Big Mac 65

Discussion in 'Sailboats' started by razor, Mar 22, 2005.

  1. Mikey
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    Mikey Senior Member

    A Deerfoot will most likely have a slightly heavier (and longer) keel - ballast ratio. If not, there will still be a difference because we are not talking about dead calm seas, it will "grip/track" better, better directional stability, sort of. Displacement will be higher so it will be less affected (by what would affect a Mac 65 more) = more forgiving - also because of lower SA/Displacement ratio. Mac 65 has a very high aspect ratio and small fin keel, compared with a Deerfoot that must show a difference, especially downwind in heavier seas. Don't know if the Deerfoot has a skeg, but probably, that will make a difference too.

    Maybe I am understanding what you mean with Stability incorrectly - I don't see that as only how much it will heel.

    Long cruising Deerfoot, fun fast cruising Mac :D

    Mikey
     
  2. skinny boy
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    skinny boy Junior Member

    Beam, it's all about the beam

    The Deerfoot beam is significantly wider than a Mac 65. The increased beam provides more inital stability as well as the other things mention by Mikey.
     
  3. razor
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    razor Junior Member

    Ok stats I found for Sundeer
    LWL 59
    LOA 60
    Draft 6.0
    Displacement 36,500
    Ballast 11,500
    Sail area 1200sqft


    So my question is if Sundeer and the Mac are with in 10% of each other why would one be so much more extreme then the other?

    I do understand that Dashew is also sort of on the edge boat design.
     
  4. mackid068
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    mackid068 Semi-Newbie Posts Often

    Keel design perhaps? Righting motion?
     
  5. skinny boy
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    skinny boy Junior Member

    Sundeer and Deerfoot have 1.5 to 2.5 foot of beam on the Mac65. This is significant additional help in staying on their feet.
     
  6. mackid068
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    mackid068 Semi-Newbie Posts Often

    Ratios!

    Macgregor 65 Simple Specs-

    LOA=65'
    LWL=63'
    Beam=12'
    Disp.=32,000 lbs., dry
    Ballast=12,000 lbs.

    Ratios-

    D/L Ratio=54, which is just above "Light Racing Multihull Category" (40-50 D/L) or just below "Ultralight Racing Monohull Category" (60-100 D/L).
    SA/D Ratio=21.2 (Found on ultralight racing boats!)
    Capsize Screening Ratio=1.52, safe for offshore sailing
    Hull Speed=10.63592027 kts.
    L/B Ratio (Length/Beam Ratio)=5.416666667
     
    Last edited: Mar 28, 2005
  7. Mikey
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    Mikey Senior Member

    I would not say that the Mac 65 is too light to be safe without a second hull, no way.

    I am currently designing a 70’ long, 14 ‘ wide, approx. 45,000lb half load yacht (my first design by the way so I don’t have hundreds under by belt...) and that one will get D/L ratio under 100, I still expect it to be a Good and Stable Ocean Cruiser, certainly nothing that fits in the ultra light racing monohull category when it comes to characteristics, absolutely not the “cut weight-at-all-cost” approach.

    There are many things more than just numbers that decide what a design is. I would put it like this: You get nothing for free in this world, the Mac 65 is designed and optimised for SPEED, it will have less of something else.

    The Deerfoot has surprisingly similar numbers, but it is not designed and optimised for speed only, it will have more of something. This “something” (I am saying without having sailed either of the two) I call “better ocean going characteristics”.

    36,500lb displacement on the Deerfoot? That surprised me, I was expecting it to be more. There is probably less of a difference between the two than I thought, but still a difference for sure (keel design, rudder design, rig weight, beam, SA/D ratio + ?)

    Razor, I do not think that the Mac 65 is a dangerously unstable boat at all. It is probably one of the most exciting boats you can buy for that price, it’s begging you to sail it. Just treat it with respect otherwise it might bite you one day. That’s too extreme for me, but maybe not for you.
     
  8. mackid068
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    mackid068 Semi-Newbie Posts Often

    The capsize screening ratio of 1.52 is considered acceptable for offshore sailing. "The Capsize Screening formula was developed by the U.S. Sailing Association to judge the safety of offshore sailboats. The beam is divided by the cube root of the displacement (expressed in cubic feet). Values lower than 2.0 are considered safe for offshore sailing. The rating improves as the displacement increases and the beam decreases." (Credit: www.gosail.com)
     
  9. SailDesign
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    SailDesign Old Phart! Stay upwind..

    Mackid,
    A DLR of 54 is still higher than most Open Class boats (usually 50 or less), while the 21.2 SA/D is significantly low (most Open boats are 50 or so)
    Steve
     
  10. mackid068
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    mackid068 Semi-Newbie Posts Often

    Open Class? Do you mean large open racers? Are you kidding: "the 21.2 SA/D is significantly low (most Open boats are 50 or so)" Take a look at this (Credit: www.ussailing.com) "SA/D Ratio is the sail area/displacement ratio.* This ratio indicates how fast the boat is in light wind.** The higher the number the faster the boat.*
    * Cruising Boats have ratios between 10 and 15.
    * Cruiser-Racers have ratios between 16-20.
    * Racers have ratios above 20.
    * High-Performance Racers have ratios above 24.
    SA / D* = Sail Area / (Displacement in Cubic Feet )2/3" According to USSailing.com's calculator: "The Sail Area Displacement Ratio is: 21.11. The sailboat is a racer."
     
  11. SailDesign
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    SailDesign Old Phart! Stay upwind..

    Open Class means like the Aground Alone and Vendee Globe boats, usually sailed single-handed. For an example, Coyote had a displacement of slightly under 20,000 lbs, and a sail area of 2218 sq.ft. You do the math....
    Modern Open boats are lighter and have more sail.
    Steve
     
  12. mackid068
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    mackid068 Semi-Newbie Posts Often

    Huge boat, one person sailing it=psycho/crazy unless they are very skilled
     
  13. Mikey
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    Mikey Senior Member

    Regardless of what the U.S. Sailing Association uses to judge safety of ocean going yachs, you can't judge this by numbers alone. That would be to simplify things more than what is safe to do. The art of designing safe ocean going yachts is a bit more complicated than that.

    razor - Another thing that should give a slight difference between the Mac 65 and the Deerfoot is the Directional stability vs. Manouverability design problem.

    There is always a trade off between the two. Better directional stability gives slower tacking and vice versa. I believe that Roger Macgregor designed the Mac 65 to be fast! in alla aspects, Dashew probably had slightly different priorities.

    I read through the Mac 65 forum when it was active, some sailed the Mac 65 single handed, I think that is fine too, IF they are Experienced Sailors and treat it with Respect. And from what I read there, Mac 65 owners love their boats sailing characteristics a lot :)

    Mikey
     
    Last edited: Mar 28, 2005
  14. razor
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    razor Junior Member

    I would very much like to speak with an owner that was not trying to sell there boat, do you know if that forum was archived some were?
     

  15. mackid068
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    mackid068 Semi-Newbie Posts Often

    Perhaps you're right Mikey, but remember: Numbers are good to know before you buy. Razor, go for the Mac65, it seems pretty good if you're experienced and want to go FAST.
     
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