Flow around a hull

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I'd angle the rudder into the general direction of the streamlines.  I've given the boat weather helm!

Rudder angled into downwash to give weather helm

As far as I can see, such a crazy idea is likely to actually decrease the overall drag of the hull making leeway.  But I really don't know if this is true.

Also, less controversially, the rudder looks like, and is acting like, the flap on a wing (taking the keel as the "wing") when extra lift is needed from that wing.  It is already accepted that a little weather helm brings the rudder more effectively into play as a lifting device, like the keel, allowing it to share the keel's job of counteracting the rig forces when beating to windward. In this sense, the rudder and keel combine to create a more effective lifting underwater appendage. (It is also the case that, once a surface begins producing lift, it also necessarily generates more drag. But my argument is that so-called neutral helm is in fact lee helm in disguise, and that the explicit weather helm is reducing the disguised lee helm, reducting the excessive lift generated by that lee helm, and thus also reducing the excessive drag... Go back to the previous page and look at the flow around the rudder -- isn't the rudder close to stalling because of its high angle of attack to the downwash from the keel?)

A number of skippers feel that any helm (other than neutral helm, of course) means that the rudder is giving more drag than it needs to.  But this idea depends upon feeling that the flow of the water past the hull is parallel to the hull centre-line.  This clearly isn't the case when the hull makes leeway. One or two skippers recognise this, and feel that angling the rudder towards the leeway (lee helm) must then decrease drag. Marchaj's photo shows why this is exactly the opposite of what is presumably required.

2005-12-18


2011 Lester Gilbert