Steel and aluminium boats: hull survey – checking for corrosion using ultrasound and other techniques.

Gwilym Harris-Evans

                Dipl. IBTC, member BMSE, Mecal.  
                   Yacht, Commercial Coding & Tonnage Surveyor.
                    ghe.yachtsurveys@googlemail.com Tel: 00351 969260096

 

 

Ultrasound testing is just one technique for assessing the health of a steel or aluminium hull. Most surveyors these days should be equipped, as I am, with multi echo ultrasound equipment. This is capable of reading through paint systems and reasonable amounts of filler, and usually avoids the necessity of grinding off expensive coatings.

The industry standard requires readings to be taken at 500mm centres: in practice many more readings will be taken, particularly around low readings and where experience tells the surveyor that problems can be expected. Like a moisture meter with GRP, an ultrasound gauge is one of a range of tools, albeit a useful one. Findings are open to interpretation and must be considered in combination with other evidence. Ultrasound meters will, for example, only read fairly parallel metal surfaces, and they won’t register scale or pitting. Essential adjuncts are a pitting gauge and a chipping hammer, together with knowledge of the most likely areas in which to find corrosion.

We know that most steel vessels waste from the inside out. There are many areas which will not be open to inspection, due to the type of construction or extensive fixed internal joinery, but a combination of the above techniques should reveal the problem areas.  These may be due to poor original construction, lack of maintenance, improper coating and general deterioration. Lack of maintenance may include failure to replace anodes, or address the sometimes complex problem of stray current corrosion.

So, the meter in its sophisticated modern multi echo form, is a very useful tool, but only one of a number of tools we employ to form the most comprehensive picture possible of the condition of the hull.

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