Sail Loading on Rig, Rig Loading on Vessel

Discussion in 'Sailboats' started by brian eiland, Oct 14, 2003.

  1. brian eiland
    Joined: Jun 2002
    Posts: 4,724
    Likes: 145, Points: 73, Legacy Rep: 1903
    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

    When I think back to my very old teachings of how this would be solved I seem to remember that we might remove the mainsail itself, and replace it with little shear force, tensile forces, and moment forces at each of its connections with the rig(ing).

    Or is that just too 'old school'??
     
  2. frers33
    Joined: Mar 2017
    Posts: 4
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: turkey

    frers33 New Member

    i am trying to figure out the chord and length of a straight daggerboard to reduce the leeway on 30-45ft displacement monohulls. i have already picked an asymmetrical foil based on Cl, Cd, Cm etc...

    my question is how much of a horizontal lift force must a daggerboard generate to work against the leeway when going upwind? typical speeds of 6-8 knots.

    100 lbs ?
    200 lbs ?
    300 lbs ?

    thank you.
     
  3. brian eiland
    Joined: Jun 2002
    Posts: 4,724
    Likes: 145, Points: 73, Legacy Rep: 1903
    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

    SMAR-azure, WOW

    I have to start out offering a big apology to you Peter.
    I skipped over giving this posting of yours its due diligence,...and particularly as I read more about the SMAR-azure software. It really does appear to offer that 'plug into a big 3D model of all the rigging loads' I was looking for all these years.

    I'm going to talk more about this very soon, and ask you some questions about SMAR-azure,...but first I thought I might briefly go back thru a couple of history marks that lead to this great new technology (I just want to confirm that I have some of this 'story' correct?)
    SMAR-azure
     
  4. petereng
    Joined: Jan 2008
    Posts: 581
    Likes: 21, Points: 0, Legacy Rep: 252
    Location: Gold Coast Australia

    petereng Senior Member

    Hi Brian - Its not new its just become more accessible. The first aero-elastic job I contracted to Norths was over 15 years ago. It was a mission back then because I had to get North engineers who could do the work in between their Americas Cup stints! but it was being done regularly. Now there are packages that are much more integrated and friendly for sail-makers and boat designers. Plus computers have become so fast it is possible to do this in a short time. In my structural work 10 years ago it was common for me to leave a computer to run overnight to figure something out. I'd check it at about 3am to see if it was on track or needed restarting. Now the same problems are solved in 30 mins! Regards Peter S
     
  5. brian eiland
    Joined: Jun 2002
    Posts: 4,724
    Likes: 145, Points: 73, Legacy Rep: 1903
    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

    History

    I first became acquainted with a genuine desire to do a 'computer mapping of the rigging loads' in a document prepared by Chris Mitchell as he had worked on such a subject for his masters degree in engr in NZ. Very likely that is what also got him involved withe some major international sailing events.

    I think the document was published somewhere around 1993 (but authored around 1986)
    I find most of what he has written very interesting. So here is one of his early installments as a PDF document with some hi-lited portions that relate to the reasons I began this thread on the forum.

    View attachment ChrisMitchell Structural Analysis of Yacht Rigs.pdf

    Quite good for its time, but could be improved upon, but still it was pointed in the direction I was seeking...a force mapping of a sailing rig.
     
  6. brian eiland
    Joined: Jun 2002
    Posts: 4,724
    Likes: 145, Points: 73, Legacy Rep: 1903
    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

    History

    Then I ran across this FEA analysis paper...

    View attachment Grabe_HP-Yacht_02(1).pdf

    So by year 2002, marginally better, but still could see improvements.
     
  7. brian eiland
    Joined: Jun 2002
    Posts: 4,724
    Likes: 145, Points: 73, Legacy Rep: 1903
    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

    When I look back I now remember that I only became computer literate in the year 2000 when I was trying to follow "THE RACE" around the world. And I only started this subject thread in 2003.

    I was (and I think a lot of the sailing public) was totally unaware of these new computer methods of rigging analysis. Many of us were still (and still am) utilizing the old text books. All this America's Cup stuff was a big secret from us ordinary guys.



    I wanted to know more about a big 3D model I could just plug different designs into, and be able to make changes too a few individual components, and see the effects on the rig as a whole. One of those items I wanted to look at was the 'aft jumper strut' on my aftmast rig and its interaction with the forward pair.

    [​IMG]

     

  8. Stephen Ditmore
    Joined: Jun 2001
    Posts: 1,383
    Likes: 43, Points: 0, Legacy Rep: 699
    Location: Smithtown, New York, USA

    Stephen Ditmore Senior Member

    You should be able to get the righting moment of your boat for each 1 degree heel, RM1, from its rating certificate, or that of a sistership. You'll also need to know the heeling lever: VCE - VCLR (vertical center of effort minus vertical center of lateral resistance. You're looking for the height between the two, so if measuring from the waterline, express the second value as negative so you add them together.) You'll want to know (for wind speed x) the heel angle and the speed of the boat through the water. Transverse force = RM1 * angle of heel / heeling lever. This will be both the transverse force on the sail / rig, and the equal opposing force on the hull and appendages, including your daggerboard. If said daggerboard is vertical when the boat is upright (not canted), then no need to separate out the horizontal and vertical components, since they will be same for the board as for the rig. Where lifting line theory wants V^2, input and square the speed of the boat, and solve for area. For your foil, look for the angle of incidence where L/D is best, and use that lift coefficient.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.