NACA Foil Sections Continued (Was "Bill Roberts")

Technical discussion of ARC products
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thommerrill
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NACA Foil Sections Continued (Was "Bill Roberts")

Post by thommerrill »

Hello Bill-

I guess I lost the string about the rudders but i know about the NACA 6300 section being used on ARC boats. I am planing on putting a 6300 section on my F25c and wanted to see the profile if possible. That was the reason for my question.

As far as liking the way the 22 handles; I would say yes in winds under 12mph. Unfortunately for me, when it blows here its usually 15-25 mph with gusts. Basically too much sail area for that kind of wind for me to enjoy singlehanding.

I made a special trip to the dry storage last weekend because the winds were blowing 45+. The mast was up on the 22 and was shuddering in the strong winds.I tied it to a corner that made it more aero and it calmed down to almost no movement.

Do you think slanting my F25c rudder forward would be a benefit? Its an under slung system.
thommerrill
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FMS 20 57 - newly faired and painted with Awlgrip -For Sale
Matt Haberman
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Rudder Discussion

Post by Matt Haberman »

Thom,
The rudder discussion is located in the technical forum.
I also moved the "crew of 3" discussion to the technical forum since we are trying to keep the 22 forum focused on 22 class discussion.
Matt Haberman
Aquarius Sail Inc.
http://www.aquarius-sail.com
Bill Roberts
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Post by Bill Roberts »

Thom,
The NACA foil sections specify the foil cross section only, the thickness distribution. The plan form, length and width or span and chord, are whatever your class requires underwater.
I'm not sure what you mean by 'underslung'. Does that mean with a large knotch cut back into the leading edge of the rudder at the waterline for a forward sailing location? Someone misinformed the F boat designer and the F28s and F31s have a large knotch cut back into the leading edge of the rudder at the waterline. This was done to get the leading edge of the rudder up under the keel at the transom. There is no advantage here, reduced drag, in this arrangement. It just cuts the strength out of the rudder structure as it continues up into the rudder head. These rudders break frequently here in South Florida. It's no fun when this happens out in the Gulf Stream.
As far as your boat being overpowered in strong winds and singlehanding.
The ARC 22 can easily be sailed mechanically by one person because of the way the boat is rigged with self tacking jib and automatic mast rotation etc. From a stability point of view in 20 knots of wind and with one person on the boat, it is very much overpowered. The boat sails, tacks, fine unirig. Therefore, if this is what you sail in and this is the way you sail the boat often, get yourself a 33ft hoist, flat cut, mainsail with small roach made out of Dacron and go sailing singlehanded in 20 knots of wind and be happy. Match the sail area to the overturning moment in the conditions you sail in. You have a good start with the 12ft beam. There is nothing slower than being severely overpowered sailing to windward. Don't think that your boat is going to be slow in strong winds with reduced sail area. Just look at those Around the World Boats. When they are running 35 knots, there is a small jib on the boat and the mainsail is about halfway up the mast. Full sail is for light air conditions.
Good Sailing,
Bill
thommerrill
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Post by thommerrill »

Bill-

I have attached a pic. This rudder rotates in a cassette. This allows full use of the swim platform rather than a tripod blocking the access from the waters level. Matt Scharl [Gamera] wins consistently with this setup.
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thommerrill
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Bill Roberts
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Post by Bill Roberts »

Hi Thom,
What I see in your picture is a swept back and curved aft rudder leading edge. This geometry leads to ventilation at high speeds, 20mph + . Of course if the boat never goes that fast, ventilation is no problem anyway.
There were several F boats here in Stewart this weekend and I noticed fences on the rudders to prevent ventilation.
By the way, how many times has your buddy beaten Randy Smyth on his F25?
Bill
thommerrill
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Post by thommerrill »

Bill-

In the 2002 nationals Matt [Gamera] came in 2nd overall where Smyth [Yo] came in 5th overall. In the 2003 Nationals Smyth came in 1st overall while Matt [Gamera] came in 2nd overall with one victory over Smyth who came in second. I looked it up last night. Matts out of Chicago and the only place I know of where they have crossed paths is the Nationals in FWB/Pcola area. As you well know beating Smyth in his home waters is very tough to do. Didn't you run aground trying to hold Smyth off in an RTI??? The closest I get is at the sign up party before the regatta...

I don't think my F25c goes over 20mph often so its probably not worth adjusting for.

thom
thommerrill
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Bill Roberts
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Post by Bill Roberts »

Hi Thom,
I think those race results speak for themselves. The Smyth boat was faster.
Local knowledge: This is something that exists sailing on lakes and rivers due to land contour around the body of water. In the ocean the closest thing to local knowledge is high and low tide time and that is published in the local newspaper.
I saw this whole rudder scheme and hull extension thing be developed right here in Stewart, Fla. on an F27 years ago. The 'swim platforms' on boats, sail and power, here in Fla. are flat extensions that hang square to the tramsom, do not line up with the bottom hull shape at all. They are porous to let the water drain through them. Many of them are hinged across the transom to be raised when the boat is underway. What the F boat dealer here in Stewart did was extend the F27 hull shape aft about a foot to gain waterline length. Then he called it a "swim platform". Most sailors would call this cheating and inconsistent with the intent of One Design Class Rules.
The casset rudder was simply a way of making the hull extension, 'swim platform', continuous across the hull centerline at the transom. The casset rudder and rudder head and SS post and heavy duty hinge at the top make a very heavy rudder assembly compared to a simple transom hung rudder.
Any F boat would benefit from a well made NACA 63 series rudder foil
transom hung with no knotch in the leading edge. I have inspected some F boat rudder foils and centerboard foils and they are someone's 'mid summer night dream' in shape. They are lumpy and very non symmetrical in foil shape with nice thick trailing edges.
Good Sailing,
Bill
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