Lifting Keel - NACA #'s ?

[Howard G]

This is my first post and 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

[Paul B]

Originally Posted by Howard G

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.

Most people who have very limited knowledge will say the 0012 is the section you want. They don't know what they are talking about.

Since you mention the nose is narrower than that it makes sense. You should look into the 0010-34, or maybe 0012-34 if it is fatter.

You could contact S2, or look for an owner's association on the web who can give you some information as to what it was originally.

[Howard G]

Paul, Thank you very much for your prompt response and suggestion.
I have been in touch with S2. They could not offer any help and did not keep any records or drawings that relate to the fabrication of this keel. I have also been in contact with the S2 6.9 class association and they are in the same position. I will share my results with the S2-6.9 class and the process that I have gone through once I have reproduced a working replacement.

Paul you mentioned a NACA foil # 0010-34. I have been using a program called naca4gen to compare some of the dimensions. Is there another program you can suggest I try to come up with the dimensions for a 24" chord to this 0010-34 # ?

Thanks again,

Howard

[Paul B]

Originally Posted by Howard G

I have been in touch with S2. They could not offer any help and did not keep any records or drawings that relate to the fabrication of this keel. I have also been in contact with the S2 6.9 class association and they are in the same position. I will share my results with the S2-6.9 class and the process that I have gone through once I have reproduced a working replacement.

If you get in touch with Scott Graham I'm sure he will have the info you need. I believe he sits on some committees for US Sailing and IYRU, so maybe you can contact him through there.

Originally Posted by Howard G

Paul you mentioned a NACA foil # 0010-34. I have been using a program called naca4gen to compare some of the dimensions. Is there another program you can suggest I try to come up with the dimensions for a 24" chord to this 0010-34 # ?

Thanks again,

Howard

The offsets for the NACA sections are available in multiple places on the 'net. I use the book Theory of Wing Sections to look up the offsets.

[Howard G]

Hello Paul,

I have ordered a copy of the book that you suggested ( Theory of Wing Sections ). It should be here next week.

I am still trying to get a handle on the basics of the numbering system for the naca #'s.

It appears that the lower the numbers are finner. You had mentioned a suffix -34 ( 0010-34 ) How can I find out what this modifier is and how it effects the dimensions for the rest of the 24" chord of my keel?

Thanks again,

Howard G.

[Paul B]

Originally Posted by Howard G

Hello Paul,

I have ordered a copy of the book that you suggested ( Theory of Wing Sections ). It should be here next week.

I am still trying to get a handle on the basics of the numbering system for the naca #'s.

It appears that the lower the numbers are finner. You had mentioned a suffix -34 ( 0010-34 ) How can I find out what this modifier is and how it effects the dimensions for the rest of the 24" chord of my keel?

Thanks again,

Howard G.

I think you will fid the book useful.

Here is one of the better on line sources for foil section offsets. http://www.ae.illinois.edu/m-selig/a..._database.html

[CRM]

Spot on callout for the S-2 boat.

CRM

[Paul B]

Originally Posted by CRM

Spot on callout for the S-2 boat.

CRM

Yep, used on most performance boats from the same time frame. I suppose you should know from doing some fairing work on boats from that era.

I should have done a better job of answering his question re: the -34 suffix. The -xx suffixes can be read as the first number is related to the LE radius, and the second number is the chord position of the max thickness. Then again, I have probably already said more than I should...