Optimum Sail heel angle on a small Tri

Discussion in 'Multihulls' started by waynemarlow, Jun 12, 2017.

  1. waynemarlow
    Joined: Nov 2006
    Posts: 399
    Likes: 31, Points: 28, Legacy Rep: 134
    Location: UK

    waynemarlow Senior Member

    Hi, Whats the optimum mast angle on any racing boat such as a small Tri.

    Thanks.
     
  2. Doug Lord
    Joined: May 2009
    Posts: 16,496
    Likes: 289, Points: 93, Legacy Rep: 1362
    Location: Melbourne, Florida

    Doug Lord Flight Ready

  3. waynemarlow
    Joined: Nov 2006
    Posts: 399
    Likes: 31, Points: 28, Legacy Rep: 134
    Location: UK

    waynemarlow Senior Member

    Thanks Doug, thats not quite what I was looking for, but a good read.

    What I'm looking for is the best mast heel angle to get optimum drive off the sail, I thought it was about 7 degrees but I may be wrong.
     
  4. upchurchmr
    Joined: Feb 2011
    Posts: 2,790
    Likes: 78, Points: 48, Legacy Rep: 579
    Location: Ft. Worth, Tx, USA

    upchurchmr Senior Member

    Zero degrees I thought. Or 90 degrees to the water. Vertical.
    Any heel angle will mean some of the total sailforce is either pressing the boat down or lifting it up, not contributing to drive.
     
    Fanie likes this.
  5. Doug Lord
    Joined: May 2009
    Posts: 16,496
    Likes: 289, Points: 93, Legacy Rep: 1362
    Location: Melbourne, Florida

    Doug Lord Flight Ready

    I would think you'd want to combine the best heel angle(or acceptable heel angle) of the rig with the lowest drag ,highest RM heel angle of the boat?
     
  6. upchurchmr
    Joined: Feb 2011
    Posts: 2,790
    Likes: 78, Points: 48, Legacy Rep: 579
    Location: Ft. Worth, Tx, USA

    upchurchmr Senior Member

    Use a heeling mast and keep it vertical at all times.
     
  7. hump101
    Joined: Oct 2004
    Posts: 261
    Likes: 14, Points: 18, Legacy Rep: 58
    Location: Brittany, France

    hump101 Senior Member

    For most rigs a heel to windward will improve flow by reducing/eliminating upwash at the upper section of the rig. Fit telltales and play a bit to find the optimum for your geometry. Heel to leeward is always slower, and should be avoided if you want to maximise efficiency.

    As an example, speedsailing a windsurfer, the rigs are kept about 5-10 degrees heeled to windward to maximise speed, though of course much more heel is used to reduce sail load when overpowered.
     
  8. Skyak
    Joined: Jul 2012
    Posts: 1,194
    Likes: 25, Points: 38, Legacy Rep: 152
    Location: United States

    Skyak Senior Member

    There is more going on on a windsurfer -the righting moment is increased by moving the boom to windward (the body can only hang an arms length from it) and the lift from the sail actually reduces displacement. But the biggest improvement from counter heel is because they can tilt the sail back to close off the gap to the board. The heel brings the wind down the sail but sealing the base against the board and water surface holds the pressure. If you don't close off the base there is less value to heeling to windward. If your sail is conventional I would just try to keep it vertical.
     
  9. hump101
    Joined: Oct 2004
    Posts: 261
    Likes: 14, Points: 18, Legacy Rep: 58
    Location: Brittany, France

    hump101 Senior Member

    My comments were generally applicable, I used a windsurfer as an example only as it is a system that is easy to test the differences. Heeling to windward reduces the losses at the tip, not the base, so is beneficial regardless of whether the base is sealed or not. Obviously, sealing the base is also beneficial in eliminating the same losses as at the tip, which will generally be exacerbated by a windward heel, but the tip losses exceed by some margin the losses at the base in a modern square top rig, so a best compromise for both will usually result in some windward heel of the rig.

    However, your comments are not correct for speedsailing windsurfing. Closing the gap off to the board requires the rig to be pitched back, which in turn requires the rig to heel to windward IF the sail is cut for manoeuvrability, but this is not the case for speedsailing, where higher speed is achieved with the mast near vertical in pitch, but heeled slightly to windward. The speedsailing sail is cut so that the gap is closed with the rig in this position, and the righting moment is optimised by modifying boom geometry.
     
  10. Doug Lord
    Joined: May 2009
    Posts: 16,496
    Likes: 289, Points: 93, Legacy Rep: 1362
    Location: Melbourne, Florida

    Doug Lord Flight Ready

    ===
    A canting mast is a good solution for a tri like mine that will sail at about a 10 degree angle of heel on foils.

    canting mast on Phaedo during the Carribean 600:
    Phaedo-canting mast.jpg

    canting mast on merlin dinghy:

    Canting mast-Merlin dinghy.jpg


    BMW Oracle 17 canting mast:

    BMW Canted Mast.jpg
     
    philSweet likes this.
  11. waynemarlow
    Joined: Nov 2006
    Posts: 399
    Likes: 31, Points: 28, Legacy Rep: 134
    Location: UK

    waynemarlow Senior Member

    It would be nice to able to cant the mast, but generally around the cans in short single handed racing which I'm looking at, they just get too time consuming for the gain in benefit.
     
  12. upchurchmr
    Joined: Feb 2011
    Posts: 2,790
    Likes: 78, Points: 48, Legacy Rep: 579
    Location: Ft. Worth, Tx, USA

    upchurchmr Senior Member

    So what did you mean?
    Were you talking about how much the ama's are raised or lowered to set the mast heeling angle?
    Or were you talking about the fore and aft angle?
     

  13. Doug Lord
    Joined: May 2009
    Posts: 16,496
    Likes: 289, Points: 93, Legacy Rep: 1362
    Location: Melbourne, Florida

    Doug Lord Flight Ready

    ================
    I don't know-they apparently use it in the Merlin dinghy? On my boat(singlehanded) I would probably only use it on long races (if at all)depending on how good the system is that I come up with.
    PS-I've been told that some Moths use a canting system to keep the mast more or less vertical when using Veal Heel.......
     
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.