Flow around a hull

I've been wanting to draw this diagram for ages. Stumbling across Marchaj's photo (see reference in Books page) gave me the incentive to scan it and trace the streamlines.

Streamline tufts fastened to a hull

The diagram shows the streamline patterns formed by tufts attached to the bottom of a hull being towed in a tank, at a modest leeway angle. The blue line gives an idea of a section through the hull, below and parallel to the waterplane. The hull appears slightly heeled, but I think this is an effect of the angle of the photograph. In the middle of the diagram is the keel, and on the left is the rudder. So what do you see?

The key observation is that there is an awful lot of downwash behind the rudder.

So before you click for the next page and my conclusions, what are yours? How would you arrange matters to lessen drag?

OK? Thought of what you'd do to the rudder? Click here...

2005-12-18