Check your vibrations this summer

Aug 8, 2016 by Rich Merhige

Before we know it, fall will be here. For the South Florida yachting industry, when fall hits, it’s time to focus on maintenance and, for some, time on the hard.

Planning for yard periods can be daunting. One of the biggest concerns is always going to be budget.

The other is adhering to a schedule, especially if an owner’s trip or charter is looming.

What’s the best way to ensure efficiency and stay within budget? Where does planning start? In terms of the mechanical portion of a yard period, a vibration analysis is a great place to start.

The definition of vibration is mechanical oscillations in relation to a set point of equilibrium. It’s usually referenced as aggravating/agitating, and is associated with being wasteful of energy.

When spoken of in relation to marine vessels, vibration is usually a symptom of mechanical misalignment, worn rubber elements, imbalances, or insufficient support of the main propulsion units.

Bottom line: When vibration is an issue, something is wrong and the yacht is not running as efficiently as it could be. Vibration analysis can pinpoint what mechanical issues a vessel has, preventing timely and costly guesswork or fishing expeditions.

Technically, everything vibrates. But vibration that deviates from the norm indicates serious issues.

In a perfect world, every vessel would get a baseline survey at launch, and then twice a year to predict any upcoming problems or notate deficiencies.

Periodic vibration monitoring, also known as condition monitoring, provides trending that can forecast unplanned downtime and catastrophic failures – a huge deal if downtime means an out-of-service vessel and lost charter or interrupted owner’s trip.

Data collection is best done while the vessel is at sea in accordance with guidelines set forth by the Society of Naval Architects and Marine Engineers, as well as various class societies. These guidelines dictate that measurements should be taken with the ship proceeding ahead, at a constant speed and course, in a depth of water not less than five times the draught of the ship, with sea conditions not greater than sea state 3 on the WMO sea state code.

A computer database of vibration measurement points is set up of the vessel’s machinery arrangement and hull in the vibration analysis software.

Accelerometers are placed on key pieces of equipment so data can then be collected. The vibration data is then uploaded and analyzed by examining the frequency, amplitude, location, and direction of each measurement point.

This data serves as a thorough machine condition evaluation, and it can detect a multitude of problems using known frequencies specific to the vessel, such as:

  • Misalignment of shaft couplings, flexible machine couplings
  • Misalignment of underwater running gear such as propeller struts
  • Propeller defects
  • Bent shafts
  • Unbalance of rotating components
  • Main engine misfire problems
  • Mechanical looseness
  • Deterioration of rolling-element bearings within transmissions and thrust bearings
  • Gear wear
  • Rubbing
  • Structural resonance
  • Machinery soft-foot conditions

The vibration analyst will then create a report with findings and recommendations.

The data collected can pinpoint the cause of faults and their source so corrective measures can be outlined and implemented. This basically provides a roadmap to achieving mechanical goals during a haul out.

Rich Merhige is owner of Advanced Mechanical Enterprises and Advanced Maintenance Engineering in Ft. Lauderdale. Comments on this column are welcome at editorial@the-triton.com.

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