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Thread: Lengthening Skeg - Options

  1. #1
    Join Date
    Mar 2005
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    Marissa, IL
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    Default Lengthening Skeg - Options

    I am building a trailerable 27’ semi-displacement hull that will be driven at displacement speeds by a bracket mounted outboard. Although, the plans list the outboard option, nothing is mentioned about modifying the length of the skeg which is terminated short of the transom for the prop shaft (see #1). I find the constant slow speed “wandering” of most un-skegged power boats annoying and want to avoid it. But at the same time don’t want to create a problem with too much skeg and make it hard to turn.

    Per plan the bottom of the skeg is parallel to the waterline. If I just extend it at the same profile (#2) it gets very large at the transom – seems excessive. My inclination is to use the same overall height as the plans but place the maximum width at the transom (#3). But the bottom profile won’t be level with the waterline. I don’t see this as a problem but am I missing something?

    OR should I just leave it alone as per plan? Open to any other suggestions.

    Last edited by raymacke; 09-05-2006 at 12:50 PM.

  2. #2
    Join Date
    Jun 2006
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    SE Mich
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    Default

    I'd copy the design from a Chris Craft Sea Skiff. While they are inboards, they handle fine at low speeds and don't wander, even with a very small rudder.

    Their skegs start normally but then but then have their after edge at a low angle instead of a rightish angle to the waterline. Kind of like #1 with a shallower angle on the after edge. If the forward edge diverges from the keel by, say, 15 degrees the after edge would go back to the keel at maybe 30 degrees.

    You can probably find pics or a lines plan by googling around.
    Denny Wolfe
    www.wolfEboats.com

  3. #3
    Join Date
    Dec 2000
    Location
    Gagetown, New Brunswick, Canada
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    548

    Default Skeg suggestions.

    I launched my 24.5' semi-displacement outboard cruiser this spring, and find that very satisfactory tracking at all speeds has been achieved by going with something like your figure 1, but instead of the 90 degree angle where the designed/pictured inboard skeg stops, have faded it out so it takes about a 45 degree bend from the shown end and terminates about 4 feet from the transom. I rounded the trailing edge strongly, so that the water flowing past the outboard prop is pretty clean and undisturbed.

    The skeg depth runs from nothing at the bow to about eight inches at its deepest, and is completely straight underneath (no "rocker") so the boat's weight is spread evenly along its length when on the trailer.

    Hope this helps.

    Tony.

    PS. Have just read MCDENNY's post - sounds like we are saying the same thing, more or less.

  4. #4
    Join Date
    Mar 2005
    Location
    Marissa, IL
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    Perhaps I should have made myself clearer. The reason I am considerating a modification is that the O/B will be bracket mounted and be spaced at least 24" aft of the transom. Conventional wisdom is it usually stopped short of the transom to avoid any problem with cavitation. But in my case stopping at the transom is still 24" away from the prop.

  5. #5
    Join Date
    Aug 2003
    Location
    Cincy Ohio
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    10,388

    Default

    Neat, I take it your 24 inch bracket is also a swim platform.

    Profile # 3, and even more chopping, or upsweep.
    check out these 2 keel profiles with outboards from atkin.

    http://www.boat-links.com/Atkinco/Oar/JogAlong.html

    http://www.boat-links.com/Atkinco/Oar/Ninigret.html

  6. #6
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    Mar 2005
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    Marissa, IL
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    Default

    Yes, it will be on a swim platform. Your example seems to make sense. Allows the majority of the skeg bottom to remain level with the waterline yet smoothly extend to the transom. I think this is similar to the Sea Skiff mentioned previously. Similar to this -



  7. #7
    Join Date
    Aug 2003
    Location
    Cincy Ohio
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    Default

    I wish I could whip out neat little things like that on a computer.....

    Suggestion, I take it you are going to use a aluminum outboard platform, you might think about in conjuction to that, mounting a short 4 inch setback manual adjustable jackplate. They will go up or down 4 or 5 inches and this way you can be sure of setting your outback at the right heigth. Also as I understand it, your outboard will be raised about a inch or so in heigth due to the bracket.
    This setup is suppose to be more fuel efficent and powerfull as well, since the prop is runnning in good solid water, and not adjetated water by the transom....
    check out cook mfg on jackplates.

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