Otter board

An otter board that expands a net opening of a trawl net by being towed together with the trawl net by a trawler in a state in which the otter board is connected to the trawler and the trawl net, the otter board comprising:

• a curved board that is formed into a shape curving in a curving direction corresponding to an expanding direction of the net opening from a front-side end section that is a front side in a towing direction in a towing state towards a rear-side end section that is a rear side in the towing direction in the towing state, and that moves in the expanding direction of the net opening in accompaniment with towing by the trawler, wherein
• the otter board further includes
• a top board formed in an upper-side end section that is a vertical upper side of the curved board in the towing state, in order for the top board to extend in relation to the upper-side end section in the curving direction and a direction opposing the curving direction of which end section on the side of the direction opposing the curving direction forms a chord of the curved board, and
• a bottom board formed in a lower-side end section that is a vertical lower side of the curved board in the towing state, in order for the bottom board to extend in relation to the lower-side end section in the curving direction and a direction opposing the curving direction of which end section on the side of the direction opposing the curving direction forms a chord of the curved board.