Page 293 - Green - Maritime Archaeology: A Technical Handbook. 2nd ed

272 Maritime Archaeology: A Technical Handbook, Second Edition
ported; the lifting chain passes through the tube and out below the boat. Although the attachment point is high, any tilt on the vessel will be righted by the effect of the chain acting at the entrance to the tube at the bottom of the hull. Hence, it would be impossible to capsize the boat (although it may be possible to sink it).
There are a number of commercially available lifting or air bags. These range in lifts from a few hundred kilograms up to several tonnes (Figure 24). Air is introduced into the bottom of the bag and it inflates until the whole bag is full and maximum lift is achieved. Where possible, it is better to have a number of small bags than one big one. This is because as a bag rises, the air in it expands. Thus, if a big bag is only partially full on liftoff,
Figure 9.24 Lifting bags of various sizes and in various situations. (a) On the Tektash Brunu site.
a