Mini6.5 design

Discussion in 'Boat Design' started by Alik, Dec 29, 2003.

  1. Tad
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    Tad Boat Designer

    Daniel;

    You may be aware already, the american who lead the last race until dismasted could adjust his keel fore & aft as well as side to side!!

    Regards, Tad
     
  2. Alik
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    Alik Senior Member

    Keel CG in my design is moved 8...10% aft from middle, to improve qualities in waves. Weight distribition we achieve using equipment location...
     
  3. henrikb
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    henrikb Senior Member

    How come you have the Cp so low? 0.53 seems very low for a fast boat like a mini? With this low Cp, and with the LCB much aft, will there be enough displacement in the front sections to carry the large hedsails?
     
  4. Alik
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    Alik Senior Member

    Average speed for Minis is 5...6kts, Fr=0.36...0.38 (or not?), so prismatic near to optimum. For headsails - the CG also moved aft...
     
  5. henrikb
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    henrikb Senior Member

    But how does a low Cp influence performance at planing speed?
    Fr? is that Froude Nr? I think that on a light displ boat with alot of sail area, the speed must reach Fn=0.4 -0.45 quite fast?

    Regards!

    /Henrik
     
  6. Alik
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    Alik Senior Member

  7. ErikG
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    ErikG Senior Member

    Without thinking to hard I wonder...

    Why would you design a (hopefully) competitive boat around avg speed?

    Surely most minis are designed for the higher speeds that they can achieve?
    I haven't had the time to analyze Alik's/Leo's link yet but you don't design for avg speed. Since avg speed is the result of the time taken to travel a certain distance, you need to be able to go a lot faster a lot of the time to compensate for periods of nonexistant wind and also the reported avg speed does not seem tocare about that you go upwind at times, then the actual boatspeed is higher but VMG goes down.

    Or am I out riding on a bike? (swedish saying)

    ErikG
    ---------------------------------------------------------------------------------------------
    << Sheez the wife is having contractions now, maybe we should go to the hospital... Mini sailor on the way... watch out! >>
     
  8. Alik
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    Alik Senior Member

    I was not correct saying about average speed, we should cosider most probable speed. If speed distribution is not antimodal (hope it is), average and most probable speeds are close. By the way, does anyone have wind speed/angle distribution for Mini events?
     
  9. danielro
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    danielro Junior Member

    Tad, I didn't know that McKee had such keel, it would be the best solution, sure, but this "sliding" keel needs more complex engineering. I have seen in the galleries on the net that as we can not seal the thru hull gap between keel and hull we must build a box from the bottom to a few cm over the waterline, and, logically this remains full of water to the waterline...
    What do you think about that?
    Alik, with my short classic knowledge i think that if we place aft the keel to compensate, as you say, we need to put the equipment more forward, including the helsman i had estimate 350 kg, more or less... implicity more gyradius and worse seakeeping performance (not planing) but by placing aft the keel we avoid the nosediving planing i suppose.
    Daniel.
     
  10. Tad
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    Tad Boat Designer

    Daniel;

    I don't know if Mckee was sliding his keel fore & aft, or pivoting the keel fore & aft? I have seen the athwartships pivots setup with a massive pin with it's axis centered at the outside surface of the hull. The keel pivots, does not change shape, so a seal (probably a flexible boot inside) would be possible, without a trunk? But how to pivot in a circle? A universal joint with pivot pins fore & aft as well as athwartships?

    If you were sliding, maybe it could be done with a double skin, one section sliding inside or outside the other?

    Tad
     
  11. Willallison
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    Willallison Senior Member

    Well...? Don't keep us all in suspense.... what did you (she) have - a galley slave or a deck hand...? :p
     
  12. ErikG
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    ErikG Senior Member

    Neither yet... It all stopped... bummer... Well if nothing happens until the 12:th they do their magic stuff...
     
  13. nemo
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    nemo Naval Architect

    hi all, I'm trying to design a Mini as well, I'm following this thread with great interest...


    I was thinking about something like that.. I think the sliding is better than the pivoting, in terms of performance.. but it's more complicated; for a pivoting keel you just need a ball bearing, and it's almost watertight.
     
  14. Tad
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    Tad Boat Designer


  15. Kristian

    Kristian Guest

    Guys, you have to be careful to pass the stability tests. 10° of static heel & 90° righting test with 45+3kg at the top of the highest sail (not higher than 12m).
    The competitive (wide & flat) boats weight about 800kg, carry 350kg of lead in the bulb and have the canting angle betwen 30 and 35°. Manuard´s design also carry the 150 liters lateral water ballast added to 32° of canting angle. He is still not entirely to the limit, static test is 9°...
     
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