Basic questions about V hulls

Discussion in 'Powerboats' started by Paul Anthony, Jan 11, 2012.

  1. Paul Anthony
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    Paul Anthony Junior Member

    Will a deep V hull turn better or slower then a comparable moderate V or warped bottom hull? I know this is a difficult question but I'm looking for generalities mostly.
    By deep V, I mean a 20 degree or deeper hull of constant dead rise, as compared to a modest 7-10 degree warped bottom.
    If I built a Hacker style of runabout, racer from the 1930 and put lots of power in it, 800 plus, with it's straight shaft and skeg, what would she max out in top speed? I know the shaft, skeg and gear will eventually max her out, but where would this occur? 60, 70, 80 MPH?
    If I had a 25' by 8', 10 degree warped bottom and a 25' by 8' deep V, both with 800 HP, which would be faster? Does it take more power to produce the same levels of top speed with a deep V?
    I know a dissertation on hull dynamics is in order but I'm looking for just basic answers, not writing a thesis.
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    "Depends" ! At high speeds skin friction is a killer, and a deep vee is potentially better able to reduce that than a flattish bottom, but it would depend on strakes and runner planks and that type of stuff.
     
  3. Paul Anthony
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    Paul Anthony Junior Member

    Thanks for the quick reply but I understand the drag issue reasonably well and that it is a complex subject but no real generalities in way of my questions.
    Lets try again. The 1930 vintage racers had concave sections, no lifting strakes, were heavy for their horse power production and had a lot of gear hanging, still managing to see over 60 MPH. The warped bottoms and concave sections made a lot of drag and suction aft, plus the gear. If the same length and beam boat had constant dead rise from the middle of the boat aft, how much more speed would they get with the same drive and horse power?
    My understanding is a flatter section would require less power for the same speed but at what point does the sectional shape make the deeper V more efficient? These old racers had a center of gravity more forward then we see today, so I guess purposing would eventually become a problem but is there are threshold that can be drawn?
    I'd like to have a boat of similar shape but able to do over 80 MPH. Another way of putting it is if I built a 1930 type hull except used a constant dead rise aft section threw 800 horse power at it would I see a dramatic increase in speed or would I run into a drag wall at 70 MPH preventing any better without strakes, cleaner gear etc.?
     
  4. yipster
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    yipster designer

    Savitsky has some answers your looking for, check this sites wiki on that calculator
    at planning speeds as mentioned a flatter hull gives quiker but bumpy'r cornering
     
  5. Paul Anthony
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    Paul Anthony Junior Member

    I understand the pounding would be worse on a flatter hull shape and it makes sense that it would bounce around in corners. Does a deep V corner tighter then a flatter shape?
     
  6. jehardiman
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    jehardiman Senior Member

    Different horses for different courses.

    The circa 20's to late 30's MAS boat/Gold Cup racers were designed for speed in sheltered (but not absolutely flat, they need some ripple to break suction being so flat aft) waters and skid turn at speed on the oval course. The Deep-V MTB/"cigarette" hull form was developed to reduce pounding in the open ocean while carrying large fuel/weapon loads at speed over long distances and not necessarily maneuver well on a tight course. Turning on a Deep-V will depend more on the power unit (IB, I/O, OB, jet) and L/B ratio than on the basic "type".
     
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  7. yipster
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    yipster designer

    Wherein the boat will heel in or out, depending on trust vector
    You may also read up Gar Wood and how a supercharger broke Miss Amerika
     
  8. Paul Anthony
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    Paul Anthony Junior Member

    So, a deep V with a shaft and rudder would be a slower turner then a boat with flatter aft sections. Thank you.
    Would the deep V hull also need more power for the same top speed in sheltered reasonably calm waters or would at some point the hull shape have a speed potential over the flatter section boat? I guess what I'm driving at might be is there a point or speed where you have to use the deeper V section in regard to top speed?
     
  9. jehardiman
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    jehardiman Senior Member

    Nope, not for flat water. In fact if you want to faster in flat water you go the opposite way...to the stepped or 3 point hydroplane.
     
  10. yipster
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    yipster designer

    I like a deep V's ride but no, for best top speed you best be as much out of the water as you can.
    Miss England who raced against Gar Wood's mahagony's Miss America was lichtweight aluminum, a fraction of Wood's power and had a stepped hul
     
  11. jedi99
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    jedi99 New Member

    Hi Paul,
    I am also inerested in building a 25-26 Hacker design, would also like to run big power 650 HP plus. I am inerested in aquiring plans, hopefully a software package that would let me cut everything on a computerized router table. It would be greatly appreciated in receiving any info you might have on a project like this.

    Thanks
    Jim dickson
     
  12. tunnels

    tunnels Previous Member

    The type of hull you want is depended on what conditions you going to race in . You sure as hell dont want a flat botton for off shore and you sure as hell dont want a deep vee for flat water !
    wetted area causes drag so tunnels that fly in shelted waters are a go but again they are not off shore boats !
    its not really that difficult to understand !!
    I cant understand your concern with cornering what are you worried about ?? :confused:off shore is straight running with a corner at each end cuircut racing in tunnels is tight cornering but tunnels corner like they are on rails anyway just have to learn how to drive them . Watch racing watch every video you can get you hands on go to race meetings , talk to people there and aske a million questions and take even more pictures detailed pictures photograph winning boats and boats that loose and understand what works and what dosent pictures are worth hours of study . video the same still frame and rewind and look at every detail watch and see how things work . get in a boat and get the feel of what it is doing ! every boat has a soul every boat has a charictor of its own , some people never understand what there boat is actually capable of doing because they dont take the time to get to know it personally .Because they dont understand the boat they are constantly fighting with the controls ! trim up ,trim down ,trottle constantly fast then slow !,back and forth!! , the poor boat doesnt know what its surposed to be doing . Seat time !,lots a seat time in all conditions winter or summer , Calm and rough , hot or cold .
     

  13. tom28571
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    tom28571 Senior Member

    This question can best be answered by thinking about how a boat turns. If its a powerboat, steering generates thrust to one side at the stern, causing the stern to move sideways away from the thrust. The boat will then pivot abut the center of lateral resistance, wherever that is. A lot of deep hull in the water aft (skeg, keel) will resist turning while a flat bottom aft will make the boat rotate rapidly. If there is not adequate lateral resistance, the boat will slide too much. A deep V resists turning unless it banks a lot.

    When a V hull banks, the keel can cause a reduction in pressure (ventilation and/or turbulence) on the inside hull bottom while the outside hull bottom generates a lot of pressure, making the bank even steeper. This is also what happens in a narrow bottom power dory where the inside chine can act like a keel and the boat can literally lay on its side in a turn. In a round hull, the sideways motion caused by thrust can generate negative lift on the round convex outside bilge and the boat can heel outward in a turn, which can be dangerous. Too much topside weight also cause outward leaning and people are thrown overboard every year in turns in the current high sided boxes. Lawsuits often follow.

    As always, there is more to it and the devil is always in the details.
     
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