Wind tunnel tests on models of merchant ships 1

Abstract

To provide accurate data on the wind resistance of certain modern ship designs, wind tunnel tests have been carried out on $\phantom{\mathrm{(}}1\mathrm{/}\phantom{\mathrm{(}}60$ th scale models of a tanker and two cargo ships and on $\phantom{\mathrm{(}}1\mathrm{/}\phantom{\mathrm{(}}64$ th scale and $\phantom{\mathrm{(}}1\mathrm{/}\phantom{\mathrm{(}}128$ th scale models of a modern passenger liner.

The tanker and cargo-vessel models were tested in three conditions of loading, and the magnitude and direction of the resultant force and moment about amidships for each complete model in the three conditions are given for a free stream tunnel velocity of 100 ft. per second over a range of relative wind from 0 to 180 deg. off the bow. These models were tested in a wind gradient.

In the case of the modern passenger liner the larger model was tested in a wind-gradient condition and the smaller model in both the wind-gradient and uniform-wind conditions. The magnitude and direction of the resultant force and moment about amidships were measured. Two $\phantom{\mathrm{(}}1\mathrm{/}\phantom{\mathrm{(}}128$ th scale models were used for measuring the wind resistance in the uniform wind condition, one of them acting as a reflexion model.

With the exception of the reflexion model all tests were carried out with the models in the boundary layer close to the tunnel roof. For the $\phantom{\mathrm{(}}1\mathrm{/}\phantom{\mathrm{(}}64$ th and $\phantom{\mathrm{(}}1\mathrm{/}\phantom{\mathrm{(}}60$ th scale models the resultant velocity gradient was considered to be reasonably close to the gradient obtained under natural conditions above the surface of the sea.

The model results are shown in a non-dimensional form using an ahead resistance coefficient K, and are compared with some published data.

Certain possible inaccuracies in applying the model results to the ship conditions are discussed. There are two appendices. The first considers the factors affecting the natural wind velocity gradient above the surface of the sea and the second gives results obtained from wind speed measurements made at various points on the models. Diagrams indicate possible serious errors in speed measurements due to poor siting of an anemometer.