ROPE LIFETIME ESTIMATION FOR THE DELTA ESCORT TUG ACTIVE CONSTANT TENSION WINCH
The IHC Delta Escort Tug (DET) assists during steering and braking on large LNG tankers using an active constant tension winch with power limitation with fairlead, preventing snap loads and minimizing rope damage.
Together with (load-bearing) fibre manufacturer Teijin Aramid and rope manufacturer Hampidjan, IHC performed the applied R&D project. Goal is to find the highest possible safely acceptable minimum rope lifetime estimation with the best discard criteria, without active rope cooling.
Considered critical operational failure modes are:
- Drum abrasion on the winch and
- Cyclic Bending Over Sheave (CBOS) at the fairlead.
CBOS is expected to be the governing failure mode.
Small scale drum abrasion tests, performed on different rope types and preliminary CBOS heating analyses resulted into a Hampidjan rope with Aramid (Teijin Technora T200WD) braided rope core and HMPE cover.
In continued small scale CBOS tests (IHC) and yarn-to-yarn abrasion tests (Teijin), endurance depending on rope temperature was assessed. Results showed that at temperatures below fibre and fibre coating maximum allowable temperature, the lifetime is approximately equal for the same amount of cycles and same rope diameter.
Scaling of rope heating needs to be validated in larger scale tests. The uniform heat source during CBOS is expected to be the most uncertain factor for rope temperature at scale. This is caused by but not limited to the increasing ratio between rope volume and rope surface area, different rope construction and different rope hierarchy levels.
Based on the performed tests and analyses, rope heating is expected to be decisive for the applicability in this DET Winch application.
Author(s): M.J. van Wezel, H.N. van den Heuvel