Page 89: of Maritime Reporter Magazine (March 1997)

Falk Gears Propulsion Update (Continued from page 53) the astern clutch. The locked shaft against the slipping clutch allows the engine to produce torque over a longer, more controlled duration, while mini- mizing clutch heat buildup.

Figure 4 (on page 51) shows an exam- ple of the astern clutch engagement during a full-speed crash reversal of a tuna seiner using the engine torque-up system. In the example, engine speed is boosted to 500 rpm, and the astern clutch begins pressurization. The accelerating engine comes under load as the shaft brake remains engaged and the astern clutch begins to trans- mit torque. This initial load on the engine causes the fuel rack to increase the fuel rate to the engine, causing the turbochargers to begin pumping, increasing the torque output of the engine. As the shaft brake is released, the engine speed falls from 500 rpm to engine idle at 350 rpm, and the pro- peller shaft accelerates in the astern direction. With the turbochargers pumping, the engine is then developing sufficient torque to overcome the rever- sal.

To overcome the high propeller back- torques in such a short period of time, the engine must be boosted to 580 rpm.

As the clutch engages, the propeller shaft brake is released, prior to the torque transmission within the clutch.

The propeller begins to accelerate in the ahead direction, driven by the entrained water within the wheel. As the engaging astern clutch begins to transmit torque, the propeller must be stopped and reversed. The engine struggles to produce sufficient torque, falls to 250 rpm and finally increases speed to complete the reversal.

In a reversal of this type, the engine is loaded so abruptly, that the tur- bochargers do not begin to increase the engine torque output until well after the clutch has become fully engaged.

This forces the engine to overcome the propeller back-torque while in the aspi- rated mode, causing the engine speed to fall well below idle speed, and possi- bly stalling and back-driving the engine.

With the engine torque-up system, the reversal is completed with much less shock to the engine, clutch and other propulsion system components.

The torque-up system also allowed the reversal to be completed in a much shorter time, and with a shorter time delay.

For more information on the system

Circle 36 on Reader Service Card

Sea Yltfer Intake, Cooling

System Designed for Overall

Cost Savings (Continued from page 93) ously higher than the water flow rate to the pumps at 100 percent loading.

Bottom Gratings:

In the JAK-system, recommended openings (usu- ally 20 x 200 mm) cut directly on the bottom plate increase the net area. The total net area of the chest bottom is selected so that water flow rate through the openings is less than 0.1 m/s at 100 percent load- ing.

On high-speed vessels, the openings should be located longitudinally to make it easier for the water to flow inside the chest. On icebreakers and other vessels operating in difficult ice conditions, the openings should be located transversely, as experi- ence gained from ice-breakers seems to indicate that the icy slosh is then compressed against the back edges of the openings allowing water to rise in the chest, as the flow rate is very low.

JAK-system does not require docking as all the service and maintenance operations can be carried out from the inside at any time, and all the equip- ment can be lifted up from the chest. The JAK-sys- tem includes no valves, fittings or filters, and is free of holes below the maximum load line.

For more information on Acomarin

Circle 38 on Reader Service Card

The preceding was excerpted from an article authored by

Kari U. Laiho, managing director of Acomarin

Engineering Ltd.

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March, 1997

Circle 214 on Reader Service Card $12,000,000 | INVENTORY OF m\ISlD

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Surplus to the ongoing operations of

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JULIUS FEINSTEIN • BILL PHILIBERT 800-325-5286 (USA) or 713-675-2729

Fax 713-675-7819 • e-mail at [email protected]

Circle 263 on Reader Service Card 97