Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Method and apparatus for position monitoring
The present invention relates to a method and an apparatus for monitoring the
position of plate gear for fishing gear. The invention is a further
development of the
method and apparatus described in NO 20040464, the content of which is hereby
incorporated in its entirety in the present application.
The object of such monitoring is to enable the position of the fishing gear in
the
water to be charted in an optimal manner.
During trawling operations it is important to know whether the trawl or
associated
equipment is in contact with the bottom. In bottom trawls, for example, it is
desirable to have bottom contact for most of the time in order to ensure that
fish
swimming close to the bottom are caught, or to establish a dust cloud near the
bottom which scares-the fish into the gear.
At other times it is desirable to maintain a certain distance from the bottom
(pelagic
trawl), in order, for example, to protect coral and other plants and animals.
Not least it is important to keep a certain distance from the bottom or
maintain a
contact with the bottom that is limited to the surface of the bottom, in order
to
prevent the fishing gear from digging into the bottom.
The position of the trawl will of course also depend on the type of fish that-
is to be
caught.
According to the prior art, bottom contact sensors are used to establish
whether the
trawl is moving along the bottom or not. A bottom contact sensor is a tubular
body
fastened to the trawl at one end with the other end hanging freely. The
bottoin
contact sensor will indicate "bottom contact" / "no bottom contact" depending
on
the angle between the longitudinal direction of the tubular body and the
horizontal
direction. When the bottom gear moves freely, the longitudinal direction of
the
tubular body will form a larger angle with the horizontal than when there is
bottom
contact. However, if there are large irregularities on the bottom, i.e.
depressions and
elevations, the bottom contact sensor will not be capable of providing
reliable
information.
Measurement of the angular position of a part of a trawl is known from, for
example, GB 1 221 276, relating to an apparatus with a measuring unit for
measuring two angles for the said part. The publication discloses spherical
elements
attached to the lower part of the trawl.
Large fishing gear such as trawls comprises modules which ensure that a
certain
position of the trawl is maintained during the fishing process. One example of
such
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a module is so-called plate gear, one of whose functions is to ensure that the
trawl
moves along the bottom with the trawl in an open position.
The plate gear is an apparatus with several plates attached to one another by
means
of wire, rope and/or other attachment devices. The term plate in the present
description refers to relatively flat bodies. Each plate normally has four
attachment
points, where the plates together with the attachment devices form a flexible
device.
The apparatus in turn is attached to the lower part of.the trawl at individual
points.
During trawling the apparatus will be bent with the result that some plates
will
remain located in a plane substantially perpendicular to the trawl's towing
direction
(the middle part of the apparatus) while others will be in a plane
substantially
parallel to the trawl's directiori of travel (the sides of the apparatus).
The plates mounted in the middle part of the trawl can assume a tilted
position
relative to the vertical plane. If the plates tilt forwards (i.e. in the
direction towards
the boat) the plate gear will partly lose contact with the bottom. The fish
will
therefore be able to swim under and out of the trawl. If the plates tilt
backwards,
they will dig down into the bottom, resulting in an undesirable accumulation
of
material in the trawl.
For this reason it is important to be able to monitor the position of the
plates at least
with regard to the vertical plane.
The angular position of the plates can be described by means of three angles:
a) Orientation angle: this is the angle that the plates' plane forms with the
trawl's
direction of travel. As mentioned earlier, with regard to the plates in the
middle of
the apparatus, the plates' plane will form an angle of around 90 degrees with
the
trawler's direction of travel, while the plates on the sides will form an
angle of
around 0 degrees.
b) Angle of tilt: this is the angle that the plates' plane forms with a
horizontal plane.
This angle must be as close to 90 degrees as possible in order for the plate
gear to
function as efficiently as possible. In the following description "positive"
angles
will be defined as angles where the plate tilts towards the trawler (i.e.
leading to
poor bottom contact if a certain threshold is exceeded), "negative" angles are
those
that will lead to the plate digging into the bottom.
c) Angle of pitch: this is the angle that the plates' upper and lower edges
form with
a horizontal plane.
As mentioned earlier the plates' angular position will vary depending on the
plates'
position along the apparatus. For the plates on the side portions of the
apparatus it
will be more important to measure the angle of pitch than the angle of tilt,
while the
angle of pitch will not be important for the plates in the middle of the
apparatus (the
angle of tilt will be the important one in this case).
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Thus it is an object of the invention to provide a method and an apparatus
that
permit monitoring of the position of plate gear comprising at least one plate,
where
measurements may be made of the angular position of either a single plate or
of one
or more groups of plate elements.
It is also an object of the invention to provide a method for automatic
selection of
the most appropriate plate/group for measuring the angular position.
The choice of plate/group for measurement can be undertaken on the basis of
the
plate's/group's fixed position in the plate gear, i.e. whether the plate is
located in
the middle of the plate gear, on the sides or in an area between these
positions.
It will also be possible to select plate/group on the basis of the
plate's/group's
orientation angle, since it will be possible to measure the relevant angle for
a plate
and/or a group with the orientation angle located within a specific range of
values.
The orientation angle can also be measured for a single plate and the same
value
assigned to other plates in the same group, in order thereby to provide a
position
indication of the whole plate gear based on only a few measurements.
The method according to the invention comprises taking measurements of at
least
one angle for at least a part of the plate gear and providing a position
indication for
the plate gear based on the measurement. The plate gear comprises several
plates
and the measurement is carried out for individual plates and/or for groups of
plates.
The groups can be defined on the basis of the position of the plates in the
plate gear
and/or on the basis of the orientation angle. In the latter case, values for
the
orientation angle will be defined that provide limits for the groups.
The method according to the invention therefore comprises:
- measuring at least one angle for at least a part of the plate gear, where
the said part
of the plate gear may comprise one single plate or at least one group of
plates,
- based on the measurement providing a position indication for the plate gear.
In an embodiment the method comprises measuring the angle of tilt or the angle
of
pitch depending on the plates'/group's position in the plate gear or the
plates'/group's orientation angle. The first alternative will lead to a
measurement
which, for example, is based on the plate gear being in a symmetrical position
relative to the vessel's direction of travel, while the second alternative
opens up the
possibility that the most appropriate plate/group for measurement varies
during the
trawling operation.
The position indication could consist of individual angular values provided by
the
measurement. Such a position indication will show whether the plates are
tilting
towards/away from the vessel and will be able to be used for controlling the
plate
gear's position.
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The position indication may also comprise an indication of the "bottom
contact/no
bottom contact" type, or a graphic presentation showing the angular variation
and/or
position relative to the bottom in time. In the same way as described in NO
20040464, moreover, it will be possible by means of the invention to know
whether
the gear is in the process of coming into contact with the bottom or in the
process of
leaving it. This will be implemented by means of average/standard deviation
calculations for groups with angular measurements.
The measurement may comprise measuring the angle of tilt, the orientation
angle
and/or the angle of pitch. Where the angle of tilt and orientation angle are
measured, the method may comprise providing position indication based on the
values of the orientation angle and the angle of tilt.
The angular measurement is preferably performed by means of an inclinometer.
The method will advantageously comprise display of the position indication,
where
this comprises the value of at least one angle. It is possible, of course, to
provide
the position indication and not display it directly, but to give a message as
to
whether a threshold is exceeded or not, or to employ the position indication
for
controlling the plate gear with or without display. The control will comprise
regulation of the tightening on the wires connected to the plate gear.
In this connection, the method may comprise comparing the value of at least
one
angle with a first threshold value and providing position indication based on
the
result of the comparison. The position indication may also be associated with
the
triggering of an alarm.
In an embodiment the method according to the invention comprises calculating
average and standard deviation for the measurements, and providing a position
indication for the plate gear with regard to the transition bottom contact/no
bottom
contact based on average/standard deviation for a collection of angular
measurements.
The position indication in the form of a position indication signal can be
transmitted
acoustically to a receiver on the surface by means of a cable conriection by
radio
signals or wirelessly or in some other way. It may also be stored in a memory
unit
on a module in the plate gear or in another location in the vessel.
The invention also comprises controlling the plate gear's position based on
the
indication signal(s) and desired values.
The invention also comprises an apparatus for monitoring the position of plate
gear
for fishing gear, where the plate gear comprises at least one plate,
comprising:
- a measuring unit for measuring at least one angle for at least a part of the
plate
gear, the said part of the plate gear comprising a single plate and/or at
least a group
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of plates,
- a processing unit for providing, based on the measured value, a position
indication
for the plate gear,
- a memory unit.
5 Advantageous embodiments of the apparatus are indicated in the attached
dependent
claims.
The invention will permit the position of the different plates in the plate
gear to be
controlled, thereby initiating measures for obtaining a fishing operation that
is as
efficient as possible. Any errors will be able to be detected and remedied
quickly by
10, means of the invention.
List of figures
Fig. 1 is a front view of a plate gear.
Fig. 2 illustrates a plate gear viewed from above.
Fig 3 is a view like that in fig. 2, illustrating the angles for the plate
gear.
Fig. 4 illustrates a plate viewed from in front and from the side.
Fig. 5 illustrates an inclinometer 50 placed on a plate 2.
Fig. 6 illustrates an embodiment of an apparatus according to the invention.
Fig. 7 illustrates an embodiment of a plate gear.
Fig. 8 illustrates a plate gear in use.
Fig. 9 is a screen image illustrating a position indication provided by means
of the
invention for fishing gear during use.
Fig. 10 is a screen image similar to that in fig. 9, during lowering of the
fishing
gear.
Detailed description
Fig. 1 is a front view of a plate gear. The plate gear I comprises several
plates 2
attached to one another by means of attachment devices 4 (wires, ropes, etc.).
Each
plate has several attachment points 3 against the attachment devices 4. The
figure
also illustrates an attachment point 6 for attaching the apparatus I to the
lower part
of the trawl by means of a rope 5.
Fig. 2 illustrates a plate gear viewed from above. In the figure the trawl has
reference numeral 20 and a part of the bottom gear reference numeral 11. B
indicates the vessel's direction of travel. As can be seen, the plate gear 1
will be
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bent during trawling and some plates 2 remain located in a plane substantially
perpendicular to the direction of travel while others are located in a plane
substantially comprising the direction of travel.
Some of the angles defined for the plate gear are illustrated in figure 3. The
orientation angle is the angle that the plates' 2 plane forms with the
direction of
travel. The figure illustrates orientation angles a30 and a31 for two plates.
It can be
seen that the nearer the middle of the plate gear 2 a plate is located, the
smaller the
orientation angle a will be.
Figure 4 illustrates angle of pitch y and the angle of tilt (3 for an
individual plate 2.
The directions towards the surface and towards the bottom are illustrated by
the
arrows 42 and 43 respectively. Figure 4a illustrates the plate 2 viewed from
in front,
and the edges 40 and 41 which will define the angle of pitch with the
horizontal.
Figure 4b illustrates the angle of pitch y. Figure 4c illustrates the
direction of travel
B and angle of tilt P. Positive angles are defined as angles where the plate's
upper
edge 40 approaches the trawl as illustrated in the figure.
Fig. 5 illustrates an inclinometer 50 placed on a plate 2. As mentioned
earlier, this
may involve an inclinometer with one, two or three axes, permitting
measurement
of the angles of orientation, tilt and pitch respectively.
In an embodiment of the invention it will be possible to choose to provide a
position
indication for a specific group of plates, and another position indication for
another
group of plates. Based on the position of the plates relative to the vessel's
direction
of travel (orientation angle), it will therefore be possible to decide whether
the
angle of tilt or the angle of pitch will be taken into account for the
position
indication.
Figure 6 illustrates an embodiment of an apparatus according to the invention.
This
comprises a measuring unit 50 (advantageously an inclinometer) that measures
one
or more angles for at least a part of the plate gear 2. The angles are
orientation angle
0, angle of tilt V and angle of pitch S. Even though the figure only shows one
measuring unit 50, it will be obvious that as many measuring units may be
employed as there are plates 2. The measurements are transmitted to a
processing
unit 60, which can either handle the measurements for all the plates or
include
individual processing units for each plate connected to a central processing
unit. In
the processing unit a position indication is provided with regard to bottom
contact.
The position indication may be provided, for example, by comparing the
measured
angles 0, V and/or S with threshold values 63 (in this case the position
indication
will be associated with the difference between measured and threshold values),
or it
may consist of values for specific angles (i.e. in the form of 0=40 degrees,
V=0
degrees), or values derived therefrom. In the same way as with the
measurements, a
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position indication will be able to be provided for each individual plate, for
groups
of plates or for the whole plate gear as a single element.
The apparatus may comprise a display unit 62 for displaying the position
indication,
and/or an alarm 64 which is triggered when a specific threshold is exceeded.
The
apparatus may also include a transmitter unit 65 for transmitting the position
indication to a receiver 66. The apparatus may also include a memory 67 for
storing
the position indication.
Finally, the apparatus may comprise a control unit connected to the processing
unit
for controlling the plate gear's position based on the position indication and
desired
values.
Figure 7 illustrates an embodiment of a plate gear 1. The reference numerals
refer to
parts corresponding to the description of figure 1. Reference numeral 70
refers to a
load, here in the form of a chain, for increasing the weight of the plates.
Figure 8 shows a plate gear in use.
Figure 9 shows a screen image with an indication of different parameters
associated
with a trawling operation. The fields on the image will be described from the
top
and downwards and from left to right. A first field DP illustrates the depth
of the
trawl in metres (130m), two TSP fields illustrate the trawl's speed and also
the
angle between water flow and the trawl's direction of travel. The DST field
shows
distance between the doors. The following TLT,fields show angular values,
where
the last field, TLT with value R -91, illustrates the orientation angle for
the middle
plate in a plate gear. This angle is 91 degrees and the plates' lower edge is
located
closer to the towing vessel than the plates' upper edge. The figure 0 shows
standard
deviation for the angle. The field at the bottom right shows amongst other
things the
distance between the trawl's lower edge and the bottom, C: 0.1 m.
Figure 10 illustrates a similar screen image but indicating different
parameters
obtained while the fishing gear is being lowered. It can be seen that the
orientation
angle TLT is -11 degrees with a standard deviation of 2. The distance C
between the
trawl's lower edge and the bottom is 5.4m.
Even though the invention is illustrated by means of an example where the
plates
comprise four attachment points, it is possible to measure the angular
position of
plates that are attached in another way, i.e. with more or less than four
attachment
points. It is also possible to provide a position indication for only one
plate, for
example the plate in the middle, and to employ the said position indication
for
controlling the tightening of the attachment devices.
