V hull design questions

Discussion in 'Boat Design' started by sartellslb, Aug 18, 2014.

  1. sartellslb
    Joined: Aug 2014
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    Location: Minnesota

    sartellslb New Member

    Hello all. Few quick questions.

    I am trying to compare two boats. Same in every way possible except for width at the chines. HP, Length, weight.... Boat will be 19' long. Option A) 72 Inches at the chines. Option B) 80". Will there be any differances in the performance? Top speed, getting on plane, displacement, ride, how dry it is, stability at rest and on plane. Anything.

    2) Will a Pad on a Deep V boat make a noticable differance when it comes to Speed? are there any other side effects to a Pad? Boat will be around 1600 LB. With a 115-150 HP motor.

    I would like it to run at 33-34 MPH with a 90 HP. My fear is a boat that is too narrow will not do that.

    Thank you in advance.
     
  2. kapnD
    Joined: Jan 2003
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    kapnD Senior Member

    I would suggest that you test drive the two boats.
    The information you have given is inadequate to even effectively comment on.
    Some pictures would be valuable.
    Is it 115, 150, or 90 hp? Big difference.
     
  3. sartellslb
    Joined: Aug 2014
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    sartellslb New Member

    Not yet built

    The boat has not yet been built. What is for sure: Beam will be 90. Length will be 19'. Weight will fall in that 1600 range.

    the biggest question that is trying to be answered is what might we expect from a wider or narrower hull. So again, everything is equal, even the motor. Just wondering what a hull that is 8" narrower will perform like as compared to a a wider hull. Speed, stability, holeshot...... Any possible differance. This is purely research phase. But would like to hear some thoughts.

    Speed and Holeshot are important. But Ride and Dryness more so.

    Thank you!
     
  4. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    It depends on the overall shape. Just using one parameter is not enough.
     
  5. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Welcome to the forum.

    As a rule the narrower boat will tend to be more efficient, lighter and quicker to accelerate to speed. This assumes the boats are identical in shapes employed, except for beam. The narrower boat will have less initial stability, but likely better penetration into chop and rough seas.

    These generalities could be said about any boat that is narrower than it's sister. The single parameter, as pointed out above is essentially meaningless in the big picture, in terms of a reasonable comparison. This is because of the many variables that can affect the abilities of any hull form, in comparison to any other. To put it into context, I'll ask this question: "which is a better car; a USA made 4 door with 16" wheels or a USA made 4 door with 17" wheels?" This is pretty much how you question appears to us.
     
  6. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    1600 lbs dry with engine ? This is light for a 19 foot powerboat, especially if there is much vee to the bottom. I think by stipulating the dimensions and weight you have, you are resticted to a moderate vee anyway. Otherwise it will be tippy.
     
  7. Wayne Grabow
    Joined: Aug 2003
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    Wayne Grabow Senior Member

    Pretty hard to change just one parameter. If you increase beam and keep deadrise and length constant, then you change the waterline or the displacement. As Mr.Efficiency states, at 1600 lb. you will have a moderate V hull. For comparison, I recently completed an 18.5' hull with 65" chine beam, 12 degree deadrise, and 75hp. Estimated weight is 1250 lb. Stability is not a concern; planes quickly due to light weight; top speed close to 40 mph (still experimenting with props); dry (due to chine flats and sufficient freeboard); ride is good in average conditions. A deep V hull would handle chop better but would end up being a whole different boat.
     
  8. Jimboat
    Joined: Feb 2002
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    Jimboat Senior Member

    sartellslb - the "best hull" is always very dependent on what purpose and performance you desire from the boat. Performance of a vee hull depends on the hull configuration, as well as hull weight and applied power. Vee pad can make a deep vee hull faster for some applications, but of course, also has some other effects to consider too.
     

  9. rxcomposite
    Joined: Jan 2005
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    Location: Philippines

    rxcomposite Senior Member

    This is where the Arneson software is at its best. Although it is designed for SP props and the output is in EHP, not SHP, it can analyze two variables at the same time.

    It has enough inputs to modify a hull form and enables you to evaluate a hull at different speeds or compare two hulls with a variable.

    Although it is a short form of Savitsky and old program at that, it is fun to use and can be very accurate for small boats. Just read and understand carefully the manual provided.

    Very quickly, a narrow boat will run faster, a deeper V will run slower. Weight of the boat is the greatest factor in determining top speed. Other inputs like chine height vs deadrise will have to be determined by drawing a scale model.

    http://www.boatdesign.net/Directory/Software/Free_or_Low_Cost/index.php
     
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