ajustable lift keel

[OrionsSword]

I have heard something from a friend about what he called an ajustable lift keel (I have know idea if this is what it is called) and i hade no idea what it was. from what he explaned it was a oriented keel shaped like a airplane wing so the boat would literaly climb to windward esencially sideways at a pretty good rate i questioned how this would work when you tacked and you suddenly started having a crazy amount of leeway he then explained that it was somhow ajustable though a set of wires. the impression i got is that the keel is something like a centapeed with many sections so the lift could be adjustable.
If any one can clarify this or has heard of it there input would save me alot of number crunching and bath tub testing and would be greatly appreciated

Orion

 

[tspeer]

It sounds like a double-hinged flap taken to extremes. It's unlikely to do what the designer claims. Check my explanation of a gybing centerboard on the Boat Design forum to see why. All the claims of increasing the lift on a keel just don't take into account the complete physics of a sailboat.

Where a variable camber keel can make a difference, and one of the reasons for the "trim tabs" on the AC boats, is to optimize the drag of the keel, not the lift. It's next to impossible to design a symmetrical laminar flow section so that it has its lowest profile drag at the conditions experienced in sailng to windward. You just can't make the drag bucket that wide without raising the minimum drag. But with camber you can center the drag bucket around the operating point.

I doubt the "centipede" section was designed to maintain long runs of lamiar fllow. So if it can't increase the lift (because the lift is determined by the sail, not the keel), and it doesn't reduce the drag, then what performance gain is there to be had? (The correct answer is a possible increase in maximum lift, allowing the keel chord to be reduced. But I doubt your friend has that in mind.)

 

[Eric Sponberg]

On Project Amazon, an open class 60, we had a keel section that was a 21% thickness aerofoil with a trim tab. The trim tab axis was at the 70% chord position. The shape of the whole was designed so that the low-pressure side of the aerofoil was a fair curve. I designed this section to create maximum lift, particularly at slow speeds, and did not try to optimize drag other than to create a shape that, when the trim tab was deflected, would not create separation of flow at the trim tab axis. This keel worked remarkably well, and the skipper was even able to qualify it as his emergency rudder. That is, to prove to the race committee that it worked, he took the boat out into Charleston Bay and maneurved a few figure 8s. This passed the test and he was qualified to start the race. A more complete description of the boat can be found on my website: www.sponbergyachtdesign.com.

Eric

 

[yipster]

if i understand rite this is about the picture yes?

http://www.heymanyachtdesign.com/in3a.html has a good article on steerable adjustable lift keels also.

Tom, what was the term you used for a lifting body? you mentioned it before but cant find it back...

 

[tspeer]

Are you talking about a "beavertail" bulb?

 

[Eric Sponberg]

Yipster,

Yes, that is the concept.

Eric

 

[yipster]

Yes, that is the concept.

Eric,
i took the liberty picturing project amazon's keel here above by making a link to your site showing that interesting high tech design. wow, what a boat!

Are you talking about a "beavertail" bulb?

Tom,
no not a keel. you did reply Doug Carlson some time back on this fine forum with a scientific aironautical term for a wingless body getting lift from shape.

yipster

 

[OrionsSword]

I think that the keels mentioned in the relpies are the general idea but with more moving sections to create a smoother flow.
Orion

 

[yipster]

Tom, i've been reading a years post back for the expressions you had for wings and for lifting body's and can almost swear it was you that mentioned those names. ( body's like at: http://www.nasa.gov/centers/dryden/news/FactSheets/FS-011-DFRC.html )

maybe its not really relevant to this thread although a canting or revolving lifting body bulb may give lift mentioned as above also? complicated and i'm way out of my league here anyway but still searching for that expression...

 

[Andreas E]

Lifting / Gybing Keel

This may be a keel design that matches the question 'ajustable lift keel' at the start of this thread. I read about it in the latest no of Seahorse mag.
It's used for the Diode 36...
http://rodgermartindesign.com/binfo_result.asp?ID=49

Moving parts seems to be the order of the day. Where did 'less is more' go?

Andreas

 

[tspeer]

Tom, i've been reading a years post back for the expressions you had for wings and for lifting body's and can almost swear it was you that mentioned those names. ( body's like at: http://www.nasa.gov/centers/dryden/news/FactSheets/FS-011-DFRC.html )

maybe its not really relevant to this thread although a canting or revolving lifting body bulb may give lift mentioned as above also? complicated and i'm way out of my league here anyway but still searching for that expression...

The question isn't getting "more" lift - the keel lift is determined by the sail rig. The question is, "How to produce the required lift with the minimum drag?" Lifting bodies have abysmal lift/drag ratios because they have very little span. Their advantage to NASA was they provide some lift on reentry when thin wings would be burned off.

From a purely hydrodynamic point of view the bulb is detrimental. But if you have to have a bulb, then it needs to be integrated to produce the minimum drag. One way to do this is to use the bulb to extend the effective span of the keel, as long as the wetted area isn't increased too much. That's what winglets and beavertail bulbs are all about.