Cat hull, one motor ?

Discussion in 'Powerboats' started by Fanie, May 11, 2011.

  1. Richard Woods
    Joined: Jun 2006
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    Location: UK, USA and Canada

    Richard Woods Woods Designs

    A fairing in front of the leg will make a huge difference

    I'm sure you've seen my central 25hp engine setup on my Skoota 20 powercat.

    I fitted a small temporary fairing in front of the leg. With it the boat goes 15 knots.

    I then tried it without the fairing. At about 6 knots the engine was drenched in spray and I chickened out of trying to go faster.

    I am now fitting the final version which will also have an adjustable nacelle.

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  2. Fanie
    Joined: Oct 2007
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    Location: Colonial "Sick Africa"

    Fanie Fanie

    Hello Richard,

    I looked at the Skoota 20 and also found the Savannah 26. Cool idea folding it with gravity and folding it open when launched.

    I couldn't see what you did with the motor. I've never investigated placing a motor anywhere other than behind a hull. How low should such a fairing go and what would the theory around it be ? I need to form something in my mind that I could perhaps try out.

    Thanks all for contributing !
     
  3. Richard Woods
    Joined: Jun 2006
    Posts: 2,179
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    Location: UK, USA and Canada

    Richard Woods Woods Designs

    I attach a couple of pdfs I did about a year ago, while below is a comment from my powering consultant.

    "That looks very good. You are adding about 15 degrees of driveshaft angle and 5 inches of depth simultaneously. So when the going is tough you can tuck your bows in and slog it out, and when the conditions allow you can let her run her bows higher. Users can experiment with trim pin positions to fine tune the system. The result is a completely tune-able boat. A 'completely tune-able, semi planing , single engined power catamaran' Brilliant. "

    I'll make the mods as soon as it stops raining (so hopefully by August!)

    Hope they give you ideas

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     

    Attached Files:

    1 person likes this.
  4. Easy Rider
    Joined: Oct 2009
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    Location: NW Washington State USA

    Easy Rider Senior Member

    Fanie,
    You've got a displacement hull and it won't plane in the traditional way. The reason the water is welling up at the engine's lower unit is from wake ...not the engine. Stumble's idea of placing the engine lower is a good idea I think as in practice and sloppy waves the prop could come out of the water. The Skoota is a planing hull but you're kayaks are not. Just run the two kayaks at 1/3 throttle (nice and quiet) until you can build two planing amas or catamaran hulls.
     

  5. Fanie
    Joined: Oct 2007
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    Location: Colonial "Sick Africa"

    Fanie Fanie

    Good morning (here anyway),

    Thanks Richard !

    Easy, I didn't expect the kayaks to plane, but they darn near do ! I don't think the kayaks have a displacement or planing shape, the bottom is quite flat so they probably have closer of a planing hull than a displacement one !

    The motor sits mounted vertical, so when I open the throttle the bows lifts by quite a bit. I was thinking if the motor gets slanted backwards, there may be an improvement as well. Thinking back it could be a lot of power may have gone in lifting the bow instead of forward propulsion.

    I don't mind operating the motor in displacement mode, will do probably in any case. I just need as much speed as possible for when we fish at sea and come out on a beach launch. The last thing you want is a wave to overtake you from behind and even worse, break on you.

    The intention is to follow a wake and keep behind it all the way out, keeping ahead of the following one. LOL, last time a friend and myself went out paddeling with a kano and on return we got overtook by that 'following' wave. The accelleration was great as it lifted the stern, but that was where the fun stopped. Couldn't keep the bow steering right even standing on the oar, and we got dumped :D Going out through the surf is not a problem as long as you keep direction and have a bit of forward speed.

    The up side was a nice looking chick in a red bikini came to talk to us. Unfortunately she left with an ugly gorilla that appeared shortly after :D
     
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