Small sea going inboard boat plans

Discussion in 'Boat Design' started by gatesy, May 19, 2012.

  1. gatesy
    Joined: May 2012
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    Location: UK

    gatesy New Member

    I would like to build a boat along the lines of the racing boat "Miss Britain III". A stepped hull boat.

    Not as big or as powerful, thinking more of a small 4-cylinder engine, and only about 18/20-ft long. Top speed about 60-70 mph. I can get plans for the original full size boat but I'm assuming scaled down versions of these will not work (I'm a metal fabricator, not a boat designer!!!). So what I'd like to know is, would it be possible to scale down the plans and modify them slightly so it would work, or are there any suitable sea-going step hull designs available I could use, which I could design my boat around. I have several friends with large jet ski's who like to go on day trips, but I'd prefer something like this myself. Needs to be capable of going out to sea, not rough conditions and not cross channel, more costal. Layout is inboard, with engine at the back with a forward v-drive, seating for 2 either side of the v-drive. Construction will be all aluminium.

    Any ideas greatly appreciated!!!
  2. Kestrel
    Joined: Nov 2010
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    Location: Milan Italy

    Kestrel Junior Member

  3. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    It is not likely that the combination of 18 to 20 feet long, four cylinder engine, and 60 to 70 MPH will occur in the same package.

    Most of the 4 cylinder engines are in the two to two and a half liter range. They will produce, in marine application states of tune, in the region of 65 horsepower per liter. You are going to need far more power than that if you hope to exceed the mile a minute mark. Think in terms of one of the ubiquitous 5.7 liter engines from GM, Ford, or Chrysler. If speed is your game then the 350 cubic inch V8 can be coaxed to produce 500 HP but will have a limited lifespan. That 500 HP engine will cost a plenty, somewhere north of $20,000. Lesser ones, which are factory built race type engines that are called "crate Motors". They are reliable and relatively cheap for what it is. 350 HP about $5000

    You can go fast for less money and less hassel with a big outboard. For inboard, go fast, easy build, boats take a look at the 'Crackerbox class".
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