Weight release device

A weight release device for releasing a weight attached to an underwater observation device having buoyancy, the weight release device comprising:

• a housing fixed to the underwater observation device;
• a thread made of thermoplastic resin, a start point and an end point of the thread being housed in the housing;
• a first electric heater portion;
• a second electric heater portion;
• a weight support plate;
• a first locking member for locking the thread made of the thermoplastic resin, the first locking member being provided on a lower surface of the housing, the number of the first locking member is n−1 (n>2);
• a second locking member of for locking the thread made of the thermoplastic resin, the second locking member being provided on an upper surface of the weight support plate, the number of the second locking member is n (n>2);
• and
• a ring for hanging the weight, wherein
• the thread made of the thermoplastic resin is arranged from the start point housed in the housing, arranged to pass through the first electric heater portion, arranged to alternately pass the first locking member for locking the thread made of the thermoplastic resin provided on the upper surface of the weight support plate and the second locking member for locking the thread made of the thermoplastic resin provided on the lower surface of the housing for sewing the first locking member and the second locking member together, arranged to pass through the second electric heater portion housed in the housing, and returned to the end point housed in the housing,
• the ring for hanging the weight is fixed to a lower surface of the weight support plate,
• the weight is hung from the ring, and
• the weight support plate from which the weight is hung is configured to be released only by conducting an electricity through the first electric heater portion and the second electric heater portion to melt-cut the thread made of the thermoplastic resin for floating the underwater observation device.