Teledyne SeaBat T Series, Operator'S Manual, Page: 78 / 152

SYSTEM PERFORMANCE AND DATA TYPES
SeaBat T-Series Subsea Operator's Manual Page 66 January 31, 2019
Version 7
7.9 Hydrodynamic Drag
Hydrodynamic drag has been determined for the T20 and T50 shallow sonar head assemblies in
brackets mounted on a short pole traveling through the water at a speed of 10 knots.
7.9.1 Drag Simulation Setup

Sonar head assemblies:
o
T20 single head (shallow
20
) with front fairing ( Figure 41 and Figure 42 )
or without front fairing ( Figure 43 and Figure 44 ).
o
T20 dual head (shallow) with front fairing ( Figure 46 and Figure 47 )
or without front fairing ( Figure 48 and Figure 49 ).
o
T50 single head (shallow
21
) with front fairing ( Figure 51 and Figure 52 )
or without front fairing ( Figure 53 and Figure 54 ).
o
T50 dual head (shallow) with front fairing ( Figure 56 and Figure 57 )
or without front fairing ( Figure 58 and Figure 59 ).

Pole mount: 350mm long, 100mm diameter pole attached to the mounting flange of
the brackets. The pole mount itself also causes drag.

Speed: 10 knots.

Finite Element simulation tool: ANSYS was used to determine the drag and evaluate
water flow around the sonar heads and brackets.
NOTE
Cable routing and accessory parts like a SVP or a motion sensor added to the bracket will
influence drag.
7.9.2 Drag Simulation Conclusions

The front fairings help reduce drag and keep a steady and clean water flow around
the receiver and projector arrays. Need of fairing depends on survey and transit
speed.

The hydrodynamic drag on the system is a combination of skin friction and pressure
drag. Both are within reasonable speed proportional to square of speed. With this it is
possible to estimate drag figures for speeds that differ from 10 knots.

The drag figures are relevant for a pole mount over the side, a sonar head installation
through a moon pool, a sonar head mounted on an adapter bracket under the hull of
the survey vessel, or a sonar head installation on a UUV.

In general, Teledyne RESON recommends the use of the optional fairing to maintain a
steady water flow around the array and reduce load on the pole/bracket.
20 The drag figures provided are also valid for a T20 deep sonar head assembly, if the installation is done in
a similar way.
21 The drag figures provided are also valid for a T50 deep sonar head assembly, if the installation is done in
a similar way.