Tugs, anchor handlers, suppliers but also other offshore vessels are designed to deliver a large pulling force at low speed. This key performance is tested by means of a Bollard Pull where the tow line is connected to a fixed bollard or pile. At maximum developed power the pulling force is then measured by means of a load cell. This value is documented on the Bollard Pull Certificate which plays an important role in the sale and delivery of the tug as well in commercial deployment and contracts.
Although tugs have been around for a long time, a proper standard for conduct, measurement and analysis of a bollard pull is not available. Bollard Pulls are conducted in various ways, measurements of developed shaft power and line load are not always accurate and an analysis procedure of the measured data is lacking.
As a consequence the issued bollard pull certificate, which are the basis for contracting the tug, is not always reliable. Although class societies issue such bollard pull certificates, their classification process and notifications are mainly aiming at the safety of the equipment and not on the tow performance of the tug. There are few bollard pull procedures available in open literature; In 1961 the BSRA issued their “Code of procedures for bollard trials of tugs”. In 2002 Steerprop proposed a bollard pull code at the International Tug & Salvage convention aimed for further unification of procedures for conduct and analysis of bollard pull trials. The code was published by ITS in May/June 2002 and is often used as ‘de facto’ standard.
The Bollard Pull Joint Industry Project is aiming at the following:
- Understanding of the main parameters that affect the bollard pull performance;
- Systematic data on thrust deduction for various configurations (tugs/propulsors, push/pull and water depths)
- Quantification of the scale effects on ducted propellers and the development of an extrapolation method for this purpose.
- Develop methods to correct for non-ideal bollard pull conditions such as restricted waters, quay geometry, line length and angles, wind, current & waves;
- Guidelines for conduct, measurements, analysis and reporting of bollard pull trials which will serve as an worldwide industry standard.
- Develop a software package to analyse the bollard pull performance and to predict the pull performance over the complete speed range.