Rudder Area In Clr. Calculations ?

[viking north]

I thank you -- certainly going to push for the max. --Had a bit of luck last week at the used metal yard-- came across a 1.75in. dia 316 stainless shaft of the exact length I need with a balanced rudder blade welded in a slot cut into the shaft and the emergengy tiller square nut welded to the top all for the price of retail scrap stainless by the pound. Just have to fabricate a glass foil rudder blade over the present stainless blade. Got to love those metal recycling yards-- Thanks again--Geo.

[DCockey]

Originally Posted by xlr8

There is a simple method to calculate rudder area:
Minimum A= 0.003 x s x h /L + 0.05 sqm
Max A = 0.004 x s x h / L + 0.15 sqm

s= sail area sqm h= height of fore triangle from DWL m L= horizontal dist from top of fore triangle to area CG of rudder

What is the source of that formula?

[xlr8]

These are wildly used in Japan including major mass production builder.

[jehardiman]

Originally Posted by xlr8

These are wildly used in Japan including major mass production builder.

Humm...yes...well. If you look at it wildly enough there is a twisted sort of logic to it. Water is ~ 850 times as dense as air. What the equation does set the rudder area force to the sail area force corrected by the effective lever arms assuming that hull speed^2 was 1/2 wind speed^2. Psudoscience perhaps, but to paraphrase: "all mathematical models are wrong but some of them are useful".

[DCockey]

Originally Posted by jehardiman

Humm...yes...well. If you look at it wildly enough there is a twisted sort of logic to it. Water is ~ 850 times as dense as air. What the equation does set the rudder area force to the sail area force corrected by the effective lever arms assuming that hull speed^2 was 1/2 wind speed^2. Pusdoscience perhaps, but to paraphrase: "all mathematical models are wrong but some of them are useful".

Good job of deciphering it.

[viking north]

So are junk rigged sails, in out traditional image of a sailing craft they look ugly and weird, not my cup of tea, but dam it they work and well at that. Different strokes for different folks as they say.--Like sails I'll stick to the simplier rule of thum calculations of rudder area-- not to say XLR8's is less accurate it's just i'm too dam old to be introduced to new tricks-- but thanks again XLR8 -- your post has introduced food for thought amoung others mathamatically more qualified than me -- Geo.

A yacht is not defined by the vessel but by the care and love of her owner---