Foil Profile

I am crafting new foils for a Hobie 20. What is the latest thinking on the optimum profile? Is it the same for rudder and dagger-board?

Regards
Chet

hello,
i don't know if the latest thinking is any different than 60-90's thinking, but here is a link to a foil that would work pretty well for a rudder. http://marlongofast.tripod.com/zipped_aeronotes/NACAfoil.htm
6% may be a hair thin, but a naca63 series foil will be good for rudder and board.
keep in mind that hand shaping may not yield a perfect replica of whatever foil you are trying to shape. if you find the ultimate foil to replicate you would need to use a cnc machine to create it if you want valid test results for that particular foil.
you can make templates for the foil you choose to check a hand shaped blade.

NACA 12. from what i've learned on the subject. this is a good basic profile. i used www.flyingfoam.com Bob there was a very nice and the price was right. maybe check with hobie as to what there foil is so they match the wells. i had Bob cut the cores. this is for a dagger board. as for rudders a naca 12 s/b close. maybe something slightly thicker/shorter chord. let the pro's chime in but i belive naca 12 is what is used on the inter 20 daggers. the rudders are a much more complex foil

Naca 12 series are good general purpose sections.

The naca 63 and 64 series are becoming more popular, especially for higher speed sailing boats.

If you can't be bothered putting a somewhat tricky concave section in, as the 63 or 64 series sections do, the 12 series is more than appropriate.

Profile wise, parallel for most of the length with tapered tips. The tips are pretty much up to your preference as there are a lot of different theories about.

The original H20 daggerboard shape was hand crafted by Phil Edwards. The rudders are certainly quite different than the daggers. We are expecting to be given the go ahead to race the 20 with the same blade as on most other Hobies, so the EPO2 will be a good choice. They work very well on the 20. We can not offer any help on either foils specs / dimensions. There are no "plans" on them. Both are readily available for purchase, so if this is a "project"... have fun with it and let us know what you ended up with.

It's probably of little use, but I'm using a 63-010 NACA foil section for our US1meter keel (www.teamseacats.com). This is the section I really want but may have to go a tad bit thicker (perhaps to a -015) in order to get the structure needed inside the keel. I'm working out the details of the lead bulb/keel/hull structure on the computer for the next couple of weeks. The 63 series is a good all-round lifting foil with a good average between drag and high-ish stall angle....though I wonder if sacrificing a little drag in return for a high stall angle is really that important on a daggerboard.

probably not really with a 1m because they manoeuvre so quickly without losing much speed.

This 63 or 64 profile sounds pretty good. How can I get my hands on a picture?

The link earlier in the postings to naca 0006 shows something not quite concave.

Regards
Chet

Typically you start with a complicated formula or x&y coordinates to draw the foil. I've got the 63 series setup in a 3-D design table such that I can change any parameter (including the % of thickness). How long and what thickness do you want (10% is pretty standard)? I'll be glad to give you a 1:1 drawing.

here's the 63-010...let me know what format you would like it in too.

Jake that looks great. You are truly a nice guy.

My length is 15 1/2" and max width about 1 1/2" so 10% is fine. I can easily enlarge drawings so a pdf file would suit.

Regards
Chet

nice guy? nah...just a geek who enjoys this stuff. PDF attached (hopefully). Scale is 1:2

In that case how about NACA 64?

Regards
Chet

yup, a couple of minutes to plug in the numbers...

again 1:2

Hi Jake

Just wondering, seeing as you seem to be on a roll...

Whether you might put one up at 63-008, for me, chord length of 290mm.

Regards

sure - when I get back to my work computer on Monday, I'll plug it in.

Many airfoil coordinates are available for download from: http://www.ae.uiuc.edu/m-selig/ads/coord_database.html

The 63-008 coordinates are available here: http://www.pdas.com/profiles.htm#63-008

Setting it up in a spreadsheet and printing the outline for a chord of 290mm is relatively trivial, if you dont want to wait until monday.
Are you going to use the 63-008 as daggerboards?

Yes thats possibly going to be the plan, I have on good authority from someone you and I both know Rolf that 8% would be fine, although he was thinking 0008 series section, but I've drawn it out and looked at factory boards and they look nothing alike, so I thought I'd compare them to the 63008 section and see what they look like.

I have a set of timber boards that should do the job for starters but once I've gotten the shape worked out, I'm planning to make a mould and my own boards.

Regards

Attached at 2:1...I could almost make this 1:1 and fit...however, watch your paper sizes, this is the US 8.5" X 11" sheet size.

Hi Jake

Thanks for that, I think I would have been able to take 1:1, I'm not much with computers, but I'll have a play later and see if I can enlarge it. The drawing I mean <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

Regards

I didn't think about rotating it. This should be 1:1 if printed on 8.5" X 11" paper (what size do you guys use down there?).

Matt,

When do you expect to have the go ahead to race the Hobie 20 with the EPO2's?

Ian

Matt Miller doesn't have anything to do with whether the EPO2s are class legal on the H-20.

Depends on the HCA Rules Committee:
Jeff Alter (chair - Hobie Family Rep)
Doug Skidmore (Hobie Cat US rep)
John Dinsdale (Hobie Cat Europe rep)
Mal Gray (AUS)
Erik Olsen (DEN)

But Matt could give us an update since he shares office space with Skidmore . . . .

A4 is standard paper size here, 210 x 297mm.

A3 is exactly double the size, 297 x 420mm.

Concave sections were mentioned (in relation to the NACA 63 and 64-series).
I have heard someone say that Marstöm's Tornado rudders have concave surfaces in front of the trailing edge.

So I would like to know:
Are concave surfaces on symmetric foils of any advantage for high-perfomance 16-20-foot cat?
Which symmetric NACA-profiles have concave sections?
Or are concave sections/surfaces only useful in asymmetric profiles?

Stein

The IHCA rules committee contacted me about this a few weeks ago. I have never sailed a Hobie 20 so I've asked our Vice Chair Phil Collins to help out. He had some questions so he's going to test the EPO2 Hobie 16 blades on the 20 and let us know what he thinks.
Bob

The only concave sections that I've actually seen are on some of the newer F18 rudders where the foil section is stretched out on the trailing edge leaving a concavity near the back. I have no idea as to what the performance advantage is supposed to be and I can't imagine why you would want a concavity on the leading edge.

Tip loss?

Or one hell of a weed catcher?

the hollows are in the foil profile. for instance, with the rudder down in the sailing position, if you hold a straight edge horizontally on the trailing edge of the rudder to the high point of the camber, you will have space under the middle of the straight edge - this is the hollow.