S2-6.9 Lifting Keel(Dagger Board)NACA #s ?

[Howard.LKN]

I am hoping to get some advice on how to determine the most appropriate NACA # for a lifting keel (leaded dagger board) for a S2 6.9 sail boat.

I have made a plug from the bottom of the trunk where the lifting keel exits the hull and have measured this profile on a Mitutoyo Coordinate Measuring Machine. It appears that a NACA foil number between a 0010 & 0011 most closely matches this opening.

I have been told that a NACA # 0012 is the most desirable. The problem I have is the exit slot is to narrow at the forward third of it’s profile to accommodate this shape.

I have harvested the lead from a keel that was on a J22. I am preparing to CNC machine the portion that I need to meet the 400 lbs of righting moment called for in the class rules.
S2 6.9 Specifications
LOA 22'
LWL 18' 9"
Beam 8'
Min draft 10"
Max draft 4' 6"
Displacement 2,200 lbs (Measures 26-2700)
Total Ballast 770 lbs
Lifting keel ballast 430 lbs
chord 24"
width (in water) 2 3/4"
Hull ballast 340 lbs
Cabin headroom 4' 6"
Cockpit length 7' 0"
Mast above DWL 32' 0"
Sail Area, sq. ft.
Main 127
Jib 102 (class)
PHRF 206
PORTSMOUTH (D-PN) 91.3
Rudder Kick up
I (jib height) 26' 0"
J (jib foot) 7' 10"
P (main luff) 25' 4"
E (main foot) 10' 0"
Produced (years) 1983-86
Designed by: Graham & Schlageter

 

[BobM]

Sorry, nothing but moral support here, since you already found the specifications I was able to find. Did you try faxing Tiara to see if they could help?

 

[Howard.LKN]

Hello Bob,

I have made a CAD drawing of the board and including the upper end where it wedge locks in the truck. I have used the profile of the slot where the board exits the hull as the default profile. This shape does not match any of the dimensions I have for a naca 0012 profile using 24" as its chord length.

I have been trying to find out what is the correct or preferred naca #

As soon as I have that I can start CNC machining my keel.

Also, another naca # 0010-34 has been suggested. I would greatly appreciate it someone could explain what the suffix number does to the 4 digit naca number.

Thanks again,

Howard G.

 

[BobM]

Have you tried contacting Roger Long? He posts on Ask All Sailors and is a marine architect. Maybe he can help.