tunnell vee?? PLEASE HELP

Discussion in 'Boat Design' started by firth_andrew007, Jan 7, 2009.

  1. firth_andrew007
    Joined: Sep 2008
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    firth_andrew007 Junior Member

    hey guys just in the process of building my first boat. : )

    im not sure where the moulds where made or what the brand or name of this vessel is..

    nor do i know any of its hydrodynamics in the water.

    has anyone here seen anything like this before? if so can you please enlighten me on how it will respond in the water. thanks alot for your time guys :)
     

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  2. tom28571
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    tom28571 Senior Member

    This looks like a horse of a different color and I don't really understand what the designer had in mind. A combination of a step hull and a tunnel hull. There is a cut away on each side which will admit air under the forward V step and a tunnel which does not like any air admitted at all. Looks like a strange idea but maybe I don't understand what I seem to be seeing:confused: Maybe the hull never gets high enough in the water to admit air behind the step, but I doubt it. There will be considerable suction trying to fill the tunnel with water and it looks like that same suction will draw in air from the sides and ventilate the prop. In that case it would need a special kind of prop which is out of my area.
     
  3. robherc
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    robherc Designer/Hobbyist

    hmmm...I'm a bit suspicious that this design might be intended to deliver a cleaner flow of water to an outboard prop. positioned directly aft of the channel there?
    Also, if my reasoning it right, you should have yourself a boat that, with 4 chines aft & only 2 fore, should be both very pointable towards the bow, and extremely stable towards the stern. It seems like it'd pivot around the channeled area fairly well. I'd be quite interested to see how well it behave in the water!
    Any ideas on who made it might be a very good lead here...ask the designer kinda thing.
     
  4. Fanie
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    Fanie Fanie

    Similar but not quite.

    Cannot say I like either very much. Looks like they tried to combine a wave piercing monohull with cat stability.
     

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  5. PAR
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    PAR Yacht Designer/Builder

    I can't real tell where the step is, relative to the LWL, but it sure does look like it'll suck air in a big kind of way. There may be very good reason(s) you don't know what it is, haven't seen any like it, possibly as a result of the trials of the prototype.
     
  6. tom28571
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    tom28571 Senior Member

    Andrew,

    I would add that, if it were me, I would not put any more work or money into it until it's sorted out. Who designed or built it? What were the expected performance outcomes? What were the results of trials, if any? Why did it become an orphan?

    It's easy to be negative but sometimes it's the most sensible course when there are so many unanswered questions.
     
  7. firth_andrew007
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    firth_andrew007 Junior Member

    thanks alot for you imput guys!! : )

    i did leave out a very important part of this thread the hull it self is 33ft in length and the beam is 8.2 ft

    and judging by the size of the hull and placment of small parts in the cockpit...the only propulsion set up that looks applicable is twin outboards sitting on each sponson.

    other than that there is just no room for anything else... there is also a small duck board that sits about 100mm above the tunnel on the transom.


    i have spoken to "jim russell" and he has said that it is a well established design.... ?? he also sent me a picture or another boat with the same hull witch i have attatched.


    Jim Russell, P.Eng.
    AeroMarine Research
    AeroMarine Research
    "Leaders in Tunnel Boat Design and Performance Improvement"
    http://www.aeromarineresearch.com
    67 Highland Crescent, Cambridge, ON, Canada, N1S 1M1
    (fax) 519-622-5468
    (tel) 519-622-3987/705-454-9260
    email: Jimboat@aeromarineresearch.com


    and also my mould list cosists of

    fly bridge
    sun lounge
    cockpit tables
    stair case
    bathroom
    lockers
    deck
    hull
    window hatch

    please feel free to giggle over my first attempt of moulding what the deck will look like haha but here it is anyways thanks guys
     

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  8. tom28571
    Joined: Dec 2001
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    tom28571 Senior Member

    Aha! Andrew,

    Comes the dawn. It's not a tunnel boat at all. It's a catamaran with a wave splitting center hull forward to prevent slamming of the bridge deck. Quite a different animal from a tunnel hull. Requires an engine on each aft hull where the prop can run in solid water free from air entrainment. I should have noticed that the transom had no obvious mounting for a central engine or outboard.

    It's meant to induce air under the aft central part of the hull. There are many similar examples, but this one is new to me. It has sort of a three point stance on the water which is good for stability (like tricycle landing gear on aircraft). I use that myself in a different form. If you get good and reliable testimonials, go for it.
     
  9. Fanie
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    Fanie Fanie

    10m length and 2.5m wide... isn't this a very narrow boat ? I would think it should be around 3m500 at least - unless it's supposed to be trailable.
     
  10. Fanie
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    Fanie Fanie

    10m length and 2.5m wide... isn't this a very narrow boat ? I would think it should be around 3m500 at least - unless it's supposed to be trailable.
     
  11. robherc
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    robherc Designer/Hobbyist

    8.2ft would appear to me to have been designed quite specifically to be U.S. trailable... just an educated guess though (that's alwo why I'm designing a 20' x 8.5' cat right now...have to get it from El Paso to the Gulf SOMEHOW ;))
     
  12. tom28571
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    tom28571 Senior Member

    Depending on the circumstances, overwidth permits aren't all that expensive. NC just repealed the 8' width law and now it's possible to tow up to 10' with some restrictions.
     
  13. Fanie
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    Fanie Fanie

    firth_andrew007.

    Geeezzz, what an allias. Had to click it at least 5 x to copy it :D

    Why don't you look at a cat like the cruising cat's if you are going to build one ? A 10m cat can be 5m + wide, much more space, stable, safer etc etc etc, the advantages are numerous.
     
  14. PortTacker
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    PortTacker Junior Member

    I'm surprised there's so much head scratching here.
    When I was a kid growing up in Florida (1970s) boat hulls like that were quite common, and still are fairly common today. (I can almost name a list of mfrs, but it's been too long and that type of boat isn't something I kept up with over the years. Penn Yann rings a bell)
    Nothing particularly special about it, they just tunneled for a single inboard to reduce draft. It worked fine. There were twins as well - two tunnels. It doesn't work too well if you want really high speed but they were used on many heavy small cruisers.

    Now that's not to say that particular boat was well designed, but for the most part those things were so heavy and relied on cubic gallons of fuel to run, effeciency and handling were secondary...
     

  15. marshmat
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    marshmat Senior Member

    Cubic gallons.... that would be a 9-dimensional fuel source! Sounds like you've got your paws on something the string physics guys would love to see ;)

    Do you recall, PortTacker, about how fast these things actually cruised? Looking at the hull I get the impression that it's not really meant to operate below hull speed, and it obviously won't catch a 3-point hydro, but where in between would it tend to run?
     
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