The hull material is of cast or wrought iron fabricated circa 1860, which at the time of the survey had been waterjet blasted to a finish of SA 2 and primed with grey paint. A Cygnus Ultrasonic Thickness Gauge was used in conjunction with a non-corrosive couplant due to the painting being carried out at the same time. The Cygnus range of multiple echo thickness gauges enable accurate metal thickness measurements to be taken without the need to first zero the gauge or remove any protective coatings.

Approximately 200 points were recorded as far as possible at the aft ends of compartments with further readings taken along the length of the compartments and spaced from the waterline to the keel on specific strakes.

Problems encountered and overcome by the Cygnus Gauge included a very heavy and deep pitting on the surface and a large number of rivets which had to be avoided at the plate seams.

Armour plating in excess of 100mm thick proved very porous, which made it difficult to measure. This was overcome by using a large diameter probe supplied by Cygnus Instruments which improves the pick-up of returned scattered ultrasound and therefore allows measurements to be easily taken on very corroded metal.

MJInformation No: 20604