WINGS---New Canting Keel Solution

Rcsailing.net Technology Discussions
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Found an interesting little tidbit in the July issue of Australian Sailing: a canting keel design for a 52 footer designed by Murray,Burns and Dovell and built by Azzura. What is unique about this boat is the wings on the keel bulb similar to an IACC boat but ,in this case, designed specifically to provide lateral resistance when the boat is heeled and the keel canted to 30 degrees.
Canting keel boats generally have adopted twin fore and aft rudders(CBTF), twin side by side asymetrical daggerboards, or a single gybing daggerboard to provide lateral resistence since the canting keel strut can be a very ineffective lift producer when canted.
This new system won’t point like a CBTF system but is simpler in many respects.
For models in classes that allow canting keels(only the F100 now) the best solution appears to be CBTF and/or a gybing daggerboard.
However, a version of this system may be an important development in the Marblehead and or US One Meter Classes since both classes allow canting masts.
Canting masts cause the hull to heel thereby developing righting moment in excess of a “normal” rig.(the rig stays more or less vertical and the hull heels)
For such a system it is possible to create a ligter boat for the same sail area but the models produced so far seem to have a big drawback in that as the boat heels the keel becomes much less effective yet both boats apparently have rudders that are kept parallel to the mast. This can cause severe balance and lateral resistance problems as the boat heels. The solution may be a system similar to that discussed in the article using wings for lateral resistance not as “induced drag reducers” as is done on IACC boats.

Doug Lord
microsail.com
monofoiler.com
High technology Sailing

2

This is a re-hash of several posts made to other topics… but since Doug started this topic, I figured I would sum up all my thoughts on the matter here…

As I concieved of my canting mast US1M, I took it as given that the rudder should cant as well to keep it nearly vertical as the boat heels. Hal Robinson and Dario Valenzia both used canting rudders on their canting mast boat. But I also need something to create lateral resistance when the keel cannot because of excessive heel.

In the US1M rules, you are not allowed to have a rudder forward of the keel and you are not allowed “Moveable keels, shifting ballast, bilgeboards, tunnel hull, trim tabs, rotating mast, wing sails.”

So a traditional CBTF system is out (it requires a rudder forward of the keel). I had thought of putting a centerboard forard of the keel that would swing from side to side with the rudder, but decided that would violate the spirit of the “movable keel” clause. A canting rudder behind the keel might be another option, but if I had an appendage behind the keel, I would want it to swing up out of the way like a centerboard so I would have a hard time arguing that it was a rudder. And even though centerboards are not listed as a prohibited item, bilgeboards are. Thus I think the spirit of the rules rules out a canting centerboard.

Then I concieved of putting wings on the keel. As the boat heel over more, the keel becomes more horizontal and less able to develop lateral resistance, but wings on the keel become more vertical and more able to develop lateral resistance. THis seemed like a perfect solution.

I shared my idea with Doug. We both agreed that it would not be as effective as a full CBTF system, but since that would not be possible under the rules, it seemed like a viable alternative. A few weeks later he came across the Article mentioned above in Austrailian Sailing about the Azzura boat. This helped to validate that this idea would work.

Of course the downside to any winged keel design onn RC sized boats is drag. Generally speaking, wings on full sized boats are designed to reduce the induced drag of the keel. But since RC boats operate with very deep keels with very low span loading, they already have very low induced drag. So adding has proven very ineffective. and given the low reynolds numbers that RC keels operate at, any extra surface area is going to have a much larger drag penalty than our full sized cousins.

However, my idea was not to use the wings for induced drag reduction, but rather for lateral resistance when heeled. As such, I think that the wings have merit, even for RC sized boats.

The wings would only come into play at higher wind speeds when the mast was at full cant and the hull is at maximum heel (60 or 70 degrees). Therfore, they could be quite small as they would not need to operate at lower hull speeds. Therefore, I can keep the extra surface area to a minimum. And since I am not relying on the keel to produce any lift at these extreme heel angles, I think I could cut some area out of the keel so that the total wetted surface area would be about the same as other US1Ms.

The other benefits of the system are that it is completely passive and requires no extra holes in the hull or fancy actuation systems.

Of course all this is good in theory, but we will have to wait and see how it pans out in practice. I plan on making the wings removable. They may be part of a keel bulb such that I can ]replace the winged bulb with a plain bulb. This will all be part of the development process for this boat.

  • Will

Will Gorgen

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Will: Again, I think its great that you plan on trying to put some of your ideas into practice. I think in physics “there is no such thing as a free lunch” and wings on the keel will only give you additional lateral area equal to the area in the fins and will not solve the balance problems inherent in canting rigs. (FYI, the issue isn’t just lateral area, its also that the center of balance of the boat shifts as the rig cants). However, experimentation is the way questions are answered, and I can only admire your determination. As to the fact you discussed your ideas about foils with Doug Lord, note that Doug has hired an expert (Dave Hollom) to design foils for him, maybe you can get Dave’s opinions on your ideas. Also, you might think about attending some of the bigger US1M races and get a sense of the current state of the art in the class and talk to some of the sailors and designers in the class before embarking on such a major project.

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Hey Roy,

The balance of the boat shifts as the boat heels. As the center of effort of the sails moves laterally, it causes the boat to want to head up. I’m sure you have experienced the massive windward helm that occurs when the boat is heeled over really far. This forces most boat designers into a comprimise where they adjust the position of the rig and/or appendages to compensate. Thus, most boats are balanced with a slight amount of lee helm at 0 heel (although you rarely feel it because when you have no heel, you generally have very light wind and thus very small sail forces to contend with).

With a canting ballast boat you generally sail the boat much closer to zero heel and thus you want to adjust the balance of the boat to remove the small lee helm. Because the boat does not heel as much when sailing, you generally do not have the shift in balance from lee helm to windward helm associated with increased wind strength. I experienced this firt hand on my Schock 40 ride. There was a lot less heel and virtually no windward helm associated with puffs. It was a joy to drive.

With my canting rig boat, the hull itself will heel alot, but if you think of the mast heel, it will be nearly zero most of the time (until the cant maxes out). Everyone who I have talked to who has built a canting rig boat has told me that as long as you have the rig in the right position, the balance of the boat is much better than a fixed rig boat - until the keel starts to loose its effectiveness. This is the “until” that I am trying to avoid.

I agree that there is no free lunch. If I heel my boat really far in order to use my ballast for righting moment, then I loose the effectiveness of the keel for lateral resistance. So I have to get that back somehow. Assuming I do it with wings, I will be paying a drag penalty. I am hoping that the increased drag will be less than the benefit of the extra righting moment in terms of early planing and overall speed.

I would love to chat with some of the top designers in the class. I have only chatted at length with a few RC boat designers (John Elmaleh, Swede Johnson, and Doug Lord). I have had some small discussions with a few others but not on this subject. I have talked to a few of the top sailors in the class, but not many.

I may never attend a class regatta with my US1M. My Fairwind will be my primary boat for the forseeable future (I’m the class secretary after all), and with 2 small kids at home, I do not have time to pursue this sport as much as I would like so campaigning more than one boat is out of the question. When I do get more time I will most likely get back into fullsized sailing instead of RC (no offense).

If I just wanted a fast US1M, I would probably just buy a good boat from an established builder. I’m not that interested in pursuing any marginal improvements in the state of art. If I am going to make a big time committment to building a boat, I’d like to try something radical. It may not work and I am fully prepared for that. I’m not interested in scratch building a radical hull - the learning curve is too steep for that. So I am going to try a radical mechanical change to the boat. I, like most of the sailing community, have found this new realm of canting ballast enticing. I think that it is worth pursuing. We’ll see…

Will Gorgen

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From the November issue of Seahorse magazine, page 16 & 18: “Dovell(designer of Bondi Tram, the boat mentioned in the first post under this topic), who is part of the Murray, Burns and Dovell group has gone away from the CBTF configuration, instead fitting the keel bulb with remarkably wide foils. They are so wide ,in fact, that under sail the windward foil tip can protrude above the waters surface when the keel is fuly canted(yes, the tips are painted bright orange so that they can easily be seen). The foils are shaped to provide lift to windward just as the forward rudder does with a CBTF boat. The new boat’s initial sailing trials on Pittwater,north of Sydney, are reported to have been returning encouraging results.
Dovell, who is part of the team behind Tom Blackaller’s radical twin-rudder America’s Cup contender USA in 1987, was originally planning a canting rig for the boat. But the keel-foil concept showed all the signs of being more efficient and certainly less complex when it came to manoeuvres.”

Doug Lord
microsail.com
monofoiler.com
High Technology Sailing/Racing

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That is the missing design element I needed for my US1M canting mast - I need to paint my wings orange!!!

But seriously, I think this “invention” may be the poor man’s solution to the lateral stability problem posed by canting ballast (CBTF being the rich mans solution). In my case, it is the rule compliant solution as the US1M rules would not allow for a forward rudder. For others not willing to pay a licensing fee to CBTF inc. this may pose an acceptable comprimise…

I don’t think the US1M needs such wide foils. I think the drag disadvantage of too much wetted surface is a bigger concern for model boats (compared to full sized counterparts). But I do think that the addition of some small wings will allow for enough added lteral resistance to more than make up for their added drag… Of course the proof will be i the pudding and I plan to experiment with both winged and non-winged keels…

  • Will

Will Gorgen