Rudder Area and Balance

Hi,

Can anyone give me a rule of thumb for the area and balance ratio of rudders for various power craft.

Obviously there are lots of different trade-offs but I'm just looking for a general rule with out going back to first principles.

Cheers

Andrew _/) _/)

 

17% - 20% max for high speed, best figure IMO 17% to 18% for speed higher than 33 knots

 

See attachment.

 

One more on rudder area. This is in Russian, but easy to understand. On the diagram: I -rudder under bottom, II - rudder behind the stern, V - speed in km/h.

 

Thanks guys, that's exactly what I'm after. Tried to find it in Lloyds SSC rules. Maybe didn't look hard enough!

Cheers

Andrew

 

You don't mention how large a boat(?) - ship(?) but an old rule of thumb from the 1890's for a "gentleman's launch" is:

Find the square root of the LWL. This is equal to the TOTAL surface area of the rudder. So divide by 2 for the surface area of one side. Since the height of the rudder is based on the wheel diameter and available space, it is fairly easy to find the length. 1/3 of the area should be forward of the rudder post for "balance". I've used this formula and recommended it to others. Seems to work quite well for "slow turning" (i.e. steam launch) wheels.