optimum foils section for dinghy??

[mistral]

i'm making a new daggerboard for a dinghy, similar to 470 in both aspect and speed; i'm considering wich section to use, keeping in mind that case dimension will limit thickness to 9-10%; NACA0009 should be a traditional choice, and NACA 63009 doesn't convince me 'cause a narrow drag bucket, wich lead to more drag at leeway angle about 2.5-3 degrees, just normal operating leeway for this kind of boat in average winds;
i've searched about other sections with lower drag, keeping laminar flow more attached to the board, but found nothin' really interesting about simmetrical sections, only asimmetrical ones :(
Can anyone help me????
i know it's a quiet academical problem, but anyway i'd like to undersand wich is the best solution!!!

Thanx
Mistral

[Tim B]

NACA 0009 is a good section because of it's wide drag bucket. the NACA 6 series only presents an advantage in a race where there is a leg dead down-wind. You might consider using Mark Drela's X-foil and the UIUC database to give some basis for comparison of foils. Remember, though that X-foil is only intended for use in air, consequently it's use for hydrofoils is only a guideline.

Also, consider how you will build the foil. can you mill it from solid wood, or would you prefer to mill moulds and lay-up a glass/carbon keel?

All the best,

Tim B.

[Andy P]

I use NACA 000x ( 10 is preferred ) for most dinghy classes.
And NACA 63A2 ( again ~ 10% ) for the fast boats that make less leeway.

I find that there is less drag even upwind in fast boats with this 6 series section.

470 speed is about at crossover point for 00 or 63 . ( however 470 board is a flat board with shaping only near the edges , and ~ 6% thickness/chord)

Andy P

www.bloodaxeboats.co.uk

[sorenfdk]

You might consider using Mark Drela's X-foil and the UIUC database to give some basis for comparison of foils.
Or you could use Profili 2. It is built on Xfoil and comes with a built-in database with more than 2000 different foil sections. And what may be the best part for you: It's made in Italy!
Check out http://www.profili2.com
Even though it's meant for airfoil section work, it can be used by a yacht designer too. I used it to optimize the keel sections of the Danish Yngling just before the Olympic Games in Athens, and I'm not saying that it was because of this they won a bronze medal, but I don't think it hurt them :)

[CT 249]

What's Italian and similar to a 470? A Strale???

[Raggi_Thor]

Profili looks very interesting, thanks Søren!
One comment to the "drag bucket". If you are sailing a dinghy, will you lift the daggerbord on a downwind leg? Then the "bucket" is not interesting, is it?

[mistral]

to CT 249: it's not a Strale, it's a Laser 2 regatta, rigged out of her class rule; the class here is definitely dead, and this boat has a taller mast, different sails, and will probably be fitted with a bowsprit and a gennaker next summer, now she has an ugly centerboard and rudder so (not original) i'm gonna make them new, in a few words i'm using her as a test-boat ;)

to Raggi Thor: of couse i'll lift board on downwind leg, but anyway drag bucket is important for upwind course; if drag bucket is too narrow (NACA63009 for example) your leeway angle will be right on the border of the bucket even going upwind;

for Soren: thank you for the precious advice!!!! God bless you, Profili is the first boat-related software that i found wich speaks italian!!!! and many compliments for Yngling medal, i guess tuning a such slow boat was not that easy!!!

anyway many thanx to everyone; i've just downloaded Profili, now it will take some more times to learn it, compare some solutions and take the right decision :-)))


Mistral

P.S: how could ISAf choose Yngling????? There's a plenty of 3-crewed modern fast and appealing boat, why that old crap????

[B. Hamm]

There's much more to choosing a boat design for match racing than it being fast. The same reason the Star has been around for so long. It's a fairly easy boat to sail, it's a tricky boat to sail well. Technique means everything, which is what you're after for a match racing boat.

B. Hamm

[mistral]

what i mean is: ok, you can even sail a box with a sail, but, why chose an old design, when there's a plenty of modern looking boat, even suited for match race; i'm thinking about este 24, tom 28, ufo22, just to promote italian boats :), Beneteau 25, Melges 24, and son on.
It's not a fault to have a reactive and speedy boat, of course the best crew will win both in an old crap an in a speedy jewel, i'm convinced about that, but the image of sailing that you convey on outer world is different, and image is important for olimpic sailing to gain visibility and sponsors; and don't tell me it's because of costs, olimpic classes costs a huge amount of bucks, comparing to what they really are; 6000€ for a state-of-the-art Laser!!!!! 10000€ or more for a competitive 470 !!!!
Anyway this is an off topic, the thread was focused on foils for a dinghy

Mistral

[Raggi_Thor]

More on the bucket: When you lift the board on downwind legs, you don't need the narrow bucket, but can choose a 00xx with a wither "bucket". I think we agree.

Yngling=Crap? As a Norwegian I must deisagree :-) They may be slow, but they are solidly built and o not get soft (like the Soling). So you can compete with an old boat that will cost you maybe 5000Euro.

[sorenfdk]

for Soren: thank you for the precious advice!!!! God bless you, Profili is the first boat-related software that i found wich speaks italian!!!! and many compliments for Yngling medal, i guess tuning a such slow boat was not that easy!!!

You're welcome and thank you for the compliments!
Tuning the Yngling is in fact quite easy - at least in this case it was. The foil sections on the boat were really crab, so...
You'd be amazed at how many boats are delivered with keels that are really awful. Even boats designed by well-known designers and built by well-known boat builders. I don't believe that there's one Beneteau 25 around that hasn't had it's keel foil sections optimized! And that's just one example!

[mistral]

So you can compete with an old boat that will cost you maybe 5000Euro.

mmmmm, maybe i'll came to Norway to get my next boat...... :) :) :) :)
mistral

[Raggi_Thor]

http://nor.yngling.org/phorum/list.php?f=2
Mostly Norwegian, prices from 25.000 to 45.000 NOK (kroner).
One Euro is approx 8.5 NOK.

[mistral]

i definitely MUST come to Norway to get my next boat, prices are about halved compared to Italy.......

Fair wind
Mistral

[Raggi_Thor]

I can deliver one to you if you pay the gas :-)

[Andy P]

In a fastish asymmetric kite dinghy, the daggerboard ( preferable to a swinging aft centreboard) is not lifted. Because you don't sail 'downwind' but at 45 degrees to the wind, and try to maximise speed which means lots of side force with the kite up, so lifting the board actually = more drag and less speed.

You still need to operate in the low drag bucket by keeping leeway small.

The faster you go, the easier it is.

Andy