90°-110° Canting Keel

Discussion in 'Stability' started by Doug Lord, Nov 4, 2006.

  1. Doug Lord

    Doug Lord Guest

    I've got a concept for a canting keel for a specific application on a foiler and I'd like to get your thoughts on the idea. It may be tried on a model. Please consider the idea and/or solutions that would accomplish the same thing better than what I've come up with even if you don't think a keelboat foiler is possible. This is about unique canting keel solutions-not foilers.
    IDEAL Solution: on any kind of keelboat foiler it will be essential that the boat is selfrighting or rightable by moving the keel. It is also ideal that all the weight in the keel bulb be used as righting moment at the max extension of the strut HORIZONTALLY. It would be ideal as well if the keel could be canted to one side completely clear of the water with the boat OFF foils to allow for faster takeoffs. In other words, the keel would cant 90° to 110° to one side. So far, the best way I've come up with to accomplish this is to design a drum that exactly matches the semicircular underwater section of the foiler hull. The topsides would be "normal" from approximately the waterline up except for a hinged lower section that folds up as the keel cants to max.. The section of hull where the rotating section is would have to be engineered carefully so that, in essence, the whole bottom plus keel strut rotates freely and the required bending strength of the hull is not compromised.
    There are a number of ways that the system could be hooked up to the power required to move it and I'm not too concerned about that. This section of the hull would constitute a watertight bulkhead as well and would probably only be considered on a racing foiler keelboat.
    It solves the problem of the drag of the keel strut before takeoff and it solves the problem of a "normal" 55° canting keel strut/bulb hitting the water at high speed.The only reason this canting strut is on the boat in the first place is to make it rightable from a capsize or pitchpole.
    So,what do you think? All comments appreciated...
  2. marshmat
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    marshmat Senior Member

    Doable; an engineering challenge, but doable. You'd be restricted to a cylindrical hull section at the keel, but that won't matter once the hull is up on foils. Take a look at the bearings of a Dobsonian-mounted telescope for inspiration on how the rotating drum would bear against the notched hull surface behind it; those guys have really refined the art of full-contact bearing surfaces. I'm not sure if I'm reading you right on this, Doug (hell, I'm never sure if I'm reading you right), but I think such a thing is at least worthy of a napkin sketch or two. I'll give it a bit more thought.
  3. yipster
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    yipster designer

    guess you can do the same by water ballasting a canting air bulb
    i'm now reformed by Juan K on mono keels :D
  4. Doug Lord

    Doug Lord Guest

    Juan K

    Geez,Yipster- you and Juan K may have come up with something!
    For the type of boat I'm considering the ballast in the canting keel is only there in case it is needed to right the boat and for stability off the foils. To use the system I have been considering(on foils) the keel would have to be moved each tack and gybe -at least 180°. But if the "bulb" was made bigger so that it would hold the same volume of water as the lead previously required then the thing could be "stored" tucked up under the racks on one side or the other! To use it the bulb/fin could be manually cranked down and then pumped up until the boat rights then emptied and stored again. Got to think more about this but thanks for the inspiration! Problem is then the thing wouldn't be a keelboat and would require "buoyancy pods" makng it a "rightable" trimaran, I guess? Even if it couldn't be called a keelboat it would be one hell of a trimaran foiler. Bears some thought....
    Update: rough calcs on the "air bulb" righting system show that adding the large "bulb tank", strut, pivot system and buoyancy pods(ama's) plus pumping system produce only a very small reduction in weight over the lead bulb based system. And, again, the boat using it could not be defined as a keelboat which is the main point of the system in the first post.
  5. Doug Lord

    Doug Lord Guest

    90° Dual Canting Keel

    A pix on SA was posted showing a smaller version of this design. Thanks to Vega we now know the designer is Martin Defline.

    ---defline, voilier de course
    Address:http://www.defline.com/architecte-naval/gamme/defline/course.htm Changed:6:15 AM on Wednesday, March 8, 2006

    ---50 footer(I think)
    Address:http://www.boatdesign.net/forums/attachment.php?attachmentid=10404&d=1164157475 Changed:8:04 PM on Tuesday, November 21, 2006
  6. SuperPiper
    Joined: Jan 2003
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    SuperPiper Men With Little Boats . .

    Air Bulb For Self-Righting Only

    If the air bulb is ONLY to self-right the boat, then why not strap my Mustang inflating life vest to the masthead?
  7. Doug Lord

    Doug Lord Guest

    "air bulb"

    Great idea! Just don't forget to fill the "air bulb" with water prior to trying to right the boat......
    For the bulb tank(airbulb) to have a chance of working your life vest or a suitable permanent type of masthead flotation would have to be there before the incident. With no masthead flotation the idea has no chance; if the rig fails no chance.
    The 90+° "drum" type canting keel on a semicircular hull also requires masthead flotation since ,if the keel is "stored" up under the racks at the time of an incident it would do no good until it was cranked "down".
  8. Willallison
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    Willallison Senior Member

    Not quite following your logic there Doug. A self-inflating system, similar to those incorporated on many RIB's would surely work. Granted, not if the mast fails. The only downsides I can see is 1. the added weight aloft and 2. even deflated they are quite cumbersome.
    How you go about storing the device once you're right way up is another matter...!
  9. Doug Lord

    Doug Lord Guest

    air bulb/tank

    Will, in the third post Yipster brought up Juan k's comment (see the first post of the "Canting keels and multihulls" thread under "multihulls")
    about having air in a canting keel bulb and therefore having a multihull. I thought the comment was tongue in cheek but that's another story.
    Anyway, when Yipster brought that up I considered the idea seriously for a minute -not in the way Juan K said it or meant it but from the standpoint of having a canting strut with a tank not a bulb on the bottom that when canted 90-110° was stored out of the way on something like a "trimaran" bi-foiler-up under the racks. The idea I considered was if such a boat pitchpoled or capsized it would be designed with masthead flotation so that it would go just so far ,then the canting tank(using the mounting/operational system described in the first post) would be deployed and filled with water to right the boat.
    I'm not sure whether it is a viable idea or not but IF it was to be tried it would require masthead flotation and a rig strong enough to take a highspeed capsize/pitchpole without failing.
    The masthead flotation could be a version of a "football" like on a Hobie Wave, flotation in the top part of the sail(like on some US scows), or some kind of auto inflate thing that would probably be my last choice.
    The "canting tank" righting system would require the same type of system described for a canting keel in post #1 and wouldn't work otherwise.And again, it would require masthead flotation.
    I did some preliminary weight calcs for this system on a "trimaran bifoiler" vs the canting keel on a "normal" monofoiler(see the 60' Moth thread and or the Sportboat thread under sailboats)-there is not much difference in weight between the two..
    This thread has digressed from my original question/ idea(in the first post) on the canting system to allow a whole lot of cant that would allow the keel to be totally out of the water when flying.
    Did I clear up anything?
  10. Vega
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    Vega Senior Member

    I have to say that I had serious doubts about the possibility of an ocean foiled monohull. The big problem is that you need a boat that heels very little for the thing to work. On small dinghies like the Moth, the weight of the skipper in trapeze is huge, considering the total weight of the boat and provides a big rightening moment. I was not seeing any possibility of having a system that could provide identical RM on a big boat till I have seen this boat:


    Then, I have imagined that such kind of a boat with different and longer arms, not with floaters, but with profiled big bulbs, could be the solution. The bulbs would only touch the water at 10º or 15º heel and one of them would be full of water, the other empty. The one full of water would provide a huge RM (long arm) and the empty one touching occasionally on the water would help to maintain the boat stable. Like the long stick that an acrobat carries when walking on a string.
    I believe that a canting keel would bring too much disruption to the system, and that a long bulbed keel with a relatively small bulb would be enough.

    That boat would not even be impractical, because with the two bulbs emptied, both arms and bulbs could be easily rotated up, towards the mast, giving the boat a normal beam.

    What do you think?
  11. Tim B
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    Tim B Senior Member

    Isn't sin(110)<1? we all know sin(90)=1 and you want to keep the bulb as far from the CG as possible which means canting at 90 degrees upright and 0 degrees when the boat is on it's side. so why bother canting further than 90 degrees?

    Tim B.
  12. Doug Lord

    Doug Lord Guest

    power to carry sail

    Vega, have you seen Sean Langmans version?
    Sailing Anarchy InnerViews Sean Langman 2005
    Address:http://www.sailinganarchy.com/innerview/2005/langman.htm Changed:10:02 PM on Sunday, October 23, 2005
    Also, if you go to Sailing Anarchy archives search and type in Julian Bethwaite an article will come up about his "Maxi Skiff" in which he says they planned on using on-deck movable ballast.
    My opinion is that their two boats and your suggetion(as understand it) would be called "multihulls" by many. Buoyancy pods don't have to be hull shaped to be effective.... I believe that what they are trying to do could be done on a boat that is clearly a monohull, is self-righting AND can foil. The idea of a 100° canting keel(1st post) was to get it as far to windward as possible AND out of the water. The disadvantage is that after a pitchpole the keel would have to be moved to right the boat but that's true on some Open 60's I think.
    Such a boat 60' LOA could be close to as fast or faster than an ORMA tri but it must be designed(in my opinion) so that there is no question that it is a monohull...
    If you haven't seen this and feel like wading thru some numbers here is a preliminary proposal for the boat I describe above:
    60' Moth-A Preliminary Detailed Design Exploration - Boat Design Forums
    And you already know about my X18T which is designed to explore some of the issues raised by this type of boat.
    Last edited by a moderator: Dec 17, 2006
  13. Vega
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    Vega Senior Member

    I am not talking of a canting keel, but I want the bulb higher to allow the boat some heel without the bulb touching the water. Remember we are talking of a foiler boat, a flying boat and if the bulb touches the water it will produce drag and a small rotating moment and that will produce a disequilibrium.
  14. Vega
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    Vega Senior Member

    Yes, I know about Sean's design.

    What I was thinking was not in buoyancy pods. I believe that in those boats the pods will touch the water almost all time (5º of heel?) and in this case it is legitimate to call it a trimaran. What I was proposing was a boat that in normal circumstances would not touch the water except with the hull. There is no buoyancy pods, just a system of water ballast were it can give Max RM and that is far away of the CG.

  15. Doug Lord

    Doug Lord Guest

    110° Canting Keel

    Tim, the reason for 110° is so that the fin/bulb will fold up parallel to the underside of the racks. This is important since the boat would be designed to sail heeled to weather upwind like a Moth.
    Vega, I see what you mean though I'm not sure I understand your system completely. The system on my 60' monofoiler uses a 110° canting keel and on-deck sliding water ballast-similar in concept to the system planned for Bethwaites Maxi Skiff. Sounds like your system would accomplish the same purpose. It is this capability for mammoth Righting Moment that sets these big boats apart from all current monohulls and allows a monohull to seriously threaten the dominance of multihulls speed wise-with the added benefit of selfrighting....
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