Power for 19' x 6' sharpie hull

Discussion in 'Boat Design' started by Homefront5, Aug 16, 2021.

  1. Homefront5
    Joined: Aug 2021
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    Location: Pennsylvania

    Homefront5 New Member

    I intend to build an outboard powered wooden boat from Harry Sucher's book, Simplified Boat Building: The Flat Bottom Boat.

    The bottom is about 4' wide at the stern and has about 6" of rocker. I know this boat will not exceed hull speed and is not meant for rough water. I will be using it on lakes, bays and rivers, with up to 4 adult passengers. I'm going to install a center console with a modest windscreen and a small top, which could be cedar or canvas. It will also get a dodger and maybe a small staysail for use when anchored or fishing.

    I want enough power to deal with winds and tides, without overkill. This design is for a transom mounted outboard and I'm considering a 9.9 high thrust. Would a little more HP be prudent or would the 9.9 HT be plenty for that hull?
  2. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    Welcome to the Forum HF.

    Can you post a drawing of the boat, or a photo of a drawing from Harry's book?
    Do you really need to have a centre console? If you have this, then you need a wheel and a steering system, and also a throttle for the engine.
    If you decide to use a 10 hp O/B motor (which should be plenty enough power for what you want to do), it would be much easier to just have a standard engine with tiller steering and the throttle in a twist grip on the tiller.
    Although for a 19' boat, with 4 people, if you wanted to go a bit faster than pootling speed a bigger engine would be useful - it depends on how fast you want to go.
    Can you explain this a bit more please?
    Will the dodger be at the front for reducing wind chill effects when you are anchored?
    And how will you rig the staysail - what is it's purpose?
  3. Homefront5
    Joined: Aug 2021
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    Homefront5 New Member

    I want the cc for convenience and to keep the sun and some weather off me. Also to keep me away from the motor noise.
    The dodger will be at the bow, from the stem back about 5' to a bulkhead. It will be there to keep certain things dry and for privacy, when needed.
    The staysail will be a simple, small triangle on a removable mast, perhaps 10' tall. It will mount at either corner of the transom, to keep her nose in the wind when I need it to.
    As for speed, I'm only interested in making 5 or 6 knots. I've had my fill of deep-v hulls and going fa$t.
    I believe forum rules prohibit me from posting images that are copyrighted.
  4. philSweet
    Joined: May 2008
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    philSweet Senior Member

    The standard cheap little 3 hp, 1 cylinder ob will do just fine. I think they are all based on the same (Tohatsu?) motor, or at least they used to be. The 9.9 high thrust is more for 25 - 35 foot boats that weigh a few tons. Two hp per ton will push anything to hull speed with a considerable reserve.

    So you really want the smallest OB that can be set up for a remote console, and probably pull from a remote tank. There used to be a 2.5-4 hp Johnson and Evenrude that would do that (no reverse, though). I loved those little motors.

    It looks like Tohatsu has remote setups for everything over a 4hp. M4C has an OEM kit for remote console. It uses the RC12D control box and a 369-83880-2 R.C. Fitting Parts Kit. It doesn't list a remote fuel tank option, though. The M6B has a remote tank and might be the best bet.
    Will Gilmore and bajansailor like this.
  5. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Forget the staysail. Not required and just an obstructive nuisance, the motor is more than just the hp required, sufficient prop immersion requires a reasonably streamlined leg above the cavitation plate so you don't create a fountain underway. Certainly four stroke is preferred. At least the 9.9 HT would tick all boxes, and wouldn't need to be revving its little heart out to keep you running at a good pace with plenty of reserve to deal with head winds and heavy loads.
    bajansailor likes this.
  6. fredrosse
    Joined: Jan 2005
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    fredrosse USACE Steam

    I have a 19ft - 3in Sharpie hull very similar to what you describe. Built rather heavy, with 1/2 marine ply sides, 5/8 bottom. While it is a steam sidewheeler, I have a 2.5 HP Ultra Low Emissions outboard, which can easily drive the boat at hull speed, as stated by PhilSweet. Total weight is about 1 long ton, and the paddleboxes have plenty of windage issues, but the little outboard can handle all this very well. margret-s-2014-04-13.181000-k.jpg
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  7. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    My least favorite outboard of all time is a Merc 25 with the gearshift/throttle combined.

    My second least favorite is the Yamaha 2.5hp. The engine's carb is simply too small and too easily gunks up.

    Go 6 horsepower and avoid the nightmares I have endured cleaning tiny carbs. I have had the 2016 motor apart for carb cleanings 3 times and probably have 5 hours run time on the engine. More time cleaning the carb! Some will say this is the reason, and maybe so, but the engine stores poorly even for a few months not run. Not to mention, not remote and no reverse.
  8. Homefront5
    Joined: Aug 2021
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    Location: Pennsylvania

    Homefront5 New Member

    All good input, thanks to all.

    I had not considered less than 9.9hp. The 2hp/ton rule would certainly allow for less since the gross weight should be under a ton.
    Tohatsu makes a 6hp sailboat engine which seems to be tiller only. I wonder if a remote control setup is available through the aftermarket?

  9. Homefront5
    Joined: Aug 2021
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    Location: Pennsylvania

    Homefront5 New Member

    I am looking into the parts you mentioned. That's great info, thank you.
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