Päivi T. Laitinen, B. Sc. (Env. Eng.) Product Marketing Specialist Vaisala Helsinki Finland Vaisala Humidity Transmitters Help to Preserve the Royal Warship Vasa Creating the Right Climate Saving the famous 17th century Swedish warship, Vasa, from further environmental damage in its purpose-built museum has been achieved by technical improvements to its air conditioning system. Central to the new system, which became operational in 2004, are a large number of humidity transmitters from Vaisala. candinavia's most visited museum, the Vasa Muse- S um is located in Stock- holm, the capital of Sweden. First opened in 1990, it is built around the royal warship Vasa, the world's only preserved 17th century wooden ship. Since the summer 2000 the warship Vasa has suffered from a serious acid attack caused by oxidizing sulfur stored in ship's wood. Re- searchers are working to stop the sulfuric acid corrosion – work which requires both long-term and short-term solutions. The critical requirement for the preservation is to maintain a stable climate in the ship hall. For sustainable humidity and temperature conditions, the museum had to have its air conditioning system updated. The new system relies on Vaisala HUMICAP® Humidity and Temperature Transmitter HMP233s. 8 166/2004 The royal warship Vasa was the most expensive and richly ornamented naval vessel built in Sweden in the 17th century. When the Vasa sailed forth on her maiden voyage, Stockholmers stood along the shore to wish her good luck. They were eyewitnesses to the disaster. The Vasa capsized and sank inside A Right Royal Disaster Stockholm harbour. After 333 years on the seabed, the Vasa ship was salvaged. Nowadays the ship is on view in the Vasa Museum, Stockholm. n the early 17th century, Swe- their mistakes and improved I den was building its empire later designs. After the Vasa, around the Baltic Sea in north- many successful ships were ern Europe. During 1620, Swe- built with two, three and even den was at war with Poland. four gundecks. Then, in 1625 the Swedish king Gustavus Adolphus ordered Salvaging the ship new warships. Among them The Vasa ship was not discov- was the Vasa. ered until 1956 when a private By 1628 the Vasa ship was shipwreck-specialist Anders ready. It was the mightiest war- Franzén finally located it lying ship in the world, armed with 30 meters beneath the surface 64 guns on two gundecks and in Stockholm. After careful 300 soldiers. When the Vasa set planning, the Vasa ship was lift- off for its maiden voyage on ed slowly to the surface. On Sunday August 10, the beaches April 24 1961 the proud royal around Stockholm were filled warship Vasa broke the surface. with spectators, among them The salvaging of the Vasa foreign diplomats. initiated intensive archeologi- The Vasa set sail and fired a cal excavation and preserva- salute. But only after a few tion. The ship and all the find- minutes of sailing the ship be- ings were preserved, which gan to keel over. She righted was an effort of gigantic pro- herself slightly but keeled over portions. The Vasa is the again. Water started to gush in biggest single object that has through the open gunports. ever been preserved. Some And, to everyone’s' horror and 14,000 individual pieces of disbelief, the glorious and wood were brought up to sur- mighty warship suddenly sank! face, including around 700 Of the 150 people on board, sculptures and ornaments that 30-50 died in the disaster. decorated the warship, not to mention the sails. The ship, as Why did the Vasa sink? well as all the objects found, In the 17th century it was not un- were preserved using poly- Demanding July 2003, the warship Vasa suf- common that warships keeled ethylenglycol (PEG). It replaces air conditioning under fered around 1,500 areas of acid- over and sank. Due to lack of sci- water in wooden objects to the Vasa's conditions ified wood and visible deposits entific methods of calculating a prevent them from shrinking of sulfates. It appears that large ship's stability, the ship builders when dried. The preservation The Vasa is housed in her own quantities of elemental sulfur used so called reckonings, which work continued for 17 years. specially constructed museum, had built up within the surface recorded certain ship-measure- The ship was located at the but despite the continued layer of the wood. The sulfur ox- ments. Therefore, the underly- time in a temporary Vasa Mu- preservation, the ship is extreme- idizes catalytically into approxi- ing cause of the Vasa’s demise seum, the Wasavarvet. ly fragile. Therefore, there has al- mately 100 kg sulfuric acid every was insufficient theoretical It was in 1990 that the per- ways been paid special attention year. It is estimated that the know how of the period. At the manent Vasa Museum was in- to create a suitable climate, a wood now contains around two time, the Vasa was something augurated. The museum is built sort of an air curtain to protect tonnes of sulfuric acid and a fur- new – a military experiment. in the heart of Stockholm, right the Vasa ship from surrounding ther five tonnes or so may build The reckonings used in next to the site where the Vasa stressful conditions that may up once all the sulfur has oxi- building the Vasa were intend- was originally built during the cause further damage. The sys- dized. ed for smaller ships with only years 1625-1628, and only few tem works with re-circulated air This acid attack on the Vasa one gundeck. The Vasa was built hundred meters to the spot that is either cooled or heated, addressed that the original air differently: she had two gun- where the Vasa sank. The pur- dried or humidified, depending conditioning system of the mu- decks with heavy artillery. Vasa’s pose of the museum building is on the temperature and relative seum was inadequate to cope builders did provide 130 tons of dual: to maintain the ship and humidity values. with the large number of muse- stone as ballast to give the ship other salvaged objects by creat- The new era in the battle to um visitors. Variations in climate stability. Unfortunately, the bal- ing and keeping suitable levels preserve the royal warship Vasa around the ship influence on the last was not enough as counter- of temperature and relative hu- for future generations started in rate of acid formation. There- weight to the guns, the upper midity, and to give possibility to summer 2000. Due to a period fore, air should be kept at 55% hull, masts and sails of the ship, preferably as many people as of warm and humid weather, relative humidity and tempera- resulting in the ship capsizing. would wish to see the Vasa in large-scale sulfur problems was ture +18.5 °C. The maintenance Shipbuilders learned from order to share the history. ● triggered in the ship's wood. By of stable conditions is chal- ➤ 166/2004 9 Vaisala HUMICAP® Humidity and Temperature Transmitter HMP233 Emergency acid neutralization is being carried out on the Vasa with a as mounted on the Vasa ship. The instrument is a part of the updated climate solution of bicarbonate and soda. The level of acidity on visible surfaces of the monitoring system that protects the ship against climatic stress. wood often shows a temporary improvement after treatment, but the acid tends to return gradually after a few months. lenging because of seasonal 90,000 m3/h of air, distributing creates a gradient of relative hu- Board (SFV) of Sweden, sched- changes, variations between day it through displacing outlets sit- midity. uled the work in close coopera- and night as well as day to day uated on the keel level but there tion with the Vasa Museum's differences such as the number is also a distribution system in- Renovating the specialists. As Mr. Jacob Jacob- of visitors that all have an effect side the Vasa ship. The source of air conditioning system son, Assistant Head of the Vasa on air quality. Also the height of air distributed around the hull is The renovation of the Vasa mu- Museum says, “We at the Vasa the ship (max. 52.5 m) causes its situated on the keel level, which seum's climate control started in Museum knew very well what own problems. The museum's means that there is a tempera- autumn 2002. The owner of the was wrong with the old system air circulation system handles ture gradient that, in its turn, museum, the National Property and we knew exactly what we wanted from the new one.” TAC, a supplier of integrat- ed systems for building automa- tion, was chosen to design and ® build up a new integrated cli- Vaisala HUMICAP Humidity and Temperature mate monitoring system for air conditioning. TAC had already Transmitter HMP233 been involved with the planning and realization of the old air he HMP233 is a versatile so immune to particulate con- conditioning system when the T and easy-to-use transmit- tamination and most chemicals. Vasa Museum was being built in ter for demanding industrial The sensor head in the 1988. TAC has also took part in and air conditioning applica- HMP233 transmitter is small similar projects in other Nation- tions. The transmitter measures and fits into tight spaces. It can al Property Board's premises, relative humidity and tempera- be equipped with two differ- such as the National Museum of ture, and also outputs dewpoint ent cables: one is for lower Ethnography, Sweden, and and wet bulb temperature as temperatures of up to +80 °C Moderna Museet, the Swedish calculated variables, mixing ra- and the other is for tempera- Museum of Modern Art.