sail aerodynamics

Discussion in 'Hydrodynamics and Aerodynamics' started by Guest, Mar 21, 2002.

  1. Stephen Ditmore
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    Stephen Ditmore Senior Member

    I'm pretty sure you are right that there is some interactive effect. I think there was an attempt to collect data with respect to this on the Pride of Baltimore II, which may have been presented at one of the Chesapeake Sailing Yacht Symposia. I expect North Sails and Doyle have done this sort of study on ketches, etc.
     
  2. Mikko Brummer
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    Mikko Brummer Senior Member

    I think you are mixing apparent wind and local flow. Apparent wind is apparent wind as defined, but local flow can be very different - inside the cabin, local flow would be nil, for instance.

    So yes, you can place your mast so that it is in a more favorable flow, both when it comes to direction or wind speed. In a regular sloop rig, the mast is on the windward side of the genoa leech, where the flow is more in line with the mast and additionally also slowed down.
     
  3. philSweet
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    philSweet Senior Member

    Working against this whole idea is the mainsail, the effect of which is to do the exact opposite and updraft the nearfield flow near the mast. So as Mikko implied, you simply need a more sophisticated approach to near-field flow to draw any conclusions about how the flow around a mast is going to pan out. The stagnation point on the mast may get wrapped way around to the back of the mast, and the air flow forward and around the front and down though the slot, even when pointing high.
     
  4. daiquiri
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    daiquiri Engineering and Design

    The splitter-plate effect I was referring to in the thread http://www.boatdesign.net/forums/sa...ff-naked-mast-drag-myth-48927.html#post664222 was a reply to a generic claim in a previous post that a mast with a sail behind it will necessarily have a higher drag than a bare mast. The splitter-plate example shows that the said claim is not necessarily true, or at least not for all possible combinations of mast/plate size ratios.
    Mikko Brummer's CFD results show it IMO in an even more effective way: http://www.boatdesign.net/forums/sa...-naked-mast-drag-myth-48927-3.html#post664718

    That being said, I would rather like to see a sketch of your idea, Brian, before ruling it out. A splitter plate could (or could not) reduce drag, depending on how it is fixed on the mast - as T. Speer has pointed out.
     
  5. brian eiland
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    brian eiland Senior Member

    I'll have to dig then up, but likely not till I return from Panama where I am going for a week,...and taking no computer or electronics :D
     
  6. brian eiland
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    brian eiland Senior Member

    50’ Jib-Schooner Sail Plan, Aero Analysis

    Dear forum members,
    I’ve recently been sent a proposal for a jib-schooner sail plan for potential use on a new 50’ catamaran, …and asked to comment on its feasibility and attributes.
    Along with this request there was included a CFD analysis that had been performed by Doyle Sailmakers. (attached)
    Sloop and Jib-Schooner.jpg

    Not being that knowledgeable myself about these CFD techniques and interpretations, I thought I might post this info on these forums for some comments by those knowledgeable members of this forum.


    BTW I have asked permission of both the vessel’s designer and Doyle sailmakers to post this material on the forum, and been given the OK
     

    Attached Files:

  7. brian eiland
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    brian eiland Senior Member

    50’ Jib-Schooner Sail Plan, Aero Analysis

    Just to start the conversation I might add a couple of my initial impressions.

    1) This jib-schooner’s rig with its two parallel ‘headsails’ is somewhat analogous to the two parallel headsails* of my aft-mast rig,…and/or the twin headsail rig of this CFD/Windtunnel study carried out in Italy. The Italian test rig with two overlapping headsails proved to be pretty productive upwind, even besting the standard sloop rig.
    Wind tunnel and CFD investigation of unconventional aftmast rigs

    Doyle’s test on this jib schooner rig is hinting at the same.
    ….and this is accomplished with 37% less sail area than the sloop utilized in the comparison study,…interesting

    But I also noted that this comparison was made at 20 knots AWS. I’m pretty sure at much lower AWS this jib-schooner would NOT fair so well,…just not quite enough sail area for those lighter winds. This presents their need for that fisherman sail.



    2) Aero drag of 2 bare mast. I am particularly sensitive about this issue, seeing as to the number of persons who have questioned me about this issue with my single bare mast on the aftmast rig. This jib-schooner has TWO such bare masts in its ‘non-fisherman’ configuration. This would seem to product a lot of drag force, particularly in relation to its relatively small sail area of just two abbreviated jibs.

    And I would ask the experts if this CFD analysis by Doyle properly accounted for this extra drag of the 2 bare masts. :?:




    * PS: Two parallel headstays on aft mast rig
    http://www.boatdesign.net/forums/sailboats/aftmast-rigs-623-49.html#post741571
     
  8. brian eiland
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    brian eiland Senior Member

    No takers on discussing the jib-schooner sail plan arrangement/aero characteristics??

    On another forum there have been several submissions of similar style rigs on large monohulls. Here is one:
     
  9. brian eiland
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    brian eiland Senior Member

    And here is one I posted a few years ago on this forum.

    Tayanna 55
     

    Attached Files:

  10. brian eiland
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    brian eiland Senior Member

    Looks like both vessels were interested in NOT using a big traditional mainsail, and substituting a roller furling second jib in its place.

    I talked about this on my website, and on this forum,...having run across a similar thing years ago with an old Outisland 41 ketch conversion.

     
  11. brian eiland
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    brian eiland Senior Member

    From the other forum there is this analysis:
     
  12. Paul Scott
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    Paul Scott Senior Member

    What kind of circulation do the bare masts contribute to the system as a whole?
     
  13. brian eiland
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    brian eiland Senior Member

    Home PC outperforms a supercomputer in complex calculations

    Home PC outperforms a supercomputer in complex calculations
    http://www.gizmag.com/nvidia-gpu-outperforms-supercomputer/44112/

     
  14. Spiv
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    Spiv Ancient Mariner

    I assume they wanted small jibs to have them self tacking.
    Whist that might be desirable in small quarters or racing around the buoys, it doesn't make a lot of sense in a cruising boat.
    I'd have two large overlapping genoas, hence more sail area than the sloop.
    The issues to overcome are forestay tension and fore-shrouds interference with staysail.
    Lowering the aft mast and shifting the aft shrouds to the transom would improve fore stay tension to the point that the fore-shrouds could be shifted forward as well.
     

  15. brian eiland
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    brian eiland Senior Member

    Aircraft Aerodynamics vs Sailboat Aerodynamics

    Here is an interesting website I ran across today as I sought out a question about the aircraft aero explanations for our sailing aerodynamic questions.
    The Airfoil Misconception(s) in K-6 Textbooks
    http://amasci.com/wing/airfoil.html

    Here is a portion of a note I sent the author Bill Beaty
    BTW, here is a quote from that webpage that I found very humorous
    :D;)
     
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