QUESTION FOR THE DESIGN TINKERERS:

[Bob23]

To all:
   I'm toying with adding a small skeg to koinonia's underside just forward of the rudder. In reading from many different sources, I'm sorta convinced that this will help direct water flow over the rudder blade better resulting in higher pointing and less weather helm. I'm thinking of something made of wood and bolted in, faired and glassed. It would stick down about a foot or so but that is not cast in concrete. This addition of a skeg makes sense to me but that alone isn't reason enough to butcher the underside of a perfectly good Compac 23.
   My father in law, a tinkerer at heart, built the same type of skeg on his Irwin FreeSpirit 21. That little boat points higher than her blown out sails should allow. Of course, with the Irwin, the vertically adjusting daggerboard and rudder help keep the boat in balance so that could be a factor too. But she can easily outpoint my 23 by 10 degrees!
   What do you guys think? Am I nuts? Bored? Been hitting the Cuervo too often?  I wonder if the designer of the 23 is still around.
   I this photo of my wood foiled blade, you can visualize the skeg just sitting forward of the blade. I'm wondering if it would reduce turbulence coming from the keel.

Of course, I'm aware that screwing with a good design could result in this:

Bob23

[trektrader]

No expert myself but you might try opening a thread on Cruising Anarchy for advice:
(http://forums.sailinganarchy.com/index.php?s=4f4d308d9bcc59b11375769b1c12ea0e&showforum=22).
Several sailboat designers frequent this board including Bob Perry and could give you good advice.

[Tim Gardner]

Bob, Bob, Bob, Bob, Bob,

Would you design a new underbelly on your wife?  If you made that suggestion to your wife about her tiller, we would be mourning your early demise.

Be thankful Koinonia is a forgiving vessel.

TG

PS: The designer of the 23 and the 16, Clark Mills, passed away a few years ago.

[skip1930]

"  I'm toying with adding a small skeg to koinonia's underside just forward of the rudder. " Hummmmmmmm you of course want to turn this barge at some point during the sail, correct?

Everything that sticks down into the water effects the flow under and around the hull. And slows the boat down. I suggest that The Nature of Boats written by Davis? be consulted as all the formulas effecting this change will be discussed. I'm not sure she point higher with this change. May have Clark Mills spinning in his grave.

Good luck with that. skip.

[millsy]

Bob,

I for one say give it a try, and let us know how it goes!

Maybe stick it on with bondo so that you can knock if off at the end of the day...

Bublous bow anyone?

Chris
Dolce C-23

[Glenn Basore]

Your new foil rudder already has its drag resitant shape to the leading edge. its rounded correct? and your rudder has an air foil design to allow the water to move more efficient..

by adding a skeg would great turbulence between the rudder leading edge and the back of the skeg.

Also, I think the center of the rudder pivot point would cause the leading edge of the rudder to move (pivot) out from behind the trail edge of the skeg acting more like a brake.

Glenn

[Tim Gardner]

Glenn,

My thoughts exactly.

tg

[Shawn]

Bob,

I would think a skeg like that wouldn't be useful in the rear. It may reduce the effectiveness of the rudder and may reduce the turning ability somewhat.

You crane launch right? If you wanted to attempt to point higher I'd extend the keel deeper. It will keep her more upright and reduce slippage when beating. That in turn will let you keep more speed up when beating to wind which will in turn keep the keel more effective. Notice how much better they point when going 4+ knots then compared to say 2 knots in light air. Or if you really wanted to go nuts extend the existing keel forward and aft to make it closer to a full keel.

The other thing would help would be sheeting angles on the headsail. Because of the shrouds there isn't much that can be done there though.

Shawn

[Bob23]

   Ok, guys. I get the general drift of where this is going. And I certainly don't want Clark Mills coming about in his grave. Maybe leaving well enough alone in well enough. I admit I do have two tendencies: Thinking too much  and not thinking enough, both at the inappropriate times!
   Maybe I have been hitting the Jose a bit too often...bulbous bow...hmmm. Now, why didn't I think of that?
  Glenn and Shawn: The way you explained the turbulence issue makes perfect sense. The rudder blade does have a true foil shape and has greatly increased the perfomance of my 23. Here is a photo of the rudder work in progress:

   Tim: I once suggested to my wife that she improve her underbelly shape via some excercise. I'll leave her response to the imaginations of everyone here, but suffice to say, it wasn't pretty. I've learned somewhat to keep my mouth shut...sometimes.
   Years ago, back in my aircooled VW days, I once decided to "redesign" the rear engine cover of my 1968 beetle. Needless to say, my "improvement" didn't work at all, although while still in my mind, it seemed perfectly fine. My boss then repsonded most cruely, "The engineers spent countless hours and money designing this. How in the world did you think you could improve it? Idiot!" I learned alot from that guy...apparently not enough.
  Thanks for all your replies. "Koinonia" and me...perfect together!

Bob23
 

[skip1930]

" ...adding a skeg would great turbulence between the rudder leading edge and the back of the skeg. "

You might want to look~see at the sharpie's bottom like a Star Boat me thinks.
I see a keel, a skeg and a BIG round rudder. If I remember, ours took a small boy and a man to hold the tiller!
But all of it around the CENTER OF THE BOAT HULL.  Not off the stern, otherwise she won't turn. The moment of effort from the mast and appendages under the boat are working in harmony.

skip.

[Glenn Basore]

Bob,

The nice leading edge on the rudder your showing looks pretty efficent to me!

Glenn

[Tim Gardner]

Skip, the skeg shown on your photo was to support the rudder stock, primarily, the foil shape was to decrease turbulence at the rudder stock support post, primarily, and to move the centroid of the boat aft of or closer to amidship.

I'm reminded of a prank played on the NY Maritime College Corps of Cadets onetime while at morning muster at sea.  The Cadet Officer of the Day Barked this command: 

Now hear this, this is not a drill!   All those forward proceed aft! All those aft proceed forward.  All those amidships --- Direct traffic!!

The resulting chaos was FUBAR!

TG

[skip1930]

Way too funny.

Those with enough 'scrambled eggs on their hat' could toy with the dive officer on board a fleet boat. "You three aft in the torpedo room proceed quietly to the fwd torpedo room. Now you three others follow them."
So the dive officer made the necessary bubble correction. Latter, ' You six fellows quietly go back to the aft torpedo room."
Another bubble correction.
It was said to be a boring day in the war although the majority of the trek was on the surface.

skip.