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Ice Boat Sail Trim

Discussion in 'Sail Trim with Don Guillette' started by Don Guillette, Mar 9, 2019. Add this thread to a FAQ

  1. Don Guillette

    Don Guillette

    Joined May 17, 2004
    1,931 posts, 95 likes
    Other Catalina 30
    US Tucson, AZ
    I had an interesting phone call yesterday. Over the years I thought I'd heard every basic sail trim question a sailor could ask. - nope. This sailors asked me to help him with the sail trim on his ICE BOAT!! I told him that years ago I watched folks sail small craft that looked like a ice boat with wheels at the El Toro Marine Base and Los Alamitos. He told me they were called BLOKARTS and he has one of those also. Watching them scoot around looked like fun but I never got to try one. Those little crafts with wheels went faster than the wind speed.

    Anyway, turned out he was pulling my leg. He knew how to sail his ice boat, which had about 60 sq feet of sail. His son sails a smaller version. I learned a lot about ice boats from him and while sailing a ice boat sounder similar to sailing a boat on water, ice boat and sand boats do require good"eye to hand "coordination and good reflexes - things happen much faster. As for trimming the sails, you pretty much "set it and forget it". You only deal with angle of attack as they have a traveler of sorts. I don't think you deal with draft position, draft depth or twist - there's probably no time for that anyway. The thought crossed my mind that these craft operate a lot like America Cup Boats up on their wings.

    The Sail Trim Forum is always in the doldrums during this time of the year so ice boat sailing might be an interesting topic. Do any of you that have sailed these craft care to share your experience?
     


  2. Hayden Watson

    Hayden Watson

    Joined Apr 5, 2009
    661 posts, 159 likes
    Catalina '88 C30 tr/bs
    US Oak Harbor, WA
    Given their speed they operate in the range of close haul to close reach.
     


  3. Don Guillette

    Don Guillette

    Joined May 17, 2004
    1,931 posts, 95 likes
    Other Catalina 30
    US Tucson, AZ
    I watched them sail downwind also but on that point of sail they only seem to go at wind speed. Watching them turn is something else!!
     


  4. Don Guillette

    Don Guillette

    Joined May 17, 2004
    1,931 posts, 95 likes
    Other Catalina 30
    US Tucson, AZ
    Jackdaw has probably sailed ice boats -- the lakes where he lives are frozen from September to April!!
     


  5. Jackdaw

    Jackdaw

    Joined Nov 8, 2010
    9,844 posts, 2,898 likes
    Beneteau First 36.7 & 260
    US Minneapolis MN & Bayfield WI
    An iceboat sails with the apparent wind always in front of the beam, both upwind and downwind. Control wise, boats like the DN only have main sheets, which also act as Vang and back stay.

    The mast is very bendy to allow the top to twist off. Trim to keep the boat on two runners. The sail has both luff and leech telltails, but mostly keep the boat fast and flat. That will give max VMG.

    A03EBAC0-3B7E-480D-85E6-C11144C8B03A.jpeg
     


    Captain Larry-DH likes this.
  6. thinwater

    thinwater

    Joined Mar 26, 2011
    2,222 posts, 524 likes
    Corsair F-24 MK I
    US Deale, MD
    On one hand, I wish it was warmer here. On the other hand, that looks that like more fun than....

    My tri is too slow.
     


  7. Benny17441

    Benny17441

    Joined May 24, 2004
    5,646 posts, 390 likes
    CC 30
    US South Florida
    Speed is relative, comfort rules.
     


  8. walt

    walt

    Joined Jun 1, 2007
    3,248 posts, 393 likes
    Macgregor 26S Hobie TI, Capri Coronado 15
    US Denver, Colorado
    Some interesting things about ice or land sailing from looking at the equations for lift and drag.
    FYI, the equations come from here https://www.engineeringtoolbox.com/lift-drag-fluid-flow-d_1657.html

    I copied the basic lift and drag equations from that web site in the image at the bottom of this post and want to note that the force equations for both lift and drag have V**2 (ie, velocity squared) in the equation. Compare what that does for a sailboat doing 6 kn in a 10 kn wind and an ice boat doing 40 kn in the same 10 kn wind (both sailing perpendicular to the actual wind direction).

    The apparent wind for the sailboat for the conditions above would be 11.66 kn. The apparent wind for the ice boat would be 41.23 kn.

    That wind speed term gets squared in the lift and drag equations and if you compare the squared apparent wind speed multiplier, that multiplier is a huge factor of 12.5 times higher for the ice boat even though the actual wind speed is the same.

    For lift force, it cant be too high or it would tip either the ice boat or the sailboat over. Lets assume the same lift force between the two craft in this example (not that far off - remember it cant push the craft over). What has to happen with the ice boat is that the term CL (coefficient of lift) needs to be a factor or 12.5 times smaller. CL is proportional to the sail angle of attack so in general a very fast craft will operate at a much lower sail angle of attack compared to a slow craft.

    Next thing to note is that the drag of the sail becomes much more important for the fast craft since the drag force term also is proportional to the square of wind velocity. Ice and land craft often have different looking sails (high aspect, wing mast for example) and part of that is keep the drag low at the high velocities that are attained.

    The other interesting thing regards the wind height gradient which is part of the reason for sail twist. If the wind is 6 kn at 2m and 10 kn at 10m, for the sailboat going 6 knots, the difference in apparent wind at the two heights is 8.49 kn and 11.66 kn or a 37 percent difference in apparent wind speed with height. But for the ice boat doing 40 kn, the apparent wind speeds over height is 40.45 kn and 41.23 kn and only a difference of 1.9 percent.

    So for the ice boat, the issue of wind speed height gradient pretty much goes away.

    lift_drag.jpg
     


    Last edited: Mar 10, 2019


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