Simrad PI TRAWL HYDROPHONE Installation Manual

Installation manual

Simrad PI Catch monitoring system

Trawl hydrophone installation

www.simrad.com

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

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

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: fish-support@simrad.com

Installation manual

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................................................

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III

Simrad PI Catch monitoring system / Trawl hydrophone

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Installation manual

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

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Simrad PI Catch monitoring system / Trawl hydrophone

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.

1 Observe the maximum allowable torque warning of 5 Nm

when tightening the hydrophone studs.

2 Use only M8x35 socket countersunk head screws for

mounting the hydrophone.

3 Secure threaded hydrophone hardware with Loctitet 270

or the equivalent.

4 Do not paint the hydrophone. 5 Do not sand-blast, power or steam wash the hydrophone. 6 Do not scrape the hydrophone with metal or other hard

objects that may damage the polyurethane sheathing.

7 Do not strike the hydrophone. 8 Do not expose the hydrophone to harsh chemicals. 9 Do not perform hot work in the vicinity of the

hydrophone.

10 Do not lift the hydrophone by its cable.

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Installation manual

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.

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Simrad PI Catch monitoring system / Trawl hydrophone

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 m ost susceptible to pounding.

Recommended location of the hydrophone on a bulbous hull: (A) = Thruster (B) = Hydrophone location

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Installation manual

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

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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 / Trawl hydrophone

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.

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Installation manual

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.

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Simrad PI Catch monitoring system / Trawl hydrophone

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.

1 Hydrophones 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.

2 Hydrophones must always have an unobstructed

line-of-sight to the sensors attached to the gear for the system to operate properly.

3 The 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.

4 If thrusters are installed, hydrophones should be located at

least four meters from them.

5 Avoid locating hydrophones behind thrusters where air

bubbles from their tunnels generated when the vessel pounds can block sensor signals.

6 Hydrophone 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.

7 There should never be possible sources of underwater

acoustic noise placed in front of hydrophones.

8 Hydrophones should be offset twenty degrees from the

vessel’s centre line for normal single boat trawling. This provides a ten degree overlap and a coverage area of ninety degrees aft. Refer to the corresponding sections of this manual for more information.

9 If there is any doubt about the best fore-and-aft location,

the port hydrophone can be placed a little farther aft (three to five meters) in relation to the starboard. Hydrophones can be tilted at slightly different angles when operating in both deep and shallow waters. Refer to the corresponding sections of this manual for more information.

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Installation manual

10 The hydrophone that is closest to the main propeller

should be located on the port side of the vessel and have the greatest tilt.

11 If both hydrophone are located equally distant from the

main propeller, but are tilted differently, the starboard hydrophone should be tilted the most because underwater acoustic noise is more prevalent on that side of the vessel.

12 Locating hydrophones at the after end of a bulbous bow

can produce good results. Previously installed sonars in this area that can subject hydrophones to direct signals will produce interference.

13 Hydrophone can also be mounted in the after end of echo

sounder shoes as long as the minimum required distances and orientation with regard to other underwater acoustic equipment is observed.

14 Remember that hydrophones are to be mounted with their

long axis up (in the vertical plane).

15 Hydrophones installed in blisters should be located away

from the vessel’s keel and as deep as possible on the hull.

16 Hydrophones installed in shoes along the vessel’s keel

should be mounted as deeply as possible.

17 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.

18 Blisters and shoes should be as streamlined as possible and

have all of their corners rounded to minimize the generation of underwater acoustic noise.

19 Conduit used to run hydrophone cables in the interior of a

vessel’s hull should extend well over its water line.

20 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.

21 Other well-founded information or experience regarding

hydrophone installation be available should also be evaluated even though not directly mentioned in these instructions.

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