Looking For Thoughts On Building A Balanced Rudder

[deblen]

Originally Posted by cottonsail

Here's what I did to get a balanced rudder. The boat turns like a fin keel racer, backs up with control and has a light helm.

Nice job! If you find you are catching rope or other junk,consider adding a "shedder",similar to what I did. / Len

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[cottonsail]

It's about 7% of the total area. That's what you want ahead of the center-line of the rudder shaft.

[TrentePieds]

Cottonsail has it right. If you're gonna do this at all, the Cottonsail method avoids the need for structural modifications, and it adds area to the control surface. If you tag on a "tip section" like this, the internal structure of the existing rudder will be quite up to handling the addition area.

A consequential problem is that lines from people's crab pots and other such can not slide harmlessly off the bottom of the rudder when you snag them - as you will :-) - but will stick in the gap twixt skeg and tip section. That would be a problem for me. I don't enter water unless I can see the steam rising from it ;-)!

As for a NACA ( National Advisory Committee on Aviation, ca. 1928) "foil", there are dozens of them, and none of them are intended to "back up". Aeroplanes don't back up while they are in the air. The hydrodynamics of the flow around the rudder blade will shift so drastically when making stern-way that considering any particular "foil" a waste of time given how little time we spend going astern.

TrentePieds

[barnakiel]

I have built a balanced rudder and placed to much area fore. Avoid this common and stupid mistake.

If you have a skeg, the easy way is to add area below and fore of the axis BUT this sort of contradicts the protective purpose of the skeg, should you touch bottom.

Is the tiller heavy on your boat? Why do you want a balanced rudder?

We have a non balanced one and it is extremely light in all conditions. And your boat is not that much bigger than ours.

Look up Jeffa white papers they show plenty of building details. Great stuff from a great company.

b.

[Martkimwat]

I agree with Fou Fou, 18% is way to much. I have a balanced rudder on my Parker 27 which has a hinged lifting rudder. When I first got the boat it was very twitchy, when I got the boat out of the water at the end of the season, I found the rudder blade was able to hinge to far forward and over balancing the rudder. I fitted an adjustable stop on the lower pintle and after some trial and error, found the perfect sweet spot which turned out to be at 10 area forward of the hinge line. Subsequent checking of the specifications showed this to be where it should be. I have the slightest amount of weather helm which is desirable so that the boat will round up (slowly) if the tiller is left unattended, ie if I fall overboard as I mostly sail singlehanded.

[cottonsail]

Nation advisory council on aeronautics.

[four winds]

Brad, I did what you are considering about a year and a half ago.

Could not be more pleased with the results.

Details here:
http://www.cruisersforum.com/forums/...al-142080.html

[TrentePieds]

Cottonsail: Quite right! 1928 wuz a helluvalongtime ago :-)

It may be of interest that for a marconi-rigged Seabird (the Mower/Day job from 1901) badly in need of new canvas I built a mainsail - eons ago - that actually had "Clark Y" upper surface coordinates when it was full of wind on a close reach. Worked wonders for the boat. The secret is in the mitre-seam :-)

Might do a mod for TrentePied's main when I rip off that silly Facnor mast furling device. Pity to waste all that luvverly new dacron :-)

TrentePieds