Subs Model A2 in High Currents (> 2.5 knots)

RDI 300 kHz ADCP mounted in Subs

A2 Tow Test Results:

Tow Tank trials were undertaken in November 1999, using a Model A2 SUB, with RDI 300 kHz ADCP mounted. The purpose was to test a high performance tail arrangement, designed to increase pitch stability in high currents.

Trials were first undertaken with standard tails installed. The tow tank carriage did multiple runs of increasing speeds, commencing at .25 m/s, followed by .5m/s, and then increasing in .5 m/s increments, with the final run at 2 m/s. Higher speeds were not done in this configuration, as the instrument reached 15⁰ pitch at 1.5 m/s, and exceeded RDI’s pitch design criteria of 15⁰ at 2 m/s (4 knots). This supported field data previously observed.

The high performance tails were installed, and the tows were repeated. The tow tank carriage did multiple runs of increasing speeds, commencing at .25 m/s, followed by .5m/s, and then increasing in .5 m/s increments, with the final run at 3 m/s (6 knots).

Pitch remained stable at all speeds, not exceeding 7⁰ at any speed. The high performance tail also improved heading alignment at low speeds. Roll remained good over the full range. Data plots are attached for each tow.

Conclusion:

The standard tail configuration works well at speeds up to 2.5 to 3 knots, which covers most applications of this instrument. For anticipated current speeds >2.5 knots, the high performance tail should be recommended.

COMPARISONS – High Speed vs Conventional Tail

Note 1: Plus pitch is nose down.