Holland 1was raised in September 1981 and taken to dry dock in Devonport
where she was cleaned with high-pressure water to remove all the concretion
and marine growth. To facilitate transportation to the Royal Naval Submarine
Museum at Gosport, Hampshire, the submarine was cut into three sections. On
arrival at Gosport, the submarine was welded back together and the exterior of
the hull painted with a commercial anti-corrosion paint, which was claimed to
give long-term protection. The interior of the submarine was painted with a
decorative white paint and the engine and its ancillary parts with a decorative
green finish. After 11 years of exposure to the marine environment of the
Museum, the exterior paint had virtually disappeared and the hull was badly
corroding. The interior was also showing signs of severe corrosion particularly
at the seams produced by the overlapping of the steel plates of the hull and
around the fasteners such as nuts and bolts. Parts of the engine had completely
mineralised and had been severely damaged by the constant stream of visitors
being shown around the interior. The exterior of the hull was once more pressure
cleaned to remove the unsightly corrosion products.
The original specification for the thickness of steel plates used in the manu-
facture of the hull was 11 mm. Core samples were taken by trepanning and the
thickness of the metal remaining was measured. The results ranged from 9.0
down to 2.5 mm, with the bow section having experienced the most severe
corrosion. In certain areas, the steel had completely corroded with gaping holes
clearly visible. This illustrates the wide variation in corrosion rates experienced
by the submarine as it lay for some 70 years on the seabed.
Metallurgical examination of the core samples indicated that the hull was
manufactured from a mild steel with a carbon content in the range 0.1–0.15%
with a hardness value of 152 VPN. The carbon content of the steel rivets was a
little higher at 0.18% a hardness value of 239 VPN. The 160 Hp engine has
been manufactured from grey cast iron. Corrosion products removed from the
interior of the hull and from internal crevices such as the overlapping of steel
plates, gave a chloride value of 2.21%. This is of a similar magnitude to that
found by other conservators on ferrous artefacts recovered from marine sites.
With this level of chloride in the rust, it is not surprising that corrosion of the
steel plate had continued underneath the paint film.
Besides the ferrous materials, several large components of the submarine
were manufactured from non-ferrous materials. These include the coning
tower, torpedo tube and propeller. These were all manufactured from the same
material, a two phase, / brass (60% copper–40% zinc alloy) with lead addi-
tions to improve the machinability properties of the material.
As the submarine was too fragile to move, the only practical conservation
method was to wash the vessel in situ. A tank was constructed from glass
fibre – reinforced polyester resin laminate. The structure was prefabricated in
sections away from the museum and assembled on site with no disturbance to
Metals 147