Ship Windlass Maintenance Procedure

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Hydraulic windlass and electric windlass
Hydraulic windlass and electric windlass

Most of the windlasses found onboard ships these days are driven directly by electric motors or by pressurised hydraulic oil.

They cater to hoisting up varying loads with the help of gear and teeth arrangement. The major parts of a windlass are main shaft, driving shaft, inspection cover, gear, gear frame, drums (one or more), warping head or couplings, brake band, brake liner assembly, chain wheel, gear wheel, pinion, clutch and high speed low speed hydraulic valve blocks.

Regular inspection of external and moving parts of gear and shaft enables a ship’s officer to judge the wear and amount of use of this important machinery.

While using windlass for hoisting, an early indication can be temperature rise on the exterior of hydraulic pipe lines driving the main shaft. This further needs to be investigated for the correct technical specification and properties of the oil used and load  on the motors and working pressure of  the driving hydraulic oil. The bearing, pin and sliding parts of the assembly require a special grease recommended to be used on open gears to prevent them from weather damage as well. Often the maintenance routines for the filters of the hydraulic pumps used for running windlasses are followed by ship’s staff. The oil samples are also collected periodically for analysis.

The main shaft or gear shaft too may be checked for temperature rise to indicate lack of or less lubrication than required. The main shaft extends outside the gear frame and is equipped with drums, warping heads or cable lifter unit. The shaft consists of shaft and pinion and shaft roller bearing, which is lubricated through the grease nipple.

The drums are usually provided with manual brakes or they can be hydraulic operated brakes. Brakes are provided with foundation plate welded to the deck.

Often windlass shaft is coupled with mooring winch and it is important to put the mooring winch brake ‘on’ and the clutch in disengage position for the winch before operating the windlass.

When anchoring speed is high the anchor runs away and the brake lining might get damaged due to heat. Thus dropping the anchor and repeating the drop and stoppage at every ½ shackle is advisable to prevent damages to brake liner due to temperature rise.

In rough weather it is necessary to loosen the anchor chain tension while heaving up by using engines to avoid excessive load on the windlass. In case excessive load is applied on the windlass while heaving, bring the operating lever to neutral position then pay out the cable little bit, increase engine revolutions and heave the chain again once the load reduces. Speed change for windlass from high to low will cause large speed change and thus they are constructed with utmost safety features.

A weekly schedule for windlass should involve lubricating all the plain bearings through the grease nipples and the gear teeth. Monthly or quarterly checks recommended for the condition of brake linings should be carried out depending on the frequency of use. Monthly routines should include all the couplings, hydraulic valves and piping to be checked for leaks, tightness and functioning. Covering couplings with anti corrosive tapes can prevent them from getting rusted. The hydraulic motor foundation to be checked for tightness and any sign of wear at the base.

On an yearly basis the bearing clearances, gear wheel contact areas and hydraulic valves to be adjusted for correct operating pressure. The bolts and nuts should be checked for proper tightness. The gear contact should be at least 70% or more failing which the gear wheel gives abnormal noise. Preventive actions can be greasing of gear teeth or the realignment of windlass.

Adjustment of brake settings of windlass : When the brake lining has worn away it can be adjusted to render the necessary holding force. Often manufacturer’s recommend after a specific reduction in thickness of the brake lining to replace it with new one. However, when the liner thickness reduces within the limits applicable, brake setting can be adjusted with the regulating screw as a makeshift measure. Both the linings, upper and lower should be changed at the same time.

Adjustment of brake settings of windlass
Adjustment of brake settings of windlass

During liner replacement it is very important to secure the chain and anchor with extra lashings if the ship’s staff is carrying out this job at sea. The job should preferably be carried out in calm waters without any uneven rolling or pitching. When the anchor and chain is secured by the stopper and extra lashings the brake assembly can be checked. For that the brake has to be fully opened and all the pins connecting to the brake has to move smoothly, cleaning, greasing or hammering of pins may be required for this purpose. The brake nut can be used to adjust the length of brake spindle which in turn corresponds to the liner thickness.

It is very important that while replacing the brake liner assembly of a windlass the position of the brake screw down lever and  position of brake bands corresponding to the brake position is marked. As after replacing the liner misalignments are often observed while reassembling the whole unit.

The spherical roller bearings assembled to the main shaft  are precision built and care must be taken while removing them. If any roller bearings fail it should be completely replaced. Never strike a roller bearing with a steel hammer. A wood hammer or soft hammer should be used to strike it lightly.

Read more : Planning and operational guidance for anchor ship

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.

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.

Hydraulic Windlass
Hydraulic Windlass

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 windlass
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.

Hydraulic motor windlass
Hydraulic motor windlass

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.

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.

Read more : Planning and operational guidance for anchor ship

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