22 Jul 2013
The revolving mast model (SLR2641) prior to conservation treatment
It was in need of extensive structural intervention. However, before I could proceed it was essential to ascertain the intended construction of these peculiar revolving masts. Without this information it would be impossible to accurately reproduce the designer’s intent.
Thankfully there was a label attached which lead me to an 1827 copy of Mechanics Magazine which we hold in the Caird library. This not only provided me with a plan of construction, but an insight into the reasoning behind this innovation in mast and sail design. The principle novelty of this design was that the sails worked by themselves, by the power of the wind, and reduced the need for the many hands required to trim the traditional square riggers as sails were set with minimal rigging to facilitate full cargo handling potential. The sails could be turned to take the fullest or the least effect of the wind and, if necessary, this could all be done below decks. It was said that the ship could be controlled by a sole helmsman on deck. This was not only a cost effective measure, by reducing the number of crew, but was seen as a potential answer to the issues facing vessels attempting the North West passage.
Vessels, on this perilous journey, not only suffered from the potential dangers of shifting ice sheets but from the loss of rigging being brought down by the weight of accumulating ice and for crew trying to survive sub-zero temperatures on deck through storms and heavy seas. This design was not only intended for speed, by harnessing the full potential of the wind, but to reduce human and financial losses.
A copy of the plans for the patent proposal as laid out in Mechanics Magazine 1827, Volume VII, p321
The condition assessment highlighted several key factors which needed to be dealt with.
The forward mast had, at some point, sustained an impact resulting in the loss of the top of the mast and elements of the lower supporting structure. The remaining elements were twisted or broken. Replacement pieces were carved for the losses and the damaged and twisted elements were carefully manipulated back into shape, re-glued and clamped.
The forward mast manipulated back into shape, glued and clamped
The aft mast had seized on its bearings and was unable to revolve. As the model had been in storage for many years the first task was to remove the build-up of dirt with special attention to dismantling the deck fixings of the aft mast to gain access to, and lubricate, the bearings.
There were material losses to the bow and stern from previous wood boring insect activity. These were replaced with carved timber fills.
This is an example of the required timber fills and illustrates the discoloured varnish which had blackened the originally intended surface finish
The revealed intended colour, sealed with MS2A varnish, with the timber fill colour matched with acrylics
The existing superstructure varnish had discoloured thus concealing the originally intended green finish below. This colour definition was important as it was designed to highlight the unique elements of the patent proposal. The existing varnish was removed using a 50:50 mix of IMS and white spirit. This needed to be done in a controlled environment as the underlying green pigment was suspected to be Emerald Green thus containing high levels of copper arsenate. For safety, the exposed surface finish was then sealed with an MS2A, a modified polycyclohexanone resin, based varnish. Emerald Green, also known as Paris Green, was popular between 1814 to the early 20th century due to its brilliance of colour and affordability. Its most notorious use was in the decoration of wallpaper until its lethal toxicity, when damp, was finally understood.
The model after conservation
Sadly Shuldham’s innovation was dismissed at the time. However, in the 1960s Wilhelm Proiss reintroduced the idea of installing revolving masts to provide additional propulsion for ships. The DynaRig system has been used on a variety of vessels as found in the unique creation of SY Maltese Falcon. The principle is being further developed by B9 Energy Group who hope to develop a fleet of zero carbon emission coasters to offer a credible solution for a green supply chain.
Flagships of the future. Image by: B9 Shipping