Keel design

Discussion in 'Sailboats' started by mojounwin, Feb 27, 2015.

  1. mojounwin
    Joined: Dec 2004
    Posts: 77
    Likes: 1, Points: 8, Legacy Rep: 10
    Location: Queensland, Australia

    mojounwin Junior Member

    Hi Folks,
    I'm after some advice regarding a new keel.
    It's for a Hartley 16, which is a 5m trailer sailer. Upwind speed would be about 5kts.

    The original keel is a steel plate, 10mm thick. The plate is about 1000mm deep x 450mm chord. It's just a flat plate, no foil shaping.

    I want to build a new keel about 1200mm deep. Naca 0010. Strip plank timber with the bottom half lead.

    Upwind sail area is about 18sqm.

    Any ideas on what sort of area the foil should be. I'm guessing I can get away with a small keel then the existing as presumably a proper foil is going to be better then a plate.

  2. SukiSolo
    Joined: Dec 2012
    Posts: 1,270
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    Location: Hampshire UK

    SukiSolo Senior Member

    It won't be a Hartley 16 afterwards if you change it!.

    The rules allow 38mm (1 1/2") fairing from each edge. Noted also is the plate thickness tolerance, pretty big. Stainless steel is also permitted as a material. Of course if your board is longer the box needs changing too. So quite a bit of work, and it will devalue the boat too, as no longer a Hartley.

    I'm a bit perplexed as to why you want to change it, rather than maybe choose another boat with a ballasted d/board? One smaller boat which uses a 60Kg bulb d/board is the K1, though AFAIK that is UK based only currently.

    The Hartley looks like a slightly more modern Wayfarer with cabin, and plenty of this type of boat have made significant passages without ballasted boards. Like Scotland to Denmark, to Iceland etc, even singlehanded.

    I suspect you need to keep all the area you can get on the board. Lateral area is most use in light winds and minimises leeway. Even a slightly more efficient board won't make up for that. Plenty of 12' and 14' + designs (in this speed range and above) use deeper and bigger boards of good section, so worth asking why? Different if you can windward plane maybe, but that might be a step to far for a Hartley...;)
  3. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Most want to ballast their boards, thinking some stability advantage will be gained. If incorporated with an improved plan for and sectional shape modifications, maybe some performance improvements too. This sort of thinking usually isn't valid and often doesn't provide anything close to what they'd hoped. Typically what happens is the new ballasted board adds huge additional strains to the case and the rig and the modified sections and plan form maybe account for a 1/20th of a knot improvement in speed, etc. and of course the class association will not like these changes if you want to race it.

    What you (MoJo) should do is ask yourself, what what are you trying to get from this modification(s) and how will these changes affect other areas on the boat. Most don't realize the rig is affected with a significant CG lowering and/or additional ballasting, which can mean new rigging, possibly a new mast too.

    Simply put, what are your goals? A new board will not make the boat point any higher, though she'll likely be able to stay "in the groove" longer, if the board is well shaped. The stability range of this boat is very good for a boat of this general class and any subtle improvements will not be noticed unless she heeled over way past what you would normally sail her.

  4. mojounwin
    Joined: Dec 2004
    Posts: 77
    Likes: 1, Points: 8, Legacy Rep: 10
    Location: Queensland, Australia

    mojounwin Junior Member

    The Hartley 16 is essentially a big dingy that you can sleep in. It will plane off the wind and the majority of the righting moment is produced by crew. I'm not wanting to add righting moment to the keel, because given that the boat is sailed reasonably flat, adding weight will only make it a horrible performer. The idea is to reduce weight of the keel, but maintain the same righting moment by lowering the CG of the board.

    Class rules don't particularly bother me. This boat in current configuration won't be competeitive under class rules and majority of racing I do is mixed fleet racing. They're a cheap boat, so resale price isn't a big deal.

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