Horizontal Keel

Discussion in 'Stability' started by adbert, Feb 12, 2009.

  1. adbert
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    adbert Junior Member

    There must be something wrong with the idea of 'horizontal keel' that's why I haven't seen much use of it. Honestly, I don't know what's called. I just call it 'horizontal keel'. Let me explain.

    Instead of having a full keel or a deep keel on the hull, can you see anything wrong with having sort of a keel along the sides of the yacht? Like having a tail fin of the plan along the sides of the yatch. Of course, they don't need to be wide, probably a foot wide that run above the water line. Pretty sure they can contribute to the stability of the yacht as well. The yacht now can easily beach.

    What I mean is instead of having deep keel, the yacht can now have shorter keel and horizontal keel. Hence, the yacht can be anchored in shallower waters.
     
  2. daiquiri
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    daiquiri Engineering and Design

    That would be kind of fixed-keel version of canting keel yachts, I presume?

    Then why not augmenting a bit the volume of keels, making them hollow and obtaining... a trimaran? ;)
     
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  3. edneu
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    edneu Junior Member

    Are you referring to a sort of bilge keel arrangement, like the kind popular in the UK?
     
  4. adbert
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    adbert Junior Member

    I don't know exactly the name or terminology for them. This type of keel commonly used in East Asian fish boats. I've seen some yachts in Australia have them too (not common though). I'm trying to find a sample photo of a yacht that has them to show you all.
     
  5. Ad Hoc
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    Ad Hoc Naval Architect

    the reason for them would be...?????
     
  6. robherc
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    robherc Designer/Hobbyist

    I think you could add a 3in (7.5cm) wide plate to the belly of a boat with any form of "V" hull, or rounded hull, and be able to use the entire submersed hull as a full-length keel, BUT, that wouldn't give you any roll stability.
    As far as using them for roll stability & righting moment, I'm going to agree with daquiri here...just make a "real" trimaran, instead of trying to imitate the effect.
     
  7. adbert
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    adbert Junior Member

    Damn when you try to find something, you'll never find it. Anyway, they look like wing keel (see attached photo). Instead of having the 'wing' on the keel itself, this 'wing' should run along both sides of the yacht in full length above the waterline.

    I don't know if they contribute the the stability of the yacht at all. Combine with the keel, the depth of the keel can be shorten. Hence, the yacht can sail through shallow waters. This design is not new. Don't know why this design is not used widely. Can you think of a fault for it?

    [​IMG]
     
  8. PAR
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    PAR Yacht Designer/Builder

    The function of the vertical appendage is to present enough area to resist leeward slip and create lift to windward. A horizontal configuration wouldn't offer much lateral area, so leeward skidding would be pronounced. Short fins also don't generate as much lift, so their effectiveness upwind would be limited as well.

    On some shallow draft boats an extended chine is employed (bilge runners). These work to a limited degree and would be just as you've described, a horizontal fin. They're only effective on hull shapes that naturally have a fair amount of lateral area (like slab sided, deep bellied Bolger boxes), at certain S/L ratios and decidedly are at a disadvantage compared to the same boat equipped with a vertical appendage.

    In shoal draft craft where you can accept the limitations of the configuration, with it's benefits, then it's an option. Most aren't willing to give up so much of their performance potential for this engagement, even if it means no board case, better beaching ability, etc. To some, particularly in small craft, the space gained with the board case removed is a God send and worth the draw backs. Leeboards can offer the same benefits as these horizontal fins, but without the performance draw backs.

    A more in-depth discussion can be found here: http://www.woodworkforums.ubeaut.com.au/showthread.php?t=51280
     
  9. robherc
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    robherc Designer/Hobbyist

    Actually, I mis-spoke there. On a significant "V" hull, you could get away with what I described, but on a milder "V" or a round-bilge, you'd still need at least a 2"-3" vertical plate to mount the horizontal plate on for it to be very effective at all (imagine it as an "I" beam with the top flange cut off). This (horizontal plate on a 3" deep keel) is the configuration I'm going to be experimenting with on my 22.5' sleep-inside-the-hulls beach cruising cat (NOT intended to be a high performance craft). If anyone's interested, I'll keep you updated on how it goes.

    @Par,
    Thanks, as always, you're quite informative.
     
  10. adbert
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    adbert Junior Member

    Thanks all for you explanation. I didn't know the physics behind it. I knew there must be some weaknesses but wasn't sure what.

    I'm planning to cruise around the south pacific in the future. I've been thinking of getting a full keel yacht for stability of long range cruise. How's the full length keel compared with other keels for long range cruise?
     
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  11. robherc
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    robherc Designer/Hobbyist

    Oh boy, I think I'll sit the ensuing debate between the full keel & fin keel crowds out on that one....NO BLOODSHED PLEASE GUYS!

    (My own opinion: It basically comes down to personal preference....each style has its own merits, and its own flaws...choose the one that YOU will work best with)
     
  12. Doug Lord

    Doug Lord Guest

    ----------------------
    See this thread under "Sailboats" for a very unique design by a top designer that features ballast that moves horizontally under a large wing off a fairly short fin: http://www.boatdesign.net/forums/sailboats/green-cruiser-50-a-26036.html
    Commentary by the designer in the thread......
     
  13. Chris Ostlind

    Chris Ostlind Previous Member

    It doesn't really move horizontally, Doug. Please take another look at the actual arrangement of the fins. Down and away from the hull surface is not horizontal.
     
  14. robherc
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    robherc Designer/Hobbyist

    Chris, I think the intent is for the fin that it's moving out on to be approximately level (due to heel) when the bulb is shifted. At least that was my take on the designer's description of it. Being a multihull guy myself, I wasn't paying THAT close of attention though...merely an interesting intellectual topic to me. ;)
     

  15. Chris Ostlind

    Chris Ostlind Previous Member

    Well, yes, of course, in one very specific angle of heel, it just might be considered as traveling in the horizontal plane.

    To get to that angle, which is probably very close to the operational max heel of the boat while under sail, the boat will be giving away a lot of its potential righting moment with the bulb not already at its max movement. So, it would seem to me that the bulb will be moved first, the main and jib sheeted hard and then the boat heels until the windward appendage is near to horizontal.

    If there is a specific bulb jockey on the boat, then it might be done simultaneously. It could even be designed to use an auto-slide function in the electrics, or hydraulics, whichever moves the bulb, and that would coordinate the movement rather than a crew person. Still, that method would probably not move the bulb horizontally until it is at its very limit of travel.

    So, technically it is feasible, but from the sailing I've done, it doesn't look likely.

    Now, if my eyes are fooling me and the fin arrray is actually horizontal as built, rather than angled downwards at something like a 40-45 degree inclination, the bulb could be going horizontal all the time unless the boat is heeled, which is very nearly all the time when sailing. Perhaps Davide can clarify that point.
     
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