1. Wire drawing method

The traditional cable method is relatively close to the measurement principle of coaxiality. Its side is intuitive and easy to understand. The cost of measuring tooling is low, the measurement accuracy is controllable, and it is suitable for stern tubes of various sizes. However, this measurement method requires high operation level for measuring this, and it is easy to generate measurement errors due to considered factors.

2. Telescope method

Collimating telescope measurement refers to the setting up of a collimating telescope at one end of the stern tube, setting up alignment brackets before and after the stern tube, and using the characteristics of the collimating telescope to read directly on its telescope, the coaxiality deviation data of the stern tube can be directly obtained.

Compared with the other two methods, it has the following characteristics: the cost of telescope equipment is relatively high, and it is believed that the factors have a certain influence on the measurement accuracy, and the output of the measurement results does not need to be calculated and is not affected by environmental factors. However, this method is limited by the size of the stern tube because the collimating telescope itself can be adjusted to 1.2mm, so the method of aligning the bracket needs to be changed when measuring the larger stern tube.

3. Laser method

Compared with the traditional wire drawing method, laser measurement has the following characteristics: the cost of laser equipment is higher. The measurement accuracy is less affected by human factors, the direct output of the measurement results does not require calculation, and the measurement accuracy is controllable. At present, the more common laser equipment is the Swedish Easylaser laser geometric measurement system. Its basic technical parameters are: the measurement distance is 20m, the geometric measurement distance is 40m, the laser wavelength is 635-670nm, the accuracy is 0.001mm, and the level accuracy is 0.5.

A laser transmitter is set up at one end of the tail shaft tube, the receiver is installed at the position of the measuring point, the receiver is connected with the hand-held connection device, and the measurement result is displayed on the hand-held device, so after the measurement of the measurement point data is selected, the measurement result can be directly read on the hand-held device, and finally the coaxiality of the whole stern shaft tube can be obtained.