DESCRIPTION The present invention relates to a thermal monitoring and/or information transmission system for ships, including for example passenger ships, cargo ships, tankers, gas carriers and others.

The technologies used up to the present time for the thermal monitoring of ships are based on single-point sensors for detecting thermal stresses, mounted at various points and at various levels on each ship. These single-point sensors can be connected to each other and to a central recording and data processing unit by a network of electrical cables in the case of electrical sensors, or by a network of fibre-optic cables in the case of optical sensors. In a passenger ship, for example, these single-point sensors are located in each cabin and in other areas of the hull and holds or on the exterior. Clearly, therefore, the cost and complexity of a conventional thermal or structural monitoring system are considerable, since a large number of single-point sensors have to be installed. Furthermore, conventional single-point sensors are undesirably sensitive to electromagnetic interference, require frequent inspection and maintenance, and cannot provide constant temperature monitoring in predetermined areas of the ship. Moreover, some of these sensors, being designed to operate with radioactive substances, have a limited life and require special attention for their disposal. Finally, optical fibres can provide further benefits, owing to the fact that they have intrinsic characteristics of versatility, making it possible to use a system installed in a ship for a number of different purposes at the same time, including, for example, the transmission of information, data or commands.

The object of the present invention is therefore a thermal monitoring and/or information transmission system for ships which can be used for constant monitoring of the temperature in predetermined areas of the ship, which is efficient and economical, and in which the sensors used for detecting and monitoring thermal quantities and/or for transmitting information are not affected by electromagnetic interference, can be used in practically any environmental conditions, do not give rise to problems of refuse disposal, have a much longer life in terms of years than conventional sensors, have high precision and accuracy in terms of detection, and require practically no maintenance, even when they are mounted in cabins or corridors, lounges and the like, or in the most critical areas of a ship such as the engine rooms, lockers, stores, cold stores, freezers or the like; or in external areas of the ship such as the decks, the circulation areas or balconies of cruise ships, and the like. This object is achieved by the present invention by means of a thermal monitoring and/or information transmission system for ships, characterized in that it comprises: at least one fibre-optic cable of adequate length which forms a set of distributed sensors and which is positioned in a linear way, or at individual points in the form of a spiral or similar winding, in contact with the surfaces of the components or with the air of the inner or outer spaces of the ship whose temperature is to be monitored and/or from which information is to be transmitted; means of generating a light signal at a specific wavelength, which is sent along the fibre-optic cable and which creates a refracted light signal having a specific wavelength and frequency within the cable; and a data reading and processing unit, connected upstream of the fibre-optic cable, for measuring the wavelength and frequency of the refracted light signal to provide an estimate of the temperature variation in a predetermined portion of the cable.

The system can also be used to communicate information to the control unit through the optical fibre by modifying (changing) the physical characteristics of the fibre which can be detected by the control unit, such as the temperature of a segment of fibre or a voltage applied to a segment of fibre. Thus the control unit can detect the presence or absence of these changes or their intensity, by comparing the thermal profile of two segments of optical fibre subject to the same ambient climatic conditions, but not to the same physical changes. This will make it possible, for example, to use the system to read the temperature in a passenger cabin, together with the desired temperature in the cabin. It will also be possible, for example, to incorporate into the system the alarms sent by fire, smoke or flame detectors, for example by creating a temperature increase by switching on a heat source which will act on a specific segment of fibre when a contact actuated by the detector concerned is actuated. Thus the system can be used not only for thermal monitoring for ships but also, and simultaneously, as an information transmission system for ships.

Other features and advantages of the present invention will be made clear in the course of the following description, to be considered as a non-limiting example, which refers to the attached drawings, in which:

Fig. 1 is a schematic view in lateral elevation of a passenger ship in which a thermal monitoring system is positioned, comprising at least one fibre-optic cable connected to the central data reading and processing unit;

Fig. 2 shows a plan view of the ship of Fig. 1 ;

- Fig. 3 is a schematic perspective view of a cross section of the hull of the ship of Fig. 1 ;

Fig. 4 is a schematic view of a unit for reading the data supplied by a plurality of fibre-optic cables positioned at various points of the ship; Fig. 5 is a first schematic diagram, showing a temperature increase in a specific position along a fibre-optic cable;

Fig. 6 is a partial view in lateral elevation of a ship in which is housed a tank, for carrying fuel for example, to which the present monitoring system is applied;

- Fig. 7 is a view in lateral elevation of a tank around which at least two fibre-optic cables are wound, and

Fig. 8 is a schematic view of a fibre-optic cable wound into a spiral in order to approximate a virtual single-point detection of the temperature and/or stresses.

Fig. 9 shows, by way of example, a smoke detector integrated into the system; - Fig. 10 shows, by way of example, a segment of fibre of the sensor cable subjected to adjustable mechanical tension.

With reference to these attached drawings and to Figs. 1 and 2 in particular, the number 1 indicates a ship, for example a passenger ship. This ship 1 comprises a hull 2 above which are shown decks 3 and control rooms 4 of the ship. A number of cabins (not shown in the drawing) for housing the passengers are provided on the decks 3. In the present temperature monitoring system, at least one fibre-optic cable 5 is extended through the areas or spaces of the ship, including both the internal and external areas, in which the temperature is to be continuously monitored. The cable 5 is connected upstream to a data reading and processing unit 6, housed in the control rooms 4 of the ship 1. This unit 6 also comprises an optoelectronic device for generating a light signal, at specific monitoring frequencies, which travels along the optical fibres of the cable 5. Essentially, because of the known properties of optical fibres, the fibre-optic cable 5 can be considered as a set of distributed sensors which detect the temperature with a specific spatial resolution and a specific degree of precision: this spatial resolution can vary from the whole length of the cable to a minimum portion of it, according to requirements.

The fibre-optic cable 5 shown in Fig. 1 therefore extends from the data reading and processing unit 6 into all the relevant areas of the ship 1 , both internal and external, and thus, for example, through all the passenger cabins, running in a visible way along the ceilings, the balconies, the main deck and the areas in the hull (see Fig. 3 of the attached drawings) in which it is important for the temperature to be monitored constantly. The length of this cable 5 can be considerable, being as much as several kilometres, and the detection takes place along this extension; essentially, therefore, the mean temperatures are found by the reading unit 6 at periodic time intervals for the whole cable 5 or for each of the parts into which it is divided according to the chosen temporal resolution. Fig. 4 shows the reading unit 6, which is provided with a display 7 for viewing the data. This reading unit can be additionally connected to a data processing unit. The reading unit 6 is provided, for example, with a channel 8 which is connected to a device 9 forming an interface with four fibre-optic cables 5, which, as mentioned above, are extended through the relevant areas of the ship and are in contact with the surfaces of objects or with the air of the spaces to be monitored. This device 9 contains the control circuitry for sequentially connecting to the reading unit each of the cables 5 connected to it, in such a way that the data obtained from the single cable 5 can be displayed and stored. Each of these cables 5 is positioned in contact with the surface of the area or with the air of the spaces of the ship which are to be monitored. The laser source injects a first light signal into each of the cables, and a reflected signal with a specific wavelength and frequency is generated in the cable as a result of the known refractive phenomena of optical fibres. This wavelength of the reflected signal is measured and processed to provide an estimate of the temperature in a specific area of the ship. In practice, each cable contains two counterpropagating light waves at different frequencies, one being transmitted and the other being reflected. The waves interact as a result of the known refractive phenomena and an estimate of the temperature measurement is obtained from the reflected wave.

The resulting display on the screen of the unit 6 and/or of the data processing unit to which it can be connected takes the form of the graphs illustrated schematically in Fig. 5, showing the variation of temperature T[°C] as a function of the position P[m] in the cable. In Fig. 5, for example, the present system has detected a temperature increase in a specific area of the ship, the position of which can be read on the horizontal axis and which relates to a portion of fibre-optic cable between the points X and X+1 , with a spatial resolution of 1 m, for example.

As mentioned above, the fibre-optic cable or cables must be extended through, and in contact with, the areas of the ship in which thermal monitoring is required. Figs. 6 and 7 are schematic illustrations of the fibre-optic cables 5 wound around a tank 10 of a tanker 1', such as a tanker for carrying fuel or other substances.

On the other hand, Fig. 8 shows a fibre cable 5 having a portion 5' wound in a spiral or similar configuration: this portion 5' can be used if the present system is to be used to provide an efficient approximation of single-point temperature measurement. For example, one of these spiral portions 5' can be placed on the ceiling of each cabin of a passenger ship in order to detect and monitor the temperature at a precise point. Fig. 9 shows, by way of example, a smoke detector with its own relay contact, the closure of which causes the resistance R to be supplied with power from the generator E, resulting in the heating of the resistance, and consequently of a portion of the sensor cable 5 which is known to the reading unit. The heating of the known portion of the sensor cable 5 can then be read by the reading unit as a signal indicating the detection of smoke by the smoke detector.

Fig. 10 shows, by way of example, a simple mechanically adjustable system for applying tension to a portion of the sensor cable 5 which is known to the reading unit. In a similar way to that described in the preceding example, the effect of the tension on the known portion of the sensor cable 5 can be measured by the reading unit and interpreted as a predetermined signal. The differential measurement of two portions of cable 5 subjected to the same temperature conditions also enables the degree of tension to be evaluated if required.

As indicated in the preceding description, the present thermal monitoring and/or information transmission system is highly efficient and economical, in that it makes it possible to monitor an entire ship and/or to transmit information within the ship, regardless of whether the ship is a passenger ship, a tanker, or other type, simply by installing one or more fibre-optic cables in the areas of the ship which are to be monitored and/or from which information is to be transmitted to the control unit, and by using the reading unit to detect the reflected signals in each portion of the cable. The spatial resolution of the measurements will depend on the frequency of the light pulses sent along the cable and can vary, as mentioned above, from approximately 1 m to the whole length of the cable 5, thus providing high flexibility of measurement of the thermal profile in any area of the cable, even where such an area overlaps or is included in other areas, where the term "area" denotes a segment of the cable 5. Advantageously, the frequencies of the light signal sent along the cable and of the reflected waves differ considerably from the frequencies used for telecommunications, enabling a single cable to be used for telecommunications as well. Furthermore, the fibre- optic cables used in the present system are not electrified, and, as mentioned above, are immune to electromagnetic interference. They are also very strong and require practically no maintenance.

The present monitoring system can be used not only in the marine applications described above (including, evidently, applications to heat and fire detection), but also for monitoring and detecting any leaks in the pipework of distribution systems for combustible fluids or gas, for monitoring air conditioning systems, for activating manual alarm systems, or for indicating faults, malfunctions, or other problems.