Page 33 - Loss of the VOC Retourschip Batavia, Western Australia, 1629

Figure21. PhotographingthetransomoftheBaJaviaduringtheprogressofthedismantlingofthehullslIUc[Ure.
Stereo-photographic recording
With the growing complexity of the site in the stern
area of the site, some difficulty was experienced in inter- preting the photographs o f the structure. I t was decided, therefore, to obtain stereo-photographs to help in this work. Initially, the stereo-photographs were made purely for visual record purposes. Later, however, grid frames were always included so that some dimensions could be determined.
TwoNikonos cameras with 28 mm lenses weremounted 0.6 m apart on a bar with their camera axes approximately parallel. The cameras were rued simultaneously by hand. A number o f problems were encountered with this system, particularly where close-up photographs were required. The pressure of excavation work did notenable the devel- opment o f a comprehensive stereo-photogrammetric sys- tem, and we were limited to simple recording. With the in- uoduction of the 15 mm lens, stereo-pairs were taken simply by taking one photograph and then quickly moving the camera laternJly about 0.2 to 0.3 m and taking another. This simple system produced excellent record stereo pho- tographs and the complex stereo-bar system was aban- doned.
The prints were processed in the normal way and viewed under a Topeon mirror stereoscope. The additional dimension elicited by this means, added considerably to interpretive work. For example, an apparenUy featureless area o f seaweed and con~retion, when viewed in stereos- copy,immediatelyenabledidentificationofthepositionof cannon balls under concretion and other three·dimen- sional features.
Excavation methods The diving
During the four seasons o f work on the B a l a v i a . a total of447 days were spent in the field. Due to bad weather, it was possible to dive on the main site on 173 of these days, during which time a total of 1916 diving-hours was logged. An additional 500 hours was logged working on the inside reef site. Thus, 11 diving-hours per diving-day were spent on the main site, and this occurred on an average of one day in three. The breakdown of the four seosons of work is given in the table below:-
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Season 1st.
2nd. 3rd. 4th.
No. days in the field
No. diving days on main site Total diving hours
Main site diving hours
Ratio o f diving to total days A verage diving hours per day
148 108 150 41 59 45 59 10 543 449 641 283 477 360 528 86 1:2.5 1:2.4 1:2.5 1:4.1 8.08 8.00 8.95 8.60
This shows the distribution of diving-hours each day for the four seasons. It may be noted that the days when it was possible to dive on the main site, occurred in a group periodically, corresponding to periods ofgood weather. In genernJ, diving occurred for about three or four days with a subsequent breakofabout 10 days. The monthly diving- day ratio was as follows: September, 1:3.4; October 1:6.2; December 1:3.0; January 1:3.3; February 1:3.4; March 1:2.1; April 1:1.8; May 1:2.5.