The engine fuel throttle of a marine engine and the associated speed of the boat are typically controlled by a throttle lever at the helm of the boat. The throttle lever typically manipulates the engine throttle assembly through cabling, either mechanically or electromechanically.
The engine controls can also include a clutch control lever that controls the clutch assembly of the engine. The clutch assembly includes clutch plates which are forced together by high fluid pressure to transmit engine power to the propeller drive train.
In some boats, the engine controls further include a trolling valve, which relieves varying levels of the fluid pressure that releases and compresses the clutch plates and allows slippage in the power transmission through the marine gear to the drive train. By manipulating the trolling valve, the idle speed of the boat can be adjusted from a normal idle speed of four to seven knots down to perhaps one knot to enhance fishing conditions and the like.
Use of the trolling valve, however, presents a significant danger of marine gear damage. The typically high oil pressure and associated oil circulation rate around the marine gear during normal operation transfers a significant amount of heat generated by the marine gear away from the marine gear. However, when the pressure is reduced by the trolling valve, the flow rate is reduced, and the marine gear can overheat as a result of inadequate heat dissipation, when the engine is reeved above factor limits during use of the trolling valve.