| 摘要 |
The mast (1) top section (2) is internally watertight (15) and contains an electric motor (4), near its top (3). The mast is retained in an envelope (10), up to water level (12). The motor is connected by a universal joint (5) to a rotatable threaded shaft (6) engaging in a ball nut (7) in part (8) of the lower envelope.Operating the motor rotates the shaft to screw or unscrew it from the nut, lowering or raising the mast within the envelope. The lower part (8) is retained (9) in the envelope. During mast elevation, water may enter the envelope around the mast/envelope junction (13), but air is sealed inside the upper mast (15) preventing water entry. The mast acts as a piston, forcing water out during descent.
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