33.5 winged bulb keel, what's the airfoil?
- Thread starter Divingnflying
- Start date
There’s a Sabre 34 I race against on Thursday nights. For several years we were pretty competitive. A couple winters ago he managed to get a hold of the as-designed measurements for his keel and faired it all back out. I can still keep up with him on the downwind legs but now he out points me by 10 degrees upwind. Evidently the foil shape can make a difference.
I have this drawing that, based on the date and boat length, is probably for the Hunter 376. It specifies several NACA 64-XXX series sections. I found this PDF with foil section coordinate tables including 64- series, where the sections in Abbott and van Doenhoff are recomputed more precisely using later methods. https://www.pdas.com/avd.pdf
Paul
Paul
In the J24 world templating the keel is a big deal. The shape does make a difference, however, if one is serious about racing there are other places that will make a bigger difference, like getting a good on time clear air start, good clean mark rounding, sail trim, good sails and steering.
Most sailors are crusing sailors, not serious racers. However racing incudes knowledge of the waters, weather, crew experience/training and so forth. As a dealer for Beneteau, Catalina, Hunter, Precision, MacGregor, ComPac and others. The decision to buy a sailboat came down to amenities and looks.
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Thanks, this is sort of what I was looking for.
I have to fix some rust spots and refair the keel, looks like it's been done poorly before. Was just curious if it was still anywhere close to original. Right now it's more slab sided than tapered haha.
My guess is the difference is in making it smooth and keeping the flow as laminar as possible rather than conforming to any specific airfoil shape.
How would you do that anyway? If you knew the airfoil was NACA 2412 for example. You could get the specs for that airfoil, which essentially consist of formulae. Then you'd have to convert that to a set of scaled templates, say on 1" spacing, that you'd somehow have to compare to the keel, and remove or add material to conform. Sounds simple, bet its not.
You'd be better off spending that time practicing your gybes and figuring out optimum jib sheet car placement for different wind speeds and directions and making a card/marking the deck.
Yes, I'm looking for an NACA reference. I need to fix some rust spots and old repairs, and if I've got to refair it anyway, I might as well try to get back to original profiles
@Divingnflying
Post a couple of pictures of the damaged keel and ask how to repair the damage. There are some who can help here
Post a couple of pictures of the damaged keel and ask how to repair the damage. There are some who can help here
That is basically the process. There are usually 3 or 4 templates cut in a stable material, like aluminum and preciously guarded against damage. The keel is then faired, with fairing material added and subtracted to get smooth curves. It's a lot of tedious work for any one but the most competitive racer who is going to race against other equally or more competitive racers. Most of us are not in those groups.
The design specs and the reality may not be in good alignment. The cast iron and lead keels come out of the castings in pretty rough condition and needing a lot of fairing compound. I find it difficult to believe a production boat builder would invest the time and effort to fair the keel to a template. I suspect they get is smooth and close enough knowing most buyers wouldn't know what templating a keel is.
These pictures may help since I had do same repairs to my H430.
and
Jim...
PS: The Fluid Flow Profile is this type on that Keel type is
https://en.wikipedia.org/wiki/Laminar_flow
and
Jim...
PS: The Fluid Flow Profile is this type on that Keel type is
https://en.wikipedia.org/wiki/Laminar_flow