MX Nova Winged Keelboat Concept

The further development of the concept was trialled in the USA years ago. If I recall correctly it included very long wings of variable angle of attack, so the leeward wing could develop positive lift and the windward one negative lift. I didn't hear of it apart from one Sailing World article.

In the real world such a concept would be problematic because of the potential cost of the "hinges" and controls, the fouling, the weed catching, and of course much of the time when you really need stability is when you are going slow, punching upwind into a chop or when trying to recover from a windshift or broach.

It's a little bit like the '80s 18 Foot Skiffs with 30' wingspans. Yes, they were fast in ideal conditions of open water with little traffic and steady winds. As soon as they returned to real world sailing, they were impractical.

 

Dear all, thanks to your comments, it sounds like an hopeless research ... , nevertheless, it is my pleasure to continue to dig the idea a bit more.
My present message is on line with tspeer, you made a good point on the importance of the leeway forces and the T shape proposal in order to maximise the restoring moment which could maintain the foil close to the horizontal (If I well understand your arguments).
To ease the dialogue, I translate your proposal in small sketches here attached (T1 solution) and also added two other solutions, called T2 and R1 (a solution with a rotule), tentatives to deal correctly with the leeway issue. My arguments are in the document.

 

Tom,
Exactly, all true, but I still think there is some value to be found. One difference might be that I am planing on the keel Cl increasing automatically with heel angle so the induced drag would drop when you don't need the righting. I don't expect to make a boat that is just faster or much faster. If you just want a faster boat the foils should be lifting up, not down -like Q23. What I see in this is the potential for a very rewarding ulralight keel boat that is easy to rate, easy to trailer, motors fast and efficient, and behaves better short handed and in heavy weather than conventional ultralight sport boats (as long as you keep the speed up).

I am struggling trying to quantify the hydrodynamic interaction between the keel and the ballast wings. I am trying to build a spreadsheet of the keel forces. My best guess is that the keel will go toward an endplate condition and all the pressure distribution effects will push out onto the keel wings. Can you help me at least come up with some bounds high and low? If you have any Rudder T-foil in negative lift CFD info it would be a great help.

 

Ct,
I would greatly appreciate anything you could do to help me track this down.

Thanks!

 

Correction of my first sentence here above : I wanted to say "thanks for your comments" and not "thanks to your comments", sorry for my bad English that makes me do this kind of unfortunate misinterpretations. I do appreciate your comments and suggestions.

 

The main advantage I encountered with wing keels was that the heave (vertical movement), roll and pitch were greatly reduced. This is from sailing on the same hull design with conventional and wing keel. (on a Sadler)

 

It seems to me that a T foil on the bottom of the keel is perhaps the least efficient method of acquiring additional righting moment, since the force vector is only in the ideal direction when you don't need any RM (i.e. the boat is upright).

Consider the extreme when the boat is capsized and the keel is horizontal. In this condition, if the foil produces any force at all beyond it's own weight, it will be providing zero RM.

RM should be provided at 90° to the keel, always. And the best place to generate the force is at the very tip so it has the greatest leverage. So rotate the foil 90° to align it with the keel. Now RM will be provided purely as a function of the amount of lift being generated by the foil and regardless of the heel of the boat.

It might tend to act a bit like a rudder though, so it needs to be in the right place.

I think if you follow the idea through, you end up with "moustache" foils sticking out the side, or a canting keel with a flap just above the bulb (or maybe a twistable canter).

 

Dear Gonzo and Ozfred, many thanks for your comments.

The idea is to compare this solution with either water ballast system or extra crew sit windward solutions to boost the RM (proven solutions despite the extra displacement), and with a potential drawback to quantify : the extra drag of the device itself. But anyway to keep a passive RMo sufficient to deal with the capsize issue and the tack change one when the boat has to recover its full speed.

I see 3 items to deal with : an efficient design of the device, this extra drag consequences (+ yaw and pitch moments ones), the best efficiency window and boat design to take profit of the formula : for displacement hull classic/peaceful sailing with its limitation to Froude 0,4 ? , or for more speedy boat ?

 

To be clear to the forum, Dolfiman and I are considering only designs with a hinge that leaves the keel bulb wings roughly horizontal -not the original post we all agree would do no good. The idea is to replace a significant portion of the static ballast with dynamic 'lift'. This lift is proportional to the square of the velocity so I look for value is fast keel boats. The dynamic lift costs us induced drag, so my intent is to design the keel wing to only lift when the boat is heeled and pulling downward on the keel tip would offer valuable righting. This righting need not be limited to replacing the weight we pulled out of the bulb. It doesn't need to always pull downward. Down wind it could take the weight of the keel to zero or less. With the keel able to lift, aft end of the hull might have less need for beam to aid planing. With dynamic ballast the hull might need less form stability.

About induced drag; we are lifting against fluid in two directions. The conventional keel lift horizontal would have an induced drag corresponding to it's AR and geometry -we have an accurate estimate. The horizontal foil has an induced drag based on it's AR and geometry -I can figure that. Put them together and I am grasping for answers. The best case would be for the two to act together -take the resultant lift of the two added and figure a combined induced drag based on the larger AR (perp to the lift) of the two foils together -with some correction for the choppy lift profile. The worst case would be calculating separate induced drags for the windward and leeward sides based on their respective AR and lift profiles. If anyone has some T foil CFD we could use it.

I know these forums are stacked with people that think faster=better and getting righting from lifting leeward is faster than pulling down windward -but that was also true with buoyancy, and look at the ratio of monohulls to multihulls over the past century. Clearly there are more values than speed. There is a very different view from the eyes of investors -TAM (total addressable market), and value proposition. With that view in mind this dynamic ballast deserves investigation, and I am very impressed with Dolfiman's capabilities.

Canting keels are another opportunity. New foilers appear to have just taken over the box rule classes and made the rest of the fleet obsolete. If the old boats can pass the capsize tests with less ballast then dynamic keels might put old boats back in the hunt for the win. The DB foil might be pulling down, but it is farther from the center of buoyancy for more leverage and operating at depth for greater efficiency.