Improving yacht hull inspections with infrared imaging
One of the maritime industry leaders in Thermography, Geo Therm Ltd has over the past 20 years provided impartial thermal infrared inspections for all forms of surface watercraft. In his latest article for ONBOARD magazine Tony Dale Geo Therm Ltd Company MD discusses the use of thermal imaging to provide enhanced hull inspections, rather than traditional labour intense methods.
A typical tried and tested technique to differentiate structural integrity in fibre-reinforced plastic (FRP) hulls is to apply a consistent low-impact force using a plastic or rubber headed sounding hammer. This impact-echo response is immediate, exciting vibrations of delamination and differing tonal reverberations evident as a hollow sound for voids.
Although effective, the technique needs a sensitive ear and must be repeated over the entire hull surface by a competent inspector. This technique can potentially lead to unwarranted damage, furthermore, it is time consuming and difficult to uncover the total damaged area by hammer tapping alone – and often facilitated with moisture meter readings and exploratory destructive testing such as core sampling, gel-coat removal, drilling and grinding to differentiate the extent of the affected area.
Thermography or thermal imaging is very different, it is a non-invasive technique using thermal cameras to sense the invisible infrared (IR) range in the electromagnetic spectrum to detect, display and record in real time the surface thermal patterns across its entire field of view, to locate and map damaged areas and moisture intrusion.
Thermal IR imaging cameras convert heat emitted from a surface into a two-dimensional false-colour image called a Thermograph, wherein thermal patterns (and accurate temperature values) are represented by varying shades of grey or colour, that emphasise thermal anomalies deviating from the norm. With a suitable thermal imaging camera positioned on a sturdy tripod, an entire surface area of a yacht hull can be systematically scanned relatively quickly. Post-imaging processing an entire hull profile can be generated.
Accurate thermal acquisition – or how to set the thermal imager parameters, heat transference principles, experience on what to look for all require appropriate IR training, as does a knowledge of yacht design.
To be effective, each captured IR image must be carried out under proper environmental conditions, with unfettered direct line-of-sight access to the surface of the hull. Other factors to be considered include imager type and lens, emissivity setting, time of day, shadowing, reflections, surface moisture, camera angle to the hull, distance, solar loading uniformity, interior and exterior temperature differences.
Using thermal imaging it is possible to:
• Investigate the entire hull area quickly – to classify and quantify immediate risks
• Identify pending failure zones – where no trouble was suspected
• Justify works by adopting a risk-rank methodology – IR justification is obvious and unquestionable
• Follow-up after corrective repairs – rescan and document
With the right conditions and IR camera settings, the effects of solar loading or applying heat generated by high-energy lamps, (a process called pulsed thermography) natural or induced heat will propagate through the FRP hull, and upon encountering a discontinuity such as a water filled void or delamination the thermal capacitance changes, which is captured by the thermal imager as changes in surface temperature.
Once the entire hull surface has been scanned successfully, secondary test measures as noted above can be accurately applied to further disprove (or prove) hull integrity.
In summary, thermography provides an accurate, low risk, timely means to quickly locate surface and sub-surface anomalies for damaged, resin starved laminate, voids, cracks, crushes, and fractures in FRP hulls. Acknowledging hammer tapping, moisture meters and destructive hull testing are still creditable techniques yet consigned as a secondary means to confirm those hull anomalies as found by Thermography.
For more details Tel: +44(0)1502 723241
or visit www.geothermltd.co.uk/marine
