The new keel for the old boat

Discussion in 'Sailboats' started by Alexander UA, Feb 6, 2013.

  1. Alexander UA
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    Alexander UA Junior Member

    There are thousands of old boats with fin keels sample of 70-80's in the world. Owners and shippers of that boats are not going to measurements in latest measurements systems but nevertheless they want to go faster. Old keels have too much drag. Although the body can go even faster. Which bulb-keel can be designed for an old boat that:
    1. Decrease or do not increase the draft.
    2. Have the same weight. For ½ tons class - 2000-2200 pounds.
    3. Have the lateral surface of the keel commensurate the same.
    I see a similar keel shape from Olympic Star class or Uffa Fox's
    Flying Fifteen. Developing a new keel for the old boat is a new boat’s life in an era of high speeds.
     
  2. michael pierzga
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    michael pierzga Senior Member

    The classic shoal draft keel is called the "Scheel keel."

    There are also many variations of the bulb keel.
     

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  3. Petros
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    Petros Senior Member

    This is a complex issue and yes it can be done, but to optimize the design you will need to learn a lot about modern sailboat design and fluid mechanics, or get professional guidance from a designer that does modern racing sailboat design. If you just slap on a modern keel to an old hull, without paying attention to balance, the rudder size and location, mast location, hull shape, righting moment, etc. you could end up with something that is difficult control and will not perform well.

    The other problem is if you are altering a well know design, it would not be able to race in one design class or handicap yacht club races since it will no longer be properly rated.

    And than you will need to take on the task of redesigning the sailing rig to something more modern as well.
     
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  4. jehardiman
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    jehardiman Senior Member

    Also FWIW, bulb keels are not always better or faster than conventional keels. They are usually fitted for other reasons than reduced drag as most bulb keels have increased drag over comperable conventional keels of the same plan area. As Petros said, you have to consider the keel in the total performance package.
     
  5. sean9c
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    sean9c Senior Member

    I remember the good old days where we'd do these nice trapezoidal keels, we all called them Peterson keel since Doug Peterson was one of the first designers that started using them. Leading edge was raked about 35 degrees so they'd shed kelp and weed. Then designers started making leading edges more vertical, then adding bulbs, just about anything they could do to make a keel catch kelp and weed. Any sailor whose fought to get weed off a keel will tell you how much fun the good old days were.
     
  6. gonzo
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    gonzo Senior Member

    What makes you state that the hulls can go faster and the keel is the single element slowing the boat down?
     
  7. PAR
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    PAR Yacht Designer/Builder

    Agreed, this is a huge assumption and suggests a lack of fundamental understanding. For the most part, if you pull the fin keel off a Swan 44 (Frers) as and example and install the best darn new fin and rudder you can dream up, you're not going to make the boat any faster. So what's the point and more importantly, how can you sell the major renovation/upgrade.
     
  8. Alexander UA
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    Alexander UA Junior Member

    Thank you! "Scheel keel" I know. I am yachtsman in 1968, the yacht - Finn dinghy, Star, Dragon. 1978 cruising yacht. Today: fiberglass, 1/2tonn 27 feet, kill trapeze.
    max top length 5ft, 6 in. 6%, down 3 ft. 4 in. 20%, height 3 feet 9 inches.
    I want to make a prototype as Star class or Uffa Fox's
    Flying Fifteen. How do I increase proportionally?
     
  9. Paul B

    Paul B Previous Member

    Many of the old Half Tonners sailing in the recently resurgent Half Ton Cup racing (http://www.belgi.net/halfton/news.htm) have been updated to modern bulb keels.

    My question for you is why are you limiting the draft to not increase it? The old IOR requirements did not allow optimum draft. If you add a bulb and keep the same draft you will be taking span off of the lifting surface. This decreases efficiency and increases drag. I think you should increase draft by no less than the height of the bulb you add.

    You can have a similar weight using a bulb, but you will most likely have to use a steel or carbon fin with a lead bulb. This is probably going to require you to have a different way to attach the keel to the hull (flange like a Farr 40, or socket like most AC boats, TP52s, etc).

    The lateral surface of the old IOR keels was too much. If you change to a new bulb keel you can probably reduce the fin area by a good amount. The old 1976/77/78 IOR daggerboard boats had far less area in their boards than keelboats of similar design. The boards were more efficient and therefore smaller area.
     
  10. Alexander UA
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    Alexander UA Junior Member

    Thank you! I'm not going to do measurement. I want to go faster. Side of the lot does not happen. I can make out of steel 7.85 g. / Cm. cu.
    Flying fifteen keel where you can find a design?
    With respect.
     
  11. Paul B

    Paul B Previous Member

    The boats with the new keels do not race under IOR anymore. They race under IRC.


    I don't understand this statement above.


    You can find the FF keel design here: http://www.uffafox.com/flying15.htm

    I would not use that design (scaled up) for your boat. It is very archaic. If you are going to go to the effort of building a new keel you should do something better.
     
  12. Alexander UA
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    Alexander UA Junior Member

  13. PAR
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    PAR Yacht Designer/Builder

  14. sean9c
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    sean9c Senior Member

    How does that satisfy your original brief? That shape is an antique.
     

  15. Alexander UA
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    Alexander UA Junior Member

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