Simrad ES38-12 - REV C, Installation Manual, Page: 16 / 46

Simrad ES38-12
Common guidelines
The best performance is obtained with a blister height of 40 cm or more. A streamlined
shape and rounded edges reduce the flow noise. A vertical leading edge or front will
guide the aerated water to the sides of the blister. The orientation of the blister should
follow the water flow.
The interior of the blister must be filled with sea water. Use drainage holes in the
bottom and an air outlet on the top. The water pressure behind the transducer will then
compensate for the outside pressure during vessel movements in rough sea.
We recommend that large diameter transducers are fitted with a horizontal U-shaped
support bar. This bar can then be secured to the mounting ring using threaded rods.
The transducer cable penetrates the hull in a stuffing tube. Leave an adequate loop of the
cable behind the transducer for easy mounting or removal of the transducer.
Toe-in
Figure 7 Toe-in principle A Keel
B Blister
C Toe-in angle
The primary consideration must be to allow
laminar water flow. In most cases this is
achieved by designing the blister in parallel
with the keel. However, if the blister is
located close to the bow, the front of the
blister may have a few degrees toe-in
towards the bow.
The angle must be chosen to allow for most efficient water flow. It will vary with the
location of the transducer; the depth below the hull, the distance from the bow, and the
distance to the keel. Typical angles are from 0 to 3° on deplacement hulls. On planing
hulls, the angle is normally close to 0°.
Physical location
The blister is placed on one of the sides of the hull, and the distance from the keel is a
trade off between a close distance giving a turbulent flow of water in a narrow passage,
and a large distance bringing the transducer higher up and also more affected by vessel
roll. Normally a distance of approximately 1 m is a good compromise.
14
344276/A