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When she was launched in 1843,Brunel’s SS Great Britain was the world’s largest screw propelled,wrought iron,steamship.Built in the Great Western Dockyard in Bristol,she had a distinguished history as the world’s first ocean liner,carrying emigrants to Australia and as a troop ship during the Crimean War but came to an ignominious end as a storage hulk in the Falkland Islands.Now she is back home in Bristol and nearing the completion of an £11.3m restoration supported by the Heritage Lottery Fund.
Visitors to the ship,from July,will have full access to all parts of the ship as no passenger of her heyday could and will be able to see her in all her Victorian splendour.
A major aspect of that work is to stabilise her wrought iron hull and protect it from the ravages of further corrosion.The most innovative part of that work consists of constructing a sealed glass plate around the waterline of the ship to form a giant airtight chamber surrounding the ship’s lower hull.The glass plate will be covered with a 50mm layer of water,so that the ship appears to be floating at anchor.
Beneath the glass plate,moisture will be removed from the air using a specially designed air-handling unit operating 24 hours per day, seven days per week.It consists of two sections,a process section within which air will be passed through desiccant in a hydroscopic wheel to remove excess moisture and take the humidity within the dock down to RH 20 percent - about the same as the Arizona desert.
Within the regeneration section,direct fired gas heaters dry the desiccant after which the air is passed via the heat recovery system to the exhaust port.A similar but larger unit will be installed within the ship’s boiler room to control the ship’s internal temperature and humidity and thus protect the hull both externally and internally from corrosion.
The temperature and humidity control system is being provided by Tour Andover Controls,South West division.They specified a 15kW Danfoss VLT 6000 drive to power the process supply fan for the enclosed dock,controlling volume between 5.7m3/sec and 1.7m3/sec, facilitating energy efficiency when ambient humidity is low.The larger system within the ship itself will utilise a 55kW drive to provide up to 13m3/sec of controlled air circulation.
Control is exercised via wireless temperature and humidity sensors, three along each side of the ship and 16 inside her.Every 30 seconds,readings are transmitted to the receiver in the ship’s plant room and relayed to the Ship’s Management System via the Ethernet communications system.PID control averages out the humidity reading and controls the dryer burner rate.
Fan speed is linked to the burner rate and the fans are run at full speed when the regeneration burner rate exceeds 20 percent output. When the ship and museum are closed and output to the regeneration burner drops below 20 percent,the fan operates at a preset low speed.The circulating air temperature is controlled by an indirect gas fired heater battery and a water cooled chiller battery in the air path to maintain temperature between 16O°C and 23O°C.
Should the cooling requirement exceed 15 percent at times when the visitor centre is open,then fan speed is increased to maximum to achieve a more rapid return to the preferred control zone.
A 100 ton crane lowered the first dryer unit,the size of a shipping container,into the dock on 8 December.The larger second unit has been installed within the ship’s boiler room and the completion date for the programme of works is mid July,2005,in time for the SS Great Britain Trust’s anniversary celebrations on 19 July - the date of her launch in 1843 and of her return to Bristol in 1970.
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