RATIONAL SHAFT ALIGNMENT CALCULATIONS

The shaft line is a key component of the ship. It is responsible for transmitting the power of the propulsion machinery to the propeller. The shaft line is submitted to important axial and torsional loads, as well as vibratory torque and fluctuations in the hydrodynamic loads that can generate fatigue problems, therefore a suitable alignment is fundamental.

Contrary to what it may seem at first sight, a correct shaft alignment is not that in which all the support bearings of the installation are collinear. Although this is a very extended practice, correct procedure (which the classification societies insist upon) is to carry out the rational alignment calculation, in which suitable positions of the bearings are determined in order to achieve:

- inferior loads to those permitted in all working conditions, in all bearings
- vertical downwards loads in all the bearings
- acceptable stress along the whole shaft line
- acceptable load distribution in the reduction gear bearings.

These conditions must be verified in the working conditions of the installation, taking the following aspects into account:

- Hydrodynamic loads generated by the propeller
- Thermal expansion of the components due to the increase in temperature
- Forces on the wheel of the reduction gear originated by the contact between teeth

The consequences of a failure in the propulsive installation are very serious as much from the point of view of the implied equipment cost (support bearing, reduction gear, etc..) as the time lost in the repair with the immobilized ship, possibly requiring dry docking and complete alignment and chocking of all the installation.

VICUSdt, in a very short space of time, can make a complete alignment calculation including a report with instructions for correct alignment and verification of the line, diminishing possible problems. These calculations are regularly submitted for approval of the main Societies of Classification.

Rational alignment calculation is simply the best investment for your shaft line.