1980s DOSBouw clinometer

This clinometer was donated to my collection in 2008 by a former colleague. Although a seemingly little interesting device, it has an interesting provenance.

The clinometer is made of aluminium and a standard micrometer and vials. The orange vial has an accuracy of 60"/2mm and can be estimated down to 12". Wild Heerbrugg delivered the green coincidence vial, which has an accuracy of 30"/2mm and can be estimated down to 2". Mitutoyo created the half a millimetre per turn drum micrometer, which can be read down to 0.002mm. The overall length of the clinometer is 270 millimetres, while the working length (distance between the hinge and drum micrometer) is 200 millimetres. For stability the base of the clinometer has three little feet to rest on.

The interesting part of this little device is where it was made for. It was purposely made by or for DOSbouw, a joint venture of eleven companies that were responsible for the construction of the Oosterschelde Storm Surge Barrier of the Dutch Delta Works.¹

Building the storm surge barrier was a major operation and included the design and construction of several vessels.² The barrier consists of sixty-five 30-39 metres tall concrete piers holding sixty-two steel slides that weigh up to 480 tonnes.³ In order to get these slides running smoothly the accuracy at which the piers had to be placed was 30 centimetres. Positioning of the piers during placement was done using the AGA/Minilir.⁴ As back-up Wild Heerbrug TC1's were used.

From the measured point the position of the base of the piers had to be calculated, which was accomplished by installing 0.01 degree accurate electronic clinometers on board. These clinometers were placed on the pier shortly before placement and had to be aligned with the pier's geometry. For this a base plate was created at the top of the pier during the construction, the attitude of which was determined in respect to the geometry using this purposely built clinometer. Being the joint venture colour, orange was chosen as its main colour.

After the barrier was finished the survey department of the works became the Marine Geodesy department of the Dutch Ministry of Transport and Public Works.⁵ In 1996 I joined this department and worked with some of the equipment used in the barrier construction, like the Fennel/Minilir combination. During that time the clinometer was the only 'memorial' of the Delta Works hanging around in one of our offices. Several years after I left the department it was donated to my collection by a former colleague.

The clinometer had to be oriented with the pier with the drum micrometer facing northwards. The vials were adjusted in a way that a reading of exactly 12mm on the drum would level the base of the clinometer. Using a simple formula (angle = ARCTAN((12-reading)/200)) produced the inclination of the base in respect to the vial and thus of the pier's geometry in respect to the local vertical (provided that the vial was in coincidence).

[1]: The Oosterschelde storm surge barrier: Construction

[2]: The Oosterschelde storm surge barrier: The ships

[3]: The Oosterschelde storm surge barrier: Piers and slides

[4]: For a picture see the 1980 Wild TC1 page

[5]: The official name of the department was the 'Meetkundige Dienst', the subdivision where I worked was 'GAM' (Geo-Advisering Marine Geodesie).