Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1~9;~061
This invention relates to systems for launching, recovering and
towing an underwater towed body, and particularly to a towing system where
an underwater body is towed behind a vessel. In particular this invention
relates to a fairle~d sheave and saddle assembly for use in such system.
The underwater towed body with which the present invention is
used is an underwater SONAR (abbreviated from "Sound Navigation and Rang-
ing") which is finding ever-increasing use in the fields of navigation,
mapping, depth f~nding, fish finding, for detection of wrecks and in 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 under-
water 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 conduc-
tors 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 out.
In the towing system as above described, it is desirable to pro-
vide a system whereby the towed body may be readily launched and retrieved
and handled during the towing operation, which during such towing mini-
mizes damage to the towing cable and ob~ect being towed.
109;~0t;1
The hazard involved in towing any device of substantial mass
from a ship at sea is that of varying cable 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 condition. The transient
cable load, at the instant the cable becomes taut, is high by several mag-
nitudes when compared with the nominal towing load. Cable failures may
result from such a situation.
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 ou~ 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 accepta-
ble 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
fairéd 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 partial-
ly achieved by use of fairing elements on the cable. The resultant of
low drag characteristics and towing a submerged sonar body is that the
faired towing cabls extends more directly along a straight line than other-
wise. In a towing system of the latter type, it is difficult and often
impossible to obtain sufficient 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
attitIde) 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
follow the undulations o~ the floatlng
C)61
vessel. On rough water, the intensity of the transient loads can be se~
vere and particularly because of a snapping action occuring in the faired
tow line resulting from the two bodies moving relative to one another to
different speeds.
In the realm of towed sonar technology, the launch operation com-
prises lifting the sonar body from the deck of the ship, swinging it over
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 always desirable, when towing an underwater body in a
straight line, that the body, cable and ship lie in the same vertical
plane. This does not usually occur in practice. While fairings are often
used on the tow cable, instabilities, wake disturbances, cross currents or
other things may cause the cable to tow off to one side. Cross currents,
instabilities, tow cable fluctuating loads or other things may cause the
the body to tow off to one side, and this in turn may also cause cable
tow off. When the ship is turning, the cable always tows off.
~O During tow-off or snap loading in high sea states, it is always
necessary to ensure the tow cable does not jump and slip off the towing
sheave. During snap loading, this may be prevented by altering speed and/
or cable scope, although thifi cannot be accomplished instantaneously.
During tow-off, this may be prevented by allowing the cable to bear on the
saddle or other structure used to hold the towed body during launch and
recovery. Various means, e.g., cable guides and roller boxes are usually
incorporated into the saddle for this purpose.
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1(~9~061
One system for launching and recovering the towed body wlthout
:resorting to mechanical interlocking between the body and a member engage-
able with the body during launching and recovering which has been provided
in the past, is described in Canadian Patent No. 1,005,702 granted February
22, 1977 to Ronyx Corporation Limited, for "Means for Launching, Towing and
Recovering an Oceanographic Towed Body in a Seaway''. In that patent, a
towing system is provided including the combina~ion of: (a) a boom member
pivotally securable to a towing vehicle; (b) drive means for selectively
pivoting the boom member about a substantially horizontal axis; (c) a
driven winch assembly having a drum for winding in, and paying out, a faired
cable; (d) a faired cable secured by one end to, and wound on, the drum
and adapted to be connected ad~acent its outer end to an article to be
towed; (e) sheave means on the boom engaged with the faired cable during
winding in, and paying out, of the cable from the winch drum; (f) a saddle
pivotally secured to the boom for engaging the article to be towed; (g) a
cable guide assembly pivotally secured to the boom, adapted to provide a
controlled surface about which such cable is adapted to bend to one side
or the other while remaining substantially in the line with such sheave
means; (h) means for resiliently applying a torque 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; and (i) a levelling mechanism for selectively retaining the saddle in
a common horizontal position irrespective of the pivotal movement 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, particularly where there is no
space limitations on board the ship to make the stowing of the towed body
difficult.
. Another improved such system which has been provlded heretofore
is disclosed in Canadian Patent No. 1,010,308 granted May 17, 1977 to
Vf~
Ronyx Corporation Limited, for "Towing System". According to that patent,
an improvement is provided in a towing system including the combination
of: (a) a boom
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member pivotally securable to a towing vehicle; (b) drive means for
selectively pivoting the boom member about a substantially horizontally
axis; (c) a driven winch assembly having a drum for winding in, and paying
out, a faired cable; (d) a faired cable wound on the drum and adapted to
be connected adjacent the other end to an article to be towed; (e) sheave
means on the boom engaged with the csble during winding in, and paying
out, of the faired cable from the winch drum; (f) a saddle pivotally se-
cured to the boom ~or engaging the article to be towed; and (g) a cable
assembly pivotally secured to the boom to provide a controlled surface
abo~t which such cable is adapted to bend to one side of the other while
remaining substantially in line with the sheave means as the article i9
being towed; the improvement comprising: (g) a body rest secured to the
boom member (a) and adapted positively to support the article to be towed
when the boom is at itæ maximum inboard position. This system has been
found to be useful for towing a body in calm sea states and in certain
high sea states, particularly where there is no space limitations on
board the ship to make the stowing of the towed body difficult.
Most of the systems heretofore described suffer from the same
drawbacks in that they may sub~ect the cable to points of inflection or
small bending radii, severely stressing the cable and shortening it's life;
or they may damage the fairings; or they can subject the saddle or other
means for capturing the body to extremely high and damaging side loads.
;3061
Accordingly~ an object of a broad aspect of this invention is to
provide an improved means for accommodating tow-off while not severely
stressing the cable, thereby shortening its life.
An object of another aspect of this invention is to provide
such an improved means which does not substantially damage the fairings.
An object of still another aspect of this invention is to provide
such an improved means which does not substantia11y subject the saddle to
extremely high and damaging side loads.
By one 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, the system including a hoist sub-assembly and a boom sub-
assembly which are mounted on a turntable for pivoting about a vertical
axis from an inboard ~tow position to an outboard launch, recovery and tow
position, the hoist sub-assembly and boom sub-assembly being provided with
the combination of (a) a pivotal boom member; (b) drive means for selective-
ly pivoting the boom member about a substantially horizontal axis; (c) a
driven winch assembly having a winch drum for winding in, and paying out,
a faired cable; (d) a faired towing cable secured by one end to, and wound
on, the drum and adapted to be connected adjacent its outer end to an arti-
cle to be towed; (e) fairlead sheave means on the boom member engaged withthe faired cable during winding in, and paying out, of the faired cable from
the winch drum; and (f) means for resiliently providing shock absorbing
capability to the boom member in response to changes in a load applied to
the towing cable; the improvement being provided by a fairlead assembly
(g) comprising: (i) a hooded fairlead freely rot~tably mounted at the end
of the boom member for rotation around its longitudinal pivot axis; (ii)
engaging means for engaging the towed body, such means being pivotally
mounted at the end of the hooded fairlead for pivotal movement about.an
axis substantially parallel to the rotational axis of the fairlead sheave
means; and (iii)
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1~9~3061
tilting means for positively tilting the towed body engaging means through
a sufficient angle, e.g., an angle greater than 90; whereby the center
of gravity of the fairlead assembly lies along the longitudinal pivot axis;
and whereby the fairlead assembly is free to pivot about the longitudinal
pivot axis to accommodate tow-off in response to changes in loading of the
faired towing cable.
By one variant, the engaging means comp'rises a saddle mounted in
a frame, the saddle having a lower surface provided with gripping means
for engaging the towed body.
By another variant, the fairlead assembly includes a flanged
quill, the flange of which is se~ured to the end of the boom assembly, the
quill of which supports bearings on which the hooded fairlead is rotatably
mounted; and means positively actuatable to permit, or to prevent, rota-
tion of the hooded fairlead with respect to the flange.
By a variation thereof, the means comprises brake shoes, e.g.,
external brake shoes, bearing on the flange of the hooded fairlead, and
being actuated by an hydraulic cylinder molmted on the flange of the
quill.
By another variation, the means comprises a pinning arrangement~
By a further variant, the fairlead sheave includes a towing sheave
which is disposed at the end of the hooded fairlead, the saddle being on
the shaft of the towing sheave.
By a variation thereof, the saddle is actuated to pivot about
the shaft of the towing sheave by means of a hydraulic cylinder mounted
between the hooded fairlead and the saddle frame.
By a further variation, the frame for the saddle includes a
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~}9~
rectangular framework including a hollow aft cross member containing, e.g.,
filled with ballast ma~erial, to provide an exact
counterbalance about the longitudinal pivot axis.
In general, a structure is provided for accommodating tow-off
without substantially overstressing of cable o. saddle, and without permit-
ting the cable to jump out of, or scuffing, the towing sheave. This struc-
ture includes a hooded fairlead and a saddle wh.ich is actuated to tilt up
out of the way during normal towing. In so tilting, the saddle balances
the fairlead about its pivot point, and allows free, counterbalanced
pivoting of the fairlead and towing sheave in response to variations in
the direction of cable pull.
While a saddle is shown as the preferred variant, the saddle
could be replaced by a set of clamps or any other structure used to capture
the towed body and having sufficient mass to act as an effective counter-
weight.
In the accompanying drawings,
Figure 1 is a longitudinal cross-section through the fairlead and
saddle in an aspect of this invention;
Figure 2 is an outside longitudinal view similar to that shown
in Figure l;
Figure 3 is an outside longitudinal view showing the saddle and
tow cable leaving the sheave in a normal towing situation; and
Figures 4a, 4b and 4c show, schematically, aft views of the
assembly in both pivoted and unpivoted positions during towing.
Before discussing the aspects of the invention shown in the
drawings in detail, it is desired to point out that the fairlead and
saddle as shown are preferably used with the system for launching and
recovering the towed body as disclosed and claimed in the above-mentioned
Canadian Patent ~o. 1,005,702.
That patent provides a towing system in which a variable depth
~'
109;~0~
sonar towed body is transferred from an inboard stowed position to an
outboard launch position. 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 launch
ing procedure. In addition to having means for.launching, towing, depth
changing and recovery operations, the preferred embodiment described
includes a shock absorber system that prevents excessive variation of the
cable tension caused by wave action.
The embodiment specifically taught a towing winch assembly, a
lifting boom assem~ly, a saddle/cable guide/sheave assembly, and a shock
absorber system. In addition, a hydraulic power unit and motor controller
are also provided.
The towing winch assembly, in one of its embodiments, consists
of a winch drum mounted on a base frame which is secured to the aft upper-
deck of the ship. The winch drum is driven by a hydraulic motor which
incorporates a spring applied-hydraulic release-type band brake. The winch
drum drives a conductor winder mounted on the starboard side of the winch
drum and which provides electrical continuity from the conductors (not
shown) of the tow cable to the internal sonar circuits (not shown) of the
ship.
The function of the winch assembly is to pay out and haul in the
desired length of tow cable and to assist the boom and actuator assembly
in the launch and recovery of the towed body.
The winch drum may be fabricated from aluminum plate, consisting
of an outer shell with reinforcing plates on the inner surface and on the
ends. The reinforcing plates are all of open-type construction for light-
ness and for allowing access to the electrical conductor cable inside the
winch drum. The outer surface of the winch drum is grooved with grooves
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lVg3~61
to accommodate the required length of faired tow cable in a single layer.
Holes are drilled at intervals around the periphery of the winch drum to
permit drainage.
The anchor of the tow cable is clamped within an anchor block
which is bolted to the inside face of the port end plate of the winch drum.
Another clamp is secured on the inside of the winch drum to one of the
reinforcing plates for holding an electrical con~Pctor that is on the end
of the conductor cable. A stub shaft is bolted to both end plates of the
winch drum. Each shaft rotates within bearings, preferably fabric-rein-
forced phenolic bearings, which are mounted in pillow blocks that are
secured to the winch frame. Grease nipples are readily accessible on the
pillow blocks for lubrication of the bearings.
The winch frame in one of its preferred embodiments is a welded
aluminum structure that supports the complete hoist. Suitable surfaces
are provided on the winch frame for attachment of the winch bearing assem-
blies; of the winch motor and band brake assembly; of the boom actuator;
of the conductor winder; and of the gas bottles, linear actuators and
sheaves for the shock absorber system.
The winch drum may be driven through a starboard stub shaft by a
low speed, high torque radial piston type hydraulic motor. The motor is
integral with a spring-applied, hydraulic release-type band brake complete
with mounting bracket.
A conductor winder is included to provide the means for maintain-
ing electrical continuity between the conductors of the tow cable and the
internal sonar circuits of the ship without the use of slip rings. It is
positioned on the port side of the winch drum and in one of its embodi-
ments is contained within a watertight enclosure, preferably formed of
aluminum, which has two inspection windows. The winder consists of a
primary drum, a stationary spool and a negator s-pring assembly.
The winder mechanism consists of an arm attached intermediate
~- 8b -
lt)9~0~
the ends thereof to a shaft for rotation in the hub and has a portion pro-
jecting beyond the side wall of the spool for the purpose which will
become apparent hereinafter. The arm terminates at one end in a bifurcated
portion having a sheave pivotally secured thereto, for example, by a pin.
A plurality of counterweights are detachably secured to the opposite end
of the arm. The arm, accordingly, rotates about the axis of the shaft
which, in turn, is coincident with the axis of the shaft. The sheave is
r freely rotatable about the pin with the axis thereof being perpendicular
to the axis of the arm.
The winder mechanism is attached to a negator spring assembly
which consists of a drum, secured to a portion of the shaft which projects
through the casing side wall, a coiled band spring and an anchor for the
spring. The drum is secured to the shaft and wound on the outside thereof
is the band spring anchored at one end to the drum and the other end is
wound around a storage spool, which is pivoted onto a stub shaft secured
to the casing side wall. The band spring has a selected length which is
coiled onto a storage spool and the stored coil spring resists uncoiling.
The outer end of the coiled spring is attached and coiled in the reverse
direction onto the drum (work spool). The spring, acting to try to coil
itself clockwise onto the storage spool, exerts a relatively constant
counterclockwise torque on the work spool (drum). This results in biasing
the drum to rotate in an anti-clockwise direction. Since the drum is
secured to the shaft, the winder bar is accordingly spring-biased in an
anti-clockwise direction. The band spring has preferably substantially
constant torque characteristics.
The conductor cable i9 connected to the tow cable by a plug-
receptacle arrangement which is clamped to the inside of the winch drum.
Cable is routed through the drum hum and the port stub shaft onto the
primary drum of the winder. It then passes over a pulley assembly and
onto the stationary spool. From this spool, the cable passes through a
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~0~3V~il
stuffing tube in the bottom of the winder enclosure to the internal cir-
cuits of the ship. Rotation of the winch drum in either direction causes
the cable to pass back and forth between the primary drum and the station-
ary spool via the pulley assembly. The pulley assembly which is counter-
balanced at one end by a weight is connected to the negator spring assem-
bly. This spring assembly maintains the pulley assembly spring biased in
a counterclockwise direction (looking to starboard), thereby maintaining
a nominal tension in the conductor cable at all times.
A maximum cable-out limit switch is also mounted within the
winder enclosure. It is actuated by a cam which is driven via a worm
gear reducer and chain drive by a sprocket that is secured to the port
stub shaft of the winch drum. The winder enclosure is heated by two
heater strips complete with a fixed thermostatic control to ensure that
the conductor cable remains flexible at all times.
The operation of the winder mechanism may be described as
follows: The winch drum is appropriately rotated to wind in and pay out
cable. When the tow cable is stored on the winch drum, that is, in a
wound-in position, the majority of the multi-conductor cable extending
beyond the winch drum is stored on the stationary spool. As the winch
drum is rotated clockwise to pay out the cable, primary drum rotates in
unison with the drum causing the cable to be wrapped, turn by turn, on
the primary drum. Since the supply of the cable is on the non-rotatable
stationary spool, the resultlng pull on the cable causes a turning move-
ment to act on the winder bar mechanism. This turning force in consequence
causes the bar to rotate in the same direction as the winch drum against
the bias of the spring. As the winder bar rotates, it pulls the cable off
the stationary drum and this effectively transfers the cable from the
primary drum to the rotary storage drum. The bias of the spring prevents
slack cable from developing and thus the cable removed from the stationary
spool will travel over the sheave and will wrap onto the drum because of
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1~9~0~1
the bar rotating at a slower speed than the drum. The speed of rotation
of the winder bar should be ~ust sufficient as to maintain tension in the
continuity cable and it will find its own speed since it will be dragged
around by the pull on the multi-core conductor cable.
The above operating description is based on the case of the
winch paying out cable. When the winch is reeling cable in, the conductor
cable winder performs the same function except ~hat the spring bias takes
up the slack of cable removed from the drum and transfers it to another
drum.
Two camrol bearings are mounted on the winch frame such that
each bearing has a small clearance with the side edges of the port and
starboard winch drum end plates. The purpose of these camrol bearings is
to distribute side shock loads from the winch drum into the winch frame.
A grease nipple is installed on each bearing for lubrication.
Two boom stops are mounted on the winch frame to stop and
support the boom in the inboard stowed position. Each stop in one embodi-
ment thereof consists of an aluminum weldment fitted with an elastomeric
rubber bumper pad. A lower body stop is mounted on the winch frame to
support the forward portion of the towed body from underneath when in the
inboard stowed position. It consists, in one embodiment thereof, of an
aluminum weldment fitted with an elastomeric rubber bumper pad.
The boom assembly, in one of its embodiments, includes a boom
which is fabricated of arms consisting of aluminum beams and plates
rigidly bolted together with a cross brace to form an "H" configuration.
Two pillow blocks, preferably made of steel, are bolted to inboard ends
of the boom arms and are then keyed to the stub shafts of the actuator.
Rotary actuator is mounted on the base frame of the towing winch assembly.
The purpose of the boom and actuator assembly is to transfer
the towed body from the inboard stowed position to the outboard launch
position and vice versa, with the aid of the winch assembly.
8e -
1~9;~
The boom is moved from the inboard stowed position to the out-
board la~mch position and vice versa by a rotary actuator, which prefer-
ably is a hydraulic rotary actuator. The actuator is secured to the under-
side of that part of the winch frame that overhangs the stern of the ship.
The horizontal center line of the actuator is positioned at 2 - 3, pre-
ferably at 2-1/2, from the athwartship cente~ line. This results in the
boom sheave moving with a slight sideways motion during the launch and
recovery cycles so as to aid the correct spooling of tow cable on the winch
drum.
Secured transversely across the boom arms is an H-shaped beam
stop member. When the boom is in its outboard launched position, stop mem-
ber engages rubber bumpers, secured to the stern of the ship.
The saddle/cable guide/sheave assembly is carried on a hori~on-
tal shaft which is supported at the outboard extremities of the lifting
boom. The saddle provides a stable seating for the towed sonar body during
launching and recovery, and is maintained in a near horizontal attitude by
means of a levelling mechanism. It also affords protection to the towed
body by means of bumpers, preferably formed of polyurethane, mounted on
its underside. The cable guide assembly includes a cluster of side guide
rollers against which the tow cable bears during towing operations. To
compensate for the various tow cable angles, the guide is made spring-
biased using two laminated band springs in a direction such that the
rollers will always be at right angles to the tow cable.
The sheave shaft consists preferably of a chrome plated steel
tube secured to the outboard ends of the boom arms. Sheave shaft supports
the sheave, saddle assembly and cable guide assembly.
The sheave in one embodiment is an aluminum structure which
freely rotates on the sheave shaft on bearings, preferably fabric-rein-
forced phenolic bearings. It is made up of a weldment to which are bolted
two rims which form the groove of the sheave. In this groove are located
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~093061
a plurality, e.g~, eight, arcuate segments of a plastics material, e.g.,
polyurethane material, which serve to protect the nose pieces of the
fairings of the tow cable. A grease nipple is readily accessible for
lubrication of the bearings.
The saddle assembly in one embodiment is a welded structure
made of aluminum plates whose purpose is to provide a stable seating for
the towed body during launching and recovery. The assembly is supported
on the sheave shaft in bearings, preferably fibre-reinforced phenolic
bearings. A grease nipple is readily accessible on each bearing for lubri-
cation.
A plurality, e.g., eight, semi-spherical bumpers, preferably of
polyurethane, are bolted to the underside of the assembly. They are posi-
tioned to conform with the upper curvature of the towed body and afford
protection to the body during launching and recovery operations.
The design of cable guide effectively eliminates the need of
having long side rollers extending aft sufficient to accommodate the
various tow cable angles. The cable guide assembly, in one of its embodi-
ments, consists of two welded aluminum arms each supported at one end of
the sheave shaft in bearings, preferably fibre-reinforced phenollc bearings.
A grease nipple is readily accessible on each bearing for lubrication. The
assembly is cross-connected at the other end of each arm with three spacer
tubes. On two of the tubes are mounted freely rotating rollers, prefer-
ably fibre-reinforced phenolic rollers, one roller being forward of the
tow cable a~d the other being aft. Similar rollers are mounted on the
side of each arm so that tow cable passes through the middle of the cluster
of rollers. The cable guide assembly is connected to the saddle assembly
by two constant torque band springs. These springs make the cable guide
spring biased in a direction such that the forward roller always bears
against the nose pieces of the fairings of the tow cable regardless of tow
cable angle.
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1(~9;~
The saddle assembly is maintained in a horizontal attitude at
all boom positions by a levelling assembly. Such assembly consists of two
sets of two pulleys 9 one set being located on the port side, the other set
being located on the starboard side. One pulley of each set is secured to
the housing of the boom actuator and the other pulley of each set is on
the saddle assembly. Each set of pulleys is connected by a cable, prefer-
ably a stainless steel cable that is fixed to each pulley by clamp pins.
The shock absorber system consists of two identical sets of com
ponents, one set being located on the port side of the winch frame, the
other set being located on the starboard side. Each set consists of a
spring return-type linear actuator which is hinged at its head end by hinge
pins to the extreme forward side of the winch frame. The rod end only of
each actuator is charged with a compressible fluid, e.g., a gas, for
example, nitrogen gas, from a supply of two gas bottles which are mounted
on the forward end of the winch frame. The gas pressure in the actuators
can easily be changed by manipulating two valves on the hydraulic power
unit. The piston rod of the actuator is connected to a length of cable,
which passes over a freely rotating pulley mounted on the winch frame.
The cable is then connected to a torque arm that is secured to the boom
assembly hinge point.
When a towed sonar body is brought on board conventionally, it
is lowered down to the deck of the ship into a cradle suitably located and
fixed to the deck. On smaller ships or on a crowded deck, it may not
always be possible to provide the required space for a cradle.
As a solution for such cases, a body rest has been attached to
the boom in such a way that the towed body comes automatically to a seat-
ing in this body rest, when the boom arrives at its most inboard position.
This body rest might support the body fully or only partially, in which
case a supplementary deck-mounted support will coexist.
The towing syste~ is hydraulically actuated, the system being
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l(~9;~V6i
manually and electrically controlled from a hydraulic power unit. A feat-
ure of one embodiment is that during launch and recovery operations the
towed body is held firmly in the saddle by tension in the tow cable. This
tension is maintained near constant by a pressure compensated, closed loop,
hydrostatic drive system.
Movement of the boom 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 within the actuator.
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 relatively 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 the moment on the boom due to the actuators will decrease sufficiently
to counteract the moment caused by the decreased cable pull.
A hydraulic power unit is provided to operate the system. It
includes a variable displacement axial piston pump system having both
manual and pressure compensation controls. A closed loop, including a
double shaft electric motor and pump, provides a hydrostatic drive system
that drives the winch motor at variable speed and in both directions.
Also included in the hydraulic power unit is a fixed displace-
ment tandem gear pump. One outlet of the pump supplies oil, filtered
through 10 micron filter to the boom circuit; the other outlet supplies
oil,.filtered through 10 micron filter, for release of the winch bra~e and
for the swash controls of the variable displacement pump.
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3061
The above components together with several valves are mounted on
a 55 gallon capacity reservoir. The reservoir, in one of its embodimen~s,
is a welded aluminum structure provided with the usual gear, e.g., clean-
out covers, a filler-breather cap, an oil level gauge a~d a drain valve.
It is also provided with oil strainers of 250 micron size to protect the
pump from contamination.
The winch assembly, in one of its embpdiments, is driven by a low
speed, high torque, radial piston hydraulic motor which is of the rotating
housing type. The band brake which is spring applied and hydraulically
released by a linear actuator acts on the ou~er surface of the motor hous-
ing. The motor, band brake and actuator are mounted on a common base.
The boom is preferably moved by a hydraulic, double vane-type,
rotary actuator, which has a maximum angular travel of 155.
Accordingly, the fairlead and saddle of aspects of this inven-
tion are preferably used in conjunction with the system of Canadian Patetn
No. 1,005,702 including the combination of: (a) a pivotal boom member
pivotally securable to a towing vehicle; (b) drive means for selectively
pivoting the boom member about a substantially hori~ontal axis; (c) a
driven winch assembly having a drum for winding in, and pyaing out, a
faired cable; (d) a faired towing cable secured by one end to, and wound
on, the drum and adapted to be connected adjacent its outer end to an
article to be towed; (e) fairlead sheave means on the boom member engaged
with the faired cable during winding pin, and paying out, of the cable
from the winch drum; and (f) means for providing shock absorbing
capabilities in response to changes in a load applied to the faired towing
cable. The saddle is mounted in a frame and has a lower surface provided
with gripping means for engaging the towed body. The means (b) preferably
is a boom bobbing means for resiliently applying a torque to the boom mem-
ber about the pivotal connections of the boom to the surface vessel com-
mensurate with, and in response to, changes in a load applied to and/or
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1~9;~061
the moving moment of, the boom member.
The improvement in the aforementioned system is provided by the
fairlead assembly to be described hereinafter.
~ enerally speaking, Figures 1 and 2 show the saddle and tow cable
leaving the sheave in a position more or less corresponding to a launch or
recovery situation (although the towed body i,tself is not shown). Refer-
ring now specifically to the Figures, the assembiy 10 is mounted on a
structure 11 usually a towing boom which may be that disclosed in pending
application Serial No. 327,663 filed ~ay l5, 1979 for a "Retractable Boom
Assembly and Apparatus for Towing an Underwater Body". I~hile not shown
here, the boom is part of a hoist sub-assembly and boom sub-assembly which
is mounted on a turntable for pivoting about a vertical axis from an
inboard stow position to an outboard launch, recovery and tow position,
as more fully described in pending application Serial No. 324,215 filed
MarOEh 27, 1979 for "Means for Launching, Recoverying and Towing an Under-
water Body".
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0~1
The saddle 12 is open ended at the forward end and consists
of the usual side members 13, 14 with an aft cross member 15, which may
or may not be filled with heavy ballasting material (16, as shown), as
required, to obtain an exact counterbalance when tilted as shown in Figure
3. The saddle 12 is shown suspended from the towing sheave shaft 17, but
may instead be supported from a separate shaft on pins (not shown). The
saddle 12 is also connected to the fairlead housing 18 by a hydraulic
cylinder or cylinders 19. The towing sheave 20 is mounted on bearings 21
on its shaft, or the shaft itself may be mounted on bearings (not shown)
in the fairlead housing. The tow cable 22 extends through the throat 23
and 50 of the assembly 10 and over the towing sheave 25. The fairlead
housing 18 is mounted on a bearing or bearings 26 which allow the housing
18 to pivot or twist about the axis 27 through the throat 23 and 50 of the
assembly 10. The bearing or bearings 26 are in turn mounted on a quill 28,
the flange 28 of which is bolted to structure 11. A set of external brake
shoes 29 is supported on a pin 30 attached to the quill flange 28. These
shoes 29 bear on the flange 31 of the fairlead housing 18, and are caused
to release or apply by a double ended hydraulic brake cylinder 32, also
mounted on the quill flange 28. Other types of brakes or various pinning
arrangements may be used in lleu of external shoe brakes.
The operation of this device of an aspect of this invention is
as follows:
During launch and recovery saddle 12 is held in a hori~ontal
position approximately as shown in Figures 1 and 2 (which are correct if
boom
~ D g
1~9~
structure 11 is horizontal, but somewhat different if boom structure 11 is
tilted down towards the water or up into the air by hydraulic cylinder(s)
19. It is to be observed that saddle 12 itself is controlled and held
horizontal during launch and recovery. Brake shoes 29 are applied to fair-
lead housing 18 to hold the bottom surface 13 of the saddle 12 level in the
athwartships direction, i.e., substantially to prevent the fairlead 24 from
pivoting. When the body is released and normal ;towing conditions prevail,
hydraulic cylinder(s) 19 tilts the saddle 12 up into position shown in
Figure 3, at which point the combined center of gravity of fairlead housing
18, cylinder(s) 19, sheave 20, bearing(s) 21, sheave shaft 17 and saddle
12 lie along the pivot axis 27 of the fairlead housing 18. The brake
shoes are then releasedby brake cylinder 32 and the entire assembly of
fairlead housing 18, cylinder(s) 19, sheave 20, bearing(s) 21, shaft 17 and
saddle 12 is free to pivot effortlessly about the axis 27 in response to
changes in direction of tow cable loading. By virtue of the counter-
balance feature, it will automatically assume any pivotal position in res-
ponse to the direction of tow cable loading and remain effortlessly in
that pivoted position with the sheave shaft 17 perpendicular to the tow
cable 22 as shown in Figures 4a, 4b and 4c until the direction of tow
cable loading changes once again.
The hood 24 of fairlead housing 18 will also prevent the tow
cable 22 from jumping off sheave ~0 under snap loading of the tow cable.
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