructure above deck level.

11. Apparatus for monitoring the effects of waves on structural stresses on the hull of a ship, which apparatus is substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

12. A method for monitoring the effects of waves on structural stresses on the hull of a ship, which method comprises providing on said ship apparatus as claimed in any of the preceding claims, frequently or continuously monitoring signals from the pressure monitoring devices, and calculating hull stress values from said signals.

13. A method as claimed in Claim 12, wherein said signals from each device are sampled at a rate which is at least ten times the frequency of the highest-frequency sea waves likely to be encountered in operation of the ship.

14. A method as claimed in Claim 12 or 13, wherein said signals are monitored at a frequency of the order of five times per second.

15. A method as claimed in any of Claims 12 to 14, wherein the signals from all of the pressure monitoring devices are monitored essentially simultaneously.

16. A method as claimed in any of Claims 12 to 15, wherein the total bending moment and shear force acting on the hull at a point along its length are calculated by a said computer and presented as a running average value over a moving time interval.