0n the Thrust Deduction of Ducted Propellers : 1st Report

Abstract

Many researches have becn done on ducted propellers experimentally and theoretically, but few of them touches the thrust of duct and thrust deduction with regard to its form and attack angle. This paper presents an approximate formula of the duct thrust and thrust deduction as a linear function of its attack angle, camber and slip ratio of the propeller assuming the duct is very short and thin. Secondly, the mutual interference between duct and ship main hull are discussed in relation to the thrust deduction of ducted propeller behind ship. Finally, the propeller in the duct can be treated as an axial flow pump and then its efficiency as a pump can be estimated. Then, it is shown that the propulsive efficiency of ship is a product of this pump efficiency and the duct or hull-duct efficiency as like as a product of propeller one and hull efficiency. This duct or duct-hull efficiency is a ratio of the effective work done of whole system divided by the work done by the propeller as a pump. This method of analysis enables us to design a ducted propeller by the theory of axial flow pump.