2,205 lbsf: 1 METRIC TONNE BOLLARD, COUNTER ROTATION THRUSTER

Optimized for Both Shallow and Deep Running.  Also available:  Propellers for the same duct which give 1 ¼  Metric Tonne below 100 ft depth. Dp = 3600psi

Mean rpm = 1657 ±75 rpm, downstream shaft is slower.

Full Power Oil Consumption =  (2 x 1657 x 2.69) / (231 x .99) = 39.0gpm  (148 L/min)

Dp = 3500psi (241 bar)

Oil Horsepower = (39.0gpm x 231 x 3500)/(12 x 33000) = 80

There is no reaction torque on the vehicle with the Counter Rotation(C.R.) Thruster:

      For instance the vertical thrusters, for a single rotation case, directly affect the vehicle’s 
      heading, making precise positioning and navigation of the vehicle very difficult.  For
      example, the unbalanced torque of a similar or equivalent single rotation thruster 
      at 1200 rpm and 80 oil horsepower with a motor torque efficiency of .92 is:

      Torq = (80 x .92 x 33000)/(2p x 1200) = 322 lb-ft

      The motor displacement for single rotation at 3500 psi and 1200 rpm is:

              (330 x 2p x 12)/(3500 x .92) = 7.7 cu. in.

The hydraulic motors are Innerspace 8400A’s.  They are streamlined to reduce flow blockage and drag, and they are of stainless steel construction with a displacement of 2.69 in³ each.  They carry the prop thrust without an additional shaft, box, bearings, seals and compensation chamber.

The two streamlined motors used in the C.R. Thruster permit complete end-to-end symmetry so that the ahead and astern modes of operation produce identical thrust.

The C.R. 1 Metric Tonne Thruster is screened at each end by hydrodynamic scientific screens*. These screens are so strong and rigid that they are used to support the motors and props.                               * US Patent 6,152,793

The screens protect divers, marine life, the props, ROV's, etc.

The C.R. Thruster is so powerful that the sometime inevitable diver is likely to be injured unless protected by the screens.

• The first thing to notice in Figure 1 is that the reverse and forward curves are separated. Since the unit is otherwise symmetrical in both directions   including the props, which are uncambered, the difference is in the drag of the unfaired hydraulic lines that extend across the high-speed jet.  In the C.R. thruster in question this reduction in the reverse thrust of the ½ Metric Tonne Thruster is eliminated by installing fairing cuffs on the lines. 
  
  Although the test depth of this thruster was only 15 feet, the minimum depth of non-cavitating performance can be estimated by extending the linear portion of the curves of thrust vs. pressure as straight lines from the point of 100 bar.  The straight line extrapolation is conservative due to the increased efficiency of both the thruster and hydraulic motor with increasing Reynolds number.  The depth required for non-cavitation for the 4 bladed prop in the chart is ( 33’ + 15’ )241/100 = 116 ft abs. – 33’ = 83 feet.  Where 33 is the feet of sea water equivalent to one atmosphere pressure.   A maximum thrust of approximately 275 Kg at 15 ft and 510 Kg at 83 ft is achieved with the 4 bladed prop.  Similarly for the 8 blade prop the max thrust is 420 Kg at 15 ft and 470 Kg at 83 ft.  Thus, there is a trade off between deep and shallow performance.
  
• The counter rotation vs. single rotation feature substantially increases the efficiency due partly to the elimination of the whirl in the exit jet. Thus, extrapolation of the test results from the single rotation ½ Metric Tonne Thruster above to the 1 Metric Tonne C.R. thruster is conservative. 

• The Venturi shape of duct is used to allow a higher rotation speed with higher pitch-to-diameter ratio props.  This increases the efficiency and the rpm and allows for smaller props and motor displacements. 

Picture of the ½ Metric Tonne Thruster on the left and the 1 Metric Tonne at UI 2002

                    Figure 1.

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