Simrad PI TRAWL HYDROPHONE - INSTALLATION REV B User manual

Simrad PI
Catch monitoring system
Trawl 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

851-164472 / Rev.B
Simrad PI
Catch monitoring system
Trawl hydrophone installation

About this document
Rev Date Written by Checked by Approved by
Rev.B 03.06.05 RBr KRa KRa
Information reorganized
© 2005 Simrad AS. All rights reserved.
ISBN 82-8066-055-0
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
851-164472 / Rev.B
Introduction 1.......................................................
Installation precautions 2..............................................
Considerations 3.....................................................
Pre-installation check-list 8............................................
Optimal location of trawl hydrophones 10..................................
Coverage area, orientation and tilt 13......................................
Mounting arrangement 17...............................................
Dual hydrophone installation 23..........................................
Hydrophone protection 24..............................................
Hydrophone cable 27..................................................
Installation drawings 32................................................

Simrad PI Catch monitoring system / Trawl hydrophone
IV 851-164472 / Rev.B

Installation manual
1
851--164472 / Rev.B
Introduction
The purpose of this document is to provide general guidelines
for the installation of the PI hydrophone for trawling.
Note: If your vessel shall be fitted for purse seine operations, DO NOT
install the hydrophone(s) as explained in this document!
Order numbers
Trawl hydrophone, complete: HYD-205254
Trawl hydrophone, without cable gland: HYD-205826
Topics
→Precautions, page 2
→Considerations, page 3
→Pre-installation checklist, page 8
→Location, page 10
→Coverage area, orientation and tilt, page 13
→Mounting arrangement, page 17
→Dual hydrophones, page 23
→Hydrophone protection, page 24
→Hydrophone cable, page 27
→Installation drawings, page 32

Simrad PI Catch monitoring system / Trawl hydrophone
2851--164472 / Rev.B
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 Trawl 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
3
851--164472 / Rev.B
Considerations
Correct installation of PI hydrophone(s) is vital to system
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 / Trawl hydrophone
4851--164472 / Rev.B
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