Simrad PI PURSE SEINE HYDROPHONE - INSTALLATION REV... User manual

Simrad PI
Catch monitoring system
Purse seine hydrophone installation
Installation manual
M A X I M I Z I N G Y O U R P E R F O R M A N C E A T S E A
www.simrad.com

851-164149 / Rev.D
Simrad PI
Catch monitoring system
Purse seine hydrophone installation

Document information
Rev Date Written by Checked by Approved by
Rev.D 03.06.05 RBr KRa KRa
Information reorganized.
© 2005 Simrad AS. All rights reserved.
ISBN 82-8066-054-2
No part of this work covered by the copyright hereon may be reproduced or otherwise
copied without prior permission from Simrad AS.
The information contained in this document is subject to change without prior notice.
Simrad AS shall not be liable for errors contained herein, or for incidental or
consequential damages in connection with the furnishing, performance, or use of this
document.
The equipment to which this manual applies must only be used for the purpose for
which it was designed. Improper use or maintenance may cause damage to the
equipment or injury to personnel. The user must be familiar with the contents of the
appropriate manuals before attempting to operate or work on the equipment. Simrad AS
disclaims any responsibility for damage or injury caused by improper installation, use
or maintenance of the equipment.
If you require maintenance on your Simrad equipment, contact your local dealer. You
can also contact Simrad using the following e-mail address: [e-mail]

Installation manual
III
851-164149 / Rev.D
Introduction 1.......................................................
Installation precautions 2..............................................
Considerations 3.....................................................
Pre-installation check-list 7............................................
Optimal location of purse seine hydrophones 9.............................
Coverage area, orientation and tilt 10......................................
Mounting arrangement 13...............................................
Dual hydrophone installation 16..........................................
Hydrophone protection 18..............................................
Hydrophone cable 21..................................................
Installation drawings 26................................................

Simrad PI Catch monitoring system / Purse seine hydrophone
IV 851-164149 / Rev.D

Installation manual
1
851-164149 / Rev.D
Introduction
The purpose of this document is to provide general guidelines
for the installation of the PI hydrophone for purse seining.
Note: If your vessel shall be fitted for trawl operations, DO NOT
install the hydrophone(s) as explained in this document!
Order numbers
Purse hydrophone, complete: HYD-202711
Purse hydrophone, without cable gland: HYD-205075
Topics
→Precautions, page 2
→Considerations, page 3
→Pre-installation checklist, page 7
→Location, page 9
→Coverage area, orientation and tilt, page 10
→Mounting arrangement, page 13
→Dual hydrophones, page 16
→Hydrophone protection, page 18
→Hydrophone cable, page 21
→Installation drawings, page 26

Simrad PI Catch monitoring system / Purse seine hydrophone
2851-164149 / Rev.D
Installation precautions
Caution: The following precautions must be observed. Failure to
do so can result in damage to the hydrophone which
may render the PI Hydrophone system inoperative.
1Observe the maximum allowable torque warning of 5 Nm
when tightening the hydrophone studs.
2Use only M8x35 socket countersunk head screws for
mounting the hydrophone.
3Secure threaded hydrophone hardware with Loctitet270
or the equivalent.
4Do not paint the hydrophone.
5Do not sand-blast, power or steam wash the hydrophone.
6Do not scrape the hydrophone with metal or other hard
objects that may damage the polyurethane sheathing.
7Do not strike the hydrophone.
8Do not expose the hydrophone to harsh chemicals.
9Do not perform hot work in the vicinity of the
hydrophone.
10 Do not lift the hydrophone by its cable.

Installation manual
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851-164149 / Rev.D
Considerations
Correct installation of the PI hydrophone is vital to the system’s
performance. Several variables must be taken into consideration,
the most important of which is the vessel’s construction. This
guide is for use in selecting the best location for the hydrophone
and includes a brief description of areas to be avoided.
Note: Simrad strongly suggests that this information is read
thoroughly, and that the instructions are understood and
followed. Proper hydrophone placement is difficult to achieve,
but essential for correct system operation.
Depth
Water just below the sea surface contains a myriad of small air
bubbles created by the turbulence of breaking waves. The first
five to ten metres may be heavily saturated in moderate seas
with the greatest concentration and largest bubbles closest the
surface. Air bubbles disrupt sound waves in water. The degree
to which they absorb and reflect such energy vary, but in some
cases they can block hydrophone reception. It is therefore
recommended to mount the unit as deep as possible.
Pounding danger
When a vessel is in ballast and pitching in heavy seas, it is
important that the hydrophone is not lifted out of the water.
Should a vessel pound so heavily that the hydrophone be
exposed, sound reception will be interrupted and the unit may
be damaged on impact.
The boundary layer
The flow of water in the immediate vicinity of the hull of a
moving vessel is known as a boundary layer. This flow is
responsible for underwater noise that can disturb hydrophone
reception and its thickness is contingent on a vessel’s:
•Hull form
•Size and number of underwater protrusions
•Velocity
•Hull roughness
The boundary layer is thin (laminar flow) near the vessel’s bow
and becomes thicker (turbulent flow) as it moves aft. Laminar
flow is smooth with streamlines approximately parallel to the
hull and contributes relatively little to noise created by flow.
Conversely, turbulent flow is more disorderly and in turn
contributes to a greater extent.

Simrad PI Catch monitoring system / Purse seine hydrophone
4851-164149 / Rev.D
Boundary water layers:
(A) = Turbulent flow
(B) = Laminar flow
(C) = Air bubbles in the water
Air bubbles may also be introduced into the boundary layer. If
the vessel’s hull has little flare and is relatively narrow, bubbles
may escape to the sea surface without incident. On the other
hand a wide, flat hull with minimal deadrise is prone to trapping
air bubbles no matter how little flare it has. Regardless of a
vessel’s hull form, hydrophones are generally recommended to
be installed on the forward part of the hull to minimising the
influence of both turbulence and air bubbles.
Bulbous bow
The bulbous bow may be an acceptable hydrophone location.
Should this position be chosen, the foremost part of the bulb is
often best, but also the most susceptible to pounding.
Recommended location of the hydrophone on a bulbous hull:
(A) = Thruster
(B) = Hydrophone location

Installation manual
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851-164149 / Rev.D
Propeller noise
A vessel’s main propeller is the dominant source of underwater
acoustic noise. When ever possible, hydrophone(s) should be
located as far a way as possible from the main propeller and
never closer than ten meters. Hydrophone(s) should not be
mounted in the direct acoustic path (line-of-sight) of the main
propeller unless absolutely necessary.
The primary cause of propeller noise is cavitation (small
bubbles generated by the partial vacuum created by the blades as
they pass through the water). The resulting underwater acoustic
noise from cavitation is normally weakest on the side of the
vessel were the propeller blades rotate toward the surface and
most pronounced on the side were they rotate toward the
bottom. Most vessels have clock-wise rotating propellers
resulting in their port sides being less effected by cavitation
induced noise than their starboard.
To minimise the negative effect of cavitation noise on
hydrophone performance, installation is generally recommended
as follows:
•Single hydrophone - if only one hydrophone is to be
installed on a vessel with a clock-wise rotating propeller, it
should be located on the port side of the hull.
•Dual hydrophones - if two hydrophones are to be installed,
they should be placed on either side of the vessel’s keel.
When in doubt about the best fore-and-aft location for
hydrophones, they can be placed at different distances from
the bow (for example the port hydrophone can be a little
further aft than the starboard, approximately three to five
meters for a thirty-five meter vessel). When trawling in both
deep and shallow water the hydrophones should also be tilted
differently with respect to each other. The hydrophone that is
closest to the propeller should have the greatest tilt and be
located on the port side of the hull for a vessels with
clock-wise rotating propellers.
Bow/sternthruster noise
Bow and sternthruster operation may severely effect
hydrophone reception. Hydrophone installation closer than four
meters to either is strongly discouraged.

Simrad PI Catch monitoring system / Purse seine hydrophone
6851-164149 / Rev.D
When not in operation, bow/sternthruster tunnels create
turbulence and hence underwater noise when a vessel is under
way. Also, as a vessel pitches in heavy weather, thruster tunnels
may fill with air or aerated water which can disturb hydrophone
reception when released. Hydrophone installation should take
into regard the noise and down stream disturbances found
around and aft of thrusters.
Note: Hydrophone installation must take into regard the noise and
down stream disturbances found around and aft of thrusters.
Noise from protruding objects and other sources
The primary sources of underwater disturbance (other than a
vessel’s main propeller and bow/sternthruster) that affect
hydrophone reception are:
•Main or bilge keels
•Zinc anodes
•Cooling elements protruding from the hull
•Equipment such as sonar hydrophones and pitot tubes
•Sea chests
•Overboard discharges
•Dents in the hull
All appendages to the hull, indentations and pipe outlets are
potential sources of underwater noise. They may act as resonant
cavities amplifying noise at certain frequencies, create cavitation
or turbulence. Hydrophones should not be located in the vicinity
of such objects and especially not immediately aft of them.
Minimum distance to sonar and echo sounder
transducers
To avoid interference, PI hydrophone(s) must be installed as far
away as possible from other sources of underwater acoustical
energy such as active sonars and echo sounder transducers.
Hydrophones should be placed at least two meters from such
equipment when ever possible and distances of less than one
meter avoided. Hydrophones installed in close proximity to
underwater acoustical sources should be located as far aft as
possible from them, and most importantly, not be subjected to
direct (frontal) transmission from such equipment.
Drop keel
In the event the vessel is equipped with a drop keel, the
hydrophones should be mounted aft of it. The choice between
installing a one, or two hydrophone system should be based on
the same horizontal and vertical coverage requirements for
vessels operating under similar conditions with fixed keels.

Installation manual
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851-164149 / Rev.D
Pre-installation check-list
Choosing the optimal locations for hydrophones is not always
easy, but decisions made at this phase of the installation process
are critical to future system performance. Determining the best
configuration for a given vessel often involves a compromise
between contradicting requirements.
To aid in this evaluation process Simrad recommends that this
installation manual be read thoroughly and the following check
list completed before deciding on a final installation strategy for
the PI system.
1Hydrophones do not have a direct line-of-sight to the main
propeller and are placed where the vessel’s hull protects
them from underwater acoustic noise as well as possible.
2Hydrophones must always have an unobstructed
line-of-sight to the sensors attached to the gear for the
system to operate properly.
3The distance from the main propeller to the hydrophones
should be greater than ten meters. A separation of less
than ten meters can reduce system range significantly.
4If thrusters are installed, hydrophones should be located at
least four meters from them.
5Avoid locating hydrophones behind thrusters where air
bubbles from their tunnels generated when the vessel
pounds can block sensor signals.
6Hydrophone should not be placed forward of other
underwater acoustic equipment and preferably behind it as
far away as possible, distances of less than one meter
should be avoided.
7There should never be possible sources of underwater
acoustic noise placed in front of hydrophones.
8Remember that hydrophones are to be mounted with their
long axis up (in the vertical plane).
9Hydrophones installed in blisters should be located away
from the vessel’s keel and as deep as possible on the hull.
10 Hydrophones installed in shoes along the vessel’s keel
should be mounted as deeply as possible.
11 Hydrophone cables that are run in conduit along the
outside of the vessels hull should be arranged as to
produce the least amount of underwater acoustic noise as
possible.
12 Blisters and shoes should be as streamlined as possible and
have all of their corners rounded to minimize the
generation of underwater acoustic noise.

Simrad PI Catch monitoring system / Purse seine hydrophone
8851-164149 / Rev.D
13 Conduit used to run hydrophone cables in the interior of a
vessel’s hull should extend well over its water line.
14 If you install both trawl and purse seine hydrophones, do
not confuse the two types. The Trawl hydrophones are
marked with order number 314-205250, while the Purse
seine hydrophones are marked with order number
314-202275.
15 Other well-founded information or experience regarding
hydrophone installation be available should also be
evaluated even though not directly mentioned in these
instructions.

Installation manual
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851-164149 / Rev.D
Optimal location of purse seine hydrophones
The most influential factors effecting hydrophone reception
common to most vessels are:
•Noise from cavitation generated by the main propeller.
•Air bubbles in the water around the hydrophone which
impede acoustic signals.
•Noise from other acoustic equipment mounted in close
proximity.
Taking these main sources of disturbance into consideration, the
generally recommended location for mounting a single
hydrophone is approximately one third the vessel’s water-line
length from the bow.
Installations requiring the use of two hydrophones may position
the first as described above and the second forward of the bow
thruster in conjunction with the transducer shoe for the echo
sounder. Both hydrophones must be located at least four meters
from the bow thruster.
Optimal hydrophone placement differs from vessel to vessel.
Variables effecting hydrophone performance must be understood
so that the best location may be chosen given a vessel’s design
and particular operation.
The illustration shows the recommended fore (B) and aft (A)
locations for single hydrophone locations. For a dual
installation, both are used. (L) is the total length of the hull
measured at the waterline.

Simrad PI Catch monitoring system / Purse seine hydrophone
10 851-164149 / Rev.D
Coverage area, orientation and tilt
General
Once the fore and aft placement of the purse seine hydrophone
is decided, it is equally important to carefully consider its
horizontal and vertical orientation. Hydrophone orientation can
have a large influence on system performance.
The hydrophone’s beam sensitivity is concentrated within a 90_
horizontal and -30_vertical sector. Both keel and hull
installations are to be located on the side of the vessel that the
seine is shot.
Note: These installation instructions and related drawings are for
vessels shooting and pursing to STARBOARD.
Horizontal coverage area
When the seine is normally located forward of the starboard
beam when pursing the following information should be taken
into consideration:
1When the seine is pursed in the sector from approximately
000_to 120_relative to the bow, the hydrophone should
be installed at an angle of 70_to the vessels centre line.
2When the seine is pursed in the sector from approximately
030_to 150_relative to the bow, the hydrophone should
be installed at an angle of 90_to the vessel’s centre line.
The most important elements with regard to the horizontal
coverage area of the hydrophone are:
1An unobstructed line-of-sight to the PI sensor(s) attached
to the purse seine.
2The hydrophone is directed at the middle of the net when
pursing.
3Two hydrophones may be used for applications requiring a
large coverage area.

Installation manual
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851-164149 / Rev.D
Figure 1 Horizontal
coverage area
The illustration shows a hydrophone installed at an angle of 70
degrees to the vessel’s center line.
(A) = The PI hydrophone
(B) = The horizontal coverage area
Vertical coverage area
The hydrophone has a vertical beam width of -30_and should
be tilted so that the most important part of the seine is
adequately covered. Tilt should be no less than -15_in most
instances with the optimal tilt angle depending on the size
(length/depth) of the seine in use. Heeling of the vessel after the
seine is set must also be taken into consideration. For a large
purse seine (about 1000m or longer) the recommend a tilt angle
is -15_plus the estimated angle of heel when the net is set. For
smaller and deeper seines it may be necessary to increase the tilt
angle.

Simrad PI Catch monitoring system / Purse seine hydrophone
12 851-164149 / Rev.D
Tilt angle
The tilt angle is a function of net length and depth and may be
estimated as follows:
α= -[arctan (depth/length *π)-15_+β]
α= tilt angle
β=angle of heel (to port) after deploying the purse seine to
starboard
The following table gives some examples of recommended tilt
angles for common size pure seines:
Recommended tilt angles
Net length/depth
in meters 250 / 50 350 / 100 650 / 150 850 / 180 1500 / 200 2000 / 200
Recommended
tilt angle * -- 1 5 _-- 2 5 _-- 2 0 _-- 2 0 _-- 1 5 _-- 1 5 _
*The tilt angle should be increased accordingly if the vessel heels after the seine is shot. Tilt
angles of less than --15_are not recommended.

Installation manual
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851-164149 / Rev.D
Mounting arrangement
The PI purse hydrophone are delivered ready for installation in
either freestanding or keel mounted shoes (which are to be built
by the shipyard responsible for the installation). Several
alternatives with corresponding detailed drawings have been
included in this manual to cover the majority of installation
options available. Information regarding through-hull
penetration is also described to compliment the rules and
regulations of the respective vessel’s classification society.
Referenced drawings
→PI Purse hydrophone, outline dimensions, page 27
→PI Purse hydrophone, cutout, page 28
→Purse hydrophone, keel mounted, steel or aluminum, page 29
→Purse hydrophone, keel mounted, sandwich or wood, page 32
→Purse hydrophone, blister installation, page 35

Simrad PI Catch monitoring system / Purse seine hydrophone
14 851-164149 / Rev.D
Keel mounted shoes
The hydrophone shoe may be keel mounted to avoid creating an
appendage to the hull which may foul the purse wire.
Keel mounted hydrophone shoe:
(A) = Tilt angel
(B) = Vertical coverage area
(C) = Keel mounted hydrophone with
fairing
Should this solution be chosen, the
following must be taken into
consideration:
•The hydrophone must have an
unobstructed line-of-sight to the PI
sensor(s) attached to the seine.
•The centre of the hydrophone’s beam
must be directed as much as possible
toward the bottom of the net where
the PI sensors are located. The tilt
angle must be increased with regard
to the expected heel of the vessel.
•For a short and deep seine a tilt angle (A) of 20_to 25_is
recommended. For a short and shallow or large seine a 15_
tilt angle may be best.
•If monitoring of the headline under pursing is desired the
hydrophone should not be tilted more than 15_.
•The hydrophone shoe must be mounted as deep as possible
on the keel, but not so deep that it may be damaged while
docking.
•The hydrophone shoe must be streamlined to avoid creating
turbulence and underwater noise.
•For applications that require extensive coverage, regardless
of net size, several hydrophones may be installed with
different tilt angles.