Page 15: of Marine News Magazine (March 2013)

Shipyard Report: Construction & Repair

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What is Bollard Pull? Bollard pull is the static force ex- erted by a tug at zero speed on a Þ xed line. Almost always, a test involves af- Þ xing a line to a shore-based bollard and ramping the RPMÕs of the engine to full- throttle, typically in ahead and astern conditions. The vessel is then held at full RPMÕs for between 1 and 10 minutes. Some versions of this test are completed quickly and some, like in Brazil, last for over an hour. Test Variables Many variables can inß uence a bol- lard pull test reading, including water depth, prop wash, wind, tidal forces or currents, rudder angle, and stretch of the tow line. Finding an ideal site is difÞ cult, so external forces must be Þ gured into the Þ nal analysis. Beyond this, A bollard pull test requires a ten- sion sensor which is put in series with the tow line, a local display of the line tension and a process to record that data. Often, an engineer will be pres- ent in the engine room to evaluate en- gine RPMÕs and another engineer will stand on the back deck to track the forces on the load cell by noting them on a display and manually track-ing the Þ gures by hand. This process can be challenging and inaccurate in rough weather and in river conditions which change quickly. In river situa- tions, the tug may start upriver of the shore-based bollard, bring the tug up to full power and when the vessel is perpendicular to the shore, the engi- neer must quickly capture the data from the tension sensor. This short window for readings can make it chal- lenging to capture accurate data. Advances in Technology Measurement Technology NW of Seattle has developed a PC-based soft- ware solution that allows data capture up to 100 times per second (Hz). The software time-stamps the incoming data so that it is easy to match up with other data in post-event analy- sis; automating and simplifying data correlation. Recently, MTNW sup- ported Glosten AssociatesÕ work with a tugboat bollard pull test intended to verify the bollard pull of a number of tugs. ÒThe MTNW tension moni- toring system and engineer provided the tension data that we required to MN MN March2013 Layout 1-17.indd 15MN March2013 Layout 1-17.indd 153/5/2013 10:26:55 AM3/5/2013 10:26:55 AM

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