Benetau 42 keel modification.

Discussion in 'Boat Design' started by raf pali, Dec 12, 2016.

  1. raf pali
    Joined: Mar 2012
    Posts: 71
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    Location: Australia

    raf pali Junior Member

    Hello everyone!
    Planing to cut the keel off a Benetau 42 and transform the boat into a live-aboard shallow draft vessel.
    Anyone done it before? Suggestions and advise are much appreciated.
    Thank you.
     
  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    You'll be cutting off 4 tons of ballast doing this and this is nearly half the boat's total weight. If the boat has it's rig removed and is used solely as a liveaboard, you can simply add some ballast to the bilge, to bring her back down close to her lines, so she can be used as a powerboat. If she's to remain a static floating object, you can live with a bit less ballast than if used as a powerboat. She will not sail without the ballast and she'll have difficulty holding up the naked rig, in any kind of breeze, even if tied to a dock (she'll roll like crazy).
     
  3. raf pali
    Joined: Mar 2012
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    Location: Australia

    raf pali Junior Member

    Thanks PAR, much appreciate your input! The boat belongs to an old yachty who is getting too old to sail. The boat owner is valuating the pro and con of modifying his boat vs seling and buy a house-boat. He wants a shallow draft vessel and a very short mast for a small sail for down wind work.
    We thought to make a block of cast iron for ballast, a pointy olive shape biscuit, about 100mm / 4'' thick and bolt it on with the same original keel bolts. The weight of the ballast is what we are puzzling on. The more the ballast the more the sea-worthiness and the more the sail area allowed. Of course there is a limit on how much ballast a boat can carry so, how many tonne should the ballast be at the very max.
     
  4. PAR
    Joined: Nov 2003
    Posts: 19,133
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    You're asking questions that have fairly complex answers. Not only is the weight of the ballast important for sailing, but also its location and depth under the boat. The Bene 42 carries half of its displacement, in ballast and the shoal version of this design was still 6' 2" (1.9 m) deep, with the standard rig (there was a tall rig too). The belly of the boat is pretty deep and well shaped, but it too will need about 30" (.76 m) of draft, before any new appendage (bulb, stub keel, etc.) can be installed. Of course, this modification will dramatically limit how much sail you can effectively carry, though if it (the new ballast) weighs 4,000 kg, you will be able to sail reasonably well downwind. Up wind, without an effective fin, you'll just skid sideways. Even if the new ballast is attached to a stub like fin, you'll struggle up wind. You just need the lateral area and effective lift to make progress up hill.

    Again, if just motoring, 3,000 kg. in the bilge will likely do fine, with a very small, low aspect downwind rig for coasting along. The Bene 42 has nice live aboard accommodations. Stripped of its rig and some of its ballast (1,000 kg or less), she'll make a fine motorboat, though some effort to control rolling might be necessary (chine runners?). Making her sail, with such a dramatic change (removing most of her ballast and lateral area) to her RM, while keeping a short rig, will make a very ill handling sailor. In short, make her a powerboat, maybe with a steadying sail aft to calm her down a little. Anything more would require a lot more information and effort about your desires and the boat's requirements to meet them.
     

  5. SailorDon
    Joined: Apr 2013
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    Location: Livingston, TX

    SailorDon Senior Member

    Or you can pay to have professional keel modifications.

    I got some estimates from Mars Keels many years ago on converting a deep draft 42 foot sailboat to a shallow draft wing keel.

    I recommend you check them out.
    http://marskeel.com/
     
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