Abstract:
There is provided a breakaway safety system for a vessel. The vessel includes: (a) a hull; (b) one or more engine arrangements supported by the hull; and (c) one or more propeller extensions mounted to the hull and coupled to receive motive power from the one or more engine arrangements in operation. The safety system includes: one or more sensors mounted to the vessel for measuring operating parameters of the vessel and generating one or more corresponding input signals; a control unit for receiving the one or more corresponding input signals, and for processing the one or more input signals to generate at least one control output; one or more fracturable regions for mounting the one or more propeller extensions to the at least one hull; and one or more fracturing devices operable to fracture the one or more fracturable regions for jettisoning associated one or more propeller extensions in an event that the control unit detects a potentially hazardous impact event and activates its at least one control output accordingly.

Description:
BACKGROUND AND SUMMARY 
     The present invention relates to breakaway safety systems for aquatic vessels, for example for boats, yachts and ships. Moreover, the present invention also concerns methods of protecting aquatic vessels from damage by using breakaway safety systems. 
     As illustrated in  FIG. 1 , there is shown an illustrative side view of a contemporary aquatic vessel indicated generally by  10 . The aquatic vessel  10  is susceptible to being implemented, for example, as a yacht, ship or boat. The aquatic vessel  10  includes a hull  20 . One or more engine assemblies  30  are mounted towards a rear end of the hull  20 , wherein the one or more engine assemblies  30  are operable to provide motive power to propel the vessel  10  through water  40 . Moreover, each of the one or more engine assemblies  30  include an extension  50  including one or more propellers  60  at substantially a distal end of the extension  50  remote from the hull  20 . The extension  50  protrudes into the water  40  beneath the hull  20  when the aquatic vessel  10  is in operation. The one or more extensions  50  are potentially vulnerable regions of the vessel  10  in an event that the one or more extensions  50  impact onto submerged objects  70 , for example submerged rocks, submerged harbour structures, ship wrecks and sunken components such as discarded oil rig components. 
     Contemporary yachts weigh in a range of 10 to 75 tonnes and are often equipped with two engine assemblies each delivering 250 kW output power or four engine assemblies each delivering 750 kW output power. Moreover, these contemporary yachts are operable to attain speeds in a range of 3 to 45 knots (circa 5 km/h to 80 km/h). In operation, these contemporary yachts are susceptible of having an operative kinetic energy approaching several MegaJoules. Such a large amount of kinetic energy focussed inappropriately in the aquatic vessel  10  is an impact situation is susceptible to causing considerable damage. 
     It is known to include sacrificial mechanical structures in the aquatic vessel which fracture in an emergency situation to try to prevent damage occurring to the hull  20  and a risk that the aquatic vessel  10  sinks in the water  40 . However, these sacrificial structures, for example fractural “weak points” whereas stress is deliberately concentrated by design, are not optimal in that they do not appropriately protect the aquatic vessel in all sailing situations. 
     It is desirable to provide a breakaway safety system which better protects an aquatic vessel in an event of potential impact. 
     According to a first aspect of the invention, there is provided a breakaway safety system for a vessel, the vessel including 
     (a) at least one hull; 
     (b) one or more engine arrangements supported by the at least one hull; and 
     (c) one or more propeller extensions mounted to the at least one hull and coupled to receive motive power from the one or more engine arrangements in operation; 
     characterized in that the safety system includes: 
     one or more sensors mounted to the vessel for measuring operating parameters of the vessel and generating one or more corresponding input signals; 
     a control unit for receiving the one or more corresponding input signals, and for processing the one or more input signals to generate at least one control output (Q, A); 
     one or more fracturable regions for mounting the one or more propeller extensions to the at least one hull; and 
     one or more fracturing devices operable to fracture the one or more fracturable regions for jettisoning associated one or more propeller extensions in an event that the control unit detects a potentially hazardous impact event and activates its at least one control output (Q, A) accordingly. 
     The invention is of advantage that use of the one or more fracturing devices to separate the one or more propeller extensions in a controlled manner is capable of improving safety and reducing the at least one hull from becoming damaged. 
     Optionally, in the breakaway safety system, the one or more fracturing devices each includes an energy storage element, a piercing element operable to fracture its associated fracturable region when impacting thereinto, and wherein the energy storage element when activated is operable to apply a force to the piercing element to force it into the fracturable region to cause the fracturable region to fracture. Use of the energy storage element is beneficial in jettisoning the one or more propeller extensions more rapidly from the at least one hull in comparison to relying on unassisted fracturing of the one or more propeller extensions from the hull in direct response to excessive applied stress as employed in contemporary known solutions. 
     More optionally, in the breakaway safety system, the energy storage element includes at least one of: an explosive charge, a mechanical spring, a volume of compressed gas. Use of such energy storage elements is capable of providing considerable immediate energy for jettisoning the one or more propeller extensions from the at least one hull. 
     More optionally, in the breakaway safety system, the control unit is provided with the input signals from one or more of: 
     (a) a strain sensor mounted on the at least one hull of the vessel; 
     (b) a strain sensor mounted at the one or more fracturable regions; 
     (c) an engine revolution rate sensor operable to measure a rate of rotation of one or more engine arrangement of the vessel; 
     (d) a speed sensor operable to measure a speed of the vessel through water; 
     (e) an accelerometer mounted to the vessel, or to the extension thereof, for measuring acceleration and/or deceleration thereof; 
     (f) a turning rate sensor for measuring changes in angular orientation on the vessel; (g) a gear engagement sensor for measuring engagement of one or more drive gears of the vessel; and 
     (h) a sonar sensor for detecting a presence of one or more objects underneath, behind and/or in front of the vessel likely to present an impact hazard for the vessel when in operation. Any combination of these diverse sensors are susceptible to being employed depending on requirements. 
     Optionally, in the breakaway safety system, the control unit includes a data recorder for recording a sequence of the one or more input signals in a period prior to jettisoning the one or more propeller extensions from the hull. Use of such a data recorder is useful for determining whether or not the system has responded in an intended manner for avoiding damage to the at least one hull. Such information is relevant for insurance purposes for example. 
     Optionally, in the breakaway safety system, the fracturing device is operable to be disarmed when the vessel is in a stationary state in water, thereby preventing activation of the fracturing device when in the disarmed state. Such disarming of the piercing device is valuable for substantially preventing any risk of jettisoning one or more propeller extensions when the vessel is substantially stationary. 
     According to a second aspect of the invention, there is provided a method of providing a vessel with breakaway safety using a breakaway safety system, the vessel including 
     (a) at least one hull; 
     (b) one or more engine arrangements supported by the at least one hull; and 
     (c) one of more propeller extensions mounted to the at least one hull and coupled to receive motive power from the one or more engine arrangements in operation; 
     characterized in that the method includes steps of: 
     (d) mounting the one or more propeller extensions to the hull by one or more fracturable regions; 
     (e) arranging for one or more sensors mounted to the vessel to measure operating parameters of the vessel and to generate one or more corresponding input signals; 
     (f) arranging for a control unit to receive the one or more corresponding input signals, and to process the one or more input signals to generate at least one control output (Q, A); and 
     (g) using one or more fracturing devices to fracture the one or more fracturable regions for jettisoning associated one or more propeller extensions in an event that the control unit detects a potentially hazardous impact event and activates its at least one control output (Q, A) accordingly. 
     Optionally, the method includes steps of: 
     (h) arranging for the one or more fracturing devices to each include an energy storage element, a piercing element operable to fracture its associated fracturable region when impacting thereinto; and 
     (i) using the energy storage element when activated to apply a force to the piercing element to force it into the fracturable region to cause the fracturable region to fracture. 
     Optionally, when implementing the method, the energy storage element includes at least one of: an explosive charge, a mechanical spring, a volume of compressed gas. 
     Optionally, when implementing the method, the control unit is provided with the input signals from one or more of: 
     (a) a strain sensor mounted on the at least one hull of the vessel; 
     (b) a strain sensor mounted at the one or more fracturable regions; (c) an engine revolution rate sensor operable to measure a rate of rotation of one or more engine arrangements of the vessel; 
     (d) a speed sensor operable to measure a speed of the vessel through water; 
     (e) an accelerometer mounted to the vessel, or to the extension thereof, for measuring acceleration and/or deceleration thereof; (T) a turning rate sensor for measuring changes in angular orientation of the vessel or a portion thereof; (g) a gear engagement sensor for measuring engagement of one or more drive gears of the vessel; and
 
(h) a sonar sensor for detecting a presence of one or more objects underneath, behind and/or in front of the vessel likely to present an impact hazard for the vessel when in operation.
 
     Optionally, the method includes a step of: 
     (i) recording using a data recorder a sequence of the one or more input signals in a period prior to jettisoning the one or more propeller extensions from the at least one hull. 
     Optionally, the method includes a step of disarming the fracturing device when the vessel is in a stationary state in water, thereby preventing activation of the fracturing device when in the disarmed state. 
     According to a third aspect of the invention, there is provided a software product stored on data carrier, the software product being executable in computing hardware for implementing a method pursuant to the second aspect of the invention. 
     According to a fourth aspect of the invention, there is provided a method of protecting a hull of a vessel in an event of a potential impact, the vessel including one or more engine arrangements, and one of more propeller extensions coupled to the one or more engine arrangements for receiving motive power therefrom in operation, the method including steps of: 
     (a) detecting potential occurrence of an impact event which is susceptible to damaging the hull of the vessel; and 
     (b) jettisoning the one or more propeller extensions when potential occurrence of an impact event is detected. 
     According to a fifth aspect of the present invention, there is provided an aquatic vessel equipped with a breakaway safety system pursuant to the first aspect of the invention. 
     Features of the invention are susceptible to being combined in any combination without departing from the scope of the invention as defined by the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described, by way of example only, with reference to the following diagrams wherein: 
         FIG. 1  is a side view illustration of an aquatic vessel in water and in motion towards an impact with a submerged object; 
         FIG. 2  is an illustration of a breakaway safety system pursuant to the present invention, the system employing a pyrotechnic piercing device as a piercing energy storage element; 
         FIG. 3  is an illustration of a second alternative implementation of a piercing device for use in the system of  FIG. 2 , the device employing a linear spring as a piercing energy storage element; 
         FIG. 4  is an illustration of a third alternative implementation of a piercing device for use in the system of  FIG. 2 , the device employing a rotary hammer arrangement with a spring as a piercing energy storage element; 
         FIG. 5  is an illustration of a fourth alternative implementation of a piercing device for use in the system of  FIG. 2 , the device employing a pressurized gas cavity as a piercing energy storage element; 
         FIG. 6  is an illustration of a control unit coupled to associated sensors for implementing the system of  FIG. 2 : and 
         FIG. 7  is a schematic illustration of a detection threshold for use when triggering the system shown in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     In overview, the present invention is concerned with breakaway safety systems for use in aquatic vessels. The vessels each include one or more hulls wherein one or more of the hulls are equipped with one or more engine assemblies whose one or more propeller assemblies protrude in a region of water beneath the one or more hulls when the vessels are in operation. One or more propeller assemblies are coupled to their respective one or more hulls by corresponding one or more sacrificial breakable regions which is susceptible to being triggered from an intact state to a fractured state by control signals generated in expectation of an impact event, thereby preventing the one or more hulls being stressed as occurs with contemporary known safety breakaway systems. Moreover, the present invention is of benefit in that the one or more propeller assemblies are capable of not being jettisoned unnecessarily, thereby saving repair costs. 
     The present invention is distinguished in that pre-stored energy is released in a controlled manner and at an appropriate time and situation to fracture a mechanical connection between a propeller assembly and its associated engine assembly for jettisoning the propeller assembly. The pre-stored energy can be derived for an explosive pyrotechnics component, from a compressed gas chamber or any other type of energy storage element operable to generate a mechanical force of sufficient magnitude to fracture the mechanical connection. By employing such a breakaway system, the propeller assembly is susceptible to being jettisoned from its engine assembly and associated hull potentially within milliseconds within the engine assembly and its hull being stressed, thereby averting any damage from occurring thereto. 
     The pre-stored energy is susceptible to being released in response to a control signal output Q from a control unit changing from an inactive state to an active state. The control unit is coupled to one or more sensors which are operable to measure various parameters in their associated aquatic vessel, In an event that certain conditions arise is respect of the various parameters as detected by the control unit, the control unit is operable to switch its aforesaid control signal output from the inactive state to the active state. The control unit is beneficially implemented in analogue electronic circuits, digital electronic circuits and/or computing hardware operable to execute a software product recorded on a data carrier. The data carrier is optionally non-volatile solid state memory or a magnetic or optical data recording medium. 
     Referring to  FIG. 2 , there is shown an illustration of a safety breakaway system in the aquatic vessel  10 ; the safety breakaway system is indicated generally by  100 . The vessel  10  includes an engine transmission housing  110  into which is accommodated a transmission shaft  120  which is operable to rotate relative to the transmission housing  110  to deliver mechanical propulsion power in use. The transmission housing  110  is attached by way of fasteners  140 , for example threaded bolts, to a mounting plate  130  of the aforementioned extension  50 . The extension  50  beneficially includes a wing member as illustrated formed in a manner of a vane. Moreover, a transmission unit  150  is included at distal end of the extension  50  for coupling power delivered via the transmission shaft  120  to clockwise and anticlockwise rotations for driving a pair of mutually counter-rotating propellers  160 ,  165  implemented to pull the vessel  10  through the water  40  in a tractor manner in a direction denoted by an arrow  170 . 
     The transmission housing  110 , namely a part of a suspension structure of the vessel  10 , includes a rounded annular recess  180  defining a relative thin annular fracture region  190 . In close vicinity to the annular recess  180  are positioned one of more fracture initiating devices indicated generally by  200 . Each fracture initiating device  200  includes a pointed piercing element  210 , an energy storage element  220  spatially behind the piercing element  210 , and a detonator  230  adjacent to the energy storage element  220 . Optionally, the energy storage element  220  is an explosive pyrotechnics device operable when detonated to force, as denoted by an arrow  240 , the piercing element  210  into an end surface of the rounded annular recess  180  to cause the annular fracture region  190  to fracture. The transmission shaft  120  is disconnectably enmeshed into the transmission unit  150  so that the extension  50  is capable of being jettisoned in an event of potential impact with the submerged object  70 . 
     Fracturing the annular fracture region  190  in anticipation of an impact with the submerged object  70 , or alternatively at an early phase of impact onto the object  70 , enables stress being applied to the hull  20  to be reduced, thereby protecting the hull  20  which is potentially a high proportion of total value of the vessel  10 . 
     As shown in  FIG. 2 , the fracture initiating device  200  is coupled to a control unit  250  which, in turn, is connected to receive signals from one or more sensors denoted by  260 . The control unit  250  is operable to continuously monitor signals provided by the one or more sensors  260  and detonate or otherwise activate the one or more fracture initiating devices  200  in an event that the signals indicate that an impact is imminent or in a process of occurring. Operation of the control unit  250  will be elucidated in greater detail later. 
     The fracture initiating device  200  is susceptible to being implemented in several different ways. When it is implemented as a pyrotechnics device, a very considerable amount of energy is susceptible to being substantially immediately release from the energy storage element  220  to propel the pointed piercing element  210  to fracture the annular fracture region  190 . However, pyrotechnics devices, in a manner akin to air-bags in vehicles, are potentially susceptible to exploding spontaneously if their explosive charge deteriorates; however, when contemporary pyrotechnics materials are employed, a risk of such spontaneous detonation is relatively low. 
     For enhancing safety, the control unit  250  is operable to monitor whether or not one or more engine assemblies  30  of the vessel  10  are actively in operation, namely supplied with fuel with their internal parts rotating. In an event that the one or more engine assemblies  30  are inactive, the fracture initiating device  200  is beneficially is switched to its disarmed state, for example by way of a disarming signal A issued from the control unit  250 . Conversely, when the one or more engine assemblies  30  are activated, the fracture initiating device  200  is armed so as to be able to release its energy in an event that the control signal Q from the control unit  250  indicates that the propeller assembly  50  is to be jettisoned. 
     A first alternative implementation of the fracture initiating device  200  is illustrated in  FIG. 3 ; the alternative fracture initiating device is indicated generally by  300 . The fracture initiating device  300  is shown in its non-deployed state. Moreover, the fracture initiating device  300  includes a robust mechanical housing  310  including a compressed helical spring  320  as an energy storage device. The compressed spring  320  includes a first end thereof abutting onto an end face of the robust housing  310 , and a second end thereof abutting onto a rear face of hammer component  330 . This hammer component  330  includes a waist region into which a retaining pin  335  is engaged to prevent the hammer component  330  being ejected from the robust housing  310 . Moreover, the hammer component  330  includes an impact plate for impacting in operation onto a rear end of the pointed piercing element  210  when the fracture initiating device  300  is deployed. 
     The retaining pin  335  is coupled to an actuator  340 , for example an electro-magnetic solenoid actuator, which is energized by way of the signal Q when the device  300  is to be deployed. In operation, during deployment to protect the hull  20 , the control unit  250  energized the actuator  340  to cause the retaining pin  335  to be retracted laterally as denoted by an arrow  350  to enable the spring  320  to accelerate the hammer component  330  to impact onto the piercing element  200  to cause. In turn, the piercing element  200  to fracture the annular fracture region  190 . It will be appreciated that the fracture initiating devices  200 ,  300  employ linearly-acting energy storage arrangements for forcing the piercing element  210  to fracture the fracture region  190 . 
     A further alternative implementation of the fracture initiating device  200  is illustrated in  FIG. 4 ; the alternative fracture initiating device is indicated generally by  400 . The fracture initiating device  400  includes a hammer component  410  which is rotatably mounted at a pivot  420 . Moreover, the hammer component  410  is furnished with a spiral spring  430  which functions in operation as a mechanical energy storage component. The hammer component  410  includes a hammer surface adapted to impact upon the rear end of the pointed piercing component  210  when the fracture initiating device  400  is deployed in operation. The device  400  includes a retaining portion provided with an indented notch comprising an abrupt edge. 
     Furthermore, the hammer component  410  includes an L-shaped release member  460  also arranged to rotate substantially at a central portion thereof about a pivot  470  in operation. 
     When the device  400  is in its non-deployed state, a retaining edge  480  at a first remote end of the release member  460  is engaged into the aforementioned indented notch to prevent the hammer component  410  rotating in response to rotational force applied thereby by the spiral spring  430 . 
     When a force is applied to a second remote end of the release member  460  as illustrated, for example the force being provided from an electromagnetic actuator controlled via the output Q from the control unit  250 , the release member  460  is forced to rotate about its pivot  470  and thereby causes the retaining edge  480  to disengage with the indented notch. As a result, the spiral spring  430  rotationally accelerates the hammer component  410  to impact onto the pointed piercing element  210 . The piercing element  210  is, in turn, forced into the annular fracture region  190  causing the region  190  to fracture, thereby enabling the extension  50  to be safely jettisoned. 
     A yet further alternative implementation of the fracture initiating device  200  is illustrated in  FIG. 5 ; the alternative fracture initiating device is indicated generally by  500 . The device  500  includes a robust housing  510  having a cavity  520  therein filled with a gas at high pressure, for example in a range of 50 to 100 Bar. The robust housing  510  includes a valve  530 , for example a needle valve, included within a venting tube linking the cavity  520  to a piston chamber  550 ; the valve  530  is coupled to an actuator  540  which is operable to receive the signal Q and to control release of the valve  530 . When the device  500  is in its non-deployed state, the valve  530  is in a closed state to prevent loss of gas from the chamber  520 . Moreover, the piercing element  210  is provided with a piston member  560  provided with an annual flexible seal  570  for ensuring a gas-tight seal to inside walls of the of the piston chamber  550 . 
     In operation, when the control unit  250  detects that an impact event is imminent or commenced, the control unit  250  switches a state of its output Q from an inactive state to an active state to cause the actuator  540  to release the valve  530  to allow pressurized gas within the cavity  520  into the piston chamber  550  to propel the piercing element  210  into the fracture region  190  to jettison the extension  50  from the hull  20 . A separation is beneficially provided between a pointed tip of the piercing element  210  and an impact surface of the fracture region  190  so that the piercing element  210  is accelerated before it impacts, thereby providing greater fracturing force to the piercing element  210 . 
     The control unit  250  will now be described in greater detail with reference to  FIG. 6 . Beneficially, the control unit  250  is coupled to a data-bus of the vessel  10 , for example to a CAN data-bus; when such a CAN data-bus is provided in the vessel  10 , the control unit  250  is able to receive signal data which is conveyed via this data-bus. However, implementation of the present invention is not dependent upon the provision of such a data-bus within the vessel  10 . Beneficially, the control unit  250  includes a data recorder, for example in a manner of a “black box” data recorder, for enabling signal characteristics leading up to jettisoning of the extension  50  to be retrospectively analysed, for example for insurance purposes. 
     The one or more sensors  260  beneficially include one or more of: 
     (a) one or more strain gauges mounted at the fracture region  190 ; the one or more strain gauges are operable to generate signals indicative of this region  190  suddenly suffering high strain as a consequence of sudden stress being applied thereto; 
     (b) one or more accelerometers mounted onto the vessel  10 , for example onto the extension  50 , to measure sudden accelerations applied thereto, for example indicative of an impact event; 
     (c) one or more turning rate sensors, for example one or more solid state micromachined gyroscopes and/or small optical gyroscopes, mounted onto the vessel  10 , for example onto the extension  50 , for measuring sudden changes in angular orientation of the extension  50  or the hull  20  indicative of an impact event;
 
(d) an engine revolution rate (RPM) sensor for measuring a revolution rate of an engine arrangement  30 , for example for determining whether or not an engine arrangement  30  is revolving at a rate higher than a certain threshold rate;
 
(e) a sensor for detecting a sudden deceleration or acceleration of the hull  20 , the extension  50  or the vessel  10  in general being above a defined threshold, for example as determined by strain gauges mounted at one or more locations onto the hull  20 ; (T) a sensor for sensing a speed of the vessel  10  through water  40 ; for example for determining whether or not the vessel  10  has exceeded a threshold speed; and (g) a sonar sensing system for detecting submerged objects beneath or in water along a path in which the vessel  10  is travelling.
 
     The algorithm F is optionally operable to activate its output Q on a combination of parameters (a) to (f) being simultaneously satisfied. For example, the vessel  10  is potentially more likely to suffer damage at a relatively lower speed in a harbour when its extension  50  impacts onto a submerged structure in the harbour than at high speed when the running onto a sandbank when considerable flow of water accompanies motion of the vessel  10 . The breakaway safety system is also operable to protect one or more persons on board the vessel  10  which be susceptible to being thrown overboard in a situation that the vessel  10  is suddenly decelerated as a result of one or more of its extensions  50  impacting onto one or more submerged objects. 
     In  FIG. 6 , the control unit  250  includes a processor  600  coupled to a data memory  610  including one or more executable software products. The one or more software products are downloadable to the data memory  610  via a physical data carrier such as a plug-in read only memory (ROM) and/or via a signal coupled to the control unit  250 , wherein the signal is operable to function as a data carrier. Beneficially, one or more software products in the data-memory  610  are thereby susceptible to being updated. 
     The aforesaid one or more software products executed within the processor  600  are operable to implement an algorithm corresponding to a method of processing signals provided from n sensors denoted by S 1  to Sn constituting the one or more sensors  260 ; n is an integer of value unity or greater. Moreover, the aforementioned outputs Q, A are generated by the control unit as an output of executing the one or more software products upon the processor  600 . 
     A schematic illustrative graph is shown in  FIG. 7  to elucidate operation of the one or more software products. An abscissa axis  710  represents a speed of the vessel  10 , either forwards or reverse. Moreover, an ordinate axis  720  represents whether or not the fracture initiating device  200 , or alternative implementation thereof, is to be activated or not, namely a representation of the signal Q. A threshold  760  determines a state of the signal Q as described by Equations 1 and 2 (Eqs. 1 and 2):
 
 H=F ( S   1   , . . . , S   n )  Eq. 1
 
wherein
 
 Q= 1 when  H&gt;Th , and  Q= 0 when  H&lt;Th   Eq. 2
 
and wherein
 
F=an algorithm data processing function;
 
Th=a threshold determining activation of the piercing device; and
 
H=an Intermediate parameter.
 
     Optionally, the threshold Th is a function of a speed of the vessel  10  as indicated by  800  such that the extension  50  is more readily jettisoned when the vessel  10  is travelling at high speeds to prevent damage occurring to the hull  20 . As elucidated in the foregoing, the algorithm implemented in the processor  600  is operable to set the output signal A to a disarmed state, when relevant to the implementation of the piercing device  200  and its alternative implementations, when the vessel  10  is stationary, namely not having any of forward or reverse gears engaged in the vessel  10 . 
     The algorithm F is optionally operable to activate the output Q in an event that any one of several criteria are satisfied as follows: 
     (a) the system has passed its start-up checks in an event that the vessel  10  is stationary, namely without its one or more gears being engaged; if a fault is detected, a warning is sent to a driver of the vessel  10  indicative that an abnormality has arisen; the driver then has a choice whether to override the breakaway safety system and sail off, or to investigate a cause of potential malfunction; such malfunction can occur because of failure of one of the sensors  260 ; and
 
(b) the signals provided from the sensors S 1  to Sn indicate that a impact event is imminent or is commencing.
 
     In one example implementation of the breakaway safety system, the piercing device  200  is only activated provided that the engine arrangement  30  of the vessel  10  is running, the vessel  10  is engaged in gear for coupling propulsion to its one or more propellers, and the engine arrangement has an RPM rate exceeding a threshold, for example 1200 RPM. “RPM” is an abbreviation for revolutions per minute. 
     Optionally, the propeller extension  50  is provided with one or more features which enabled it to be located when jettisoned from the vessel  10  in operation. The one or more features include: (a) a sonar location module which is operable to transmit a sonar signal once the propeller extension  50  is jettisoned; and (b) a location buoy, for example implemented as a flexible inflatable gas-tight material which is deployed after the propeller extension has been jettisoned. 
     Expressions such as “has”, “is”, “include”, “comprise”, “consist of”, “incorporates” are to be construed to include additional components or items which are not specifically defined; namely, such terms are to be construed in a non-exclusive manner. Moreover, reference to the singular is also to be construed to also include the plural. Furthermore, numerals and other symbols included within parentheses in the accompanying claims are not to be construed to influence interpreted claim scope but merely assist in understanding the present invention when studying the claims. 
     Modifications to embodiments of the invention described in the foregoing are susceptible to being implemented without departing from the scope of the invention as defined by the appended claims.