marineSOLUTIONS

Your Marine Surveyors in the Eastern Mediterranean…


Percussion Testing

Percussion Testing

The traditional coin-tap testing is one of the oldest methods of non-destructive testing and it is regularly used for testing laminated structures. Percussion testing requires the marine surveyor to tap each point of the structure to be inspected with a coin and listen to the resulting sound radiated by the structure.

Unfortunately, the coin tapping method is dependent upon the inspector’s hearing and interpretation, the results are subject to interference from workplace noise, and this technique is unable to provide quantitative data.

Surveyor Cem Baykent carrying out Percussion Test
Percussion Test

Composites are widely used in aerospace industry. One of the biggest players in that industry; Boeing; has developed an Electronic Digital Tap Hammer that provides a quantitative measure of the hammer/composite impulse time that can be correlated to flaws such as delaminations in the structure. The instrumented tap hammer supplements the tonal discrimination of the operator with a numeric readout that is related to local part quality. The effects of background noise and operator differences on the inspection results are eliminated. This hammer is relatively insensitive to the magnitude or forcefulness of the hammer hit, but very sensitive to the local stiffness of the structure. This method provides objectivity in the test, increases the sensitivity of the test and enables the inspector to collect quantitative results of the actual impact response.

This method and device is used by both Boeing Commercial Airplane Group as well as Boeing Defense & Space Group on the composite commercial and military aircraft.

marineSOLUTIONS has invested in this Electronic Digital Tap Hammer which can be applied to many composite requirements on boats.

Hull Inspections with Ultrasonic Testing

Hull Inspections

Corrosion Measurement of Hull Plates with Ultrasonic Testing (UT):

Hull Inspections are often overlooked by boat owners. Just about anything that is made of common structural metals is subject to corrosion – more so in the marine environment than elsewhere and hull plates of boats are no exception.
Usually, boats are lifted ashore regularly, thus ensuring a superficial inspection of hull plates from the exterior. The particularly important problem on boats is the measurement of remaining wall thickness of hull plates which may be corroded on the inside surface. Such corrosion is often not detectable by visual inspection as the access to bilges is limited due to various components and structures such as tanks and machinery.
If undetected over a period of time, corrosion will weaken hull plates and possibly lead to dangerous structural failures. Both safety and economic considerations require that hull plates that are subject to corrosion be inspected on a regular basis.
To make things more complex, boat hull exteriors are coated with fillers often applied thickly for fairing, antifouling paints and various other types of coatings. Measurement with simple thickness gauges can be less effective at detecting pitting and measuring the true minimum thickness. An Ultrasonic Flaw Detector is by far superior to thickness gauges as it displays ultrasonic waveforms. From waveform, attenuation and phase shifts, an experienced NDT surveyor can infer remarkable information about the structure under inspection. The surveyor can also directly distinguish between true and false echoes. Furthermore, we are able to determine the exact wall thickness of hull plates without removing the fillers, paints or any coatings and without any harm to them.
We use Olympus Epoch 650 Ultrasonic Flaw Detector, a state of the art digital flaw detector and Olympus Panametrics transducers for inspections. The instrument configuration is accepted and used in aerospace industry. We keep the instrument calibration up to date.

Ultrasonic Testing (UT)

Ultrasonic Testing (UT) of Composite Boats and Spars:

Many modern boats are built from composites – a combination of fibers and plastic matrices. Fibers might be randomly arranged, then flattened

Non Destructive Testing NDT Survey
Non Destructive Testing (NDT)

into a sheet (called a chopped strand mat), or woven into a fabric. The fiber material is often glass, aramid or carbon where the plastic matrix is most often based on polymers such as polyester, vinylester or epoxy resins.
Moreover, the trend for carbon fiber spars for sailboats is on the rise. Nowadays, carbon fiber spars are not only seen on racers but are also placed on a range of vessels such as cruising yachts, mega yachts and even on classic yachts.
Due to the prevalence of fiber-reinforced composites (whether it is glass, aramid or carbon fibers) in boats, and due to lower safety coefficients, the need for damage-detection and characterization has increased.
Hidden internal flaws and defects within a composite structure are not uncommon. These hidden flaws and defects might be resulting from manufacturing anomalies, applied stresses or weaknesses, accidents or improper repairs. They can have a significant impact on the structural integrity of the boat and are normally not detectable by radiography or by NDT techniques other than Ultrasonic Testing (UT).

Ultrasonic Testing (UT) can be used to detect the following:

  • Uniformity of laminate thickness
  • Presence and type of delaminations
  • Presence of voids and/or porosity
  • Quality and bonding of laminate and integrity of repairs
  • Inclusions and alien material presence in laminate

Advantages of Ultrasonic Testing of Composite Boats and Spars:

  • One-sided access is sufficient
  • Highly portable equipment provides inspections at remote locations and – at a pinch – even working aloft
  • Minimal or no surface preparation is needed
  • Highly accurate in determining the exact point of a hidden anomaly and its main characteristics such as depth, size and shape
  • Provides instantaneous results and objective data

Ultrasonic testing with the correct equipment and standard samples and with well-trained operators is a powerful and non-invasive method of detecting flaws and defects in composite materials. marineSOLUTIONS has invested extensively in the training of personnel, assortment of equipment and standard samples. Equipment and standard samples can be applied to many composite requirements.
We use Olympus Epoch 650 Ultrasonic Flaw Detector, a state of the art digital flaw detector and Olympus Panametrics transducers some of which are specially designed and developed for inspection of composites. The instrument configuration is accepted and used in aerospace industry. The instrument calibration is kept up to date.

The Shackle Revisited

During our yacht surveys we rarely see shackles that have been moused. We remark that regularly in our reports, but I am not sure whether our clients all appreciate the importance of this.

Mousing is a simple and good practice to secure the bolt of a shackle to prevent it from getting unscrewed intentionally. I was reminded of this in a marina in Croatia where the pontoons had been shackled to the quay and all shackles had been moused.

Galvanized shackles tend to unscrew when they are under a pulsating load. Even if you tighten them carefully they eventually get unscrewed because the micro-stalactites of the zinc coating eventually get faired under the strain. Stainless steel shackles are also prone to unscrewing as the bolt’s thread usually is seated and rather slippery in comparison to galvanized hardware.

Using rope or galvanized wire is good for mousing, monel wire is even better, but even a cable tie will do as long as it is inspected regularly.

And by the way, the safe working load of shackles is determined by the diameter of the thread root, which is often smaller than the diameter of the shackle body.

Inspect your hardware, in particular the shackles, regularly. This way you can avoid losing your ground tackle. Losing ground tackle happens – usually at a time when it is least expected and most inconvenient, thus maximizing damages.

shotblasting

Shot Blasting

I dedicate this article to Erdem and Doğan…

For decades I have carried out shot blasting of many yachts with garnet, sand and other projectiles. In this article, I would like to summarize some of my experiences.

Sand blasting and shot blasting is the technique of cleaning and abrading surfaces of metals, glass and glasslike materials, wood and plastics. Compared to a grinding wheel, needle gun, power brush, solvent cleaning and other methods, it requires a complex organization, but it gives very successful results unreachable by any other method.

In particular when it comes to surface preparation of metals there is no other method that will come close to it.