Small pads play big part in structural performance
Hatch cover bearing pads transfer the weight of the cover, and any cargo it may be carrying, to the ship’s hull while allowing for relative movement between the cover and the hatch coaming caused by hull flexing in a seaway. They must also maintain the correct compression on the hatch cover seal and avoid wearing damage to the coaming/hatch cover interface.
As bearing pads transfer weight, lateral forces are generated that are then transmitted to the ship’s coaming and hatch cover structures. These forces are used in fatigue strength analysis at the newbuilding stage, and subsequently, the structures are designed around these calculations.
To obtain the required safety margins and to guarantee a trouble-free operational lifetime, the hatch cover system has to be maintained as instructed, and critical spare part components, such as the hatch cover bearing pads, have to be of original design. This is because there can be great variations in sliding and wear properties of different bearing materials. This is applicable to both bronze and plastic composites.
Lubripad, Polypad, Unipad and Flexipad
For ships imposing greater demands on the bearing pads, increased relative movements or excessive loadings, an arrangement based on low-friction replaceable sliding pads (Lubripad, Polypad or Unipad) or non-sliding flexible replaceable pads (Flexipad) is recommended.
Steel/steel bearing pad
In general a steel/steel bearing pad is sufficient for less than 1000 TEU container ships and general cargo vessels, as well as for bulk carriers. It is essential, however, that data relating to maximum surface pressure and hardness difference between the two steel surfaces is taken into account.