Towing device with a hinged fairlead
The invention relates to a towing device intended to be fitted to the
deck of a ship and allowing the towing of an object trailed behind the ship.
The towing device in the conventional way comprises a winch, a cable and a
fairlead, the cable running through the fairlead under the action of the winch.
5 This type of device is, for example, used in the field of underwater acoustics,
and more particularly for towed active sonars. These sonars generally
comprise an emission antenna incorporated into a submersible object or
"fish" and a receiving antenna consisting of a linear antenna or "flute". When
the sonar is being used as a towed hanging sonar, the fish and the flute are
10 attached to the same cable so that they can be towed by the ship.
The cable generally comprises a core made up of electrical and/or
optical conductors allowing energy and information to be transmitted between
sonar equipment situated onboard the ship and the antennas. The core of the
cable is generally covered by strands of metal wires which provide the
15 mechanical strength of the cable. The makeup of the cable dictates a
minimum radius of curvature thereof. Below this radius, inadmissible
mechanical stresses are induced and cause these elements to deteriorate.
The winch fixed to the deck of the ship has a drum onto which the cable can
be wound when the sonar is inactive and when the antennas are stowed
20 onboard the ship. The diameter of the drum guarantees that the wound
elements will not be curved to a radius smaller than the minimum radius of
curvature.
When the towed elements are in the sea, the cable is guided by
the fairlead which safeguards its effective radius of curvature. During towing,
2s the ship may alter its speed and its heading. Other involuntary movements of
the ship may occur when the sea state worsens, notably in heavy weather.
These movements of the ship lead to a change in the direction of the cable
with respect to the axis of the ship. In order to prevent changes in direction
from damaging the cable, the fairlead may be fixed with respect to the ship
30 and have a flared trumpet shape opening toward the rear of the ship.
Furthermore, in underwater acoustics, the fairlead needs to be
suited to allowing the antennas to be raised up onto the deck of the ship. The
fairlead is, for example, open at its top. The ship may be equipped with an
articulated arm that allows the fish to be passed over the fairlead.
The existing devices are bulky and require an actuator to move the
articulated arm. In addition, as the fish is being passed over the fairlead,
s anti-unrigging systems need to be employed to prevent the cable to which
the towed elements are fixed from leavihg its housing in the fairlead.
The invention seeks to alleviate all or some of the
abovementioned problems by proposing a towing device that guarantees that
l o the cable cannot bend beyond a minimum radius of curvature and that makes
it easier for towed bodies to pass the fairlead. The invention also makes it
possible to dispense with an articulated arm intended to take hold of a towed
body before it reaches the fairlead as the cable is being wound in.
To this end, the subject of the invention is a towing device
15 intended to be fitted to the deck of a ship and comprising a winch, a cable
and a fairlead, the cable running through the fairlead under the action of the
winch, characterized in that the fairlead comprises at least a first and a
second sector, the sectors allowing the cable to be guided in a groove made
in each of the sectors, a first articulation with a degree of freedom to rotate
20 about an axis, the articulation connecting the two sectors, the axis being
substantially perpendicular to a direction in which the cable runs substantially
through the fairlead at the articulation, and limiting means that limit the
angular travel of the articulation, and in that the sectors and the limiting
means are dimensioned so as to prevent the cable from exceeding a lower
25 limit of radius of curvature. .
The invention will be better understood and other advantages will
become apparent from reading the detailed description of one embodiment
given by way of example, which description is illustrated by the attached
30 drawing in which:
figure 1 schematically depicts a ship towing an active sonar;
figures 2, 3 and 4 depict an example of a fairlead used in a towing
device intended to be fitted to the ship for towing the sonar;
figures 5, 6 and 7 depict various alternative forms of fairlead in
35 cross section in a plane containing a cable;
figure 8 depicts the fairlead of figure 7 in another position.
For the sake of clarity, in the various figures the same elements
bear the same references.
5 The invention is described with reference to the towing of a sonar
by a surface vessel. Of course, the invention may be implemented in the
case of other towed elements.
Figure 1 depicts a ship 10 towing an active sonar 11 comprising
an acoustic emission antenna 12 often referred to as a fish and an acoustic
10 receiving antenna 13 often referred to as a flute. The sonar 11 also
comprises a cable 14 that allows the two antennas 12 and 13 to be towed.
The cable also carries signals and power between the ship and the antennas
12and 13ofthesonar 11.
The antennas 12 and 13 are mechanically anchored and
15 electrically and/or optically connected to the cable 14 in a suitable manner.
Conventionally, the receiving antenna 13 is formed of a linear antenna of
tubular shape identical to those found in passive sonars, hence its name of
flute, whereas the emission antenna 12 is incorporated into a voluminous
structure of a shape likenable to that of a fish. The receiving flute is generally
20 at the rear, at the end of the cable 14, the fish being positioned on that part of
the cable 14 which is nearest to the ship 10. During an underwater acoustic
mission, the antenna 12 emits sound waves into the water and the receiving
antenna 13 picks up any echoes coming from targets off which the sound
waves from the antenna 12 are reflected.
25 The receiving antenna 13 is generally permanently anchored to
the cable 14 whereas the fish 12 for its part is anchored removably. For this
purpose, the cable 14 has an anchor zone 15 for the fish 12, in which zone
means are installed for mechanically fixing the fish 12 and for electrically
andlor optically connecting it to the cable 14.
30 The launching and retrieval of the antennas 12 and 13 are carried
out using a winch 16 arranged on a deck 17 of the ship 10. The winch 16
comprises a drum 18 dimensioned to allow the cable 14 and the reqeiving
antenna 13 to be wound on. The winding of the cable 14 allows the frsh 12 to
be hauled onboard the ship 10, for example onto an aft platform 19 provided
35 for this purpose.
A fairlead 20 guides the cable 14 downstream of the drum 18. The
fairlead 20 constitutes the last element to guide the cable 14 before it drops
down into the water. During towing, the inclination of the cable 14 may vary
with respect to the longitudinal axis of the ship 10. The variations in
s inclination are caused notably by changes in the heading and speed of the
ship and also in the sea state. One of the functions of the fairlead 20 is to
guarantee that the radius of curvature of the cable 14 does not drop below a
lower limit. The cable 14 for example comprises a core formed of electrical
andlor optical conductors that allow energy and information to be transmitted
10 between sonar equipment situated onboard the ship 10 and the antennas 12
and 13. The core of the cable 14 is generally covered by strands of metal
wires that provide the cable 14 with its mechanical strength, notably its
tensile strength. Below the lower limit of curvature, there is a risk of
permanent deformations or breaks of parts of the cable 14.
15
Figures 2, 3 and 4 depict the fairlead 20 when a fish 12, attached
to the cable 14, passes through it. Figure 2 is a perspective view, figure 3 is a
view in a plane in which the cable 14 bends and figure 4 is a view in cross
section in a plane perpendicular to the cable 14.
20 According to the invention, the fairlead 20 comprises at least two
sectors articulated to one another. In the example depicted, the fairlead 20
comprises three sectors 21, 22 and 23. Of course a higher number of sectors
is possible without departing from the scope of the invention.
Each of the sectors comprises a groove 24 for sector 21, 25 for
2s sector 22 and 26 for sector 23. These grooves guide the cable 14 along the
entire length of the fairlead 20. They are more or less in the continuation of
one another. Each of the sectors 21, 22 and 23 runs substantially in the
direction of the cable 14 while at the same time allowing the cable 14 to
bend. Each of the sectors 21, 22 and 23 is dimensioned in such a way as to
30 limit the maximum curvature of the cable 14.
In addition, the fairlead 20 comprises an articulation 27 connecting
the sectors 21 and 22. The articulation 27 has just one degree of freedom to
rotate about an axis 28 substantially perpendicular to a direction in which the
cable 14 runs substantially through the fairlead at the articulation 27. The
articulation having a degree of freedom to rotate is also referred to as a pivot
connection.
Likewise, the fairlead 20 comprises an articulation 29 connecting
the sectors 22 and 23. The articulation 29 has just one degree of freedom to
5 rotate about an axis 30 substantially perpendicular to a direction in which the
cable 14 runs substantially through the fairlead at the articulation 29. The
axes 28 and 30 of the two articulations 27 and 29 remain parallel to one
another as the sectors 21, 22 and 23 rotate relative to one another. The axes
28 and 30 are perpendicular to the plane of figure 3.
10 For each of the articulations 27 and 29, the fairlead 20 comprises
means of limiting the angular travel thereof. More specifically, the sectors 21,
22 and 23 can come into abutment against one another in order to limit the
angular travel of each of the articulations 27 and 29. This butting-together of
the sectors 21, 22 and 23 also limits the radius of curvature of the cable 14.
is In other words, the radius of curvature of the cable 14 is limited both by the
shape and dimensions of the sectors considered individually and by the
maximum ability of the sectors to move relative to one another.
The various sectors 21, 22 and 23 allow the cable 14 to change
direction in the plane of figure 3. For example, each of the sectors 21, 22 and
20 23 can be defined in such a way that they allow the cable 14 to change
direction by a maximum of 30". For three sectors a maximum change in
direction of 90" may therefore be obtained when the sectors 21, 22 and 23
are in abutment against one another. This change is realized in the plane of
figure 3. The fairlead 20. makes it possible to limit the radius of curvature of
25 the cable 14 during this change in direction.
It is possible to fix the sector 21 onto a supporting structure
secured to the aft platform 19. When this is so, the fairlead 20 will be
arranged in such a way that the articulations 27 and 29 are horizontal. This
layout allows the cable 14 to be pivoted from a substantially horizontal
30 direction with respect to the ship 10 into a substantially vertical direction. The
horizontal direction is, for example, the direction adopted by the cable 14
upstream of the fairlead 20, between the drum 18 and the fairlead 20. The
vertical direction is, for example, that adopted by the cable 14 downstream of
the fairlead 20 as the cable 14 enters the water. A 90" change in direction is
35 obtained when the ship 10 is stationary or when a towed body is being
' immersed. The cable 14 therefore drops vertically down into the water. The
sectors 21, 22 and 23 are then all in abutment against one another.' As the
ship 10 picks up speed, the cable 14 becomes inclined to reduce the
inclination of the change in direction. The sectors 21, 22 and 23 are then no
5 longer in abutment against one another and pivot relative to one another
about'the articulations 27 and 29.
This fixed arrangement of the sector 21 with respect to the ship 10
does, however, present a disadvantage when the ship changes heading. In a
horizontal plane, the cable 14 has then to change direction with respect to
10 the ship's heading. This change in direction may, for example, be achieved
by means of a flared trumpet shape of the lasi sector of the fairlead 20 which,
in the example depicted, is the sector 23. This flared trumpet shape does not
allow significant changes in direction. Advantageously, the first sector 21 is
articulated with respect to the ship 10 so as to allow a greater amplitude of
1s change in direction of the cable 14 when the ship 10 changes heading. Such
an articulation also provides better guidance of the cable 14 over the entire
length of the fairlead 20 and notably in the final sector 23.
More specifically, the fairlead 20 comprises a supporting structure
and an articulation 40 with a degree of freedom to rotate about an axis 31,
20 the articulation 40 connecting the sector 21 and the supporting structure. The
supporting structure may be fixed to the ship 10, for example on the aft
platform 19 or on a reeling system allowing correct stowage of the cable 14
on the drum 18. When the supporting structure is fixed to the reeling system,
it is the entire fairlead 20 that effects translational movements parallel to the
2s axis of the drum 18 in order to stow the cable 14 correctly on the drum 18.
The axis 31 is contained in a plane 32 perpendicular to the axis 28 of the
articulation 27. This is the plane of figure 3 which is also shown in figure 4.
The plane 32 can be inclined with respect to a vertical plane of the ship 10,
notably when the ship 10 changes its heading. The inclination of the plane 32
30 is achieved when the articulation 40 pivots. When the cable 14 passes
through the fairlead 20, it is always contained in the plane 32 and the loads
experienced by the cable 14 upstream and downstream of the fairlead 20 are
always contained in the plane 32. The fairlead 20 pivots about the articulation
40 according to the direction of the loads applied to the cable 14.
The axis 31 may be parallel to the direction followed by the cable
14 between the fairlead 20 and the winch 16. This layout of the articulation
40 nonetheless leads to lateral travel of the cable 14 in the sector 21. To
alleviate this problem, the axis 31 advantageously intersects the groove 24 at
5 a point 41 at which the cable 14 is designed to come into contact with the
groove 24 on the winch 16 side. This orientation of the axis 31 allows a
marked improvement in the control over the actual point at which the cable
14 and the sector 21 come into mutual contact. It is then easier to correctly
manage the position of the cable 14 between the fairlead 20 and the winch
lo 16 and thus avoid problems of poor winding of turns of the cable 14 onto the
drum 18. It will be noted that when the supporting structure is fixed with
respect to the ship 10, there can be a small offset between the point 41,
defined during the design of the fairlead 20, and the actual point at which the
cable 14 comes into contact with the sector 21. This offset is caused, for
15 example, by the winding of several turns of cable 14 onto the drum 18.
However, this offset remains small in relation to the possible lateral travel of
the cable 14 when the axis 31 is parallel to the direction of the cable 14. By
contrast, when the supporting structure is secured to a reeling system, the
actual point of contact remains coincident with the point 41.
20 Along the entire length of the three sectors 21, 22 and 23, the
corresponding grooves 24, 25 and 26 have substantially constant cross
sections. The shape of the cross section of one of these grooves can be
made out in figure 4. The groove 24 has a cross section in the shape of a
letter C with the opening at the side, i.e. open along an axis 33 substantially
25 perpendicular to the plane 32. The opening 34 of the groove 24 may allow
the cable 14 to be inserted into the fairlead 20. The opening 34 above all
allows a fixing 35 for the fish 12 to pass along the fairlead 20. The fish 12 can
thus be raised back onboard the ship 10 and detached from the cable
between the fairlead 20 and the winch 16. That being the case, the position
30 of the fish 12 with respect to the ship 10 can be perfectly known and
controlled. The only parameter capable of influencing the position of the fish
12 is the control of the winch 16. It thus becomes possible to dispense with
an articulated arm for maneuvering the fish onboard the ship 10, notably for
attaching it to and detaching it from the cable 14.
35
Figures 5, 6 and 7 depict a number of alternative forms of fairlead
in cross section on the plane 32. These figures are depicted in cross section
in a plane passing through the axis of the cable 14, considering the boat to
be following a substantially straight heading. In these various figures, the
5 cable 14 is substantially horizontal upstream of the fairlead 20, between the
drum 18 and the fairlead 20. Downstream of the fairlead the cable inclines by
1" downward. This value has been chosen so that the cable 14 will definitely
bear against one of the faces of the groove of the first sector 21. Of course,
the fairleads depicted in these figures can be used for other sizes of angle.
10 In figure 5, the grooves of the various sectors 21, 22 and 23 have
constant cross sections over most of the sector concerned, with the
exception of the sector entry and exit zones in which the groove may be
chamfered in order to avoid any risk of damaging the cable 14. In the
example depicted, the groove of the sector 21 has two bearing zones 36 and
15 37 against which the cable 14 can bear. When the cable 14 is inclined
downward, as depicted in figure 5, the cable 14 bears on the lower zone 36
and when the cable 14 is inclined upward, the cable bears on the upper zone
37. The two zones 36 and 37 have a curvature in both instances centered on
a point 38 situated underneath the fairlead 20. The radius of curvature of the
20 zone 36 is defined by the minimum radius of curvature below which the cable
14 must not be bent. The other sectors 22 and 23 have zones of contact with
the cable 14 which are identical and therefore identified in the same way: 36
and 37. This alternative form is of benefit when the inclination of the cable 14
is almost definitely oriented downward downstream of the fairlead, which it
25 usually is during a towing operation.
Figure 6 again shows for the three sectors 21, 22 and 23 the lower
bearing zones 36 that ensure a minimum radius of curvature for the cable 14
as this cable inclines downward. By contrast, in this alternative form, each
sector comprises an upper bearing zone 38 that is substantially planar,
30 allowing better distribution of the contact between the cable and the sectors
as the cable is raised downstream of the fairlead 20 until it comes into
contact with one or more bearing surfaces 38. There is thus less of a risk of
wear in the zones where the cable 14 rubs against the groove.
Figure 7 again shows, still for the three sectors 21, 22 and 23, the
35 lower bearing zones 36 that ensure a minimum radius of curvature for the
cable 14 as it inclines downward. In this alternative form, each sector
comprises an upper bearing zone 39 the curvature of which is the reverse of
that of the lower zone 36 so as to allow the cable 14 to come up downstream
of the fairlead during repeated use. It is beneficial in this alternative form to
5 provide a possibility for the three sectors to come into abutment with one
another in order to prevent the cable from exceeding a limiting curvature in
the upward direction.
Figure 8 depicts the fairlead of figure 7 in a position in which the
cable 14 is inclined by 31" downward downstream of the fairlead 20. In this
10 figure, the cable 14 is wound onto the drum 18 in successive layers, and in
one of the final layers, the inclination of the cable between the drum 18 and
the fairlead 20 increases by comparison with the first layer. The sector 21 is
dimensioned to allow the cable 14 to enter whatever the layer on the drum
18.
CLAIMS
1. A towing device intended to be fitted to the deck of a ship (10)
and comprising a winch (16), a cable (14) and a fairlead (20), the cable (14)
running through the fairlead (20) under the action of the winch (16),
characterized in that the fairlead (20) comprises at least a first and a second
5 sector (21, 22), the sectors allowing the cable (14) to be guided in a groove
(24, 25) made in each of the sectors (21, 22), a first articulation (27) with a
degree of freedom to rotate about an axis (28), the articulation (27)
connecting the two sectors (21, 22), the axis (28) being substantially
perpendicular to a direction in which the cable (14) runs substantially through
10 the fairlead (20) at the articulation (27), and limiting means that limit the
angular travel of the articulation (27), and in that the sectors (21, 22) and the
limiting means are dimensioned so as to prevent the cable (14) from
exceeding a lower limit of radius of curvature.
1s 2. The device as claimed in claim 1, characterized in that it
comprises a third sector (23) and a second articulation (29) having a degree
of freedom to rotate about an axis (30), the second articulation (29)
connecting the second to the third sector, the axis (30) of the second
articulation being parallel to the axis (28) of the first articulation (27).
20
3. The device as claimed in one of the preceding claims,
characterized in that the fairlead (20) comprises a supporting structure and a
third articulation (40) having a degree of freedom to rotate about an axis (31),
the third articulation (40) connecting the first sector (21) and the supporting
25 structure, the axis (31) of the third articulation (40) being comprised in a
plane (32) perpendicular to the axis (28) of the first articulation (27).
4. The device as claimed in claim 3, characterized in that the axis
(31) of the third articulation (40) intersects the groove (24) of the first sector
30 (21) at a point at which the cable (14) is intended to come into contact with
the groove (24) of the first sector (21) on the winch (16) side.
5. The device as claimed in one of the preceding claims,
characterized in that the grooves (24, 25, 26) of the various sectors (21, 22,
23) have substantially constant cross sections in the shape of the letter C
with the opening to the side.
6. The device as claimed in one of the preceding claims,
5 characterized in that each of the grooves (24, 25, 26) has a lower bearing
zone (36) and ari upper bearing zone (37, 38, 39), against which zones the
cable (14) can bear, and in that the lower bearing zone (36) has a curvature
centered on a point (38) situated underneath the fairlead (20).
10 7. The device as claimed in claim 6, characterized in that the
upper bearing zone (38) is substantially planar.
8. The device as claimed in claim 6, characterized in that the
upper bearing zone (39) has a curvature that is the reverse of that of the
15 lower bearing zone (36).