Steel and aluminium are popularly used as a hull construction material for blue water cruising yachts commercial vessels and workboats. They are extremely tough and able to deform to absorb impact. Steel can also be repaired by relatively unskilled labour in any part of the world.
Metal hulls can be progressively eroded by electrolytic and electrochemical erosion. Particular attention in survey is given to measuring the plating thickness for erosion using ultrasonic thickness gauges. There are two different types of devices and both are used to cover all conditions and reduce the risks of spurious readings. An Single Echo Audit 110 gauge with a 5MHz probe can test thicknesses down to 0.5mm. A Multiple Echo Cygnus 6+ with a 2.25MHz and 5.0MHz probes which can read through paint and coatings. The gauge also has single echo and echo/echo modes and A and B scan displays for more detailed analysis The whole hull is mapped and recorded using data logging for thickness where critical.
Paint film thickness is tested with an Electromagnetic Inductance Tester which will show where filler and fairing materials have been used. Weld lines are closely examined and suspected flaws examined with a Crenova Digital Microscope camera. Flaws and cracks can be tested if necessary with a Dye Penetrant Testing kit.
Below is a sample ultrasonic hull survey of a steel vessel which will show the full scope and depth of the survey report.
Click to open a pdf file.