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Ship Windlass

Anchor_windlass

Ship Windlass

WINDLASS

  • Windlass seating:- The forces  acting  on  the  windlass when  the  ship  is  anchored  is  much  more  than  the  mass  of  the  windlass  and  hence has  to  be  specially  strengthened ,  the  details  of  which  are  as  described  under  and  illustrated  by  sketch below
  • The  deck plating  at  forecastle  and  main deck  in  forecastle  space scantlings
  • The windlass is  mounted  on  a  doubler  plate welded  to  the  forecastle  deck
  • The deck  girders in  forecastle space  is increased in  The  deck beams  pitch distance  decreased to  accommodate  more  beams.
  • Four  round  pillars  at  four  corners  of  the  base of  windlass  doubler  plate  connect  to  the  main  deck  plating  to  give  continuity  of  strength  to  deckShip Windlass

The  windlass   machinery  is  combined  with  the  forward  mooring  winch  as  one  unit. The  main  winch  consists  of  a  double  reduction  gearing  arrangement  to  produce  a  ;large  torque.

The  wind  lass  is  arranged  on  a  further  reduction  arrangement.The   windlass  part  consists  of  a  solid  cable  lifter  wheel combined  with  the  brake  wheel keyed  to  a  shaft  properly  supported  on  two  bearings  with  its  clutch  arrangement. The  clutch  connects  the  cable  lifter to   driving  gear  when  the  anchor  has  to  be  hauled  up.

For  anchoring  purpose  the  clutch  is  released with  the  cable  ;lifter  in  braked  position. When  the  anchor  has  to  be  dropped,  the  brake  is  released and  the  anchor  along  with  the  chain  drops  by  gravity so  that  it  strikes  the  ground  with  sufficient  force  to  get  entrenched  in  the  mud. The  sketch  of  the  wind  lass  part  is  as  given  under.

Ship Windlas

Ship Windlas

 

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.

 

The  electrically  operated  windlass is  given  under

Ship Windlas with mooring rope drum

Ship Windlas with mooring rope drum

 

Hydraulic Windlass

The hydraulically  operated windlass has  larger  torque capacities  because the  hydraulic  motor  can  operate  at  very  low  speeds  even  at  5 to 10 rpm, there by  building a  very  high  torque.  The  torque –speed  characteristics  of  hydraulic  system  is  much  better  and  flexible  than  electrical  systems. Their  comparison  is  shown  in  the  sketch  given  under

Ship Windlas torque-speed charecteristics

Ship Windlas torque-speed characteristics

 

The Hydraulic  machine  is  robust  and  can withstand  a  lot  of  shock.  The  components are  less since  the  double  reduction gear  box  and  the  slip  clutch  are  eliminated thereby  reducing  the  cost  of  the  machinery. For  safety  a  spring  loaded  shock  valve  is  provided  in  the  system  which  will  connect  the  high pressure  to  the  low  pressure side  when  overload  occurs. The  hydraulic  windlass cum  mooring  winch  is  illustrated  below

Ship Mooring winch and windlasShip Mooring winch and windlas

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.

Variable torque hydraulic system for windlas

Variable torque hydraulic system for windlass

 

For  mooring  winch  operations  no 1  and   R positions  are  used  as convenient. For   normal  anchor  lifting  no  1  position  is  used. For  walking  back  the  anchor  R  position  is  used.  For  breaking anchor  from  ground  no 2 position  is  used.

When   changing  over  from  1  to  2  more  oil  is  required  and  this  is  provided  by  oil  flow  from  expansion  tank  to  pump  through  a  non  return  valve. When  changing  over  from  2  to  1  excess  oil  from  system  flows  back  into  expansion  tank  by  another non- return  valve.

Hydraulic  motor

The  motor  is  simple  in  construction  at  the  same  time  it  is  robust  and  can  take  a  lot  of  rough handling. The  rotor  is  a thick  disc  with  rectangular  slots  cut  on  the  circumference. Each  slot  accommodating  a  thick  vane  held  in  place  by  the  cover plate.  The  vanes are made  to  press hard  on  the  casing (internal)  surface  by  a  bow  spring  held  under  the  vane.

The  rotor is  mounted  on a strong  roller bearing  and  also  carries  an  oil  seal  which  prevents leakage  of  oil  during  operation.

Maintenance

During  lay ups   at  special  surveys, the  end  cover  is  opened  up  and  vanes  as  well as  springs  which  are  damaged  are  renewed.  The  oil  seal  and roller  bearing  also  renewed  if  they  are  worn  out. The  sketch  of  the  winch  motor  with  detail  of  vane  assembly  is  shown  under.(Fig 13b)

The  electric  motor  driving  the  gear pump  is  a three phase  double  squirrel  cage  motor  with  high  slip  capability  combined  with  higher  rotor current  capacity  because  of  the  two  layers  (radially) of  copper  bars   embedded in  the  iron   rotor. The  sketch  of  this rotor  is  reproduced  as  under.

Rotor of windlass motor

Rotor of windlass motor

 

Relevant  important  classification  rules  on  Windlass

7.1 General

7.1.1 Windlass of sufficient power and suitable for the size of chain cable is to be fitted. Where wire ropes are proposed and approved in lieu of chain cables, suitable winches capable of controlling wire rope at all times are to be fitted.

7.1.2 Windlass is to have one cable lifter for each anchor required to be kept ready for use. The cable lifter is normally to be connected to the driving shaft by release coupling and provided with brake.

7.1.3 For each chain cable, a chain stopper is normally to be arranged between the windlass and hawse pipe. The chain cables are to reach the hawse pipe through the cable lifter only.

7.1.4 Electrically driven windlasses are to have a torque limiting device(slip clutch). Electric motors are to comply with the requirements of Pt.4, Ch.8.

7.1.5 The windlass is to be capable of exerting, for a period of 30 minutes, a continuous duty pull corresponding to the grade of chain cable, as follows :-

36.8 dc        for grade CC1
41.7 dc        for grade CC2
46.6 dc        for grade CC3

 

Where dc is the chain diameter [mm]. The mean hoisting speed is not to be less than 9 [m]/min.

Also See Sec. 7.2.1.

The windlass is to be also capable of exerting, for a period of not less than 2 minutes, a pull of not less than 1.5 times the continuous duty pull. The speed in this period can be lower. The above criteria do not require both anchors to be raised or lowered simultaneously on windlass fitted with two cable lifters.

7.1.6 The capacity of the windlass brake is to be sufficient for safe stopping of anchor and chain cable when paying out.The windlass with brakes engaged and release coupling  isengaged is to be able to withstand static pull of 45 per cent of the tabular breaking strength of the chain without any permanent deformation of the stressed parts and without brake slip. If a chain stopper is not fitted, the windlass is to be able to withstand a static pull of 80 per cent of the tabular breaking strength of the chain without any permanent deformation of the stressed parts and without brake slip.

The chain stoppers and their attachments are to withstand a pull of 80 per cent of the tabular breaking strength of the chain without any permanent deformation of the stressed parts. The chain stoppers are to be so designed that additional bending of the individual link does not occur and the links are evenly supported.

7.1.7 Attention is to be paid to stress concentrations in keyways and other stress raisers and also to dynamic effects due to sudden starting or stopping of the prime mover or anchor chain.

(Note   The  rules  printed  in  red  colour  are  important)


 

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