Stability of three kinds of pots for catching shrimp used in Hokkaido

For the optimum design of a shrimp pot to control the catch size, experiments were carried out to study the pot stability. The pots used to catch shrimps in Hokkaido have two shapes (hemispherical and conical). To estimate the pot stability, drag and static frictional forces were measured in experiments. The drag of each pot was measured in a flume tank. The relation between the current speed and drag is presented. Static frictional forces, on a sand surface and on a rock surface, were measured for a model seabed respectively. The results showed that the drag of Usujiri shrimp pots was lower than those of Sawara and Yubetsu shrimp pots depending on the current speeds and angles. When the seabed was sand or rock, it was harder for Yubetsu shrimp pots to slide than the others. On the flat seabed, the Yubetsu shrimp pots turned over more easily than the others. In conclusion, the possibility of turning over was smaller with the hemispherical shrimp pot than the conical shrimp pot.