which type of hull is in this pic??

Discussion in 'Boat Design' started by Zain, Jan 8, 2014.

  1. Zain
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    Zain Junior Member

    i want to know which type of hull is this? the characteristics of this hull?....and formulas for it...?? plz help.....
     

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  2. messabout
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    messabout Senior Member

    Zain; The boat is a small, short, fat boat that is very limited in usefulness. It could be used as a tender for a large boat but it will not row as well as purpose designed tender would. It appears to be a planeing boat. It is too small for a medium sized outboard motor. A very small motor will push it along but not effcently as the bottom configuration is not appropriate for small power/low speed. You could probably go fast with a medium sized motor of 15 or 20 Kw output but it will be dangerous.

    Except for all that, the boat is capable of carrying a passenger or two. There are no "formulas" for boats of this type.
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    It would be suitable as a tender powered by a tiny outboard, seeing it won't need to travel far in that capacity the efficiency of it won't matter, but it would seem likely to be about as stable as a boat that length can be, being not much different to the shape of a shoebox ! Were it powered up to planing speed, and run down the face of a wave, I'd expect it to slow up dramatically as it met the wave ahead, that is a mighty full bow.
     
  4. tom28571
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    tom28571 Senior Member

    The interesting thing is the cavity on the bottom. Looks like a version of the "captive air" theory where air is introduced under the bottom and contained inside the fence around it. There seems to be open slots near the front where air may be introduced. Unless this air is compressed in some manner, it will not work. The idea is that since air has lower viscosity than water and thus, less drag, the resistance will be reduced.

    If there are no slots near the front, my observation is completely false and closed system will introduce lots of extra drag over a normal bottom.

    Captive air is a workable technique but needs either a large front opening with parallel longitudinal fences and high speed to gain needed pressure. The minimum required pressure equals the bottom loading in lbs per sq area of the boat bottom. There was an Australian patent granted in the 1990s' on a power cat using this system. Showed up in "Boatbuilder" magazine and was called the CAT technique.
     
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  5. Mr Efficiency
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    Mr Efficiency Senior Member

    Just what that 'fenced' area was about intrigued me a little, I can't see any aperture in the bottom that would allow air in, though. Hard to see what the idea is, really. I have never heard of the patent boat you describe.
     
  6. Mike Nickerson
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    Mike Nickerson Junior Member

    Looks to be about a 10' "Boston Whaler type" knock-off which should be able to handle 3 persons and approximately a 15hp outboard. Is there a rating plate attached to the transom?
     
  7. tom28571
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    tom28571 Senior Member

    Nothing at all like a Boston Whaler.

    If the waterplane is, say 25 sq ft and the all up weight is 600 lbs, the minimum pressure will be about 0.17 lbs/sq in above atmospheric. Doesn't sound like much but its hard to develop without some powered source supplying it. If I remember correctly, the CAT system used an auxiliary powered fan to force air under the hulls. It was a bit like a hovercraft in principle but needed far less power on the fan.

    I thought the dark areas near the front of the cavity could be the air inlets.
     
  8. Easy Rider
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    Easy Rider Senior Member

    Looks like the new "Wishbone" hull.
     
  9. tom28571
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    tom28571 Senior Member

    OK, I found the referenced article in the Nov/Dec 1991 issue of Boatbuilder. My memory was faulty about the powered fan and the inlet to the cavity is not powered but only open to ambient air.

    There have been other threads here about similar attempts like this and, like so many great advances, are never heard from again. I expect the same fate fell on the OP's boat. Not to say that this is unworkable but that it certainly did not gain any significant traction. I also remember other such design by a very prolific designer, W. D. Jackson from the 1950s'.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    OK Tom, it is an area of interest for sure, introducing air under a hull with side fences to keep it there is not without merit.
     
  11. messabout
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    messabout Senior Member

    Mr. E; the trapped air notion may have merit but I suspect that speed figures into the equation. On this wee tiny little boat I think that trapped air is not a viable design characteristic.

    Also the forward section of the trap appears to be closed. Whats up with that?
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

    Yeah, I don't think there is any air entrapment going on here, intentionally anyway. Maybe it is just made that way to act as a rub strip(s).
     
  13. tom28571
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    tom28571 Senior Member

    Look closely at the forward section. There is a longitudinal dark area that is the air entry if there is one. Like so often happens the OP disappeared and could easily solve this.
     
  14. gonzo
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    gonzo Senior Member

    I think that may be something more simple. Probably just a reinforcement/chafing strake on the bottom. Also, it lets it sit flat on the ground.
     

  15. Mr Efficiency
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    Mr Efficiency Senior Member

    I agree, nothing high-tech going on here !
     
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