In the role of human factors, environmental factors, equipment factors, measurement accuracy and other five aspects of the scope of application, the three coaxial measurement methods have their own limitations, so in the selection is the need for comprehensive analysis according to the situation.

1. Factors considered

Compared with the three measurement methods, the traditional cable method is most affected by the measurer, because the key point of the cable method is the adjustment of the zero point, that is, whether the steel wire perfectly passes through the center line of the stern tube. In addition to the measurement, the bracket should be adjusted. Surveyors have different working time and experience, so the cable method requires the surveyor to have certain construction experience, otherwise it will affect the measurement accuracy.

The laser method has lower requirements for the surveyor, and the operator only needs to master the equipment erection method and the data acquisition program of the handheld computer. The requirements of the telescope measurement method for personnel are somewhere in.

2 Environmental factors

The telescope measurement method and the traditional wire method are almost not limited by any environment, while the laser method is greatly affected by environmental factors, especially temperature. When there is a heat source not far from the measurement site or the temperature is less than minus 10 degrees Celsius, the laser beam will appear a certain deflection, affecting the straight shape of the laser, so the accuracy of the measurement is affected to a certain extent.

3. Equipment factors

Collimating telescope and laser calibrator are very expensive, so the cost of these two measurement methods is high, while the tooling and appliances used in the traditional pull wire method are much lower than that. In addition, collimating telescopes and laser collimators need to be calibrated regularly to avoid measurement deviations due to equipment accuracy.

4. Measurement accuracy

The measurement accuracy of the collimated telescope is almost no deviation in the range of 10m, the measurement accuracy of the laser collimator is less than 0.001mm, while the measurement accuracy of the traditional cable is less than 0.02mm, although the accuracy meets the requirements of the measurement, but the accuracy of the collimated telescope is higher than the other two measurement methods;

5. Scope of application

The scope of the traditional pull wire method includes all types of stern tube coaxiality measurement, while the laser method measurement due to the limitation of the bracket, the local area position of the stern tube cannot be measured, which needs to be obtained by the straight line inverse calculation of the stern tube. Since the telescope measurement method cannot adjust more than 1.2mm, the alignment method of the alignment bracket needs to be changed when measuring the stern tube with larger coaxial degree.