A significant portion of a vessel’s mechanical issues can be traced to misalignment. Chances are, a vessel’s machinery has or will be out of alignment at one point during the course of its life.
When misalignment is present, components can become worn, performance is minimized and, if left untreated, mechanical failures become much more likely.
When one thinks of misalignment on a yacht, shaft alignment is usually what comes to mind. Shaft alignment is defined as the positioning of two or more machines so that at the point of power transfer from one shaft to another, the axes of rotation of both shafts should be collinear when the machine is running under normal conditions (DB Pruftechnik, “An Engineer’s Guide to Shaft Alignment, Vibration Analysis & Dynamic Balancing”, courtesy of Ludeca).
Misalignment is usually obvious, manifesting as vibration and an increase of heat output from prime movers. Both cause a noticeable increase in fuel consumption and costs, which also increases carbon emissions. Coupling damage as well as repetitive shaft seal and bearing failure are also imminent.
One of the most common causes of misalignment is the engine mounts. They have rubber elements that degrade over time. This doesn’t allow for proper absorption of the forces transmitted by the engine, and the mounts also become dimensionally unstable, creating misalignment. The lack of proper support of the engine will cause it to shift, and may even eventually bend the shafts.
Hitting bottom or tangling rope in a propeller can move the strut, causing another common form of misalignment. Other causes include the changing of the hull shape, which is why pre- and post-hull deflection targets are crucial to achieve and maintain optimum alignment.
It is always good practice to perform a final laser check after repairs are complete, and once the vessel has been waterborne for 24 hours. In some instances, proper alignment is never even achieved during the build.
Regardless of its origin, misalignment can cause rapid wear on bearings and damage. Extreme vibration can increase damage to engine mounts and the transmissions, sometimes even causing failure. Sealing systems can also become compromised, and then need to be replaced.
When machinery is correctly aligned, a 1-3 percent increase in energy efficiency can be experienced.
Since misalignment is a major source of vibration, the most accurate, efficient and economic way to diagnose it is to conduct a vibration analysis. Vibration analysis can identify what mechanical issues a vessel has and can determine exactly where misalignment is present.
Conducting periodic alignment checks can help pinpoint issues before they become major. The general rule of thumb is to check alignment three-to-six months after a new installation, when experiencing a shaft seal or bearing failure, or when a bearing is replaced. Once the data from a vibration analysis or laser check is analyzed, a proper course of action can be implemented, which includes an alignment procedure based on the mechanical arrangement of the components involved in the misalignment, as well as the specific issue at hand.
The first laser alignment systems surfaced in the early 1960s. Lasers were applied later to alignment applications to maintain a line of sight. Prior to the use of lasers, piano wire was often used for alignment. Wire posed problems, such as sagging, and even environmental factors can cause it to move, causing great inaccuracies.
Since light travels in a straight line, lasers were an easy choice as a replacement for precision alignments. Modern laser systems can measure hundreds of positions and allows for one-step machine corrections in vertical and horizontal directions.
Generally speaking, misalignments are corrected with either laser and/or optical alignments. Optical alignments are performed using optical borescopes and must be done out of the water when the running gear have been removed. Laser alignment is the process of measuring misalignment between mechanical components, usually one or more shafts. It is a precise way to align machinery while minimizing the likelihood of human error.
Regardless the cause of a misalignment or how it is corrected, yacht captains and engineers will always see a bigger return on investment with proper maintenance.
Rich Merhige is the owner of Advanced Mechanical Enterprises and Advanced Maintenance Engineering in Ft. Lauderdale, which specializes in rotating and reciprocating machinery. This column is co-written by Teresa Drugatz, marketing manager at AME. Contact them through info@AMEsolutions.com or +1 954-764-2678. Comments on this column are welcome at firstname.lastname@example.org.