Bollard Pull

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TECHNICAL INFORMATION

BOLLARD PULL TRIAL CODE

For Tugs with Steerprop Propulsion

Steerprop

Steerprop
A Skogman / 22 March 2001

BOLLARD PULL TRIAL CODE
FOR TUGS WITH STEERPROP PROPULSORS
This Bollard Pull Trial Code is established to define the procedures of performing bollard pull trials in a manner that ensures repeatability as well as comparability for trials performed at different locations and/or with different vessels. The need for this code originates from the lack of an acceptable standard for bollard pull trials, as well as from the large variation in requirements for bollard pull trials in the rules of different classification societies. In the compiling of this code the rules and requirements of BSRA (1961), Lloyd’s Register of Shipping (1992), Det norske Veritas (2000), American Bureau of Shipping (xxx), Germanischer Lloyd (xxxx) and Bureau Veritas (1985) have been used as a basis.

1

General

Bollard pull trials are conducted in order to determine the static pull that a tug is able to employ in operating conditions. To enable fair comparison, the trials are not performed in typical operation conditions (e.g. shallow and confined harbour basin), but in conditions as close to ideal as possible, i.e. in conditions where the environmental and external effects are minimised. This code introduces the minimum requirements for trial site, vessel state and environmental conditions as well as the actual procedures for conducting the trials and definitions on bollard pull, to be used on tugs equipped with Steerprop Azimuth Propulsors.

2

Trial Site and Vessel Requirements

The trial site should be carefully chosen to minimise the effect of the environmental conditions. The following minimum requirements have to be fulfilled with regard to trial site and vessel state. 2.1 Recommendation

Trial Site

The location for the trials should be chosen with no piers, docks, jetties breakwaters or other obstructions close to the tug. The best place for the bollard is on a legged jetty with no wall, allowing the propeller wake to flow through/under the jetty. If a solid pier is chosen the bollard should be located as to give a clear run for the propeller wake, see fig. 1 and 2. The water depth on the trial site should comply with the below requirements (see chapter 2.2 Water Depth).

BOLLARD PULL TRIAL CODE FOR TUGS WITH STEERPROP PROPULSORS

Steerprop

2

Fig. 1

Positioning the tug for bollard pull trials

Fig. 2

Positioning the tug for bollard pull trials

BOLLARD PULL TRIAL CODE FOR TUGS WITH STEERPROP PROPULSORS

Steerprop

3

2.2

Water Depth

In order to achieve a fair bollard pull the build-up of water circulation has to be avoided. Water circulation is generated by the propeller wash and available amount of water below and around the vessel – in very confined and shallow water there will certainly be circulation. Hence the water depth has to be as large as possible, not only below the tug but also around it. Requirement

Minimum required water depth within a radius of 100 m from the tug is obtained as depth below the keel (see fig. 4) using equation (1), from the graph in fig. 3, or from table 1. dmin = k1 * (k2 * Pa – k3 * Pb) + 3 [m] where dmin k1 k2 k3 P a b = = = = = = = minimum required depth under the tug 0.060 52.00 46.26 total propulsion power [kW] 0.60 0.61

(1)

Minimum Water Depth
25

20 Minimum Water Depth [m]

15

10

5

0 0 1000 2000 3000 4000 5000 6000 Total Propulsive Power [kW]

Fig. 3

Minimum required water depth below the keel of the tug

BOLLARD PULL TRIAL CODE FOR TUGS WITH STEERPROP PROPULSORS

Steerprop

4

Table 1. Minimum required depth under the keel

Total propulsive power [kW] 1000 1500 2000 2500 3000 3500 4000 4500 5000

Required depth under the keel [m] 12.2 13.8 15.0 16.0 16.8 17.5 18.1 18.7 19.2

Fig. 4 Definition of towline length and depth below the keel

2.3

Towline Length

For...
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