Cheap And Simple Hi-Tech Keel?

Discussion in 'Boat Design' started by Wynand N, May 21, 2005.

  1. Wynand N
    Joined: Oct 2004
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    Location: South Africa

    Wynand N Retired Steelboatbuilder

    I'm toying with this idea for quite awhile now.
    My aim is to develop a keel with minimum losses that is simple and easy to fabricate. Because I mainly deals with steel designs, the search for an effective keel is made easier with the custom ability of the material to form, cut and bend easily without expensive tooling.

    Most keels loses lift due to the (significant) tip vortices created by "leaks" of air from the high pressure side of keel to the low pressure side - the amount influenced by aspect ratio. The hull acts as an end plate at the keel root to contain the flow at the top but the bottom has no "aid" to contain the flow on the keel and to prevent the high pressure to escape to the low pressure side.

    My idea is to make the keel sole much larger than the bottom of the keel by aboat 120mm (5 inches) on each side. This starts flash with the leading edge of the keel - not to catch lines, grass, etc on keel leading edge - tapering out fast to the the 120mm past the keel on both sides. (sort of simplified wing)
    These "wings" carries constantly along the keel side and come together about 150mm (6 inches) aft of the keel's trailing edge in a pointed fashion.
    The idea is to supply an end plate at the keel bottom to contain the flow on the high pressure side of the keel.
    This will/should bring about that no flow moves up or down the lenght of the keel and thereby in effect creates an infinite aspect ratio, with no losses at the root (hull side) and the tip.

    A bonus of this arrangement is that quite a few kilo's can be placed at the very bottom of the keel with a thick keel sole. I believe that the gains of this keel should overcome any induced drag and friction caused by the "wings"
    Attached is a rough pencil sketch showing the endplate.

    Let the jury speak out.....

    Attached Files:

  2. yago
    Joined: Aug 2004
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    Location: Budapest Hungary

    yago __

    Wynand, my friend Gerard Chaigne has designed and built some keels like that many years ago in France. Problem is that not having identical boats to compare to that remained very much in the philosophical area ;-) today, with proper software it should be possible to research that.

    These keels were easy to build, upright onto the plate, because you could weld the hell out of it witout any fear of distortion.

    I believe it can work, and you might even shape/taper the edges if the the plate is thick enough to get something a bit more elegant or effective.

    On my last boat the keel sole (without wings) was 10 cm thick. It was well placed weight and I never even botherd to paint underneath.

  3. cyclops
    Joined: Feb 2005
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    Location: usa

    cyclops Senior Member

    I am not a naval designer. BUUT. Your problem is sounding exactly like leakage or slippage on aircraft Delta Wings. The cure is to mount " vertical fences of the same general shape as the wings airfoil along the wing and 1 at the very end of the wing. They prevent Vortice losses and raise the speeds, control and mileage of the wing. If this sounds like what your after I can scan and e-mail some aircraft wings which show the size and shape layouts. It is a very effective way to greater efficiency with the present keel- wing- shapes. Your boats fly on 1/2 a wing, same logic should work with denser air- water- and slower speeds.
  4. Sean Herron
    Joined: May 2004
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    Location: Richmond, BC, CA.

    Sean Herron Senior Member



    Asymetrical bilge or twin keels with a bit of toe in - and angled out at 15 degrees or so with end plates...

    While heeled one is pulling you upwind and the high keel is trying to pull the hull upright while cancelling the bow wave...


    I want to build a proto...

    The British Redfox Vision was (is) a great thing - but with center board type thingees...

  5. Wynand N
    Joined: Oct 2004
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    Location: South Africa

    Wynand N Retired Steelboatbuilder

    Gerd and others,

    Thanks for the info.
    As for the 100mm thick sole I would disagree with you Gerd. To stay in the designed draft, the 100mm keelsole will take out 100mm keel volume at the keel bottom where it matters most. I would rather have the last bit of the keel filled with lead rather than steel.
    My idea of the endplate/sole is to use a plate of about 12-16mm (1/2 - 5/8 inch) to limited unwanted surface drag. This simple "wings" should also damped rolling motion in a seaway.

    This arrangement may not be so impressive looking and technically advanced as say on an America's Cup racer's keel, but is simple and should do the job at hand.

    There is an old saying; "any fool can be complicated, but it takes a clever man to be simple" ;) :confused:

    BTW Sean, this arrangement of keel is for a single finner.........
    Last edited: May 22, 2005
  6. yago
    Joined: Aug 2004
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    yago __

    - sure, if you have lead... ;-) on my last boat I was given a 2.5 tons of steel blocks, cutoffs, that stacked tight and nice and gave me good density at an unbeatable price.

  7. Huw
    Joined: May 2005
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    Location: England

    Huw New Member

    You will get a performance increase by useing endplates, but like you said you have to balance this with the profile drag - I don't have any data at the moment, but people were useing endplates for testing from around 1910 and they never made it onto full size aeroplanes.

    I disagree that you need what Cyclops said, wing fences work by preventing spanwise thickening of the boundary layer and by creating a vortex that re-energises the boundary layer, this isn't your problem

    The last time I used endplates they were about 4" overhang around a 8-12" aerofoil, you should also extend the plate upstream and downstream.

    The reason that EP are not used on aircraft is that the forces due to high speed flight would break them or need them to be strong and heavy. I think you should try it on your keel anyway, on a cruising yacht there will probably be little to be lost or gained.

  8. Raggi_Thor
    Joined: Jan 2004
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    Location: Trondheim, NORWAY

    Raggi_Thor Nav.arch/Designer/Builder

  9. SeaDrive
    Joined: Feb 2004
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    Location: Connecticut

    SeaDrive Senior Member

    There are many boats with keels of similar design in my local boatyard, the difference being that instead of a flat end-plate, there is a bulb squashed down to a flat to a thickness of 2 or 3 inches. That gives the end plate effect you are seeking along with a substantial amount of deep ballast.

  10. JimCooper
    Joined: Feb 2005
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    JimCooper Junior Member

    On the advice of a engineer I added endplates on a full keel slack bilged 50 foot yacht that rolled gunnel to gunnel in heavy weahter. A similar vessel had tried short bilge keels but they had made little difference

    We added (a metric size) 50mm by 8mm bar simply by welding to eitherside of the keel foot for about 15 feet. It reduced both the roll period and the magnitude of the roll so much it was a different boat. I also swear it went to windward far better , but hard to be objective there. As for drag we lost little or no speed, I severley bent one of these on a grounding and had to cut it out and re attach, but no big deal.

    Vessel was a riveted steel 1930's german yacht that I had in the 70's the next owners cut the endplates off again , but they never used her in the north sea.

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