End Plate Effect for Keel?

[Pacman]

I am wondering if anyone has tried using an end plate to increase keel efficiency.

It is common practice to use end plates on aircraft to enhance airfoil performance and it seems to me that it might be useful on our little boats.

In addition, when the boat heels a few degrees, the keel effectiveness drops considerably.  That is why C-16s sail best at minimum heel.

I am thinking that an end plate on the bottom of the keel that is a few inches larger than the keel footprint might keep the water flowing across the foil shape when the boat heels rather than simply spilling off as we slip to leward with the stock keel.

Any aeronautical engineers, naval architects, or shade-tree mechanics (like me) have ideas on this?

[Bob23]

Hmmm...from one shade tree engineer to another:
   I think this was discussed before but I could be wrong. First off, I'm not sure the 16's like the 23's sail better with minimal heel. I can't personally comment on the 16 but the 23 likes about 10-15 degrees of heel. I think as she heels that much, the waterline length is increased which results in maximum speed.
   I'm not sure what you mean by end plate and certainly with something that takes off at 175 mph, the effects at 5-6 knots may not be the same. I've toyed with the idea of extending the keel back to just forward of the rudder to minimize turbulence but I haven't done anything past ponder this idea over a cool Dark and Stormy. Problem is, given enough rum almost anything makes sense! jk.
   This would be a great question for Ted Brewer or Robert Perry. But I bet there lurketh around here an engineering mind or 2!
Bob23

[Greene]

There was a discussion recently in the 19 section.

http://cpyoa.geekworkshosting.com/forum/index.php?topic=5619.0

Mike

[Pacman]

Mike, That discussion was focused on another aspect of keel design.

I am visualizing a flat aluminum plate, maybe 1/4" thick that would be attached to the flat horizontal bottom of the keel with the edges protruding several inches from the sides of the keel.

In theory, those protruding edges would help keep the water flowing past the keel surface instead of allowing it to spill off the bottom edge thereby maximizing the benefit of the NACA airfoil shape of the keel.

Shoal keels like the one on our C-16s begin to spill a good bit of the water flow when the boat heels more than 10 - 12 degrees. 

That is why, when sailing to windward with the boat heeld over we make good speed over the water surface and it feels like we are really sailing well
but when we check our progress on the GPS we see that we lost much of our progress to side slip to leeward.

In my experience, I can make better progress to windward with 7-10 degrees of heel that I can with the boat heeled much past 12 degrees.

In theory, if the end plate does what I think it might, I could sail to windward better with more heel and less side slip.     

[gabi]

yes ,interesting idea...but what do you do with the up and down motion of the hull,..it will act like a break

[crazycarl]

sounds like your describing a wind keel...

[ribbed_rotting_rusting]

 I think this might be more along the lines of what you mean, Hutchins addressed the issue on their top of the line product
The Com-Pac 35 and the redeeming benefits of shoal-draft Scheel Keel

Also;
From:
Henry A. Scheel
15 Modern Yacht Designs
International Marine Publishing Company Camden, ME
Designer's Comments on the Scheel Keel

From Life and Times Section (approximately 1972)
About this time, too, I designed and later was granted a patent on a sophisticated keel shape-now known widely as the Scheel Keel. This keel shape makes it possible for a sailboat with moderate draft to get along to windward just as well as if she drew more water.At the same time, the Scheel Keel does away with complicated centerboard gear and equipment. Another virtue of the Scheel Keel is that it provides a center of gravity slightly lower than the keel shape it replaces, so the boats are a bit stiffer. Likewise, in a seaway, when small boats really move all over the place, the Scheel Keel shape tends to suppress some of these wilder gyrations. (Had my name been Brown, Smith, or Jones, would there have been such a keel shape? Who knows?)


http://www.tartanowners.org/content.aspx?page_id=2155&club_id=284925&item_id=299986&new_view=1
MJ Cox

[kickingbug1]

    i have also thought this might work but have also thought that hutchins would have adopted this keel design if it would have made the boat sail better. and to answer a question the 16 does sail better the more she heels as does the 23 i suspect

[skip1930]

Sailing best when up right...that be the Com-Pac 19. Different designer for the C-P 16 and maybe? the C-P 23?

Wing keels...more weight, less depth. The only reason for them.

One thing I be pretty sure about, adding more length to the back of the keel will make the boat harder to come about. Have to be able to turn this thing, not just go in a straight line. Even if the line falls off to the lee side. Sailboats are suppose to go side ways ain't they?

skip.

[gabi]

my 16 sails the best at around 15  degrees,

[NateD]

I have to agree with the original poster, Pacman, that (at least my) CP16 sailed to windward best when she was upright. I loved to put her rail into the water and really lean it over for the adrenaline, but when I wanted to get to a mark upwind in the shortest time, less heel was better to let the keel bite.

Poking around the internet you can find all kinds of opinions on keel end plates (http://forum.woodenboat.com/showthread.php?14823-Keel-End-Plates). My uneducated opinion? Someone who really understands the aerodynamics involved and could design, fabricate, and attach a plate might mildly improve the boat. But there is a pretty good chance that you end up making the boat worse if you don't truly understand the variables, materials, and craftsmanship. Of course, if you use some cheap materials and attach it in such a way that it can be removed there wouldn't be any harm in experimenting.

If I were looking to make a CP16 go to windward better for the least amount of money, I would start with a foiled rudder, then new sails. If I really wanted to get crazy, I would think about adding a centerboard into the keel.

[Pacman]

sounds like your describing a wind keel...

Yup,  

The wing keel is somewhat similar in that the wing does provide end plate effect.  

However, on a wing keel, the end plate also has a foil shape to increase righting moment.

The design I am considering is flat and would be the full length of the stock keel so it would be shaped more like the anti-cavitation plate on most outboards.

[Citroen/Dave]

I suggested some time ago, see "Removing the brakes", rounding the bottom of the C16 keel in the fashion of the top of a coning tower on a modern submarine.  My idea was to reduce drag, and secondarily, provide more of an impact barrier.  I think the design of the C16 stub keel was to let go of the water in a knock down to spill the air and round up.  A wing keel might be tampering too much with a good basic design unless you like exciting sailing.

My new '87 C16, "Slow Dancing", is still on the trailer but the trailer is in a repair shop getting a new axle.  I still don't know if she floats because I can't see all of the keel . . .  I may add a couple of inches of sexy curve with a 'keel bra' after next season just to see if that approach will increase speed by removing the turbulence at the bottom of the keel.  The curve will mimic half the cross section of the keel. Water in my neighborhood is noted for hidden rocks, not soft white sand.

[Pacman]

I suggested some time ago, see "Removing the brakes", rounding the bottom of the C16 keel in the fashion of the top of a coning tower on a modern submarine.  My idea was to reduce drag, and secondarily, provide more of an impact barrier.  I think the design of the C16 stub keel was to let go of the water in a knock down to spill the air and round up.  A wing keel might be tampering too much with a good basic design unless you like exciting sailing.

I believe you are correct regarding the current design which allows the C16 stub keel to "let go of the water" in a knock down.  It follows that, as the boat heels, it will begin to "spill" water over its bottom surface, hence side-slip.  The greater the degree of heel, the greater the side-slip.

My theory is that water that"spills" over the bottom surface does not flow along the length of the foil shape of the keel.

It that loss of flow along the surface of the keel can be reduced, the keel will become more efficient.

[kearns]

Another caution to keep in mind is that the ballast material inside the keel is concrete, not lead. Take this into account when deciding what anchoring device (bolts?) and sealant you decide to use. With the slightest moisture seaping into that concrete, you'll soon have a mud-like mess on your hands and maybe worse. I'm not an engineer, but my intuition tells me that there would be a LOT of stress on such a plate and that it would work very hard to free itself from the anchoring devices.

Kevin