Keel Ailerons

I think it has been tried. I distinctly remember reading an article in 'Small boat Journal' back in the mid 80's. the hull was very narrow and the keel very deep. By very, I mean half the boat's length appox. It did work but there wasn't much of a market for 10ft deep 20 footers.

I have thought of a different approach.

Why not but dive planes on the bottom of the keel. These could be actuated by a simple push/pull rod. It would produce downward lift only when you wanted it. And, as an added bonus, as the boat heeled over to say 30deg or so, they would produce a significant ( sine of 30deg * neg lift) up wind vector.

Then I thought about ultimate stability, which is a big thing with us off shore mono folks, then realized that the lead was doing three jobs. 1.) counterballancing the rig, 2.) giving the boat momentum, and 3.) serving as a safety device in case the olde tubb was capsized. So why not just add more lead and or make it deeper? Add lead and or make it deeper? Add lead and or make it deeper?

After a while even this, sound, time honored approach can get ridiculous. Hence we end up with ACC yachts that are 90% ballast and some early Open 60's that had drafts up to 1/3rd their length.

I guess the thing is is that many ideas are possible, but few are practical.

Bob

P.S. I think canting keels are a great improvement performance wise, but I suspect they are a marine underwriter's worst nightmare. Imagine every keelboat having one.

 

Sorry about the aileron mistake.

But I can still not get this to work. Did som fast math on it
See picture below.
F = sideforce of the sail
FR = righting force of the lower aileron
FS = sideforce from the keel and upper aileron

Now:
F = FS - FR
F*R = FR*RR - FS * RS
This leads to:
FR = F * (R + RS) / ( RR - RS)

For the case of a keel balansed without weight this means that if you want the righting force FR to be smaller than the sideforce from the sails you need RR to be larger than R + 2*RS and that is a VERY deep keel. And a large area since FS needs to be F + FR. Total hydrodynamic lift generated by the keel then needs to be F + 2*FR

Please prove me wrong ...
Anders M

 

RM from foils

The advantage of the CBTFco system is that it uses CBTF so that the lateral resistance is generated exclusively by twin foils that because of the nature of the system can be kept vertical most of the time. The twin foils can also be turned "collectively" so that leeway is virtually eliminated. Couple that with an effective strut mounted flap and canting keel and you have eliminated nearly 70% of the ballast required by a fixed keel boat and because of the 60° cant angle of the keel strut the ballast you do have is working exceptionally well.

 

Lorsail. Light keels should make the boat faster and more turn responsive also. What happens when the boat blows over and the sail fills with water from each passing wave in choppy conditions ? How does she self right without crew dangers?

 

Danger

Well,that's a function of how well the boat is designed in the first place. If you're going to use a system like the CBTFco system that combines CBTF with an actively controlled flap you'll have to do some serious design research to see just how far you can go and have the boat self righting(or devise another righting system?)
In addition the major offshore racing rules are incorporating some strict mandates regarding stability-at least those rules that affect monohulls.(Too bad about the disasters affectng the multihull fleet in the TJV today!).
I think when you look at monohull "hybrids" like Pterodactyl and Sean Langman's boat and consider the CBTFco concept serious questions regarding ultimate stability have to be looked at. I'd be real interested in seeing in the Bethwaite design whether or not if the port or stb pods were knocked off could the boat still come back from a knockdown on that side with the sails up? The CBTFco active flap concept might benefit from pods; in fact the patent includes a rather unique hull shape that they originally envisioned using the system on.
Good question, Cyclops, and one that is very important to the success or failure of these new "monohull" hybrids-at least in ocean going versions.

 

Example of Canting Keel with Trim Tab

The new Cookson 50 incorporates the system described earlier by Lorsail.



http://www.cooksonboats.co.nz/prod-50.htm

 

Cookson 50 /RM from active flap control

JPC, the Cookson 50 uses a system pioneered by Eric Sponberg on Project Amazon: it uses a trim tab on a canting keel with a max cant angle of 30°. Eric's max cant angle was 25° on Project Amazon.
Cookson claims that the trim tab enhances the performance of the keel so that they don't need to use another form of lateral resistance when the keel cants like most other canting keel boats. The tradeoff is the low cant angle. I've just read somewhere that one of the first few 50's is being retrofitted with a daggerboard to enhance upwind performance.
There is a big difference between the Cookson system and the CBTFco system I described earlier that uses a flap("trim tab") on the keel strut to develop righting moment.The CBTFco system uses CBTF that requires at least a 50° cant angle enhanced to 60° for this application. The point of the high cant angle is -in combination with boat heel-to get the keel strut close to being horizontal when at max cant. This allows the deflected(up) flap to generate maximum righting moment with minimum effect on leeway.
The Cookson trim tab is turned exactly the opposite direction of the one in the CBTFco patent(#2) and is used for an entirely different purpose:to enhance the "lift"(resistance to leeway) of the keel strut on their limited cant angle system for the purpose of(they hoped) eliminating the need for another foil to resist leeway.
Two different concepts and two different uses of a "trim tab"....

 

Perhaps it's because I've let my Sailing World subscription lapse, but I'm not familiar with the boats you're referring to, Doug. I'm interested. Any chance you could post some links?

Thanx,
Stephen

 

Boats?

Stephen, I'm assuming that you were referring to Bethwaite's Pterodactyl and Langmans new boat( "Maxi Skiffs"). I posted a thread under sailboats:" Mono or Multi...." ; here are the url's I posted there:

Langmans boat
LSS_7.jpg
http://www.sailinganarchy.com/fringe/2005/images/LSS_7.jpg

Bethwaites boat-
billochcut.jpg
http://www.sailinganarchy.com/fringe/2005/images/billochcut.jpg

Bethwaites boat uses sliding on-deck movable ballast , water ballast and minimal ballast on a fixed keel ; Langmans boat uses a lot of crew and a canting keel. Both use "pods" as backup and are considered monohulls by their designers...

 

Trim Tab versus 'flap'

Lorsail-

Thanks for the description of the two distinct applications of the trim-tab and the flap. I confess that I had been, clumsily, skeptical on the value of a trim tab (in the traditional use of the term - lateral resistance) on a canting keel. In this discussion, I had thought that -aha!- it was not being used as a 'trim tab', but as a contributor to righting moment. I think I see now that a tab could have value, in the first 45-degrees of angle (w/r/t the water, not the boat), as a contributor to lateral resistance, and, in the next 45-degrees and deployed in the opposite direction, as a contributor to righting moment.
I'm probably still missing a big chunk, but thanks for the clarification.

JPC

 

How about a little sanity check to this idea? In order for the twisted/flapped keel to counter the heeling moment from the sail rig, it has to have its center of effort located at the same height as the center of effort of the sail.

For the sake of argument, let's be generous and make the keel as long as half the mast height - that's a really deep keel! Say the center of effort of the sail rig is 40% of the mast height above the water. That means the keel has to have a center of effort above the water that is 80% of the keel depth. it will have positive lift at the top and negative lift at the bottom, with the positive lift exceeding the negative lift so as to oppose the side force from the sail rig.

The lift distribution that produces this moment with the minimum amount of lift-induced drag will have a sidewash distribution that varies linearly from root to tip, as proven by R. T. Jones (Jones, Robert T., "The Spanwise Distribution Of Lift For Minimum Induced Drag Of Wings Having A Given Lift And A Given Bending Moment", NACA-TN-2249, 1950.). So by starting with a linear sidewash distribution, you can calculate what the optimum spanwise lift distribution has to be. How you achieve that lift distribution I'll leave to you. But once you have it, you can tell a lot about how well the concept will perform without having to get into the details of the design, because you already know the very best that can be done.

The lift distribution that puts the center of effort at 80% of the keel span above the water is shown below. The angle of attack at the top of the keel is 10.2 degrees and it is twisted 19 degrees between the root and tip. This sounds pretty high, but feasible. The net lift coefficient is a whopping 0.0126 and the Oswald efficiency factor is 0.018. The ratio of the lift to induced drag is just 2.3.

If you gave the keel a more reasonable depth, the net lift and efficiency are going to be even lower. And although the instantaneous center of effort is positioned to cancel the moment from the sail rig, any change in the loading on the keel will result in a drastic change in the moment and the heeling balance. The moment from the effective twisting of the keel is largely independent of the leeway angle. Any change in leeway will produce a change in the force that is located at the keel's hydrodynamic center, which is well below the waterline. So those flaps better be pretty fast acting to continue to maintain the balance as the load on the rig fluctuates.

So if you want to know why this idea doesn't seem to be all that popular, it may be because most designers aren't willing to stand for a 5,000% (and up - way up) increase in the drag from the keel just to eliminate the ballast weight!

 

Thanks Tom

 

RM from foils

That's why I brought up the CBTFco patent that separates the function of lateral resistance from the keel strut and uses a flap on the keel strut at maximum extension to develop RM-almost exactly what I understood IQ was trying to achieve with"ailerons" on the keel...

 

tspeer
I had a very similar idea to Inquisitor's original thread two and a half Years ago, regarding an adjustable keel that could be twisted in a manor you have just described. The keel would have had to be twisted as you mentioned, the top section at a different rate to the bottom tip, as well i felt the rate of twist should be sharper at the middle which we could call an apex which should also be able to shift up and down the keel to suit differing conditions. The whole keel it self should be raised and lowered to accommodate differing speeds through the water. Due to the nature of my job allowing me much time for contemplation i have spent a lot of time designing one, mostly mentally but also with the help of a few scraps of paper. I have also made a few prototypes in metal and wood. I regret very much that i didn't study harder at school to enable me with the tools with which you have just demonstrated so eloquently. I suppose most people have a pet idea and i for one have had a great deal of enjoyment thinking on this one. Now i have received my 'sanity check' i can get back to finding ways of paying the mortgage of the house my wife would like me to buy. Many thanks two you all, Neil

 

Similar story: one of my student designs had a bulb with the CG well forward of the foil so it would twist to leeward at the bottom. I lost enthusiasm for this concept, but continued to consider keel innovations, leading to my patent.

Keeping the ballast bulb behaved underwater is a problem on America's Cup boats. There's a delay between the boat turning and the bulb turning, and the torsion forces on the blade are large.

Those boats Doug referenced.... they look like giant Moths (the development class) to me. Hence my interest in Moths.... where go the small boats, the large will follow.

I think a giant canting keel version of the Mistral hull design that dominates the Classic Moth class might have merit. Since the Mistral is developable from sheet material, building a giant one should be a piece-o-cake. It wouldn't need floats since its signif topsides flare gives it bouyancy up high already.