CA1120790A - Retractable boom assembly in apparatus for towing an underwater body - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A boom system is provided for a hoist and retractable boom assembly for towing a towed body. The boom sub-assembly includes an inner boom and an outer boom. The outer boom is connected to the inner boom by one or more hydraulic cylinders. By introducing fluid into either the head or rod ends of these cylinders, the outer boom is made to telescope outwardly from the inner boom for normal towing, or to collapse into the inner boom, thereby creating a compact stowed combina-tion of boom and towed body. In addition, two shock absorbing/motion attenuating systems are used, which are capable of being used together to provide passive bobbing motion of the boom to minimize variations in the tension of the tow line.

Description

'7~1) ~~ This invention re]ates to systems for l~unching~ recoyering and towing an ~nde~ater towed body, and particularly to a towing system wherein an unden~ater body is towed behind a vessel. In particular, this invention relates to a novel boom system for a hoist and retractable boom system which also includes a combination-type shock absorbing system for the tow line.
The unden~ater towed body with which the present invention is used is an under~ater SONAR ~abbreviated from "Sound Navigation and Ranging") which is finding ever-increasing use in the fields of naviga-tion, mapping, depth finding, fish finding, for detection of wrecks andin a military use, in the detection of enemy vessels. The system with which the present invention is used is a variable depth system, wherein an underwater sound transducer or array is mounted in a body towed from the vessel.
In a variable depth sonar, particularly as used in military applications, an array (usually cylindrical) of underwater sound trans-ducers is housed within a streamlined body which is towed from the sur-face ship via a faired cable. This cable has an internal core of con-ductors for transmitting signals to and from the ship from and to the array, and outer layers of armour to withstand towing tensions. Mounted on the ship is means for mechanically launching and retrieving the body, and for shortening and lengthening the amount of cable paid out.
In the towing system as above described, it is desirable to provide a system whereby the towed body may be readily launched and retrieved and handled during the towing operation, which during such towing minimizes damage to the towing cable and object being towed~ It is also desirable to provide a shock absorbing system which would minimi~e variations of tension in the tow line interconnecting two spaced-apart masses floating in a body of water, for example, a submerged sonar body towed by a moving ship.

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The ha~ard involved in to~ing any t~evice of substantial mass and planar area from a ship at sea is that of varying ca~le tensions due to out-of-phase undulations and speeds between the towing vessel and the towed mass. In the extreme, though not uncommon case, the towing cable is prone to falling slack then being followed by a snapping-to-taut con-dition. The transient cable load, at the instant the cable becomes taut, is high by several magnitudes when compared with the nominal towing load.
Cable failures may result from such a condition.
When two interconnected masses are horizontally separated one from the other, e.g., a tug pulling out a ship, spring can be put into the tow line by the expedient of paying out a great deal of tow line, which, for example, may be a faired cable. The weight of the faired tow line curves the span into a catenary curve and this, together with an acceptable strain within the cable, provides such a spring. In towing submerged massive bodies, for example, a sonar towed body, the problem of absorbing shock loads becomes much more difficult. With a submerged sonar body, the faired tow line has a tendency to be relatively straight and thus variable loads cause a corresponding variable strain in the tow line. In towing a submerged sonar body, from a hydrodynamic viewpoint, it is desirable to have low drag forces on the towing cable, and this may at least be partially achieved by the use of fairing elements on the cable. The resultant of low drag characteristics and towing a submerged sonar body is that the faired towing cable extends more directly along a straight line than otherwise. In a towing system of the latter type, it is difficult and often impossible to obtainsufficient internal spring within the faired cable itself to damp out transient loads. This is particularly so at slow ship speeds (in which case the faired cable more closely approaches a vertical attitude) i.e., the slower the towing speed the lesser the internal spring and thus the more critical the problem.
Transient loads in such a system result from the undulations of the , . :

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In the realm of towed sonar technology, the launch operation comprises lifting the sonar body from the ship's deck, swinging it over the stern until it is largely immersed in the water, then releasing it from the hoist mechanism to stream aft below the water surface. The recovery operation comprises the reeling in of the towed sonar body until it is captured in the hoist saddle, then lifting it aboard by operating the hoist.
It is usually a simple matter to tow a body in calm sea states.
Real difficulties occur where towing is attempted at high sea states. At high sea states, the stern is no longer a stable platform, but moves up and down under the influence of the sea on the vessel. This super-imposes variable loads on the tow cable in addition to the normal steady-state touing load, and under severe conditions the cable may be momen-tarily completely unloaded. This is extremely dangerous, as momentary cable unloading is always immediately followed by high, largely indeterminate snap loads which can cause cable breakage and loss of the towed body.
Another effect of high sea states with concomitant variable cable loads is a more or less cyclic digression of the towed body from its mean steady 'flight' path. This beheaviour is objec~ionable, if extreme, because it becomes difficult if not impossible then to deter-mine accurate ranges, bearing and depth of the target. These effects are countered by providing a means to compensate for the motion of the vessel by allowing some of the tow cable to pay out while the stern of the vessel is rising, and by causing some of ît to reel in while the stern is falling.
The methods by ~ ich this is done may be active, passive or a combination - . - . . . .

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of the two, and will be referred to i~ere as "motion attenuating/shock absorbing systems". A passive system is a simpler system, and uses stored energy in the form of a spring or springs. These may be mechani-cal, in the form of a gas or a combination of different types of springs.
One suggestion is proposed in ~nited States Patent No. 3,604,387 issued September 4, 1971 to N.E. ~lale, which provides a cable tensioning device which consists of another sheave carried on a pivotable arm which is moved towards and away from the winch by a piston and cylinder connected to an accumulator which maintains constant pressure on the arm and thereby moves it in response to the increase and decrease in the tension of the cable when the acoustic body is towed. This suggestion suffers tbe deficiency that it requires careful selection of various attachment points in the system to maintain the torque about the fulcrum constant.
Boom bobbing is one type of shock absorption/motion attenuation which was originally conceived only as a shock absorber. The original concept of boom bobbing is described and illustrated extensively in Canadian Patent No. 904,208 issued July 4, 1972 to F.W.W. Pfeiffer. This used a boo~
pivoting in a vertical plane; and also hydraulic cylinders attached at their outer ends to the booms, and at trunnions on the cylinder barrels to the for-ward end of a base. The base in turn is attached to the ship. A deflec-tion sheave was an essential part of the boom bobbing system to ensure cable excursions into and out of the water during the bobbing process with a minimum amount of rotation of towing sheave.
In Canadian Patent No. 879,530 issued August 31, 1971 to R.L.I. Fjarlie et al this boom bobbing concept is taken a step further in that during launch and recovery of the body, the gas-oil system is isolated from the cylinders and the cylinders are instead powered with high pressure hydraulic fluid to drive the boom from the extreme inboard stowed position to a launch position near the waterline, or vice versa. Thus, whereas Canadian Patent No. 904,208 only described the boom and cylinders in terms v oE their being used as part of a shock absorbing system over a restricted angle of boom rotation. Canaclian Patent No. 879,520 visualizes them as be;ng used for this purpose and for launch and recovery, during which time the angle of boom rotation is large from the inboard (stowed) to the out-board (launch) position.
Both patents above suffer from the drawback that the hydraulic cylinders are, oE necessity, used in a position or attitude where the mechanical advantage is very poor, and the system is highly non-linear.
Canadian Patent No. 1,010,308 issued May 17, 1977 to A.F.
Kemeny provides a boom bobbing system in which the hydraulic cylinders were replaced by a rotary actuator attached to the inboard pivot point of the boom, and imparting power to the boom for launch and recovery by pure torque at the pivot point. A separate boom bobbing system was used, consisting of the linear actuators (cylinders) with head ends pivotally secured to the forward end of the winch frame; a freely rotatable sheave means mounted at the aft end of the winch frame; torque arms secured to the boom member at the pivotal securement of the boom; and cables connected at one end to the piston rods, entraining the sheaves and secured at the other end to the torque arms.
It was also found possible to obtain sufficient cable excursion for shock absorbing without using the deflection roller in Canadian Patent No. 904,208.
Thus, it will be noted that boom bobbing, and launch and recovery take place with the boom rotating only in a vertical plane. More-over, all shock absorption/motion attenuation is of the boom bobbing type.
One system for launching and recovering the towed body without resorting to mechanical interlocking between the body and a member engageable with the body during launching and recovering which has been provided in the past is described in Canadian Patent No. 1,005,702 issued February 22, 1977 to A.F. Kemeny for "~Ieans for Launching, - . .

Towing and Recovering an Oceanographic Towed Body in a Seaway". In that patent, a towing system is provided including a boom mem~er pivotally securable to a towing vehicle, and means for resi]iently applying to the boom about the pivotal connection thereof to the vehicle commensurate with, and in response to changes in, a load applied to and/or the moving moment of, the boom. This system has been found to be useful for towing a body in calm sea states and in certain high sea states, and where there is no space limitations on board the ship to make the stowing of the towed body difficult.
One of the most sought after characteristics in variable depth sonar as used in military applications for detecting enemy vessels is long range. Long range necessitates the use of lower frequency trans-ducers, typically below 10 Kilohertz. Lower frequency transducer arrays are invariably large, necessitating the use of larger towed bodies, and deck equipment to launch, tow and recover same. The difficulty arises when attempts are made to fit this equipment into the restricted stern spaces of the smaller naval frigates and patrol vessels, and this diffi-culty is aggravated by the tendency in recent designs of such vessels to place a helicopter landing deck or pad above the stern spaces. For ~0 structural and other reasons, it is usually not permissible to pierce this landing deck or pad to gain working clearances. This means~ that if one uses a means as described in the above-identified Canadian Patent ~o. 1,010,30~, then large sections of the stern near the waterline must be cut into to gain working clearances below the helicopter deck or pad.
Since cutting large sections of the stern out is equally unacceptable, a compromise in sonar performance usually has to be made in smaller vessels in that only smaller, lower range transducer arrays, bodies and handling equipment can be accommodated. ;
Thus, whereas there is room for boom bobbing over a limtied verti-cal arc off the stern, the presence of the helicopter deck above prevents the boom being flipped forward past the vertical position to and from an '7~
inboard stow position. Thus, the boom bobbing method of shock absorption/
motion attenuation can still be characterized in terms of the boom and its actuators (be they hydraulic cylinders or rotary actuators) alone.
Nevertheless the launch and recovery functions can no :Longer be charac-terized in terms of the boom and its actuators alone. The slewing action provided by the turntable disclosed and claimed in copending application Serial No. 324,215 filed March 27, 1979 is now an essential part of the launch and recovery process.
The operation is as follows: The boom is lowered to put the saddle in the water to recover the body. The boom is then raised and collapsed (telescoped inward) for stowing the body. The boom (and indeed the entire hoist) is rotated 90 to bring the body athwartships to the stowed position. The boom is then lowered over a slight arc to deposit the body into a support attached to the ship. The launch process is the reverse of that described above.
The telescopic boom is an essential part of the launch and recovery system. Its use is essential in order that everything is collapsed into a stowed length which is less than the beam of the stern transom. The telescopic boom method of shock absorption/motion attenua-tion need not be unique to this system.
An object of a main aspect of this invention is the provisionof an improved boom sub-assembly for such a system for launching, towing, and recovering a towed body from a surface vessel.
An object, therefore, of another aspect of this invention is to provide a sonar mounting system which mini~es, and even overcomes, the problem of a lack of space encountered in mounting large variable depth sonar systems on small ships.
An object of a further aspect of this invention is the provision of an improved shock absorbing/motion attenuating system which provides means for achieving high sea state towing capability at low speeds.
An object of still another aspect of this invention is the , .
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provision of such an improved shock absorbing/motion attenuating systemwhich provides means for increasing the scope and capability of towing into still higher sea states than is the practLce no~.
It is known that an active system is more positive, but usually reqiuires large amounts of power, and the control is very compli-cated. An object, therefore, of another aspect of the present invention is to provide passive motion attenuator/shock absorbers, thereby to extend the capability of the motion attenuating/shock absorbing system to allow towing in ever-higher sea states.
By a broad aspect of this invention, an improvement is provided in a system for launching, towing and recovering a towed body from a sur-face vessel, such system including a hoist sub-assembly and a boom sub-assembly in which boom bobbing means are provided for resiliently apply-ing a torque to the boom member about the pivotal connection thereof to the vehicle commensurate with, and in response to changes in, a load applied to and/or the moving moment of, the assembled boom members, the improvement comprising: a boom sub-assembly comprising an inner boom and an outer boom, the-outer boom being telescopable with respect to the inner boom, and boom telescoping means for resiliently extending and retracting the boom in response to changes in a load applied to the towing cable By one variant, anti-friction members are disposed between the inner boom and the outer boom.
By another variant thereof, anti-friction members are held captive by the inner boom to assist in the telscoping action of the booms.
By a variation thereof, the anti-friction members include wheels or rollers.
By another variant, the outer boom is connected to the inner boom by hydraulic cylinder means.
By a variation thereof, the hydraulic cylinder means are ~ ~ ~q3 7 r ~
actuatable to extend the outer boom outwardly rrom the inner boom for the launching and towing modes, and to collapse the outer boom into the inner boom for the stowing mode.
By another variation, the inner end of the hydraulic cylinder means is pivotally secured at or near the hinge point of the boom assem-bly, the boom assembly having a vertical swinging movement, when driven by, or driving, a rotary actuator.
By a further variation, the arm end of the hydraulic cylinder means connecting the inner and outer booms is pivotally secured to an ear secured to the outer boom.
By another aspect of this invention, an improvement is provided in a system for launching, towing and recovering a towed body from a surface vessel, the system including a hoist sub-assembly including a towing cable, a boom sub-assembly, and boom bobbing means for resilient-ly applying a torque to the boom member about the pivotal connection thereof to the vehicle commensurate with, and in response to changes in, a load applied to and/or the moving moment of, the assembled boom members, the improvement comprising: a boom sub-assembly comprising an inner boom, an outer boom telescopable with respect to the inner boom, and boom teles-coping means for resiliently extending and retracting the boom in responseto changes in a load applied to the towing cable, and a shock absorbing/
motion attenuating system cooperating with the boom bobbing system, and including hydraulic, pneumatic and/or mechanical springs connected to the means telescopically connecting the inner boom and the outer boom.
By yet another aspect of the invention, an improvement is pro-vided in a system for launching, towing and recovering a towed body from a surface vessel, such system including a hoist sub-assembly and a boom sub-assembly provided with the combination of: (a) an inner pivotal boom member; (b) an outer telescoping boom member; (c) drive means for selec-tively pivoting the inner boom member and the winch assembly about asubstantially _ g _ - , . :, ~

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horiæontal axis; (d~ a driven ~:inch assembly having a winch drum for windIng in, and paying out, a faired cable; (e~ a Eaired cable secured by one end to, and wound on, the winch drum and adapted to be connected adjacent its outer end to an article to be towed; ~f) sheave means on the outer boom member engaged with the fa:ired cable during winding in,and paying out, of the faired cable from the winch drum; ~g) a saddle pivo-tally secured to the outer boom member, the saddle being provided with a lower surface adapted snuggingly to engage the portion of the article to be towed engaged thereby during launching and retrieval thereof; (h) boom bobbing means for resiliently applying a torque to the inner boom member about the pivotal connection thereof to the vessel commensurate with, and in response to changes in, a load applied to and/or the moving moment of both inner and outer booms assembled together; (i) boom teles-coping means for resiliently extending and retracting the outer boom into and out of the inner boom in response to changes in the tow cable loads;
and (j) a levelling mechanism, e.g., hydraulic cylinders connecting the 7~) outer boom and the saddle ~or selectively retaining the saddle in a common horizontal position irrespective of the pivotal movement of the boom member; the improvement comprising: the combination of a boom sub-assembly having an outer boom drivingly telescopable with respect to an inner boom, and a shock absorbing/motion attenuatîng system, cooperating with the boom bobbing system, and including hydraulic, pneumatic and/or mechanical springs connected to the means telescopingly connecting the nner boom and the outer boom.
By one variant of this aspect, separate springs, which may be pneumatic-hydraulic springs, are provided for the boom bobbing system and for the shock absorbing/motion attenuatin~ ~svstem.
By a variation thereof, the separate springs, e.g., the pneu-matic-hydraulic springs, comprise gas-oil springs.
By another variant, the means telescopingly connecting the inner and outer booms comprise hydraulic cylinder means, and the gas-oil springs of the shock absorbing/motion attenuating system are connected to the hydraulic cylinder means.
By a further variation, hydraulic fluid is transferred from the gas-oil spring in response to variations in tow cable tension to move the outer boom with respect to the inner boom to subdue variations in tow cable tension.
By still another aspect of this invention, boom bobbing means comprises: a rotary actuator including an incompressible fluid charged by a stored compressible fluid, the rotary actuator being secured to the aft end of the winch frame and connected to the boom via a torque tube forming a part of the inner boom.
Thus, by one embodiment of this invention, the boom sub-assembly includes an inner boom and an outer boom. The outer boom may include wheels or rollers bearing on, and held captive by, the main members of the inner boom. On the other hand, rollers may be attached : .

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to the inner'boom and be held captive by the ma:Ln members of the outer ~oom. The outer boom is connected to the inner boom by one or more hydraulic cylinders. By introducing fluid into either'the 'head or rod ends of these cylinders, the outer boom is made to telescope outward from the inner boom for normal towing, or to collapse into the inner boom, thereby creating a compact stowed combination of boom and towed body. The inner boom is connected to the turntable through a rotary actuator, and the combination of inner boom and outer boom is rotated in the vertical plane (i.e. either raised or lowered) by introducing fluid under pressure to this actuator.
In another embodiment of this invention, two shock absorbing/
motion attenuating systems are used, each being capable of being used on its own, or being used together. Both systems may be connected to a common gas-oil spring system, but it is preferred that a separate such gas-oil system be used for each. The systems are connected to the above-described boom sub-assembly which includes an inner boom and outer boom.
The outer boom is connected to the inner boom by one or more hydraulic cylinders. By introducing fluid into either the head or rod ends of these cylinders, the outer boom is made to telescope outward from the inner boom for normal towing, or to collapse into the inner boom, thereby creating a compact stowed combination of boom and towed body. The inner boom is connected to the turntable through a rotary actuator, and the combination of inner boom and outer boom is rotated in the vertical plane ~' (i.e. either raised or lowered) by introducing fluid under pressure to this actuator. The upward and downward controlled movement is supple-mented by a main pressure shock absorbing/motion attenuating system which is commonly known as a 7boom bobbing' system, and which is described in one form in the above-identified Canadian Patent No. 1,010,308. On the other hand, the system proposed here uses gas-oil springs connected to the rotary actuator of the inner boom. The shock absorbing/motion - : ~ . ... ;:

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attenuating system proposed here also utilizes gas-oil sprlngs connected to the hydraulic cylinders connecting the inner and outer booms. Cable excursions into and out of the water are caused by collapsing the outer boom into the inner boom and by telescoping the outer boom from out of the inner under the action of hydraulic fluid transfer arising from the response of the gas~oil spring to variations in tow cable tension. This auxiliary system shock absorbing/motion attenuating is intended to supplement the main boom bobbing system at low speeds of the towing vessel, under which conditions telescoping the inner and outer booms will not cause undesirable surge of the towed body.
In the accompanying drawings, Figure 1 is a side elevational view of a retractable boom assembly of a preferred embodiment of this invention mounted on a turn-table which is mounted for rotation of 70 - 110;
Figures 2, 3 and 4 are views of the inner boom forming a com-ponent of the retractable boom assembly of an aspect of this invention, in which Figure 2 is a side view, in which Figure 3 is a bottom view and in which Figure 4 is an end view;
Figures 5 and 6 are views of the outer boom forming a component of the retractable boom assembly of an aspect of this invention, in which Figure 5 is a side view and in which Figure 6 is a top view;
Figure 7 is a side view of the retractable boom/saddle assembly forming a part of the retractable boom assembly of an aspect of this invention;
Figure 8 is a top view of the retractable boom/saddle assembly of Figure 7, Figure 9 is a schematic diagram of one variant of hydraulic system for controlling the rotary motion on the boom assembly;
Figure 10 is a schematic diagram of one variant of hydraulic system by which the linear motion of the boom assembly may be controlled;
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Figure ll is a side view of the boom/saddle assembly showing the effect of the tow cable tension on the boom assembly;
Figure 12 is a side view of the boom/saddle assembly showing the effect of tow cable moment on the boom assembly; and Figure 13 is an exemplary graph created to define boom bobbing performance in a given system.
- As shown in Figure 1, an embodiment of a towing system is shown in which a variable depth sonar towed body may be transferred from a collapsed boom position to an outboa:rd launch position. The outer boom is connected to the inner boom by one or more hydraulic cylinders.
By introducing fluid into either the head or rod ends of these cylinders, the outer boom is made to telescope outwardly from the inner boom for normal towing, or to collapse into the inner boom, thereby creating a compact, stowed combination of boom and towed body. From its launch position, the towed body can be released and lowered on its towing cable to the required operational depth. This depth is controlled by adjusting the length of tow cable paid out by a towing winch and by the speed of the towing vessel. On completion of the towing operations, the body can be recovered by reversal of the launching procedure. This invention also includes the combination of two shock absorbinK/motion attenuating sys-- tems, which are capable of being used together to provide passive bobbing motion of the boom to minimize variations in the tension of the tow line.
In the preferred embodiment of this invention, the towed body is captured on the extended boom, the boom assembly is raised and collapsed, and then the turntable turns the winch, boom assembly and towed body through 90 to deposit the towed body athwartship in an in-board stowed position. Though the telescopic boom is used for shock absorbing/motion attenuating and stowage herein in the preferred embodi-ment, it could be.used merely as an additional means for shock absorbing/
motion attenuating.

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The embodiment of this invention shown in Figure 1 includes a hoist sub-assembly 10, a lifting boom sub-assembly 30, a saddle/cable guide/
sheave sub-assembly and a boom bobbing shock absorbing/motion attenuating system. In addition, a hydraulic power unit and motor controller are also provided, as will be described hereinafter.
The hoist sub-assembly 10 is more fully described in copending Canadian application Serial No. 325,652 filed April 18, 1979 and will not be described in detail here. It generally consists of a stationary frame and a moving frame translating on rollers. The assembly is secured to a turntable 13 rotatably supported on the aft upper deck 14 of the ship 15.
The turntable is supported in a manner which is fully described in copending Canadian application Serial No. 324,215 filed March 27, 1979 and is driven by a hydraulic motor 17 in a manner which is fully described therein. The turntable 13, when operative, is adapted to be positively rotated through an angle of 70 - 110, and preferably through 90. The winch 11 is driven by a hydraulic motor 18 which incorporates a spring applied--hydraulic re-lease-type band brake. The winch 11 drives a conductor winder mounted with the winch drum 11 on the starboard side thereon to save space and which provides electrical continuity from the conductors (not shown) of the tow cable 21 to the internal sonar circuits (not shown) of the ship 15.
The function of the hoist sub-assembly 10 i5 to pay out and haul in the desired length of tow cable 21 and to assist the boom member 30 and actuator assembly in the launch and recovery of the towed body 90.
The winch frame 22 in one of its preferred embodiments is a welded aluminum structure that supports the complete hoist. Suitable surfaces are provided on the winch frame 22 for attachment of t he shaft support assemblies 23; of the winch motor 18 and band brake assembly of the boom actuator; of the conductor winder; and of the gas bottles and rotary , ` actuator for the boom bobbing/shock absorbing motion attenuating system ., . .,,:
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-The winch drum 11, in one embodiment, is driven 'hrough a bull or drive pinion 27 by a low speed, high torque radial piston type hydraulic motor 18. The motor 18 is integral with a spring-applied hydraulic release-type band brake complete with mounting bracket.
The above-referred to Canadian Patent No. 1,005,702 describes a conductor winder which is included in the complete towing system to provide the means for maintaining electrical continuity between the conductors of the tow cable and the internal sonar circuits of the ship without the use of the slip rings. Since a full description is included in copending 10 Canadian application No. 325,652 and since that does not form an essential characteristic of the present invention, no description of that conductor winder will be given.
The boom sub-assembly 30 will be described in greater detail hereinafter with reference to Figures 2 - 8. The purpose of the boom sub-assembly 30 is to transfer the towed body 90 from the inboard stowed posi-tion to the outboard launch position and vice versa, with the aid of the hoist sub-assembly 10. The boom sub-assembly 30 is moved from the in-board stowed position to the outboard launch position and vice versa by turntable 13 and its drive system, and by hydraulic cylinder 120. The boom rotary actuator 122, being mounted on the turntable 13, is thus se-cured to base frame portion of frame assembly 22.
The saddlelcable guide/sheave assembly is carried on a horizontalshaft 127 which is supported at the outboard extremities 128 of the lifting boom 30. The saddle 121 provides a stable~seating for the towed sonar body 90 during launching and recovery, and is ma;ntained in an approximately horizontal attitude by means of a levelling mechanism, e.g., hydraulic cylinder(s) 129. It also affords protection to the towed body 90 by means ~s~ of a series of bumpers 75, preferably formed of polyurethane, mounted on its underside, A cable guide assembly is also provided which may de-. .
sirably be a set of cable guide plates fixed to the saddle. The sheave shaft 127 r ~ ~
consists of a steel tube, preferably chrome-plated~ secured to the out-board endsl28 of the outer boom 110. Sheave shaftl27 suppo~ts the sheave 125 saddle assembly 12land cable guide assembly . The sheave L25in one embodiment is an aluminum struc~ure which freely rotates on the sheave shaft It is made up of a weldment to which are bolted two rims . which form the groove ~ of the sheave 12~ In this groove are located a plurality of arcuate segments of a plastics material, e.g. polyurethane material, which serve to protect the nose pieces 49 of the fairings 50 of the tow cable 21. One or more grease nipples (not shown) are readily accessible for lubrication of the bearings.
The saddle assembly 121in one embodiment is a welded or bolted structure made of aluminum plates whose purpose is to provide a stable seating for the towed body 90 during launching and recovery. The assembly 121is supported on the sheave shaft 127 on bearings, prefer-ably fibre-reinforced phenolic bearings. A grease nipple (not shown~ is readily accessible on each bearing for lubrication. The saddle assembly is not a critical feature of the present invention and so will not be described in detail here. However, one type of saddle assembly 121which is operative in the present invention is disclosed in Canadian Patent No. 885,838 issued November 16, 1971 to J. Meben.
Nevertheless, it is to be noted that the-series of bumpers 7.5 , preferably of polyurethane, are bolted to the underside of the assembly 121 The special orientation of the bumpers is adapted to conform with the upper curvature of the towed body 90 and to afford protection to the budy during launching and recovery operations.
The cable guide assembly effectively eliminates the need of having long side rollers extending aft sufficient to accommodate the various tow cable angles.
When a towed sonar body 90 is brought on board conventionally, '7~V
it is lo-~ered down to the deck l4 of the ship :L5 into a cardle suitably located and fixed to the deck. On smaller ships, or on a crowded deck, it may not always be posslble to provide the required space for powering the boom past the vertical to a stowed position. Consequently, by a preferred aspect of this invention, the hoist sub-assembly 10 is adapted to rotate horizontally through an angle of from 70 to llOD, preferably through an angle of 90, to permit the sonar body 90 to rest on a lower seat shown in more detail in copending application Serial No. 324,215 filed ~larch 27, 1979 , which has been attached to the deck 14 on the other side of the center line of the ship 15 to the side where the turn-table 13 is attached.
The towing system is hydraulically actuated, the system being manually and electrically controlled from a hydraulic power unit, as will be further described hereinafter. During launch and recovery operations, the towed body 90 is held firmly in the saddle 121 by tension in the tow cable 21. This tension is maintained near constant by a pressure compen-sated, closed loop, hydrostatic drive system.
Movement of the boom 30 about its mean hinge point during towing operations will cause, depending upon the magnitude of the cable load, a compression or expansion of the gas and the springs(140 to 142 inclusive in Figure 9) of the boom bobbing system. This compression or expansion will only be sufficient to set up a moment on the boom to counteract the moment caused by the cable load. During towing operations, the boom is positioned at an angle of 0 and the gas pressure in the actuators is adjusted so that with a steady cable pull the boom remains relativel~ `
still. If the cable pull increases, the boom will drop down and the gas ~ -and springs within the actuators will be compressed. The boom will drop only that amount that the moment on the boom due to the actuators will increase sufficiently to counteract the moment caused by the increased cable pull. If the cable pull decreases, the boom will rise and the gas - and springs will expand. Again the boom will rise only that amount that ;. ' ;' , , ;: .. , ,.,. ;

7~0 moment on the boom due to the actuators will decrease sufficiently to counteract the moment caused by the decreased cable pull.
Along with this boom bobbing system, an auxiliary shock absor-bing/motion attenuating system is also provided. This system will be more fully described hereinafter, ~hich involves the use of gas-oil springs con-nected to the hydraulic cylinders connecting the inner and outer booms.
The response of this gas-oil spring to variations in tow cable tension causes the inner and outer booms to te:Lescope in the proper direction under the action of the hydraulic fluid transfer. This auxiliary system is mainly operative at low speeds of the towing vessel where telescoping of the inner and outer booms will not cause undesirable surge of the towed body.
A hydraulic power unit is provided to operate t~he system, and this is similar to that described in detail in the above-mentioned Canadian Patent No. 1,005,702. Since a complete description is given in that patent, and since it does not form an essential characteristic of this invention, no further description will be given here.
As seen in Figures 2, 3 and 4, one variant of the inner boom lO0 includes a pair of parallel, boxed-in beams lCl rigidly secured to a trans-verse torque tube 102, provided with a terminal mounting flange 103 and a depending, central hydraulic cylinder mounting ear 104. The beams 101 are preferably provided with tread liners 105, which may be formed of hard anodized aluminum. The beams 101 are joined by a cover plate 106.
As seen in Figures 5 and 6,one variant of the outer boom 110 includes a pair of parallel longitudinal beams 111 rigidly secured together, but separated by box structure 112. At one end of the box structure 112 are a pair of roller bearing wheels 113 provided with flanges 114, and mounted for free rolling rotation on bearings 115. The other (i.e. outer) end of outer boom llO is provided with a bearing mounting aperture 116.
Depending from that end of each beam 111 is a hydraulic cylinder mounting ear 117. The box structure 112 has 7r~ 0 an upper cover plate 118 and an lower cover plate 119. Secured to lower cover plate 119 is a central hydraulic cylinder rod mounting ear ll9a.
As seen in Figures 7 and 8, the inner boom laO and outer boom 110 are assembled and connected via hydraulic cylinder(s) 120, and the saddle 121 and rotary actuator 122 are attached. The outer boom 110 is attached to the inner boom 100 via one or more hydraulic cylinders 120.
The head end 123 of cylinder 120 is secured to hydraulic cylinder moun-ting ear 104, while the rod end 124 is secùred to hydraulic cylinder rod mounting ear ll9a. These are preferably fitted with adjustable custions (not shown) at both rod end 124 and head end 123. The outer boom 110 is supported from the inner boom 100 via a plurality of wheels 113 mounted on the outer boom 110 and constrained to ride on hard tread liners 105 mounted in track areas within the inner boom 100. A towing sheave 125 is mounted on a shaft 127 which is rotatably mounted in bearing (not shown) in bearing mount apertures 116 at the outer end 128 of the outer boom 110, and a saddle 121 is also mounted on shaft 127 at the outer end 128 of the outer boom 110. A set of hydraulic cylinders 129 are used to level the saddle under any inclination of the boom assembly 30. The inner boom 100 is mounted in supports 130 lined with bearings 131 bolted to the aft end of a stationary hoist base 132 (or preferably turntable 13). The boom assembly 30 is held or constrained to rotate in a vertical plane by a rotary actuator 122 supported from base 132 or turntable 13 and directly connected to the torque tube 102 via connector 103 of the inner boom 100.
It would also be possible to drive the torque tube 102 via a gear reduc-tion (not shown) interposed between rotary actuator 122 and torque tube 102. ,~
Figure 9 is a partial hydraulic schematic showing a system by means of which rotary motion of the boom assembly 30 may be controlled.
The system includes direction control valves 133, 134, 135, boom bobbing ~3 ~ 7~
engagement valves 136, a press~ire-compensated flow control valve 137 with free bypass in one direction, accumulator isolation valves 138, L39, and nitrogen-charged accumulators 140, 141, 1~2 which form the gas-oil springs for boom bobbing. There are also three pressure gauges 143, three exhaust valves 14~ for venting the accumulators, and three fill valves 145 for charging the accumulators 140, 141, 142. Any number of accumulators (not necessarily three) may be needed to obtain the correct spring constants for all towing conditions. Accumulator 140 may not be needed for all systems, but is included to prevent any tendency for the boom assembly 30 to bounce upward in high sea states. The system des-cribed here will need at least the two other accumulators 141 and 142 acting to force the boom assembly 30 up. For other applications, it may be necessary to install mechanical springs inside one or more of the accumulators to obtain suitable spring rates.
In operation, to raise or lower the boom assembly 30, it is first necessary to ensure that valves 136 are shut, isolating the boom bobbing section. With direction control valve 133 centred, all paths are blocked, and the boom assembly 30 is held stationary. To raise the boom assembly 30, the spool of direction control valve 133 is shifted to the right. Flow from the pump (not shown)-will be directed past the bypass of flow control valve 137 to ports 122A of rotary actuator 122, pressurizing pistons 122Y, and forcing the actuator 122 to output torque and rotation to raise the boom assembly 30. Exhaust oil will drain out ports 122B and back through direction control valve 133 to tank (not shown).
To lower the boom assembly 30, the spool of direction control valve 133 is shifted to the left. Flow from the pump (not shown) will be directed to ports 122B. In addition, the weight of the boom and cable tension will attempt to back-drive the rotary actuator by forcing ~
pressurized fluid out of ports 122A. A runaway condition is prevented, ~., .
- 20 - ~

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however, by the presence of pressure-compensated flow control valve 137.
Flow from the actuator 122 may only pass through this valve at a specific metered rate, thence through valve ]33 to the tank (not shown).
To engage the boom bobbing system, direction control valve 133 is first centered to block motion of the boom assembly 30. The accumu-lators 140, 141 and 142 may be gas charged to the correct pressures from nitrogen storage bottles by opening valves 145, or may be vented as necessary by opening valves 144. If it is necessary to oil charge the accumulators 140, 141, 142, this is possible by shifting the spool of direction control valve 134 to the right, then charging each accumulator 140, 141, 142 as necessary through manipulation of valves 135, 138, and 139. The boom bobbing system is directly engaged by opening valves 138, then simultaneously opening valves 136. If everything is in equili-brium, and the ship is in a calm sea, the boom will be steady, with the moment exactly balanced by the torque from rotary actuator 122. This torque in turn is imparted to the rotary actuator 122 by the gas pres-sure differences between accumulators 140 and 141, the gas pressure in 141 imparting a corresponding hydraulic pressure through the line and ports 122A to pistons 122Y being greater than the gas pressure in 140 imparting a corresponding hydraulic pressure through the other line and ports 122B to pistons 122Z. In high sea states, as the stern of the ship rises and attempts to pull the towed body higher in the water, broadside .;
drag of the body plus cable drag imparts a higher momentary cable tension to the boom assembly 30. This increases the load moment on the boom assembly, pulling it down. As the boom assembly 30 is pulled down, the rotary actuator 122 is back-driven, increasing the pressure differences between accumulators 140 and 141 and therefore the torque on the rotary -:
actuator 122 until a new position of equilibrium is found where a torque balance (between load moment and actuator moment) is achieved once more.
Compression and decompression of the gases takes place fast enough as to ,. . ~ ,.

3~

be an essentially adiabatic process, ~hereby the gas law PlVl = P2P2n applies. On the other hand, as the boom assembly 30 is pulled down, the length along the tow line from the stationary hoist d~um over the towing sheave 125 to the waterline is decreased, causing more tow cable to be put into the water. This tends to compensate for the rise of the stern of the ship by reducing both amplitude and speed of vertical lift of the body in the water, and this in turn reduces the momentary increase in tension. Valves 136 may be partly closed to provide any desired hydraulic throttling (damping). As the stern of the ship falls in high sea states, the towing line tends to go slack if the stern falls faster than the body can sink, a common condition. This reduces the moment on the boom assembly 30, and gas pressure differences between accumulators 140 and 141 cause the boom assembly 30 to rise until the pressure in 141 decreases and the pressure in 140 increases sufficiently to establish a new torque balance and position of equilibrium. On the other hand, as the boom assembly 30 rises? the length along the tow line from the stationary hoist drum over the towing sheave 125 to the water-line is increased, causing more cable to be lifted from the water. This reduces the tendency of the tow cable to go slack, and restores some of lost cable tension.
Figure 10 is a partial hydraulic schematic showing one possible system by which linear motion may be controlled. The system includes direction control valves 146, 147, a pressure-comepensated flow control valve 148 with free bypass in one directiong shock absorber engagement valves 149, a nitrogen-charged accumulator 150, a pressure gauge 151, a valve 152 for venting the accumulator 150 and a valve 153 for charging the accumulator 150 with nitrogen. It should be emphasized this is the simplest form of control - a bank ~f accumulators may be required to vary the spring rate Eor all towing conditions, and it may also be necessary to add an additional accumulator to charge the rod end of cylinder 120 ' -through port 120B.
In operation, to extend or retract the boom assembly 30, it is first necessary to ens~lre that valves 149 are shut, isolating the shock absorber system. I~ith valve 146 spring cen~ered and blocked, the posi-tion of the outer boom llO with respect to the inner boom 100 is fixed.
To extend the outer boom 110, the spool of valve 146 is shlfted to the right. High pressure fluid is directed from valve 146 through the free flow bypass of valve 148 to the head end 123 of cylinder 120 through port 120A, forcing the outer boom 110 to extend, while low pressure fluid returns out of port 120B through valve 146 and ultimately to a tank (not shown~. To retract the outer boom 110, the spool of valve 146 is shifted to the left. Flow from the pump is directed from valve 146 to the rod end 124 of cylinder 120 through port 120B. Pressure on the rod end 124 of the cylinder piston 120 is assisted by the component of cable tension tending to collapse the boom assembly 30, and to prevent this happening too suddenly, exhaust fluid from port 120A is forced to flow through the flow control section of valve 148, where it is metered through only at a controlled rate before going through valve 146 to the tank (not shown~.
! To engage the telescopic shock absorbing system, direction control valve 146 is first centered to block the outer boom 110. Accumu-lator 150 may be gas charged to the correct pressure from nitrogen storage bottles by opening valve 153, or may be vented as necessary by opening valve 152. If it is necessary to oil charge the accumulator, this is done by shifting the spool of direction control valve 147 to the right. Shifting it to the left drains oil from the accumulator 150. The shock absorbing system is directly engaged by simultaneously opening valves 149. If everything is in equilibrium, and the ship is in a calm sea, the outer boom 110 will remain stationary with the cable tension component balanced by the force in cylinder 120. This force is in turn '' .

.

imparted to the cylinder by the oil pressure ~equal to the gas pressure in accum~llator 150) multiplied by the cylinder area. In high sea states, as the stern of t~e ship rises and attempts to pull the towed body higher in the water, broadside drag of the body plus cable drag imparts a higher momentary cable tension. This increases the cable tension component ~hich causes the boom assembly 30 to collapse and to compress the gas in accumulator 150 more or less adiabatically until the gas pressure rises to the point where the resisting force in cylinder 120 once again balances the cable tension component, at which point equili-brium is reached. On the other hand, as the boom assembly 30 iscollapsed, the length along the tow line from the hoist to the towing sheave 125 is decreased, causing more tow cable to be put into the water.
The effect is exactly the same as described above - a reduction of the momentary increase in cable tension. Valves 149 may be partly closed to provide any necessary hydraulic throttling (damping). As the stern of the ship falls in high sea states, the towing line tends to go slack if the stern falls faster than the body can sink. This reduces cable ten-sion component which causes the outer boom 110 to extend and to decom-press the gas in accumulator 150 and the fluid in cylinder 120 until the point is reached once again where the cable tension component equals the cylinder force. Thus, equilibrium is once again established. On the other hand, as the outer boom 110 extends, the length along the tow line from the hoist to the towing sheave 125 is increased, causing more tow cable to be pulled from the water. The effect is a restoration of some of the momentary loss in cable tension.
Boom bobbing may be used together with a telescopic boom type of shock absorbing/motion attenuating system according to a broad aspect of this invention. ~ith respect to the rotary movements, certain forces and moments are shown in Figures 11 and 12. Referring to Figure 11, it can be seen that there is always a component of tow cable tension TRH

'7.~3~

tending to collapse the outer boom into the inner boom, and this is restricted by hydraulic cylinder(s) 120. Referring to Figure 12, it can be seen that the tow cable imparts a moment TRa on the boom assembly, and this must be resisted by rotary actuator 122. These forces and moments vary with speed, tow cable tension, angular attitude of the boom and the amount the outer boGm is collapsed into the inner boom.
With respec~ to the definition of the boom bobbing performance of a given system, attention is directed to Figure 13 which is a graph to aid in the selection of the proper accumulators, gas precharges, and spring constants. The graph is created for a particular set of towing conditions (cable scope, speed, stern heave amplitude and frequency) on a given system. The load moment curve is drawn for the mean towing tension at several boom angles. The "spring moment" curve is the torque output from the actuator at various boom angles for a particular set of "starting" gas precharges in the accumulators. The point of equilibrium, that is, the angular position the boom will assume in a calm sea state, lies where the two curves cross. Maximum and minimum tensions in high sea states (which may have to be calculated by trial and error on a computer) give rise to the loci of maximum and minimum moments. New crossover points on these loci yield the angular range of boom bobbing.
A study of these curves indicates that generally, the "spring moment"
curve must be fairly shallow to obtain a good angular range of boom bobbing. However, too "soft" a spring, yielding a "spring moment" curve which lies almost on top of the load moment curve or crosses it more than once may lead to instability. In such a case, small errors in assumptions made in the analysis can have dramatic and unpredictable effects. A spring so "soft" as to make the two curves cross in reverse makes the system unworkable and dangerous. Too "hard" a spring (large slope to "spring moment" curve) may decrease the bobbing angular range and shock absorbing potential. It may even be necessary to have an :.

-entire bank of accumulators to be switched in and out j~ldiciously as necessary to match spring rates with varying towing conditions.
Thus, for an increase in momentary tension to be attenuated, the boom assembly 30 must bob down and the outer boom 110 must come in;
for a decrease in momentary tension to be attenuated, the boom assembly 30 must bob up, and the outer boom 110 must go out. The action of the outer boom 110 extending from or collapsing into the inner boom 100 causes moment arm "a" in Figure 12 to increase or decrease, respectively.
The net effect when the two methods of shock absorption/motion attenua-tion are used together according to an aspect of this invention is tomake the load moment curve in Figure 13 more horizontal. This in turn causes a degradation of boom bobbing, and has the same effect as too "hard" a spring. To correct for this when the two methods are used together, accumulator 142 (Figure 9) is switched into the boom bobbing system, the effect of which is, when combined with accumulator 141 (Fig-ure 9) to yield a "spring moment" curve ~Figure 13) with a lower slope (i.e., a "softer" spring), and once again give a large and effective angular range of boom bobbing. Similarly, because of change of TRH with boom angle, the gas-oil spring 150 (Figure 10) will probably require different sizing when the telescopic boom system is used with a boom bobber than when it is used by itself.

Claims (15)

The embodiments of the invention in which an exclusive prop-erty or privilege is claimed are defined as follows:

1. An improvement in a system for launching, towing and recovering a towed body from a surface vessel, said system including a hoist sub-assembly including a towing cable, a boom sub-assembly, and boom bobbing means for resiliently applying a torque to the boom member about the pivotal connection thereof to the vehicle commensurate with, and in response to changes in, a load applied to and/or the moving moment of, the assembled boom members, the improvement comprising: a boom sub-assembly comprising an inner boom, an outer boom telescopable with res-pect to said inner boom, and boom telescoping means for resiliently extending and retracting the boom in response to changes in a load applied to the towing cable.

2. The improvement of claim 1 wherein anti-friction members are disposed between said inner boom and said outer boom.

3. The improvement of claim 2 wherein said anti-friction members are held captive by said inner boom to assist in the telescoping action of the booms.

4. The improvement of claim 3 wherein said anti-friction members comprise wheels or rollers.

5. The improvement of claim 1 wherein said outer boom is con-nected to said inner boom by hydraulic cylinder means for resiliently extending and retracting the boom in response to changes in a load applied to the towing cable.

6. The improvement of claim 5 wherein said hydraulic cylinder means are selectively actuatable to extend the outer boom outwardly from the inner boom for the launching and towing modes, and to collapse the outer boom into the inner boom for the stowing mode.

7. The improvement of claim 6 wherein the inner end of said hydraulic cylinder means is pivotally secured at or near the pivot point of said boom assembly, said boom assembly being adapted to swing vertically when driven by, or driving, a rotary actuator.

8. The improvement of claim 6 wherein the arm end of said hydraulic cylinder means is pivotally secured to an ear secured to said outer boom.

9. An improvement in a system for launching, towing and recovering a towed body from a surface vessel, said system including a hoist sub-assembly including a towing cable, a boom sub-assembly, and boom bobbing means for resiliently applying a torque to the boom member about the pivotal connection thereof to the vehicle commensurate with, and in response to changes in, a load applied to and/or the moving moment of, the assembled boom members, the improvement comprising: a boom sub-assembly comprising an inner boom, an outer boom telescopable with res-pect to said inner boom, and boom telescoping means for resiliently extending and retracting the boom in response to changes in a load applied to the towing cable, and a shock absorbing/motion attenuating system cooperating with said boom bobbing system, and including hydraulic, pneumatic and/or mechanical springs connected to the means telescopically connecting the inner boom and the outer boom.

10. An improvement in a system for launching, towing and recovering a towed body from a surface vessel, said system including a hoist sub-assembly and a boom sub-assembly provided with the combination of:
(a) an inner pivotal boom member;
(b) an outer telescoping boom member;
(c) drive means for selectively pivoting said inner boom member about a substantially horizontal axis;
(d) a driven winch assembly having a winch drum for winding-in, and paying-out, a faired cable;
(e) a faired cable secured by one end to, and wound on, said winch drum and adapted to be connected adjacent its outer end to a body to be towed;
(f) sheave means on said outer boom member engaged with said faired cable during winding-in and paying-out of said faired cable from said winch drum;
(g) a saddle pivotally secured to said boom member, said saddle being provided with a lower surface adapted snuggingly to engage the portion of the article to be towed thereby during launching and retrieval thereof;
(h) boom bobbing means for resiliently applying a torque to said inner boom member about the pivotal connection thereof to the vehicle commensurate with, and in response to changes in a load applied to and/or the moving moment of both said inner and outer booms assembled together;
(i) boom telescoping means for resiliently extending and retracting said outer boom into and out of said inner boom in response to changes in the tow cable loads;
and (j) a levelling mechanism for selectively retaining said saddle in a common horizontal position irrespective of the pivotal move ment of said boom member;
said improvement comprising the combination of: a boom sub-assembly having an inner boom, an outer boom drivingly telescopable with respect to an inner boom, and a shock absorbing/motion attenuating system cooperating with said boom bobbing system and including hydraulic, pneumatic and/or mechanical springs connected to said means telescopingly connecting said inner boom and said outer boom.

11. The improvement of claims 9 or 10 wherein separate springs are provided for said boom bobbing system and for said shock absorbing/motion attenuating system.

12. The improvement of claims 9 or 10 wherein separate springs are provided for said boom bobbing system and for said shock absorbing/motion attenuating system and wherein said springs comprise gas-oil springs.

13. The improvement of claims 9 or 10 wherein said means telescopingly connecting said inner boom and said outer boom comprise hydraulic cylinder means, wherein said gas-oil springs of said shock absorbing/motion attenuating system are connected to said hydraulic cylinder means.

14. The improvement of calims 9 or 10 wherein hydraulic fluid is transferred from the gas-oil spring in response to variations in tow cable tension to move said outer boom with respect to said inner boom to subdue variations in tow cable tension.

15. The improvement of claims 1, 9 or 10 wherein said boom bobbing means comprises: a rotary actuator including an incompressible fluid charged by a stored compressible fluid, the rotary actuator being secured to said aft end of said winch frame and connected to said boom assembly via a torque tube forming a part of said inner boom.