Crossbow fl

Discussion in 'Sailboats' started by Doug Lord, Jun 21, 2012.

  1. Doug Lord
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    Doug Lord Flight Ready

    ================
    Thanks, James! I hope I can get fullsize version done......
     
  2. Doug Lord
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    Doug Lord Flight Ready

    Some minor changes to specs in red below. The main change is the lenghtening of the ballast "wing" from 12-14'. Gives increased buoyancy and options for weight movement. May be reduced as a result of testing.


     
  3. Doug Lord
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    Doug Lord Flight Ready

    Crossbow fl--The (Ballast)Wing

    Here are some pictures of the (ballast)wing on the boat and the wing tips up close. The wing is mounted on the boat in a carbon retainer, that I'll show you shortly,and the retainer is attached to the boat with a heavy duty stainless steel seat swivel(see pix below). Trapeze wires go near to the outboard side of the wing and are attached to the wing with shock cord(and wire/line at full extension). The design of the retainer allows the wing to pivot athwartship which keeps it level when the boat is heeled 10 degrees. The retainer also allows the wing to pivot about the vertical axis which allows it to be stored in line with the boat for trailering. It also allows the weight to be moved aft by pivoting the windward side aft.
    For simplicity in building the wing itself is straight. The wing tips are shaped for maximum buoyancy placed in such a way that it helps the low side of the wing to pivot toward the mast head when the boat is at 90 degrees to facillitate righting the boat. They're also designed to be able to reduce any impact with the water at speed.
    Pivot control lines run from the aft corner of the transom to the wing.
    The wing has a single line from each side, controlled manually or electrically, that moves the wing. The weight inside the wing is controlled by a line running to the retainer via a sealed spool on each side of the wing. This allows the inside weight to move simultaneously as the wing is moved.
    The bouyancy of the wing is several times that required to float the lead ballast sealed inside. That makes it very, very difficult to capsize this boat but if it should be knocked down the crew need only move the wing to the the low side to right the boat. The wing will right the boat even with the ballast at max extension on the low side! Moving the wing down manually will be assisted by gravity moving the weight down.
    This is a unique system that ensures righting by the crew in the worst case scenario and preventing most capsizes by a combination of weight, fast movement and buoyancy.
    One critical aspect of the wing is that it will be able to move faster than a crew on a trapeze can move allowing excellent control of roll stability by the skipper. Further, the wing provides about 76% of the upwind RM and 35-50% of downwind RM with the balance made up by the DSS foils that are unique in this size range. The two working together allows the crew to sit comfortably in the center of the boat while carrying more SA than any other current "sit-in"* singlehanded sailboat anywhere. This power to carry sail assures planing off the wind-something that is simply not possible with any other "sit-in" singlehander. This will open up unheard of performance to people that are excluded now from this extraordinary aspect of sailing due to physical infirmities while maintaining a level of safety as great or greater than any other "sit-in" singlehander currently available.
    *"sit-in"= a boat where the crew sits down inside the boat and where crew movement is not required for generating righting moment.

    Pictures, L to R: 1) view from aft with wing centered, 2) wing angled as if port side was windward and crew wanted to move weight aft, 3) view from forward with wing centered, 4) view of starboard wing tip from forward(upsidedown), 5) view of starboard wingtip from aft(rightside up),6) view of starboard wing tip from above.
     

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    Last edited: Jul 13, 2012
  4. Doug Lord
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    Doug Lord Flight Ready

    Crossbow fl--DSS Foils

    Here are the DSS foils in their relative positions on the boat. They can be unplugged for transport. The foil develops about 14% of the righting moment(RM) of the boat upwind and up to, approximately, 50% of the RM downwind. They are designed to be parallel to the surface of the water with the boat at a 10 degree angle of heel, and a little over one chord below the surface.At that angle of heel ,the windward foil is clear of the water. Foil tip to foil tip is 10'.
    On this boat the foil mounts can easily be moved and "tweaked" should that be necessary.

    click:
     

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  5. ancient kayaker
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    ancient kayaker aka Terry Haines

    The seat swivel looks likeis a bar stool or lazy Susan bearing, which is designed to take a direct compression load with only a negligible cantilever force component as the ball race cannot react a tensile force. When I use them I put a bolt in the center to react any cantilever force which ten becomes a direct compression force on the ball race at the circumference.
     
  6. Doug Lord
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    Doug Lord Flight Ready

    Crossbow fl---swivel mount

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    Thanks Terry. Remember that, as the wing slides outboard, the load is taken by the trapeze wires and is reduced on the swivel. There should never be any load on the swivel but a compression load except if the wing was centered(max load on the swivel) and the boat suddenly stopped. In any case, the load on the swivel is much less than it would have been designed for. I'll discuss this in detail with Eric just to be sure he agrees.
    PS- the swivel is stainless and manufactured for use on boat seats.
     
    Last edited: Jul 15, 2012
  7. Doug Lord
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    Doug Lord Flight Ready

    Crossbow fl-DSS Foils

    Just heard from Rick-he's got the first clear coat on and will be done this week for sure:

    Pictures-Left to Right 1), actual foils, 2)-6), how they'll look on the boat-

    click-
     

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  8. Doug Lord
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    Doug Lord Flight Ready

    Crossbow fl--model vs full size weight

    I want to make the roll over test with the Crossbow fl with the wing mounted, like I did here( http://www.boatdesign.net/forums/sa...g-keel-extraordinary-innovation-30806-15.html post 219 ) with the model of the 18' Trapwing version.
    Here are the numbers:
    Displacement varies as the cube of length so:
    1) LOA full size= 14.6 ; 14.6 cubed= 3112.14
    2) LOA model= 1.92' ; 1.92 cubed= 7.08
    3) 7.08 / 3112.14= .002275
    4) Model weights should be: (fullsize weight multiplied by .002275)
    a. All up sailing weight=473lb=1.08lb=17.28oz..
    b. Wing + ballast=99lb=.23lb=3.68oz..
    ----
    Actual model weights:
    1) All up weight= 1.14lb=18.2oz ; Model is slightly heavier(18.2-17.28=.92oz=.0575lb). To see what that is full size, .0575 is multiplied by 437.96=25lb.
    Since, lb.per in. immersion equals 192lb, this means the model will float as if the full size boat was floating 1/8" low.
    2) Wing + ballast=.256lb=4.1oz.. Model wing +ballast is heavier by .42 oz.(equivalent to the full size unit being 11lb. heavy-11%)
    3) Hull weight of model is about equivalent to the fullsize hull +crew.
    ---------
    This is nearly perfect for testing the buoyancy of the wing at 90 degrees-if it works with the wing 11% heavy it will work when the weight is right. A nice bonus is that the thing will float almost exactly like the full size boat. Models this small are not ideal to scale down but this is ok for this boat. Weight is very close and ,of course, relative bouyancy is the same as fullsize.
    So, what the test will determine is how far the wing has to be immersed to right the boat from 90 degrees.
     
    Last edited: Jul 20, 2012
  9. alyne
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    alyne Junior Member

    Hi Doug
    This is a great experimental project, exciting to follow. I have a question around the DSS foil system.

    Last year I experimented using 2 Bruce style hydrofoils to provide stability on my sailing kayak. What advantages do you see the DSS system having over using 2 canted foils (like hydropter) to provide the stability....I am not talking about using foils to fly a hull, only to resist heeling moment.

    Thanks
    Andy
     
  10. Doug Lord
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    Doug Lord Flight Ready

    =======================
    Andy, the greatest advantage is that the DSS foil draws no water-it is the shallowest draft "foil assist" system I've run across. As long as the foil is one chord or more underwater it will work fine- and a side benefit compared to surface piercing foils is very little chance of ventilation. Depending how you do it, the foil can be removeable or 100% retractable so it doesn't have drag in light air. And I believe they will work in a slightly different configuration on multihulls as well.(see sketch below)
    You mentioned Hydroptere: that boat uses two surface piercing main foils to fly the boat AND to develop all the lateral resistance for the boat. DSS only provides vertical lift on the lee side to increase RM(righting moment). A boat using DSS still has to have another foil for lateral resistance.


    rough sketch of an application of a dss-like foil on an ama for foil assist with very shallow draft. Not retractable on small versions. This is for an 18' tri and a 10' ama with a 4' foil on each ama:
     

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  11. ancient kayaker
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    ancient kayaker aka Terry Haines

    Lateral resistance to leeway is still required: the Bruce foil does that as well as resisting heeling but I suspect it is not very efficient, based on my own results. On a kayak where hiking is impractical and heeling can occur very quickly the Bruce has the advantage of automatically providing the required amount of RM, properly designed that is. With the approach that Doug is taking I expect the DSS will do the same, and it can be combined with a daggerboard for adjustable draft in shoal waters.
     
  12. alyne
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    alyne Junior Member

    It's great to see new ideas being tried out like this. The concept of the DSS foil is very interesting as it is a relatively uncomplex thing to experiment with by an amateur boat builder. (not underestimating the requirements for exacting foil construction and placement) I'll watch development with interest.

    Doug, out of interest is there much rocker in your hull design? Keep the pics coming :)

    Andy
     
  13. Doug Lord
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    Doug Lord Flight Ready

    =============================
    Andy, there is 3.5" rocker from station 4.5 (just forward of midships) to the transom and about 2.5" from station 4.5 forward. Thats at max displacement with the full sailing weight. Why, just out of curiosity?
     
  14. alyne
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    alyne Junior Member

    Hi Doug

    Well, my designs have been very basic in shape up till now due to the cheap and cheerful build process I use. One day I would like to make a little more efficient hull shape and I am starting to research various aspects of design - especially underwater sections and what shape works to get a quick to plane hull in flat conditions.

    Andy
     

  15. Doug Lord
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    Doug Lord Flight Ready

    Crossbow fl----rocker

    Andy, keep in mind that this is not necessarily the ideal shape since what drives it is the building process and the placement of the DSS foils. Getting the foils low enough was not easy. Here are three pictures that will allow you to see the rocker: ( you can hold a straight edge up to the picture to see more clearly)

    click-
     

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