Traction Winch design Independently Driven Sheaves (TWIDS) (summary)

Delft University of Technology

Faculty Mechanical, Maritime and Materials Engineering Transport Technology

A. Roobol T raction Winch design Independently Driven Sheaves (TWIDS) Masters thesis, Report 2005.TL.6928, Transport Engineering and Logistics.

The desk research, (A. Roobol 'Analysis of traction winch performance', report 2004.TL.6882 preceding this master's thesis, was used as a comprehensive analysis of the different types of traction winches. The aim was to find which of these traction winches would be suitable for use in an abandonment and recovery winch arrangement (also called A&R winches). It was concluded that there are two types of traction winches suitable for this purpose, being the double capstan winch and the traction winch using independently driven sheaves (TWIDS winch). The double capstan winch is commonly used in A&R winch arrangements but has several drawbacks. The conclusion was that it is worth the time and resources to further develop the TWIDS winch.

This master's thesis describes the functional design of an A&R winch using the TWIDS winch. The design purpose was to explore all facets of the winch and determine if the design could be realised. The design had to fulfil all required functionality, performance criteria and safety features. It was found that TWIDS winch was able to satisfy all requirements.

Summary

A&R (abandonment and recovery) winches are used on ships to deploy and recover loads to and from great water depths. The depths to which these loads need to be deployed to and recovered from keep increasing. When A&R winches are used onboard ships, they must be able to work in active heave compensation mode (also called AHC). Active heave compensation is used to compensate for the wave induced heave motion of the vessel. The heave motion needs to be eliminated to avoid resonance of the submerged load and enable easy pick and placement to and from the seabed.

The A&R winch configurations often use a wire rope traction winch to step the wire rope tension down before the rope is spooled onto the storage winch. This is done to avoid high tension multi-layer wire rope spooling. High tension wire rope spooling will result in excessive loads on the drum barrel and flanges, and it will lead to a tremendous reduction in wire rope lifetime. A traction winch (also called friction winch) uses the friction between the rope and groove to apply traction on the rope. The normal force required to induce friction is a result of bending the rope over an arc of contact and the wire rope tension. The desk research was used to evaluate the different types of traction winches such as the single capstan, double capstan and the independently driven sheaves traction winch. The single capstan traction winch is not suitable for use in an A&R winch arrangement. The assessments done during the desk research showed that the traction winch using independently driven sheaves (also called TWIDS) has several advantages over the double capstan winch. The most important advantages are extended wire-rope life, winch performance independent of winch wear and reduced wear of both the rope and winch. In addition, the TWIDS winch system allows for AHC without the use of an additional heavy loaded heave cylinder. Based on this assessment, it was decided to further develop the TWIDS winch. More significantly, Kenz-Figee made the decision to add this winch to their list of special features devices.

For further development of the TWIDS winch, the decision was made to make a functional design of an A&R winch using a TWIDS winch. The main objective was to make the functional design safe for the deployment and recovery of loads to and from the seabed. For the design, a request to tender document issued to Kenz-Figee by one of its customers was used. This was done to obtain realistic load cases and design requirements. The design had to be in accordance with the DNV (Det Norske Veritas) "Rules for Certification of Lifting Appliances" design code. These rules and requirements led to a functional A&R winch with the following characteristics and capabilities:

A maximum SWL of 125t single fall and 250t double fall.

Functional capabilities such as constant tensioning and active heave compensation.

Maximum hoist/lowering wire rope speeds 1m/s and maximum wire rope speeds during AHC of 2.3 m/s (hoist plus heave compensation speed). Safety features such as overload protection and emergency lowering.

Recommendations

During the process of creating a functional TWIDS winch design, all aspects such as physical design, systems design, safety features, operable capabilities etc. have been identified and dealt with accordingly. To make the TWIDS winch operable would require the details of the functional design to be put in place. Ideally, staff at Kenz-Figee should be fully briefed and instructed on the findings of this research. This to make staff aware of the challenges and issues involved in the design of a TWIDS winch.

Now that all components and requirements have been identified, it is important to determine what the total cost would be of building the A&R winch arrangement using the TWIDS winch. The next step would be to use these estimated costs to make a more detailed comparison between the A&R winch arrangement using the TWIDS winch and using the double capstan winch.

To use the TWIDS winch to its full potential, it should be made suitable for synthetic rope. The assessment made in this report is based on the use of metal wire rope. The main advantage of using synthetic fibre rope over metal wire rope would be that using identical winches, equally heavy loads can be

deployed to greater water depths. Analysis showed that for this winch using metal wire rope (single fall) a 125t load could not be deployed beyond a 188m. Using a similar synthetic rope, the same load can be deployed to a depth exceeding 4000m. Unlike metal wire rope, synthetic fibre rope is not yet proven technology when used for hoisting applications like the A&R winch arrangement. Kenz-Figee has become a member of a research group called DISH (Deepwater Installation of Subsea Hardware). This is a so called Joint Industrial Project (JIP) which is set up to tackle the technical problems associated with installing subsea hardware in very deep water (>2000m). The focus of this project is on the use of synthetic fibre rope in A&R winch arrangements. Members of this research group can be divided into oil and gas operators, installation and engineering contractors and specialist suppliers. DISH membership is important for Kenz-Figee for two reasons: to gain the know-how to successfully implement synthetic fibre rope into the A&R winch arrangement and to use DISH to get into contact with potential customers.

It seems very unlikely that the A&R winch arrangement using the double capstan winch would be suitable for the use of synthetic fibre rope. This

assumption is based on the characteristics of the double capstan winch and of the synthetic fibre rope. The synthetic fibre rope has a low resistance against heat, while the creep power when using the double capstan winch is substantial in comparison to the TWIDS winch. Creep power is a measurement of power loss in a traction winch. This power loss will result in the generation of heat which is the major limiting factor for the safe operation with synthetic fibres.

Reports on Transport Engineering and Logistics (in Dutch)