There are al ot of references in how to info about balanced rudders, but there is no info on what one actaully is.
What constitutes a balanced rudder?
Here’s an official definition for you Nev…
“a rudder in which the turning stock is not on the leading edge, but close to the rudder’s centre of pressure; about one-quarter abaft of the leading edge; since the center of pressure shifts as the rudder is turned, no rudder can be fully balanced for all rudder angles; hence a rudder is considered balanced when it can maintain so for about 15 degrees”
That means the shaft around which the rudder pivots is somewhere a bit forward of the middle of the rudder. Most of the boats you see here with a rudder underneath the hull use an approximation of a balanced rudder. That is in contrast to an unbalanced rudder where the pivot shaft is on the leading edge of the rudder. The boats you see with the rudder hanging off the stern are unbalanced.
Bill
A bit more to Bill’s post…
With a balanced rudder, as Bill notes, there is some rudder stock ahead of the rudder post. Once you have begun to turn your rudder, the part forward of the post receiving water pressure actually helps turn the rudder, thereby reducing the need for heavy duty servo. As the front leading edge of the rudder deflects, it helps the servo in trying to turn the rudder. While this is helpful, too much frontal area can work against the servo, and thus energy spent trying to turn the rudder is now required to keep the rudder from turning. The effort is in trying to determine how much area forward of the rudder post is good —until it becomes bad ! :indiffere
Some transom hung rudders can be made to act like a balanced rudder by having a bit of the leading edge of the rudder blade actually extend forward and under the hull a bit. To better illustrate this description, this can be seen in the photo of a transom hung catamaran rudder, that when in the “down” position, has it’s leading edge slightly ahead of the end of the transom.
That makes sense, thank you for that.
I thought it may have been more complex. I have been making rudders similar in shape to the 2 shown, but have a narrower top and with the shaft in similar position and direction as the larger of the 2 shown.
I found that a rudder with the pivot point too near the centre will slow the boat in a turn more than where it is near the leading edge.
Also it seems the shape has a bearing on boat speed, the profiles shown appear to work best on my M.
Does anyone have a photo and specs for a balanced rudder they can share with us all?
Nev -
try this link to the US 1 Meter site. Profile size would be size dependant, but gives a good idea of what is available and being used.
http://www.amya.org/us1mcatalog.pdf