MX Nova Winged Keelboat Concept

Vlad has a potentially great idea here: using flaps on keel mounted wings to reduce displacement downwind and increase RM upwind(and improve pointing as well). I think a rudder t-foil would be really helpfull and allow the lift fraction of the mainfoil to be greater.
Why not build a big model or a small fullsize prototype?

https://www.facebook.com/mxNova

Brian Hancock speaking for Vlad Murnikov:

SpeedDream is about innovation. It’s our touchstone yet it doesn’t have to be as radical as a Flying Keel or a wave piercing bow and stepped hull. In fact, we have been working for a while on a classic racing keel boat, something that nobody has taken a fresh look at for a very, very long time. We are calling the project mxNova.

The iconic Star is well over 100 years old, and the Dragon is not much younger. More recent designs, the Etchell and Soling, are closing in on a half century since they were introduced. All of them have provided decades of glorious competition and spawned some of the world’s best and best known sailors; guys like Dennis Conner, Russell Coutts, and Lowell North, to name just a few. In no way do we think that mxNova is going to take away any of the illustrious accomplishments of these classes, but we do think that it’s time to take a new look at keel boats and bring in some fresh ideas.

Most recent keelboat designs are more ballasted dinghy than they are classic keelboat, intended to sail flat and relying on the crew for righting moment. We became curious as to whether there was room in sailing for a truly modern keel boat, a boat that is long, gracious and narrow and intended to sailed heeled with the ballast keel providing the power rather than bodies dangling over a lifeline. The result is the mxNova prototype.

Naturally, the boat features SpeedDream’s signature wave-piercing bow which gives way to a pleasantly narrow hull. There is nothing extraordinary about the design other than it’s thoroughly modern, even slightly futuristic. There is ample sail area with a square top mainsail that can be easily twisted off to depower in the puffs. The rig is simple and does not require complicated running backstays. All in all you have a powerful boat that is easily driven, which is in itself is not revolutionary, but that’s until you look below the waterline.

MxNova does not have SpeedDream’s Flying Keel; instead she has a keel that can make the boat fly - or at least, change its displacement substantially.
Attached to the bulb of a normal looking fin keel are two transverse wings. On the trailing edge of each wing are adjustable flaps similar to a trim tab sometimes found on the aft end of a keel or rudder. Their purpose is to turn a symmetric foil into an asymmetric one, thereby creating either downforce or lift when the boat sails upwind or downwind respectfully.

In the upwind configuration, the flaps are up, which creates a downwind force. This force 'sinks' the boat, providing 'virtual displacement', more stability and, by extension, more sail carrying capability. The opposite is needed when sailing downwind. With a control similar to one found on the Moth dinghy you adjust the angle of the keel flap to make it point down. The effect provides lift which in turn reduces displacement just when you need it. This minimizes drag and increases the boat’s ability to plane. This simple mxNova feature brings the classic keel boat into the 21st century and provides a great tool for competitive sailors to maximize its performance.

That’s the theory, but to make it work would require a lot of work – and money - and before committing to developing the new design we would like to hear back from the sailors of all stripes whether it’s worth it or not. The attached renderings are here to inspire conversation. What do you think?

 

An interesting Idea.

But I'm kind of prejudiced. I remember discussing it one day in the Fall of '89. I was telling a fellow design student that I thought ballast keels were way too heavy (bulb keels had yet to come back in fashion) and that I had come up with a way to lighten them up.

Since we were all familiar with the concept of a winged keel, due to the America's Cup races of six years previous, I suggested adding "elevators" to the wings. In exchange for this, I suggested cutting the ballast weight down, because when you really needed all this weight most was when you were sailing to windward against a strong wind.

The idea was to crank in some negative lift, on the part of the wings, to take the place of the removed ballast, in holding the boat upright.

I never even sketched the idea, because I found a major flaw in it. The flaw is this:

The wings and their elevators can not tell vertical from horizontal.

Meaning that, when the boat heels, the negative lift does nothing to correct it. It merely pulls away from the hull, like and underwater kite.

To make this work as intended, I realized that the wings themselves had to pivot side to side, so they would always be parallel to the horizon. This way, the negative lift is always pulling downward.

As for creating positive lift, for going down wind, this is probably not a good idea.

This is because the lift, with the fixed wings, is always pushing towards the hull, no matter what its vertical orientation. This means, that when the hull is heeled over, it can act much like a rudder as well as a vertical lifting device. This can make down wind steering, as treacherous as it already was, in racing boats of that time, even more dangerous.

With the wings always staying parallel to the horizon, the situation is made even worse. The vertical lift gets off center and encourages the boat to heel even more. And the more the boat heels, the worse this gets.

I knew that back then, so never suggested an upward lift setting.

The settings I suggested were neutral and negative.

With the wings always staying parallel to the horizon, the negative lift would be used in down wind sailing as well, especially in strong winds.

So, now, to make this work, you need not only elevators, on your wings, but a way to keep them parallel to the horizon as well.

I saw this as being far too complicated and vulnerable, to underwater obstacles, such as rocks and lobster pot lines, to pursue any further.

Best of luck to Vlad for resurrecting the idea.

 

MX Nova Winged Keelboat

sharpii2, I think you may have missed a point-see the sketch below. I had pretty much written this idea off until I did the sketch. It clearly shows that with the right hull the foils would contribute substantially to upwind RM. As well as to better VMG upwind with the vector to windward of the downforce. See the MPX sketch below that illustrates that. I haven't quite decided yet but it might work better than DSS because it's not operating near the surface and theoretically works well heeled. But downwind in waves is where Vlads idea will shine with oodles of vertical lift.
I'm toying with the idea of building an RC version of the Crossbow system and I could use that model to test this idea.
Thanks for posting- you helped me see that there was more value to this idea than I had originally thought.

 

Hi Doug.

I looked at your vector drawing. It is very convincing but it is wrong.
The wings, with negative lift, are always pulling away from the
CENTER LINE of the Hull, where the keel is attached.

Kind of like flying a kite. The kite may be way up in the air, or swooping near the ground, but it is always pulling on your hand. And the direction of that pull is always where the kite actually is. If it's over your head, the pull is straight up. If it is 50 ft high and 50 ft out, then its pulling at a 45 deg. angle.

What this means is that downward lift is most effective when the boat is
dead upright. As the boat heels, the downward lift vector is the cosine
of the angle the boat is heeled at.

Say the boat heels 20 deg. The cosine of 20 deg. is 0.94. This means the down ward force caused by the negative lift is 94% of what it was when the boat was upright. But the sin of 20 deg. is 0.34, which means the downward vector causes a righting moment of

the cosine of 20 deg * (the sine of 20 deg + the righting arm of the buoyancy shift).

So. Say we have a boat with a ten foot Beam and say the buoyancy shift is 10% of that Beam, or about 1.0 ft. Now, lets say the vertical distance from the boats CB to the wings is 6.0 ft. And let's say the negative lift is 200 lbs.

Now, let's do the math: 0.94 * (( 0.34 * 6.0) + 1.0) * 200 = 572 ftlbs of
added righting moment.

Sounds like a good deal and it is. But wait a minute. The negative lift is also creating a capsizing moment. Let's see what that is.

200 lbs * (((cosine of 20) * 6.0) - 1.0) * cosine of 20 deg.

Or 200 lbs * ((0.94 * 6.0) - 1.0) * 0.34 = 315 ftlbs

So, our net righting moment is: 572 ftlbs - 315 ftlbs = 256 ftlbs. Still
a good deal. So good so far.

Now lets heel the boat over further, say another 20 deg. and do the math again. To keep things as simple as possible, lets keep the amount of negative lift the same, as we're really looking for proportionate increase.

200 lbs * (( 0.64 * 6.0) + 1.0) * 0.77 = 745 ftlbs for the righting vector.

200 lbs * (( 0.77 * 6.0) - 1.0) * 0.64 = 463 for the capsize vector.

745 - 463 = 282 ftlbs net righting moment. Some increase for sure but
pretty paltry, considering we've heeled the boat over twice as far.

We ended up with a mere 26 ftlbs of additional net righting moment.

Now, as a further thought experiment, lets add 200 lbs to the keel,
forget about the wings, and do the same degrees of heel.

200 lbs * (((Sin of 20 deg.) * 6.0) + 1.0) or

200 lbs * ((0.34 * 6.0) + 1.0) = 608 ftlbs of net righting moment for 20
deg. of heel. That's more than double of what we would have gotten from the wings!

Now for 40 degrees of heel.

200 lbs * (( 0.64 * 6.0) + 1.0) = 968 ftlbs of net righting moment, which is almost three and a half times as much as we would have gotten from the wings!!

Now, to be honest, this is the first time I've ever worked this out
mathematically, because, back then, I didn't know how.

But, intuitively I knew.

Now, once we keep the wings parallel to the horizon, there is no added
capsize vector, but pure righting vector. Then and probably only then, the wings will beat out additional ballast. This is because the faster the
boat goes, the more negative lift the wings produce. Where as the net
righting moment of the additional ballast stays simply proportionate to
the rate of heel.

 

So as I understand you there is a net gain of RM up to around 20 degrees of heel-is that right? The design would have to be real carefully done, thats for sure. The vertical lift off the wind would surely be a plus if the wing paid for itself upwind. Upwind isn't the high point of effectiveness for a DSS foil either, but it can be retracted. Still seems worth a further look-thanks for your reply!

 

You seem to be completely missing the point. The "net gain of RM up to around 20 degrees of heel" is only the same as the net gain in RM you would get from an additional 80 lbs of ballast at the bottom of the keel.

Using an additional 80 lbs of ballast at the bottom of the keel will be far simpler, far cheaper, have far less wetted surface, and less induced drag. This means it will be faster upwind, as well as being cheaper and less prone to damage.

The only time this idea might work is downwind, where DSS would do the job same better. Even if you do get lift downwind it will be precariously balanced, because as soon as the boat heels at all the lift will be to windward of the CG, which means it will be trying to capsize the boat (ie: reducing RM). DSS doesn't have that fault, since if a DSS boat heels the foil still contributes to increasing RM.

Short version: just because it has a "foil" doesn't mean that it is always going to be awesome. Life's not that simple.

 

I think there is the possibility that the area of the vertical fin could be reduced by the contribution to leeway resistance made by the wings when generating downforce. In order for the concept to be viable, the wings must pay for themselves upwind. And the wings have to be looked at as a probable liability in very light air. If those problems can be resolved the downwind contribution will be tremendous.

It might be possible to use a version of the K Foil where the keel wings retract:

 

Dear all,

I discover this old thread via the inflated wing one, as it is listed in similar threads.

I had also a similar idea to use a depressor foil hinged at the tip end of a classic keel, to create what can be called a "dynamic ballast". Such depressor foil are of common use for instrumented tow fishs in oceanography, in order to be able to keep the fish immersed despite the drag on its towing rope which tends to make it rise to the surface, and I have some experience of their design.
You have both mentioned potential advantages and drawbacks, I have also my list of points to study carefully and quantitatively on a concrete case so to build a true assess of the concept. Before doing this study, I would like to share with you my present "pre quantitative" thoughts :
- From the attached sketch, it is easy to understand that this dynamic ballast is equivalent (in terms of weight contributing to the righting moment) to either more crew sit windward or a water ballast winward + (Alas !, ...) the drag of the foil itself. (Note that I not mention the extra drag of the hull du to the extra displacement, because it is a common fact with extra crew or water ballast which was not proved a disadvantage since used for racing). So this extra drag due to the foil, and also their moments (pitch and yaw), could be a fatal drawback, it is the stake of the quantitative study to carry out.
- To make it very simple, the incidence angle of the foil is kept constant and adjusted a priori for the maximum Cz/Cx or bit more depending of the weight of the foil drag in the boat total drag. The only hinge (as sketched) is so to maintain the foil horizontal whatever the heel angle.
- The negative lift is in proportion of squared speed, so low lift in light breeze, high lift with winds : it is similar with the common use of water ballast. Negative lift is always provided, downwind as well as upwind, it is not a disavantage for the righting moment (even when downwind you can take advantage of more RM), but clearly the foil drag is like a brake that probably prevent to go surf.
- From these two points, I preliminary conclude that such device could be better suited for displacement hulls, and especially the ones with high ballast ratio and speed limited to Froude 0,4, what I call "classic sailing" : the metric rules yachts using ballast ratio of 50%, or equivalent yachts (and I think there is still a future and a market for such classic/peaceful sailing, the pleasure of sailing is not just just for speed but for sailing boat that give you pleasant sensations).
- As regard advantage : in case of a wind gust, the move of the boat is extra heel, and so extra incidence on the foil and extra negative lift is immediately provided : the foil will act as a damper of the hull heel.
- As regard another drawback, mentioned by Sharpii : "vulnerable to underwater obstacles, such as rocks and lobster pot lines". I would say yes of course but in the other hand you can use use plenty of weight to dimension your mechanical device and make it very robust. Let's imagine to replace a classic 3000 lbs passive keel by a 1500 lbs one + 0 to 3000 lbs dynamic lest, you can take a lot of the passive 1500 lbs to build in steel for example a robust hinged foil. No carbon foil necessary there, at the contrary.

So in premiminary conclusions before turning to a quantitative study : the depressor foil for dynamic ballast is actually in competition with a water ballast system with :
- disavantages : an extra drag due to the foil, an exposure to obstacles and pot lines
- adavantages : the device takes no space in the cabin, is not visible (stay fully immersed), damp the heel motion in case of wind gust.

 

Unless you can control its plane orientation, it will not work. The reasons for this I have stated in earlier posts on this thread. It will need an active mechanism to keep it parallel to the horizon. There is no way to make it do so passively. This means you are going to need a tilting mechanism of some kind, and this will probably mean push-pull rods or pull-pull cables of of some sort.

 

On a second thought it just might. Being hinged so it can tilt side to side may make all the difference. It may very well be able to orient itself to the horizon by itself. This being said, it would have to be at the bottom of a very deep keel span to be of much use. but, because it would be much lighter than a full weight ballast keel, it may come in handy for a drop-keel application.

 

Dear Sharpii2, many thanks for your interest and comments,
I am pretty sure that the foil so mounted will stay horizontal without the need of any active control system, it is based on experience with towed fishs : the restoring moment will come from the apparent weight of the foil (let'say 100 kg, as we have plenty of weight to build this foil in steel) x by the height between its center of gravity and the hinge axis (let's say 12 to 15 cm) = 12 to 15 kg.m thanks to gravity. For example with a towed fish, typically we can have a depressor foil providing a dynamic charge of 400 kg at 8 Knts, mounted on a body of total apparent weight 15 kg, of which center of gravity is about 20 cm below the pulling point >>> so a restoring moment of 15 x 0,2 = 3 Kg.m. The fish body stays perfectly horizontal, even after a bend during which it flies like a plane (due to the centrifugal force in addition to the gravity one), when the boat return to a straight route, the towed fish return to horizontal without oscillation. Anyway, a cheap small scale experience can confirm that point.
My real concern is the extra drag of the foil, + the yaw and pitch moments due to its eccentric application which can unbalance the boat. Only a fully quantitative study including all aspects can give a reliable first assessment and tool for design optimisation, I will try to begin that when I could (need free time with rested mind ...) with a dedicated spreadsheet application.

 

Towing a fish is completely different. They only need a vertical force to maintain depth. The proposed foils have to provide a moment around the CG of the boat while creating minimum drag.

 

Dear Gonzo,

Thanks for your comments,

I refer to towed fish, beyond just the mention of negative lift use, mostly to show that a quite low restoring moment thanks to gravity can be sufficient for a self maintaining horizontal foil. This restoring moment to overcome what ? : a possible dissymetry of the lift forces due to a non uniform incident flow (due to the leeway angle, due to the presence not so far of the hull), friction in the hinges when lift forces are high (so to pay attention to low friction, but technology exists for that). So I am reasonably confident on that horizontality point, but of course to be confirmed by ad hoc tests.
Your second point, moment around CG : of course yes, it is the objective of a first "proof of concept" numerical study that I expect quite complex, involving at least 4 of the 6 degrees of freedom, in running conditions + some dynamic considerations (wind gust, helm change), one potentially positive effect and 3 potential drawbacks, respectively : heel/righting moment , drag, pitch moment (foil drag will tend to raise the boat stern), yaw moment (foil drag will tend to turn upwind the boat).

 

A sailboat operates with a leeway angle and there is side force on the keel. This results in a sizable induced asymmetric loading of the horizontal wing and a rolling moment about the hinge that must be continuously reacted. The down force on the leeward panel will be increased and the down force on the windward panel will be decreased.

From both a hydrodynamic and practical perspective, it would be better to make the rotating portion in the form of a T, with ballast at the bottom of the T and the hinge near the junction. The moments on the wing will be reacted by the ballast, leading the wing to tilt to leeward. Lift on the wing will contribute to side force as well as down force, offloading the keel. Rotation of the wing will result in greater depth and reduced span loading for the side force. This will help offset the drag of the added wing area and ballast.

I doubt, however, that the drag of the assembly will be less than a conventional keel and ballast. The only thing you're gaining through using dynamic lift to pull down on the keel is not having the weight of ballast when there's not enough wind to heel the boat, because when the wing is active the displacement of the boat is equivalent to having ballasted the keel to the same force. I doubt that will be worth all the added drag.

 

A fish has foils with a horizontal axis. That is completely different from a foil on a keel where the axis is changing angles to the horizontal plane.