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Overhead Suspended Boat Davits
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Safety Handcranks
application. Each arm is mounted on rollers which run on an inclined trackway that is mounted on the deck. The incline on the trackway(s) is sufficient for gravity to cause the boat and arm(s) to move down the track- way(s) from the inboard position to the outboard position so the boat may be lowered into the water. Depending on the model, the boat davit arms are connected  by  either  a  strongback  or  a  span  wire (fig. 4-13 and 4-15). Trackway boat davits are gravity boat  davits. BOAT  DAVIT  SAFETY  DEVICES Boat  davit  installations  have  various  safety  and protective  devices.  These  safety  devices  are  visual, electrical, and mechanical in nature. We will describe some  of  the  safety  devices  in  the  following  paragraphs. Safe Hoisting Position Stripes Safe hoisting position stripes are usually red in color and 2 inches wide, and they are used as a visual aid for the boat davit operator. They are painted on the davit  frame  and  the  davit  arm(s)  at  a  minimum  distance of 8 inches from either the two-blocked position or the solidly compressed position of the buffer spring. They indicate when the electric motor must be de-energized during hoisting to avoid a two-blocked condition. A two-blocked condition is where the boat fall(s) are pre- vented  from  movement  either  by  design  or  obstruction. Continued  hoisting  against  a  two-blocked  condition could  result  in  over  stressing  or  failure  of  davit components. Slewing  Position  Stripes Slewing position stripes are used for a slewing boat davit (SLAD) as a visual aid to indicate when to de- energize the electric motor during slewing. There are three stripes, usually red in color and 2 inches wide. One stripe is painted on the arm and two stripes are painted on the pedestal. One of the two pedestal stripes in- dicates when the arm is slewed to the STOW position and the other indicates when the arm is slewed to the LOWERING   position. Emergency  Disconnect  Switch The emergency disconnect switch is located at the boat davit operation station to allow the operator to interrupt power to the motor. It is used in an emergency situation to prevent a two-blocked condition if another control  component  fails  to  function  properly. Double  Break  Feature Electrical  contacts  subjected  to  momentary  jogging service are prone to sticking or welding. This can cause uncontrolled operation of the winch. The double break feature   is   the   arrangement   of   two   independent contactors in the supply leads to protect against this danger. When the motor power supply is interrupted by the master switch the supply leads are opened in two places by contactors which are not interlocked. In the Figure  4-16.–Fall  tensioning  device. 4-16

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