According to the present invention, buoyancy control of a sinker is convenient, and minute manipulation is possible, and a taper (11) is installed so that a member spring (9) wound on a member holder (6) and a member plate (10) are easily inserted into a member cover (5). In addition, as the member cover (5) is installed, the outside of the sinker is streamlined to reduce the resistance of water in the rising and falling operation, and an upper water pipe (12) and a lower water pipe (13) are installed to remove air from a member cover chamber (14) to maintain the buoyancy of the sinker constant.COPYRIGHT KIPO 2018봉돌의 부력 조절을 편리하게 하고, 미세한 조종이 가능하도록 하며, (11)테이퍼를 설치하여 (6)부재홀더에 감겨진 (9)부재스프링 및 (10)부재판을 (5)부재커버에 삽입하기 쉽게 하며, (5)부재커버를 설치하므로 봉돌의 외부를 유선형으로 하여 상승과 하강 동작에서 물의 저항을 줄여주며, (12)상부수도와 (13)하부수도를 개설하여 (14)부재커버실에 공기를 제거하여 봉돌의 부력을 일정하게 유지하도록 한 것을 특징으로 하는 봉돌
