Page 275 - Green - Maritime Archaeology: A Technical Handbook. 2nd ed

254 Maritime Archaeology: A Technical Handbook, Second Edition
Figure 9.10 Two types of airlift design, one with a flexible hose and rigid riser and the other rigid.
consuming and frustrating operation. A removable pin fitted across the mouth of the airlift is a simple solution and there are complicated stone ejectors which can be constructed to remove an oversized object jamming the opening.
The only way to work an airlift in areas where there is archaeological material is to hand-feed the airlift with the intake about 100 mm above the seabed. In this situation, the excavator puts selected heavy material into the airlift, but hand-fans the archaeological layer. The hand-fanning removes the light sediments from the seabed which are then sucked up the airlift, leaving the water clear and enabling the excavator to reveal light, delicate