468 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1963 



vertical pole that could be moved back and forth on the beam as 

 well as up and down. The sides of the frame, the horizontal beam 

 and the vertical pole were all calibrated in centimeters. By placing 

 the bottom of the pole on an object, therefore, it was possible to read 

 both coordinates and an elevation for its position. Again, too much 

 time was taken in recording each point, so a movable, 2-meter square 

 grid was placed on the wreck. Detailed drawings, photographs, 

 and elevations could be made through the wires of the grid, making 

 it necessary to record only the four comers of the grid with the 

 mapping frame. 



These aids were excellent for a beginning, but all needed refine- 

 ment before being used on a detailed plan of the wooden hull that 

 came to light under the cargo. In the second season on the Byzantine 

 wreck a variation of the mapping frame was used (figs. 2 and 3). 

 This is essentially a combination of nine frames, each 2 meters by 

 6 meters, assembled like steps over the entire length of the wreck. 

 Each step is horizontal and may be moved down independently of 

 the others on its legs as the excavation goes deeper into the sand; 

 this insures that the frames are always level and are always near the 

 objects to be plotted beneath. A number of 2-meter square grids 

 ride over the frames, each having three positions on each step. Thus 

 the wreck is broken into 27 squares that can be independently exca- 

 vated, drawn, and photographed. Photographic towers of light metal 

 are bolted to the grids to insure perfect grid pictures of each area. 

 Objects are identified in the photographs by numbered plastic tags 

 attached to the objects on the wreck as they appear in the course of 

 excavation. Distortion caused by the slope of the ground, which 

 puts some objects at an appreciably lower level than the grid, must 

 be corrected by the arcliitect before he can use these grid photographs 

 in making his plans and sections; lens distortion has not been sig- 

 nificant when using the proper cameras. 



Improvements in the airlift were also made. The airlift is no 

 more than a large, vertical pipe with a flexible lower end. Air is 

 sent to the lower end of the pipe through a hose. This air rises 

 through the pipe, pulling water, sand, and mud with it. The airlift 

 should be used only for removing loose sand and not, as is common, for 

 actual excavating. Wood can be easily broken by it, and the original 

 location of small objects sucked up by it is never known. Tiny 

 pieces from time to time do enter the pipe, so at Yassi Island a 

 wire basket was bolted to the top of the pipe. The mesh of the wire 

 allows most of the sand to be carried away by the current, but coarse 

 sand and small objects are trapped and fall into a bag attached 

 beneath the basket. The bag is raised whenever full and the sand 

 within is carefully inspected on land. 



