Driving unit of Ship Windlass

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Nowadays, different types of windlasses are used according to the weight of the anchor and various other vessel requirements. The driving unit can be electrical, pneumatic or hydraulic, which also depends on the ship's system requirement.

Electrically operated windlass

The  windlass  including  mooring  winch machinery  is  common  for  both  hydraulically  operated   or  electrically  operated equipment .  In  the  case  of  the   electrically  operated  windlass cum  mooring  winch the  driving  motor  is  a  two  speed  motor  controlled  by  a  suitable  pole  changing  device.  The  lower  speed  gives  higher  torque  suitable  for  the  initial  breaking  of  the  anchor  from  the  ground  when  more  force  is  required and  the  design  torque  provided  for  this  condition  is 150% of  the  full continuous  torque  for  a  period  of  at least  30  minutes. All three phase  induction  motors  are  steady  speed  motors  with  a  small variation of  load  torque.  The  speed  is  fairly  high  since  the  frequency  is  high  and  to  reduce  the  operating  speed  electrically  is  inconvenient  since  it  involves  increasing  the  number of  pairs of  poles.  To  avoid  this   a  double  reduction  gear  box  with  oil  lubricated  machine  cut  gears  has  to  be  incorporated  in  this  system. As per  class  rules  an  over load  slip  clutch  has  also  to  be  included  for  safety,  since  electrical  safety cut outs  are  time  based and may  not  cut  out  when  overload  happens  suddenly. For  these  reasons  the  electrically  operated  windlass  and  mooring  winch   has  its  limitations  and  are  used  only  on  small ships.

Hydraulic System

The  hydraulic  system  schematic  sketch below is  illustrated  as    The main  components  of  this  system  consists  of  the  following:

  • An expansion tank located  on  the  forecastle  deck  to  give  a good  head  to  the  oil  to  flow
  • The gear  pump located  in  the  forecastle
  • The oil  storage  tank  located  in  the  fore castle  store  with  attached  hand  pump  to  transfer  oil  to  the  expansion tank.
  • The hydraulic  motor  mounted  on  the  windlass  frame  and  connected  to  the   primary  driving  The  control  block  is  integral  with  the  motor  casing  and    cut  sectional  sketch  of  the  motor  is  illustrated  separately.
When  the  control  block is  placed  in  the  neutral  position  the  oil  flow  to  the  motor  is   prevented  by  the  blanked  connection  in  the  block in  this  position. When  the  block is  shifted  to no 1 position only  two paths  are  connected and  the  flow  quantity  being  moderate  it  gives  the  rated  speed  and  torque. When  it  is  shifted  to  the  2nd  position the  oil flow  has 4  paths  and  this  conforms  to the  higher  torque  and  speed  rating.  This  position  is  used  for  breaking  the  anchor  hold  in  the  ground  and  when  free the  block can  be  used  for  lifting  the  anchor  along  with  chain  When  the  block  is  shifted  to  the  upper  R position  the  passages  in  the  block  are  crossed   causing  the  flow  of  oil  in  reverse  direction thereby  turning  the  motor in  the  reverse  direction.



DC, AC OR HYDRAULIC?

The wattage of a DC electric motor is not the important factor. Rather it is the efficiency of the whole winch, including the gearbox and motor, which counts. With the increasing popularity of powerful and compact on-board generators, AC powered winches are becoming a practical consideration for bigger boats. Hydraulic systems provide another power source well worth considering as they have the advantage of constant speed under all load conditions and can be run almost constantly while coupled with safe guards such as pressure relief valves.Modern hydraulic systems offer an integrated, low maintenance and ef­cient, centrally managed, power pack.

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