It is interesting to note that based on investigation of incidents from Western Australian ports, that a frequent cause of mooring line failure is incorrect or non-existent mooring winch brake render testing.  With every mooring line parting there is always potential to cause serious harm or death to personnel.

The Ship Design MBL (SDMBL) should be the initial reference for Brake Holding Capacity (BHC) tests. When a ship is built, the mooring winches are equipped with mooring lines of an MBL roughly equal to the SDMBL. In cases where a greater strength line is used, the Line MBL can be higher than the Design MBL but must always be less than the mooring fittings (bollards, chocks etc.) SWL values.

It is imperative therefore, that Brake Holding Capacity test calculations must be based on the SDMBL and not the Line MBL.

The table below demonstrates the relationship between SDMBL and Mooring Lines and Fittings and Operational Values:

The tanker industry recommends that the Brake Holding Load (i.e. render setting) be set at 60% of the SDMBL which corresponds to the Operational Minimum Brake Holding Capacity in the diagram above.

Before testing a winch brake, the condition of the brake, its mechanism and the brake drum should be confirmed as satisfactory.  Any damage, failure or excessive wear should be rectified before testing takes place.

It is strongly recommended that ship-specific instructions developed by the vessel’s Technical Managers are on board.

The test itself is essentially a jacking test against the winch brake.

When testing, the aim is to apply a hydraulic force to the winch drum equivalent to the 60% of the SDMBL on the first layer of the rope (for split drum winches) and to ensure that winch brake slips (or renders) at that point. Then, the tightened brake screw must be marked at the point it slips.

It is not a load test to determine how strong the winch brake is, but a test to confirm that the brake holds up until 60% of the SDMBL. Applying more force causes slippage of the brake to ensure that the winch brake remains the weakest point of the mooring system.

One common mistake when calculating the required hydraulic jack pressure, is that Line MBL is used as the reference rather than SDMBL.

Another common mistake is that when the calculated hydraulic jack pressure is reached and brake is still holding, that the test is deemed successful. It must be clearly seen that after exceeding the calculated limit, the brake slips.

Split Drum Mooring Winch with Test Equipment in Place

Undivided Drum Mooring Winch with Test Equipment in Place

Undivided (ie single drum) Mooring Winches become a bit more difficult and it is recommended that the manufacturers be consulted in terms of how many line layers should be used in the calculation.  This may require ship operational experience input to determine the normal number of line layers on the drum during normal mooring configurations.

One common mistake is using a Split Drum calculation (based on one layer of line) when testing an Undivided Drum, the effect of doing this is that rendering will occur at 11% less force for a second layer of line and 25% less force for a fourth layer of line.  This can be visualised in the Force / Lever diagram (below):

• What is the relation between Brake Holding Limit and mooring equipment?
• Why BHC Testing is important for safe mooring operations?
• Why BHC marking reference is important and how it must be used?
• What is the importance of mooring line layers on split drum winches?
• What are the risks of over tightening or under tightening the winch brakes?

Training should be carried out at regular intervals in order to familiarize all crew responsible for mooring.

Why is SDMBL as the governing reference and not Line MBL?

The SDMBL is a fixed parameter derived from the EN and cannot be readily altered whereas lines can conceivably be fitted with MBL’s that differ from those required by the EN.

Do I need to re-test and re-mark the BHC after changing lines or brake linings?

Re-testing and re-marking would be required if brake linings are changed or brake drums are skimmed or re-surfaced, however changing lines like for like (ie with same diameter) would not be required. Re-testing is also recommended when brakes have rendered or slipped in service.

What happens if I tighten the brake more or less than the reference point?

The brake would simply render at unknown lower or higher loads which is undesirable as all winch brakes should be set to render at the same load across the mooring set-up.

Do I need a third party for regular BHC tests and marking?

No, but it is advisable that the persons conducting the tests are competent, properly trained and provided with ship-specific instructions.

Vessel has single drum winches. How will I determine how many layers of line to be considered for calculations?

For undivided winch drums, it is recommended that the manufacturers be approached for guidance. This may require ship operational experience to identify the normal number of layers in use for most mooring operations.

I have marked the reference point with a jubilee clip / wire and it has moved. What should I do?

If the reference point marking has moved accidentally (during operation, maintenance, greasing, painting over etc) the test must be carried out again and re marked. Marking should not impede further tightening in case of emergencies and must be clearly visible and fixed such that it does move easily.

What information should be marked on the winch after the test is completed?

Marking the test date, tested force (in tonnes or KN, same as mooring fitting markings) and respective percentage of the SDMBL (e.g. 60%) should be marked on the winches.