Baltic 55 new keel

Discussion in 'Motorsailers' started by Sensor9615, Sep 22, 2014.

  1. Sensor9615
    Joined: Sep 2014
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    Location: Newport

    Sensor9615 New Member

    Just purchased a 1984 Baltic 55 with a powerful rig considering changing the keel to a t - blub keel any thoughts ?
     
  2. Eric Sponberg
    Joined: Dec 2001
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    Location: St. Augustine, FL, USA

    Eric Sponberg Senior Member

    Sensor9615,

    Welcome to the forum. You will need a naval architect to design a new keel for you. The shape and volume of the keel and bulb will be critical to a successful design. Plus, you'll have to be assured the the boat's structure is modified appropriately to fit the new keel, and that involves the naval architect doing engineering calculations and producing drawings to show how the change should be made. Once you have a new keel design, then you can go to any of the keel molding companies, such as Mars Metal in Toronto or I. Broomfield in Providence, RI, to cast the keel. A local shipyard can make the changeover.

    Your ID says you are in Newport, and I presume that is Newport, RI. There are plenty of naval architects in Newport, and it would be best to use one of them close to you. I can make recommendations if you wish--I used to live there and I know all those guys, as well as the shipyards.

    For other insights, you can see a story about a keel change I did: http://www.sponbergyachtdesign.com/Magic.htm.

    I hope that helps.

    Eric
     
  3. robinHT
    Joined: Aug 2014
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    Location: Miramichi, NB

    robinHT New Member

    I am not sure but I think you are trying to get the Baltic 55 to have more ballast or righting moment and perhaps less draft.

    I would suggest you look into a Scheel keel. A lot of the design problems have been worked out by Scheel.

    hope this Helps Robin
     
  4. robinHT
    Joined: Aug 2014
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    Location: Miramichi, NB

    robinHT New Member

    About this time, too, I designed and later was granted a patent on a sophisticated keel shape-now known widely as the Scheel Keel. This keel shape makes it possible for a sailboat with moderate draft to get along to windward just as well as if she drew more water. At the same time, the Scheel Keel does away with complicated centerboard gear and equipment. Another virtue of the Scheel Keel is that it provides a center of gravity slightly lower than the keel shape it replaces, so the boats are a bit stiffer. Likewise, in a seaway, when small boats really move all over the place, the Scheel Keel shape tends to suppress some of these wilder gyrations. (Had my name been Brown, Smith, or Jones, would there have been such a keel shape? Who knows?)


    Quote Henry A Scheel

    If that helps

    Robin
     
  5. MikeJohns
    Joined: Aug 2004
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    Location: Australia

    MikeJohns Senior Member

    This is an urban myth that needs killing.
    The scheel keel was supposed to do two things, get the ballast COG lower and provide an end plate, it does neither very well, tank testing showed a significant increase in drag and reduction in lift over a simple straight sided keel and that it's more effective to make a keel wider at the bottom than the root and keep the sides straight.

    Scheel didn't test his keel, just marketed it well. They were shown to be very draggy in tank testing. You can contact Ted Brewer who once went to the effort of testing a Scheel keel before using it and abandoned the idea.

    It's quite the wrong section shape for a longer low aspect keel where you require a clean separation from the base of the keel since the flow is spanwise not chordwise. The lift from a low aspect keel is from the generated vortex from spanwise flow (not from the foil shape). The Scheel cross section creates an excessive adverse vortex counter to the lift vortice which it reduces and consequently adds significant drag for the same amount of lift.

    You get a better result by simply flaring the foil at the bottom to accommodate the ballast and keeping the edge square with no fancy curves. If at the same time you can narrow the foil at the top you can reduce root drag.
     
  6. MikeJohns
    Joined: Aug 2004
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    Location: Australia

    MikeJohns Senior Member

    Welcome to the forum, congrats on your new boat. Is it this planform:

    http://sailboatdata.com/viewrecord.asp?class_id=3265

    If you want to reduce the draft that might be easily accomplished with a new keel, if you want a stiffer boat that's more costly since the structural design of the mast, it's rigging chainplates and support is based on a speciifc maximum righting moment which determines the max rig load.

    A bulb is going to be draggier than a foil shape as shown and will give less lift. I'd be inclined to leave it as it is.

    cheers
     
  7. robinHT
    Joined: Aug 2014
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    Location: Miramichi, NB

    robinHT New Member

    Mike

    Thanks for the info on the scheel keel and that Ted Brewer did some testing on it. So perhaps you just chop the keel to the draft that you want and bolt on molded lead ingots to each side to generate the same righting moment.

    very Best Robin
     

  8. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    I think a piece meal approach to a boat of this caliber, is just plain silly. This is an eight ton casting and on a cruiser with a 42% ballast ratio, nothing but crazy to not have it drawn up professionally. Just way too much weight the screw around with. There are a few options available: a bulb, maybe winglets, beavertailed, who knows, but these are decisions best left to someone, that can engineer a new casting that will not put undue loads on the attachments in this Peterson design. Certainly, bolting pigs or whatever onto the side of the current casting is nuts. These boats range from a 1/4 to a half a million, if in reasonable shape and equipped, so Scheel keels or other contrivances need to be wholly justified.
     
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