Abstract
The twin quadrilateral spanker consisting of two sails and two booms as shown in Photo.1, set on the afterside of the aftermast is used in saury stick-held dip net fishing and mackerel angling for the purpose of keeping the bow toward the wind direction while drifting. For the study of the aerodynamic characteristics of the spanker, the writer performed wind tunnel experiments using the sail models with parameter θ, open angle between twin booms, indicated in Table 1. Their coefficients to various angles of attack α about each model expressed by equations (1) are obtained as shown in Figs.3-10, and the distinctive features of the spanker were made clear. Making use of the results in experiments, some considerations about the advantageous quality of the spanker for the above-mentioned purpose are presented in the latter part of this paper.
