Prior to the assembly of the glass fibre-reinforced polyester resin laminate
tank, as many of the non-ferrous fittings as feasibly possible were removed. The
stripping of the paint coatings on the interior of the submarine and on the cast
iron engine did pose problems, particularly on the latter, as it was severely
graphitised and brittle. Conventional grit blasting would have damaged the orig-
inal shape of the engine to say nothing about the dust problem within the con-
fined space of the interior of the submarine. This was solved by using the
Spongejetsystem, which has mild abrasives encased in sponge particles. These
composite particles are directed at the surface by high-pressure hoses. The
sponge absorbs the paint plus any contaminants on the surface thus minimising
the amount of dust generated in the atmosphere within the submarine. The very
gentle nature of this abrasive cleaning process causes very little damage to the
underlying metal.
One of the main considerations in the conservation of the submarine was the
galvanic corrosion between the body of the submarine (ferrous), the coning
tower, torpedo tube and propeller (brass) and the copper windings of the elec-
tric motor. In seawater, the copper and brass would be protected while the steel
body would corrode. In 5% sodium carbonate solution, there is a polarity rever-
sal with the steel being protected and the copper-based materials corroding. If
traces of copper ions were to escape into Portsmouth Harbour through a leak
in the tank for example, severe biological problems would ensue as copper
ions are very toxic to marine life. Research showed that by dropping the con-
centration of sodium carbonate to 3%, this reversal could be prevented.
Reducing the sodium carbonate to even lower levels decreased the pH to below
Metals 149
Figure 9The complete cell formed around Holland 1 for aqueous washing of the chloride
ions from the submarine