Small Fast Boat

Discussion in 'Boat Design' started by rossiroller, Sep 3, 2008.

  1. rossiroller
    Joined: Sep 2008
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    rossiroller New Member

    I want to make my own boat, but Ive never done it before.
    I looked for a small 2 person o/b that could go pretty fast, found this one.

    http://www.svensons.com/boat/?p=HydroPlanes/SportsHydro

    Looks pretty old, so might have to mod the plans.

    So in the end several questions,
    -are the plans too old to trust/ how much do they need to be changed
    -how fast could i go and still be reasonably safe
    -how big a motor do i need
    -estimations on cost, and where to buy an outboard for cheap

    only for lake cruising, so not very big chop
     
  2. eponodyne
    Joined: Aug 2007
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    eponodyne Senior Member

    Water hasn't changed at all in the past 50 years. The plans will probably be jsut fine as is; might want to consider using 1/2" ply for the bottom--or better yet, 2 layers of quarter-inch. How big a motor do you need? How much do you and your buddy weigh? How fast do you want to go? How safe is 'safe?'

    You may find this link very useful.
     
  3. rossiroller
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    rossiroller New Member

    safe, would be not breaking the hull and sinking or flipping over,
    like 50 mph would be fine, but if i can get to 80 mph that would be great,
    probably max weight would be 500 pounds, but average would be like 300-350,
    according to the plans, they got 50 with 2 people and a 50hp engine,
    and any changes in controls or engine mounting would need to be addressed it shows tiller cables in one of the diagrams

    it looks easy enough to build, i was looking for some experience with a similar boat for anyone to tell me how stable they are
     
  4. BHOFM
    Joined: Jun 2008
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    BHOFM Senior Member

    I am building a small sailboat by the same designer,
    in fact, I got the plans at the same site.

    I am very happy so far with the plans and instruction.
    The price is right.:D :D

    I don't think the steering is a deal at all, when you buy
    your steering unit, they will help you I am sure!

    The look of the boat is great, with a lot of wood showing, it
    would be an instant classic!

    It is mostly dependent on your wood working skills or
    your desire to learn the needed skills!

    I see nothing in the plans that is a great challenge to
    a moderate wood worker!
     
  5. kengrome
    Joined: Jul 2006
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    kengrome Senior Member

    I think it's time to stop dreaming, rossiroller. All boats that move that fast are at risk of breaking apart, flipping over, etc.
     
  6. lewisboats
    Joined: Oct 2002
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    lewisboats Obsessed Member


    Or worse...hitting something just barely submerged at 60+ mph. Then you will be doing all of the above and then some.

    Steve
     
  7. kmorin
    Joined: Apr 2005
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    kmorin Senior Member

    Boats and Cars Compared

    rossiroller,

    I believe the guys have understated things a bit, you may be confusing speed in autos with speed on the water.

    Cars and trucks only get the speeds you've casually referred to, 50-80 mph on extremely expensive prepared surfaces- roads or highways. And more to the point, the typical interstate is some fine quality road that costs thousands or hundreds of thousands per foot to build.

    Instead, I think you'd do much better to skip the roads in ALL your thinking about boats. The water has no 'roads' since bit of a breeze and the surface goes from glass-like to some serious off-road Baja-endurance surfaces in a very short time.

    So think of any vehicle doing 50 or even 80 across the desert and what happens to it when the surface changes shape- like a rock in the way or a small gully? Now you'll have a better mental picture of what a small fast boat is like.

    If the vehicle were a 40 ton tank and has suspension designed to tote a 4" artillery piece at 60 mph over the out-back landscape- well, that's one "ride". But if you take a light little dune buggy and do the same thing? Well, let's just say you'd learn fairly quickly about mass as a contribution to "ride".

    If you build in metal, welded or riveted, the boat will last fine when and if it trips or spills. If you build in high tech fibers and resins or even plywood- the boat will probably survive most 'terrain related obstacles' but isn't the weak link in all this the "hide full of flesh and bone" driving?

    Good luck with your boat project, I'm old and no longer bullet proof, so I may be overcautious in my thinking.

    I hope you're careful and not casual with a 50 on this tiny hull looking for 50 mph;
    in a hull this size you'll need a mill pond surface or a day on the lake might get a bit aeronautical.

    Cheers,
    kmorin
     
  8. messabout
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    messabout Senior Member

    Kmorin is preaching the gospel. He may be old but he is still plenty smart. Experience is a persuasive teacher. Take it from this old (former) hydro racer. The water is about the consistancy of concrete when traveling in the 50 MPH realm. I have some broken bones, shattered boats, and destroyed engines, to attest to that.

    If you are a young guy you are going to abandon common sense and ignore good advice and do it any way. I confess that 50, 60, 70 mph on water is a real rush. I suppose that you gotta do what you gotta do. "May the Force be with you".
     
  9. tom28571
    Joined: Dec 2001
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    tom28571 Senior Member

    rossiroller,

    It's pretty clear that you have never gone 80 or even 50 in a small motorboat. When you are sitting with your bum at water level and running even 30mph in a small boat, it will feel like more than 90 on the interstate in a modern car. The guys above give good advice. I've been boating for well over 50 years and have never gone 80 and only reached 50 to 60 twice. Once in a Scarab and another time in a Rascal. My little runabout runs 31 in smooth water with a 25hp outboard and all who drive it remark on the feeling of speed.

    Glen L has some decent plans for runabouts and you might be happier in the long run with a true runabout than a raceboat lookalike. My favorite is the Zip which will zip with a 40 outboard.
     
  10. dsuursoo
    Joined: Aug 2008
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    dsuursoo Senior Member

    i've been in some wicked fast boats(coast guard OTH pursuit boats-in excess of 50+ knots/more like double that, and coast guard 25' interdiction boats by safe boat international-40 knots +/much better than that) and they were a real pounder of a ride. generally the crews and passengers tend to spend most of the ride belted in, with extra padding on the seats and some sort of impact protection strapped to their lower backs.

    and then there's the whole issue of surface as well. glass-smooth high speed is great, but at 50 knots, even a two inch wave feels like you ran over a log. it's a jarring slam in a light boat. in a heavy boat, it's not so bad, but then you need gobs of horsepower and corresponding fuel consumption.

    don't use more than 200 horse, and you'll probably be able to get 30 gallons of fuel. if you spread that 200 horse between two engines, you might get better economy, but don't quote me on that.

    but 30 knots or so feels like you're screaming along. take it from someone who spent a few years going significantly faster than 40 knots for a living.
     
  11. Jack Daniels Eq
    Joined: Aug 2008
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    Jack Daniels Eq Shockwave

    Depending on how much ya value your bud, and whether ya wanna go boating or putz around in the shed waiting for Gawd, and wasting money.
    Buy a used Boston Whaler + OB, some beer & fishing poles
    Or stay in the City
    BR>Jack
     
  12. kach22i
    Joined: Feb 2005
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    kach22i Architect

    Good point, reminds me of a comment in a hovercraft forum.


    http://www.hoverclubofamerica.org/forum/index.php?showtopic=1659
    [quote name='ken' date='Sep 10 2008, 10:33 AM' post='15895']
    [/quote]
     
  13. dsuursoo
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    dsuursoo Senior Member

    actually, a boston whaler's a pretty sound idea for a fishing/fun boat. if you think they're slow, slap 400-odd horsepower on them. just have everyone hang on when you run it up, or you'll be doing man overboard drills.
     
  14. Jack Daniels Eq
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    Jack Daniels Eq Shockwave

    I like the way ya think - always outside the box - who wants to die in a wheel chair @ 60mph, when ya can obliterate ya self @ 150mph !!!
    Feed the fish.
    BR>Jack

    slap 400-odd horsepower
     

  15. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    I would like to add just one more thing to the wise advices which you've been given by kmorin and others.

    The hull form of that boat makes me think that a flip-over, either longitudinal or lateral (during turns), is almost guaranteed at the speeds you want to reach. It is very light-weight boat, with planform which resembles a rectangular flat plate. That, plus CG all backwards due to engine and pilot position, will make it very unstable aerodynamicaly as soon as the bow rises up due to waves.

    Try to move quickly a styrofoam rectangular plate by holding (and pushing) it with two fingers at the trailing edge with your fingers and see what happens. It takes just a small initial positive angle of attack to start a 360° flip-over.

    This thing was (IMHO) designed to safely skim over oil-flat surfaces and you will hardly have a big enough oil surface available for skimming over. Unless you live in Dubai, have 5 wives and 3 or 4 megayachts, 300 ft each... ;)

    If I were you I would go for a hull with a nice V bottom.
     
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