|Número de publicación||WO2014186875 A1|
|Tipo de publicación||Solicitud|
|Número de solicitud||PCT/CA2014/000455|
|Fecha de publicación||27 Nov 2014|
|Fecha de presentación||23 May 2014|
|Fecha de prioridad||24 May 2013|
|Número de publicación||PCT/2014/455, PCT/CA/14/000455, PCT/CA/14/00455, PCT/CA/2014/000455, PCT/CA/2014/00455, PCT/CA14/000455, PCT/CA14/00455, PCT/CA14000455, PCT/CA1400455, PCT/CA2014/000455, PCT/CA2014/00455, PCT/CA2014000455, PCT/CA201400455, WO 2014/186875 A1, WO 2014186875 A1, WO 2014186875A1, WO-A1-2014186875, WO2014/186875A1, WO2014186875 A1, WO2014186875A1|
|Exportar cita||BiBTeX, EndNote, RefMan|
|Citas de patentes (4), Citada por (2), Clasificaciones (12), Eventos legales (4)|
|Enlaces externos: Patentscope, Espacenet|
TITLE OF THE INVENTION
AIR CAVITY CUSHION VESSEL
FIELD OF THE INVENTION
The present invention relates to a vessel, such as a barge or ship, having an air cushion, which can be used in wave conditions and trans ocean voyages. More particularly, the cushion has a plurality of air filled channels lining the bottom to form the air cushion upon which the vessel sits and thus reduces water resistance when the vessel is in motion.
BACKGROUND OF THE INVENTION
With the ever increasing world population and move towards a global economy, more and more consumer goods are being transported around the world. Transportation of bulk materials, including fluids (oil, liquid, gases), minerals, agricultural produce, ores, containers, heavy products or items of large volumetric dimensions, have historically been, and remain, most commonly and economically transported over very long distances by marine vessels of many different types. These vessels are typically powered by non-renewable fossil fuels, with the resulting pollutants being released into the atmosphere.
With the rapidly increasing cost of fuel oil, many ship and towboat owners are finding that the price of fuel is the single most expensive operating cost, which can be reduced by implementing this air cavity cushion invention in a new vessel or retro-fitting it to an existing one. Using this new technology the air retained within the air cavities can alternatively be utilized to carry a greater cargo deadweight at the same or increased speed, using the same or lesser amount of fuel. There are also environmental concerns associated with the effects of green house gases. Efforts have therefore been made to increase the fuel efficiency of vessels in order to reduce the consumption of non-renewable hydro-carbons and the resulting pollutants. Previous attempts have been made to utilize the minimal friction between water and air, as opposed to water and the bottom surface of a vessel which it is in contact with, in order to reduce the friction resistance and thus fuel burned in towing or propelling a vessel through the water. For example, U.S. Patent No. 1621625 teaches floating a barge or boat on a sheet of air in still water. The bottom of the vessel is formed with a plurality of longitudinal open bottom air channels formed between depending flanges in the form of angle bars rigidly secured to the bottom of the vessel. The channels are bordered at the front and rear by the bottom of the vessel. Air is pumped into the channels continuously from the front travelling to the rear where most of it is recirculated into the system. However, this system requires the constant pumping of air, which is inefficient. Furthermore, this system is not suitable for propeller driven vessels as the air escaping out the rear of the channels would result in significant propeller cavitation issues. The design includes one transverse depression of the vessel's bottom plating towards the forward and aft ends of the sheets of air, where they terminate just above the still waterline in each channel. Forward motion of any vessel, even in calm water, produces a cresting bow wave with a series of diminishing troughs and crests running along both sides to the aft end. These waves are reflected in some fashion on the surface of the water inside the air cushion cavity. As the internal cresting waves encounter the transverse depressions significant resistance forces will develop, which is counterproductive to making savings in bottom friction. In addition hydrostatic pressure in way of a trough of a wave, will be less than at the flat calm waterline therefore less than the internal air pressure. This pressure differential will allow the air cushion to expand and escape to atmosphere especially in way of the transverse depressions. Replacing this loss of air alone will require power to be used in order just to maintain the air cushion.
U.S. Patent No. 3,788,263 teaches an integrated barge tow for use on inland waterways only having a plurality of inter-connectable box barges, the box barges having recessed bottoms to capture an air bubble. The recessed hull of each box barge is formed by longitudinal skirts on each side of a center partitioning element and a transverse skirt at each end, the longitudinal and transverse skirts extending an identical distance below the box barge. While providing some reduced loss of stability through the addition of the center partitioning element and the transverse skirts, stability in both the transverse and longitudinal directions will be such that the deck cargo must have its centre of gravity, almost exactly on the fore and aft centre line and at mid-length of each box barge, if unworkable trim and heel for making inter-unit connections is to be avoided. Also unless the loaded weight of each unit is within a very small margin, each box barge will float at a different draft, exposing a significant depth of front, mid-unit and after transverse plane surfaces to the water flow, plus the unavoidable eddy currents which will be developed at the sides and bottoms in way of the gaps for the connectors. The added resistance caused by the foregoing reasons, could probably exceed any savings which are anticipated. Finally, there are no teachings of a favourable design for determining and adjusting the depth of the air bubble within the recesses of the box barges.
Accordingly, it is an object of an embodiment of the present invention to provide a vessel having an air cushion hull that is cost effective to operate and that does not require constant re-filling of the air cushion during use even under ocean going wave conditions. Other objects of the invention will be apparent from the description that follows. SUMMARY OF THE INVENTION
The invention consists of an air cushion system for a marine vessel. The air cushion vessel comprising a hull having a top, bow, stern, sides and bottom; a cavity defined in the bottom, the cavity having a top surface, front, rear and side walls and being open at the bottom. The vessel is equipped with an air system for delivering compressed air to the cavity and an air retrieval system for venting compressed air from said cavity.
The vessel is also equipped with a control system for monitoring the level of air within said cavity and maintaining it at a pre-set level.
In another aspect, the air cushion vessel further comprises a plurality of longitudinally extending keelsons being airtight to the cavity top and end walls and dividing said cavity into a plurality of air cavity channels, which are open to water at the bottom. The keelsons are preferably made of welded plate steel but the use of materials having different physical or chemical properties may be used in combination with, or in lieu of steel. Each of the keelsons can be fitted at intervals with flexible joints to prevent them from being exposed to a vessel's longitudinal bending stresses.
In a further aspect, each of the plurality of air cavity channels in the air cushion vessel has its own air source and vent system, both being separately monitored and adjusted by the control unit, in order to maintain the greatest depth of air in each separate cavity best suited for the sea conditions being experienced. Maintaining the air/water interface closer to its bottom locations in each cavity will bodily raise the vessel in the water thus increasing its freeboard and ability to carry more cargo and also reducing sideshell friction plus the direct frontal resistance of the bow.
In another aspect, the air cushion vessel further comprises a water jet turbine. The water jet turbine operates to charge a bank of batteries when the vessel moves through the water. Alternatively, the water jet turbine may be operated to provide an astern thrust to assist with braking by using the battery bank to run the generator and water jet turbine in the reverse direction. The foregoing was intended as a broad summary and of only some of the aspects of the invention and is not intended to define the limits or requirements of the invention. Other aspects of the invention will be appreciated by reference to the detailed description of the preferred embodiment and to the claims.
BRIEF DESCRIPTION OF THE SKETCHES
These and other features of the invention will become more apparent from the following description in which reference is made to the appended drawings and wherein:
Fig. 1 shows a schematic section side view showing a vessel equipped with the air cavity system of the present invention recessed into the bottom of a vessel. Fig. 2 shows a schematic plan view arrangement at the top of the air cavities shown in Fig. 1 including a compressed air supply system separately feeding each air cavity channel according to the invention.
Fig. 3 shows a schematic plan view at the top of the air cavity channels of Fig. 1 including a separate air venting system to each channel according to the invention.
Fig. 4A shows a schematic transverse section view of the vessel shown in Fig. 1 in a stablehorizontal position, with each cavity partially filled to the same depth with air. Fig. 4B shows a schematic transverse section view of the vessel shown in Fig. 1 with the same amount of air as in Fig 4A in a position heeled over to one side until the deck edge and the level draft waterline coincide.
Fig. 5A shows a schematic transverse section view of an alternative embodiment of an air cavity vessel in a stable horizontal position.
Fig. 5B shows a schematic transverse section view of the alternative embodiment of an air cavity vessel shown in Fig. 5A, with the vessel in a position heeled over to one side until the deck edge and the level draft waterline coincide.
Fig. 6 shows a schematic section side view of the bow of the vessel of Fig.1 showing a turbine system according to the invention.
Fig. 7 is a flow chart showing the interaction of the various systems of the preferred embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The preferred embodiment of an air cushion equipped vessel 100 is shown in the figures and described in more detail below. While the vessel shown is a barge, it is also contemplated that the air cushion system of the present invention could be used in other floating vessels such as articulated pusher tug/barge units, cargo ships, ferries, naval vessels, large motor powere^ yachts and other large, non-planning displacement vessels. The air cavity cushion can also be retro-fitted to the underside of an existing vessel. As shown in the figures, vessel 100 has a hull 1 with a bow 2, stern 3, deck 4, sides 5, and bottom 6. An air cavity cushion 7 is defined in the bottom 6 of the hull 1 by top surface 15, forward wall 10, after wall 11 and outboard port and starboard walls 8. Preferably, the air cavity 7 is sub-divided into a plurality of longitudinally extending air cavity channels 9 by keelsons 16 extending longitudinally the full length of cavity 7, from forward wall 10 to after wall 11, the height of each Keelson corresponding to the depth of the air cavity (ie. it extends from the top surface 15 to the bottom 6 of the vessel). The keelsons 16 are preferably welded to the top surface 15, forward wall 10, and after wall 11 of the cavity 7 to form an airtight barrier between adjacent air cavity channels 9. The air cavity channels 9 are open to the sea at the bottom such that when they are partly filled with air as described below, an air cushion is formed having an air/ water interface 17.
Each air cavity channel is supplied with its own air inlet 12 and vent outlet 22 which allows the depth of air in each separate air cavity channel 9 to be adjusted as necessary by a control unit 13 to maintain adequate depths of air 14 below the top surface of the cavity 1 . Air at atmospheric pressure is drawn in through air inlets located in a suitable location, to an air compressor 19. Compressed air from the air compressor 19 is supplied to an air receiver 18 by high pressure piping which in turn leads to the various air inlets 12 by supply pipes 23 and thus into the air cavity channels 9. The air inlets are preferably controlled by servo operated ball valves 30 or other suitable valves. The air outlets are preferably servo operated ball valves or equivalent, which are protected against water incursion by automatic float check valves 28.
Each air cavity channel is also equipped with an air pressure sensing gauge 29, which can be positioned in the vent pipe 25 close to its respective automatic float check valve 28, in order to protect the sensor from water damage and are preferably located above the deepest operational waterline 27, but could be connected to the top of each air cavity channel by a separate vent pipe, the automatic float check valve being located at an intermediate position. If water from an air cavity channel continuously fills a vent pipe, the float check valve will stay closed, thereby protecting the sensor from water damage and advising the control unit that one, or a plurality of channels, require to be replenished with air in order to regain the air water interface.
Alternative means of determining and monitoring the mean level of the respective air water interfaces 17 of the individual air cavity channels 9 may include methods such as surface float switches, electronic, laser, radar, sonic proximity devices or the like. The control unit 13 monitors information provided by the air pressure sensors to determine the depth of air in the individual air cavity channels and adjusts the air input and venting systems to ensure that the desired level of air remains in place in the individual air cavity channels. In plan view as shown in Figs. 2 and 3 air cavity channels are generally rectangular in shape, however it is contemplated that any poly or curved sided shape can be used as may be determined by the shape of the vessel. The control unit 13 will normally be set to operate automatically within pre-specified parameters, but may also be operated manually or remotely should it be necessary.
The control unit 13 is preferably operated by DC power and will be located in a suitable location above the deepest operating waterline to continuously monitor air pressure in each channel in order to determine the depth of the air water interface and compare them to pre-set parameters, adjusting them automatically to suit changing wave conditions. At any time, manual or remote control can override the automatic functions of the control unit. For a towed vessel there is a direct two-way wireless link between a tow boat and the control unit aboard the towed vessel 100 to relay data and allow all servo valves to be operated remotely, if required. When the air pressure monitoring section of the control unit 13 registers an average reading in an individual air cavity channel 9, or plurality of air cavity channels 9, that is above or below the pre-set pressure over a selected period of time, it sends a signal to the appropriate valve (or valves) to admit compressed air, or vent some cavity air until the pressures are returned to the desired working levels. The control unit 13 also continuously senses the air pressure in the air receiver 18, starting and stopping the air compressor 19 when pressures reach low or high levels. In most vessels a low pressure air system will more efficiently serve each cavity without using an air receiver. The control unit preferably includes an electronic inclinometer that is used to record angles of heel and fore & aft pitch against time. The data produced by the inclinometer will be analyzed automatically and used to ensure that the air/water interface in individual air cavity channels remain properly adjusted at all times, but particularly in severe weather conditions. Should some anomaly in the behaviour of the vessel be detected, a warning will be automatically transmitted by wireless means from a barge to its towboat. If corrective measures are not taken or are unsuccessful in rectifying the barge's response, the air in the cavity channels can be vented using large diameter emergency servo valves 44, piping 45 and associated manifolds 46 and 47, as shown in Fig. 3.
A barge's resistance can be most readily measured at the towline connections on the barge, from where data is continuously monitored by the control unit 13 against speed. Any elevated change in resistance compared to pre-set speed parameters will be automatically analyzed over a period of time, and sent by safe radio link to the towboat. Decisions regarding changing the speed of tow being made at the tow boat master's discretion. In the case of a barge, a duplicate continuous readout of all barge condition data will be transmitted to the towboat which will also have override control on all functions.
Fig. 7 may be referred to for the control unit's 13 general interconnections with other operational equipment.
SPACING OF LONGITUDINAL KEELSONS IN CAVITY FOR MINIMIZING
During a complete roll period of a vessel the draft of the water at its centerline will only vary marginally, but the depth of water at a deck edge will vary significantly, with a consequent variation in the bottom water pressure plus or minus that at the centerline. This variable hydrostatic pressure is balanced by an equal air pressure in each separate air cavity channel. The transverse spacing of the keelsons should be varied to accommodate different ratios of expansion of air in the outer 20 and inner 21 channels in order to retain as much air as possible when rolling and reduce demand on the air compressor to replenish air.
As shown in Fig. 4B, when one side of a vessel rises, water pressures fall in the high outer channel 41 to a greater amount than in the high inboard channel 42, thereby causing air to expand within the outer channel more than in the inboard channel. Air from the high outer channel will thus tend to "bubble out" at a lower angle of heel than the high inner channel, assuming that they are of an equal breadth, depth and volume (Boyle's Law). By making the inboard channels of larger width than the outboard channels, the expansion of the air in both channels will be somewhat self-regulating and greater angles of heel can be accommodated before significant air loss will occur. Air will not escape from the low side of a vessel. In order to maintain an effective air cushion with minimum air loss from each channel during heavy rolling of a vessel, the width of the outboard channels 20 should therefore be made say about 60% of that of the inboard channels 21. The reason for this is because of the cyclic changing of the port and starboard drafts as the vessel rolls from side to side, with accompanying changes in hydrostatic and air pressure from above to below the median pressure at the air /water interface of each part of the air cavity. It may be noted that initial preset air water interfaces of port and starboard air cavity channels, will under normal conditions be identical as the vessel rolls through the upright position, changing the water pressure from the port to starboard sides. When the air water interface is properly located at about 70% of the depth of a channel below its top surface the air in the channels will not migrate to adjoining channels over the keelsons or escape at the bottom of the high side wall 8 of the outboard air cavity, unless very high angles of roll are experienced. None of the interfaces will be allowed to cyclically reduce so significantly in height that the water will come into contact with the top of a channel, which would have an adverse effect upon the reduction in frictional resistance, nor reduce the up-right freeboard below a pre-set level.
Considering the case of a 400' x 100' x 30' Air Cavity Barge with freeboard = 5.0' and corresponding Draft = 25.0 rolling in very heavy weather conditions, the following approximations can be made while referring to Figures 4 A and 4B. When a uniform 2.5 Ft. depth of air is introduced into all cavities the barge will rise bodily in the water by about 1.4 Ft. which reduces the draft to 23.6 Ft. with the average pressure at the air 7 water interface = 11.8 PSI Approx. See Fig. 4 A.
With a barge now heeled over to one side by about 7.0°, where the deck edge and waterline coincide (See Fig. 4B), the pressures on the high side of the Barge decrease allowing the air in the high outer 41 and high inboard 42 channels to expand, possibly allowing some outer channel air to escape to the atmosphere at location 26. Conversely, the air in the channels on the low side becomes more compressed decreasing the volume of air. The combined effect of expansion and compression of the air in individual air cavity channels will not normally effect the mean draft of the barge significantly once the air I water interfaces 17 of the respective air cavity channels 9 stabilise, as the roll back through the upright condition to the other side will reverse the pressures, equalizing any air lost on the first oscillation of the Barge and maintaining its mean up-right condition.
After the barge has completed a number of rolls to about 7.0° the average heeled air/water interface pressures will equalize approximately as follows:
In order to achieve the most efficient design, the actual depth and width of the air cavity channels for each vessel should be designed with due consideration being given to the loading and weather conditions to be expected in the vessel's area of operation and seasons, freeboard being adjusted accordingly. The main design features are: the number of air cavity channels, 3 being the normal minimum. Outer channels will normally be of a smaller width than the inboard ones, depth of channels will vary with the size of vessel and service conditions but need not be uniform in depth as shown in Figs. 4A and 4B. An alternative embodiment is shown in Fig. 5A & 5B, wherein the depth of the air cavity channels increases (by angling its top surface 55) from the longitudinal centerline 43 towards the vessel's sides. This alternative design will allow more air to be retained in the outboard channels and permit the vessel to heel to an even higher angle without losing significant amounts of air. Varying the relative width between the outboard and inboard channels (or designing additional channels) will extend the air endurance of the inboard channels significantly.
Both the forward wall 10 and after wall 1 1 are hydrodynamically designed to efficiently direct the flow of water into and out of each channel. These are important details which will change somewhat with any new design of the bow and the type of the vessel. Alternative shapes, including smooth sweeping curves directly from the top surface of the cavity to the bottom hull at each end, should work well for most weather conditions. In all but flat calm conditions the air / water channel interfaces will be effected by variations in bottom water pressure across the breadth of the cavity, caused by regular waves of varying heights and angles off the bow, angles of roll or pitch and bodily heave in the vertical direction. All of the above can lead to a slightly different random wave system within each individual air cavity channel but with suitable air pressures, wave cresting against the cavity tops should not occur.
In addition to and built upon the random wave system in each channel is the ever present bow wave effect, which can be observed on any moving vessel. This produces a more or less consistent series of waves running the length of a vessel, with diminution towards the aft end. The bow wave will be the most regular and influential factor in determining the general wave profiles especially in each outer air cavity channel, and can be altered by various methods in order that the air/water interface does not crest at the aft cavity wall, where it could cause an unnecessary increase in resistance.
Means of changing the position and height of waves in the air cavity channels include: a) Modifying the speed of the vessel or heading into waves;
b) Modifying the trim by altering water ballast in an on board water ballast system from Aft to Forward (or vice versa);
c) Changing the depth of the mean air / water interface, as needed in individual air channels.
To help in making a decision on the above, local wave height monitoring devices may be fitted in the location of the after wall or the variations in towline tension, which is continually relayed to the control unit 13 may be used. If the cresting water cannot be rectified by automatically modifying the height of the mean air water interface, the vessel's control station, or tow boat, will be automatically advised that the air cushion is not being as efficiently used as possible for optimum fuel consumption.
PITCHING OR SLAMMING IN HEAVY SEAS
Under these conditions the bottom forward end of a vessel experiences heavy shock loading as it progresses through heavy waves. All sea-going vessels of any size therefore have special reinforcement made to the bottom forward end, in order to absorb the deceleration forces generated when the forward end slams into the trough of a wave. The additional progressive compression of the air at the forward end of each channel will absorb much of this loading by immediately distributing the increased air pressure equally throughout each channel, thus acting as a shock absorber and easing the pitching motion of the vessel. INDEPENDENT POWER SUPPLY FOR BARGES
In the case of a towed barge, the power requirements for supplying compressed air to the cavities and maintaining the air/water interface at a desired level is preferably provided by a water jet turbine generator system 31 installed below the light waterline at the bow, as best shown in Fig. 6. In this location the system can utilize the height variation between the bow wave and following trough (with a consequent water pressure differential) in addition to raising the water funneling arrangements at the forward end. The water jet turbine generator system 31 preferably comprises a conduit 32 travelling through the hull and having an inlet opening 33 and an outlet opening 37. The diameter of the body of the conduit 32 is smaller than the diameter of the inlet opening 33, the inlet opening acting to funnel water into the conduit with a resulting increase in speed as the volume decreases. The inlet opening 33 is located above the outlet opening 37, such that the water pressure at the inlet is less than at the outlet when the barge is stationary. An impeller 34 is positioned within the conduit and is connected via a rotating shaft with flywheel 35 to a belt drive 38 which in turn drives a generator 39. A watertight gland 36 is fitted at the shaft penetration of the conduit. As the water travels through the conduit 32, it drives the impeller 34, which in turn drives the generator 39, by way of the belt drive 38. When a barge is being towed at its design speed the bow wave can be greater than 10 Ft. above the following trough, with a pressure differential of approximately 5 PSI. The outlet opening 37 from the conduit 32 is elongated in the fore and aft direction, and preferably has a larger exit area than that of the inlet opening and is located in the low pressure zone, where it can utilize the bow wave hydrostatic pressure differential of say 5 PSI plus the increased water exit speed over that of the barge, to increase the turbine generative power. The flywheel in the drive train is ised to steady the fluctuations of the speed of the impeller, which will be subjected to very significant rapid changes in energy levels when a barge ploughs head-on into large irregular waves, thus steadying the RPM in the system and saving on wear and tear of all moving parts. Maintenance or repairs can be done on the turbine set, without dry-docking, by trimming the barge by the stern until it is clear of the waterline. The water jet turbine generator system fitted into the bow of a vessel uses the towed speed to generate and store electrical power in a battery bank 40. DC current from the generator system will run all components, maintaining the air channels during a towed voyage, thus making a barge self-sufficient for power with an adequate reserve for operating on board electrical equipment, at sea or while awaiting discharge alongside a dock. In an emergency, or while docking, the water jet turbine can be run in reverse or ahead using the electrical generator as a propulsion motor which will provide an independent source of forward or astern power. Any other type of mechanical device which can convert the speed of passing water into electrical power could alternatively be fitted at the bow or stern.
The conditions of the battery bank 40 will be monitored when under tow and the water jet turbine generator system will engage the clutch to the generator to top off the battery charge when necessary. When the clutch is not engaged, the impeller rotates freely in response to the water travelling through the conduit 32.
A small diesel powered air compressor / DC generator can be installed as a backup independent source of power, or as an alternative to the water jet turbine generator unit. All other systems would remain basically as described, but the reverse thrust option would not apply in those vessels that are not equipped with the water jet turbine generator unit. The intermittent use of the diesel compressor / generator which would be to top off the battery bank and the air receiver will have negligible effect on the total fuel consumption.
USE OF AIR IN CHANNELS WHEN DISCHARGING CARGO
The air in the channels is designed to be a part of an auxiliary electrical system which can generate power when necessary; for example, in harbour where shore power is unavailable, or when there is insufficient water flow to operate the main water turbine and power is required for barge operations.
A barge can also preferably be equipped with an air turbine 24 generator unit which can use the air within the air cushion and that remaining in the high pressure air receiver and piping to generate auxiliary D.C. Power when discharging cargo at a dock. Air vented from the air cushion and the air receiver travels through the air turbine to produce electricity that is stored in the battery bank for use as necessary.
Using the harbour scenario as an example, when the air cavity barge arrives in a port and starts to discharge cargo, the air pressure in the channels will reduce in direct proportion to the reduction in draft and thus increase the volume of air, which would normally bubble out from under the vessel, with a loss of Potential Energy.
This design shows how this potential energy and that of the remaining compressed air in the piping systems, can be used independently of any other power sources to generate DC Power by controlled venting of each channel through air pipes 25 to an air turbine 24 coupled to a DC power generator, which feeds the battery bank 40. The power stored in the high efficiency batteries can be utilized for other barge services (lights, refrigerated containers etc.) or partially restoring the air cushion by powering the air compressor, prior to the newly re-loaded barge leaving for its next port of call.
EMERGENCY BRAKING FOR A BARGE
Slowing or stopping a barge which is underway and thus has a vast amount of kinetic energy, is an on-going concern in crowded sea lanes, harbors, etc., where a single towboat cannot quickly provide an effective means of stopping the barge's forward progress. The problem is addressed in this invention, by allowing the tow master to remotely and quickly evacuate all of the channel air very quickly and in a controlled manner. As the air in the cavities is vented the draft increases, immersing more of the side shell plating, skegs, keelsons, bow, stern and also exposing the top of the Cavities to the passing water. The foregoing components will quickly combine to form a substantial additional resistance, especially at high towing speeds, which will slow the barge's forward motion. This resistance can be further increased if the water jet turbine generator unit is run in reverse, (using power from the battery bank) to reverse the water flow through the impeller to produce an astern thrust. This astern thrust option would also be of assistance when docking a barge even with the help of a docking tug. Towboat controlled emergency air evacuation equipment for the air cushion consists of fitting one fairly large servo valve 44 on the top of each individual cavity channel 9, as shown in Fig. 3. From each pair of Port and Starboard outboard and inboard channels, large diameter air pipes 45 are run to respective outboard 46 and inboard 47 larger diameter air manifolds. The manifolds automatically ensure that the air from each pair of port and starboard channels is evacuated evenly, thus avoiding any tendency for the barge to heel. Hydrostatic water pressure in the cavities will force the air through the piping system to the atmosphere until the water levels in the pipes equals that of the mean draft or the servo valves are closed. The system may be equipped with air boost fans 48 which increase the rate at which air will be exhausted to the atmosphere, reducing the time taken to evacuate the cavity. During emergency braking the high pressure air supply to all channels is automatically shut off. After the emergency situation has been dealt with the servo valves may be opened and air pipes and manifolds automatically cleared of water and the air supply to the channels resumed.
STABILITY OF MULTI-CHANNEL AIR CAVITY VESSELS
Any floating vessel which contains liquids within an enclosed space is subjected to a loss of stability unless the spaces are completely full. This is called a free surface effect (FSE) which occurs in even minor rolling conditions when a liquid moves between the Port and Starboard sides of its enclosure, rapidly building up and shifting its depth and weight from one side to another with the same frequency as the vessel's period of roll. This overturning moment will alternate in the direction of the roll to the lowest side of the vessel, detracting rrom a vessel's stability and ability to regain its upright position. As several tanks or spaces in a vessel usually have a free surface, the total of all tanks with a free surface must be taken into account in determining the total FSE overturning moment and deducting it from the buoyancy righting moment, which is a function of the GMt (metacentric height) in feet or meters. This measure of static stability must be positive in all specified heeling conditions in order to avoid capsizing.
With the air cavity system the bottoms of all air channels are completely open to seawater, therefore with no obstructions to the free flow of water entering or leaving as the vessel rolls in a seaway. Consequently as build-up and retention of water at the low side of a channel during a period of roll cannot occur, neither can an overturning moment be developed. Naval architectural theory also clearly defines that a free surface effect only applies when a liquid is contained within an enclosed space. The foregoing refutes prior incorrect comments in some published articles regarding the problems of free surface effects of air cushion vessels in general. This said it must not be assumed that all air channel/cavity vessel will be stable. As in all floating vessels the GMt of an air cavity vessel must be positive when the vessel is upright and remain positive through a specific range of heel, with a free surface effect being made only for the liquids contained within separate tanks on board the vessel.
Although the deep keelsons do not contribute directly towards the stability of a vessel they do act as very large bilge keels in sea-keeping by slowing a vessel's response and reducing the angles of roll in a heavy seaway.
USE OF FLEXIBLE JOINTS IN KEELSONS OF VESSELS OVER ABOUT
270 FT. IN LENGTH
Any sea going vessel upwards of about 270 ft. in length is subjected to significant longitudinal wave bending moments, caused by the passage of long waves along its length. The highest stress levels are experienced at the deck and bottom structure when sailing directly into waves of the same length as that of the vessel. For example, when the troughs of a wave are at the forward and aft ends and the wave crest is amidships, both the bow and stern experience a loss of buoyancy, while the mid-body has an increased buoyancy. This is known as a hogging condition and drooping of the ends relative to amidships, induces a hogging wave tensile bending stress at the main deck level, as an opposite hogging compressive stress is simultaneously experienced by the bottom structure. However, with passage of the crest of the wave to the aft and forward ends and its trough amidships, the resulting reduction of buoyancy amidships causes sagging of the vessel amidships making the deck to go into compression and the bottom structure into tension. The frequency of this reversal of stress from tensile to compressive occurs a number of times per minute depending upon the relative speeds and directions of the waves to the vessel and is taken into consideration when designing the longitudinal strength of the vessel.
If the Keelsons are continuous over the length of the cavities, as shown in Fig. 1, they will be an integral part of the vessel and contribute to its longitudinal strength. Keelsons being at the extreme bottom fiber, will therefore be required to withstand the full fluctuating bottom stress levels. While this does not produce insurmountable structural problems, it is more practical and economical to fit the Keelsons in a number of separate 40 to 60 ft. lengths, with full height short intermediate flexible airtight and watertight joints between each section of Keelson, in order to completely exclude the Keelsons from exposure to the main longitudinal bending stresses. These flexible joints have no continuity of structural steel between adjacent sections of Keelson and use flexible materials such as neoprene sheathing with suitable adhesives, sealants, and airtight perimeter compression bars, bolts with oversize holes at the ends and top to make the joint airtight and slightly flexible. The joint need not, however, be airtight over the bottom few inches and the bottom plates of each adjacent section of Keelsons may be extended to within a small distance of each other, to reduce local turbulence in the water. The spaces left between the longitudinal side plates of adjacent Keelson sections are closed by removable bolted flush plates which also do not transfer longitudinal forces, but protect against damage to the joints and prevent local water turbulence. Various other means of making an effective air tight flexible joint could include inflatable or buoyant devices, which seal against the top, ends and sides of adjacent Keelsons. Using alternative materials with suitable properties of strength and flexibility could also be utilized in the design of the "fiexi-joint", which must be able to withstand rolling and wave forces. Means are arranged to permit inspection of the sealing arrangements at each dry-docking and the replacement or repair of parts when required. RETROFITTING AN AIR C AV^Y SYSTEM TO THE UNDERSIDE OF AN
This is a simple job which can be done in dry-dock or, in the case of a barge, by over turning it to float upside down until the bottom air cushion with air cavities formed with hydrodynamically shaped ends and keelsons have been welded in place, after which it can be righted. Apart from improving the hull efficiency of vessels, the air retained within the cavities will also increase the cargo deadweight capacity very significantly.
ALTERNATIVE USES FOR BOTTOM CAVITIES IN OFF SHORE
Any large barge built or retro-fitted with an air cavity system could readily be used to move a sunken vessel or a heavy weight without using tidal effects or additional buoyancy, providing the load is adequately spread along its length. Repeated venting then refilling of the air cavities, while shortening the length of rigging after progressively moving into shallower water, would significantly reduce removal or recovery costs of diving crews etc.
CONCEPT AND BENEFITS
This concept has been developed to allow an air cavity cushion vessel to operate as safely but more economically in all ocean conditions from flat calm to heavy weather, than current vessels. Under extreme weather conditions the air in outboard cavities can be allowed to decay with air being added to the center channels, as/or if necessary, until sea conditions abate and the sir cavity/cushion is fully re-established by the addition of make-up air. The air cavity system can be used in various ways which are best suited for any particular service. For example, in the case of a 400ft long barge, filling the cavity channels to about 60% of their depth with air would bodily raise the vessel in the water by about 48 inches. This additional freeboard could be used in several or a combination of ways as circumstances change. a) The barge could load about 3,000 to 4,000 tonnes of additional cargo, at its normal freeboard, but with an increased speed.
b) With the same additional cargo and at the vessel's original design speed, fuel consumption of the towboat would be reduced significantly, c) Without additional cargo the vessel's design speed could be increased by several knots providing the barge and towboat were suitable for the higher speed.
d) Any combination of the above options and benefits can be selected at any time to suit service and conditions,
e) These options are also available when the air cavity system is retro-fitted to the bottom of an existing vessel. It will be appreciated by those skilled in the art that the foregoing preferred and alternative embodiments have been described in some detail but that certain modifications may be practiced without departing from the principles of the invention.
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|CN105235676A *||24 Sep 2015||13 Ene 2016||哈尔滨工程大学||Hovercraft multi-control surface coordination control method based on control distribution|
|CN105235676B *||24 Sep 2015||4 Ago 2017||哈尔滨工程大学||基于控制分配气垫船多操纵面协调控制方法|
|Clasificación internacional||B60V3/06, B63B43/12, B63B39/00, B63B1/38|
|Clasificación cooperativa||Y02T70/122, Y02T70/70, B63J2003/046, B63J2003/002, B63B35/28, B60V3/06, B60V1/046, B63B1/38|
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