New Foil

[Alixander Beck]

Hello All,

I recently built a Foil for a 12.5" Dinghy. The Dinghy draws 32" from the flat steel CB and I decided to make a rudder that had a better profile to give the Dinghy some more lift and pointing ability.

I chose a NACA 0012 Section scaled to 6" Chord with a draft of 32" equal to the CB. The area of rudder to CB is about 60%. The area of the new rudder to old rudder has been increased 32 sq".

I chose no taper, slightly balanced and a rectangular edge becuase of the relative ease of shaping.

I would appreciate any comments as I don't have the benefit of a formal Engineering education or years experience.

Thanks

http://www.imagestation.com/picture/sraid191/p78319f7fc87232e2b0623be4b3f1b2d4/f1d11fb4.jpg

http://www.imagestation.com/picture/sraid191/p50c8b16e5bb0b748da4bdfeffc6e269a/f1d11fae.jpg

[Noah]

Nice foil.

Typically a rudder with a short chord like that can stall out at small speeds, but for a 12.5ft dinghy you shouldn't have any problems.

Next you need to add foils to the bottom of the rudder and centerboard so you can start to fly.

What is the boat?

[John Meachen]

Not so much a comment as an enquiry.Could we have a shot of the foil end on to see which way the growth rings are facing?

[huisjen]

I've been thinking about airfoil carving a bit lately, related to wind generator thoughts. I'd be interested in seeing pictures of the process of carving that foil.

Dan

[Dave Fleming]

What wood specie is that foil made of?
Is the wood air dried or KD?

Do you have photos of the shaping process?

Can you post the NACA foil diagram for us?

[Paul Pless]

Nice workbench, is that a traditional design? Where can I find one like that?

[ 10-19-2005, 06:58 PM: Message edited by: Paul Pless ]

[huisjen]

http://www.basiliscus.com/ProaSections/AppendixD/NACA0012.jpg

[Peter Malcolm Jardine]

Welcome Alixander ;)

[Alixander Beck]

Noah, I hope it won't stall either. I went for a 12% section so that I could increase the AoA, I was going to go for 15% for the stall factor but chickened out. I think anything will be an improvement from the barn door that was on the boat before. The dinghy is a wooden S&S Bluejay http://www.sailbluejay.org/
restoration pics to come)

John, Here are some shots of the rings best I could get.
http://www.imagestation.com/picture/sraid191/pe9e3cfe3ccf68fa1b16e1a5fade74639/f1d0a1fe.jpg
http://www.imagestation.com/picture/sraid191/pc80d67f9d65954d936554076710ce548/f1d0a1c9.jpg
http://www.imagestation.com/picture/sraid191/pb3a83d5a62f95d2c2873ed589b4c21bb/f1d0a191.jpg

Dan, I would like to have the pictures also, unfortunately it didn't occur to me to take them until after. I used a spokeshave and a pencil and template for the entire shaping of the foil.
http://www.imagestation.com/picture/sraid191/pafa764ab959b8fb1bca654db6561f2fe/f1d0a156.jpg
I will take progress shots on the next one.

Dave,The wood is Bearclaw Pine. A white pine I believe. My father-in-law is an engineer, cabinet, template maker and wood collector. He found this 12x6 years ago and bought it becuase it was virtually perfect. It's been air dryed on racks for about 5 years.
There is an excellent shareware foil database program called Profoil from which I got the diagram, I scaled it in AutoCAD.

Paul, yes very traditional. ;) I got this one at HomeDepot. intersting is that the deck is made of bamboo.

I am hoping that the bearclaw grain livens up under the epoxy, I think its a beautiful piece of wood. I hope that the Pine is strong enough for the stresses, part of my thinks that it may not be, but i guess thats what the fiberglass is for.

Thanks Peter smile.gif

[ 10-19-2005, 09:11 PM: Message edited by: Alixander Beck ]

[paladin]

Welcome aboard.....on that particular airfoil the end should be relieved 7 degrees and a short splate added to reduce the tendency to stall at speeds above 60 mph.....and the blade with an aspect ratio such as yours will start to vibrate at 15-20 mph...
Good luck :D :D

[huisjen]

And how often will this 12.5' dingy get above 60 mph? :D

Dan

[Alixander Beck]

Paladin,

I think I'll be lucky to pull 10 mph out of this boat.

Could you please explain the 7 degree relief and spate - I don't understand.

what would cause the vibrations? Is this common in high aspect designs?

thanks

[Joe ( Cold Spring on Hudson )]

Glad to see see ya hang around Alixander ;)

Seems ya got more gronicals than Barry did, eh Dutch ?

Nice fair foil good work.

[imported_Craig]

Nice work Alix. I too love that grain; she should look very nice finished bright. My only comment pertains to the trailing edge. I have read; but not experimented with, reshaping the trailing edge to about a 1/8" flat surface over the effective length of the rudder. Possibly someone could discuss the applicability to your project and the general application of this technique. As I think I understand it, the flat edge improves the stall parameters.

[Thorne]

Huisjen -

The "dinghy" will go over 60 mph every time he tows it somewhere on the freeway.

;- )

Don't know if I'd call a BlueJay a "dinghy" -- the S&S part of their heritage makes them a "mini-yacht" at the very least!

I've owned a '57 and '67 BlueJay and they were VERY fast downwind with a chute, but you want smooth water and a steady wind direction for secure planing.

[ 10-20-2005, 10:03 AM: Message edited by: Thorne ]

[Klaus]

Originally posted by John Meachen:
Not so much a comment as an enquiry.Could we have a shot of the foil end on to see which way the growth rings are facing?Its not my foil but looking at the wood grain on the foil side I can tell you its NOT quarter sawn. The growth rings probably show a nice curve, the type that likes to cup with time.
There's more than wood shaping to make a foil that keeps its shape and lasts.
If it were mine I would have used 3 or 4 wood staves, epoxied together, even for a 6" chord. I'm also a fan of kick up blades for dighies, mine has one, I only have to pull up the C/B when coming ashore. Fixed rudder blades can be a pain sometimes.

But its done now, one more thing I would do to it before glassing is to cut the bottom off in a diagonal (maybe 3" up from bottom at leading edge, 1" aft edge) line and then epoxy the cut off piece back on. This makes a watertight glue line so when the bottom wears due dragging the water cannot soak up the whole length of the board.

Klaus

[Alixander Beck]

Craig, I think I read something about that too. I'm all for lessening the stall factor so I think I will square the trailing edge off and see how it works.

Thorne, I've ridden some good surf on her and aside from the old rudder stalling out, we hit max hull speed easily - that is until the rudder stalls and I capsize - good fun smile.gif
I'll see how the guys at the club take to my "mini-yacht". I may be laughed out of there for such a comment, but I agree the S&S heritage is priceless.
"The Bellefonte" never came with a chute but I would love to get one. She's a stable and fast little boat for sure.

Klaus, thanks for your suggestions. I am in the process of designing a kick-up rudder stock, which is a little complicated. Luckily the club harbour has enough depth I don't really need one at the moment.

Thanks for the comments everyone. Much appreciated.

[paladin]

Alix...
Holding the blade perfectly vertical...with the leading edge to your right,......if the bottom is perfectly flat...draw a line from the lower leading edge to the trailing edge of the foil but upward at a 7 degree angle from the leading edge...
a spalte would be like the wing fence on an aircraft to direct airflow over the control surfaces....you would lose control pressure in a steep bank or slip.....at your speeds I wouldn't worry.... :D :D

[John Meachen]

Klaus got there first but I would be concerned about the possibility of warping occurring if you are not very careful.With really diligent sealing and if you make a point of keeping the rudder out of the sun whenever possible,you should be fine.