shovel noes tunnel hull! ???

Discussion in 'Boat Design' started by firth_andrew007, Sep 11, 2008.

  1. firth_andrew007
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    firth_andrew007 Junior Member

    Okay guys just in the process of constructing this boat.

    I recently bought the moulds from a procrastinator who left this sitting in his yard for a few years. Just in the process of making the lamination schedule

    Now something that is very interesting is the design of the hull.

    HAS ANYONE SEEN THIS DESIGN BEFORE!!!??????????

    103_1407.JPG

    hull fwd looking aft.jpg

    005.JPG
     
  2. firth_andrew007
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    firth_andrew007 Junior Member

    p.s

    the lenght is 33ft and the beam is 10ft

    the tunnel starts off shallow and deepins out at the transom. i dont think you can see that in the pics.
     
  3. Village_Idiot
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    Village_Idiot Senior Member

    Looks kinda like a fat Panga...

    The only thing that strikes me is the potential for turbulent water flow at the leading edge of the tunnel. I would fill that in so that it starts gently a foot or two back from where it is now. While you're at it, maybe you could make the tunnel a round design (half-pipe), as those are said to be more efficient.
     
  4. Village_Idiot
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    Village_Idiot Senior Member

    Oh yeah, I would also narrow the tunnel a bit. I don't think it needs to be much, if any, wider than the prop itself, say 14-15 inches and maybe six inches deep max. I would also make the tunnel no more than six feet long (1:12 depth/length ratio). That will give you more hull in the water for better flotation at the stern (important with today's heavier outboards).
     
  5. messabout
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    messabout Senior Member

    The tunnel appears to be offset to starboard. If so what is the rationale for that ? That is a pretty big boat to be experimenting with. The risk of possible compromised performance is too great to be messing with an odd ball design of that size.

    Consider removing the tunnel entirely and build the boat in a conventional manner. It is a pretty safe assumption that it will work that way. The rectangular tunnel is a sure turbulence maker and you may experience excess cavitation at the prop. Tunnels are a tricky design element that need to be thoroughly researched before commiting to build. You will find several references to tunnels on this form. Use the search function.
     
  6. firth_andrew007
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    firth_andrew007 Junior Member

    re

    o deff not going to change the design.

    i spoke to the guys at volvo penta.
    they seem to think that its a good design.

    recomended twin couter rotating 300hp outboards.
    from what they said the bow pulls out of the water it only has to pull out 75mm for the mono bow to get out of the water. plains on the back 9 inches. steering the b ow comes back into the water creates a pivot point and has very effective steering but.

    just to paint a piture. other moulds to this project are:
    bathroom, i can stand up in this thing. 195cm high just over 6 feet
    fly bridge
    sun lounge on second level
    hatches
    duck board
    kitchen
    deck....no walk around huge cabin space.
     
  7. Village_Idiot
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    Village_Idiot Senior Member

    OK, don't say we didn't warn ya...

    Twin outboards on a pocket tunnel? Methinks those VP guys don't know much about tunnels. This is not a catamaran. I can't think of any advantage a pocket tunnel boat like that would have with twin outboards, since the only purpose for the tunnel is the ability to operate in shallower waters when the outboard is IN the tunnel. I don't think there is room for two 300hp outboards IN that tunnel and it wouldn't make sense to have them that close together anyway. Besides, the presence of the tunnel just creates loss of buoyancy in the hull and you end up needing DEEPER water than a non-tunnel hull when running the outboards off the sponsons...
    :confused:
     
  8. firth_andrew007
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    firth_andrew007 Junior Member

    hmm kay. appreciate any thoughts but i think the water is getting muddy.

    i should get up some better pictures so the design can be seen clearly. this boat is designed for speed. now the outboards do not sit in the tunnel they sit either side of it. the tunnel is used to pull the boat out of the water completly, leaving the back 9 inches of two hulls plaining on the surface. at the stern the angles of the hulls are 0-1degree, witch is the planing surface. its hard to explain with no photos but this is a off shore cabin boat. large cockpit, upstairs a fly bridge and sun lounge 5m x 4m walking space. down in the cabins bathroom kitchen. and so on. its an offshore boat.
     
  9. messabout
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    messabout Senior Member

    007;
    Please do not take offense at any of our replies including this one. We are a huge community of boat people. Many of them are very knowledgeable, have decades of experience, and are generous enough to lend sound advice.

    The language that you have used makes me wonder just how seasoned a boatman you might be. (Upstairs, kitchen, bathroom, etc.) It is the best interest of beginners, or those with only casual experience, to pay close attention to the remarks of the old timers.

    We wish you the best of luck with your project.
     
  10. firth_andrew007
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    firth_andrew007 Junior Member

    re

    none taken..

    sorry just get into the habit of dumbing it down most people that ask about my boat do not no marine terminology and why should they if they don’t study it. force of habit.

    but what I was trying to get at with "the water is getting muddy" is the pictures I have up don’t show a lot...as in depth of the tunnel... angels and so on.. so how can I expect to get educated information with pictures that don’t show all. sorry if I sounded feisty it wasn’t my approach or the point I was stressing : ) sorry ill speak in terms from now on if it offends you that I don’t. cheers for the great advise.
     
  11. Jimboat
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    Jimboat Senior Member

    firth_andrew007 - if this is a planing tunnel hull, then you may find some help on my website. Or call/PM me if you want to discuss.
     
  12. firth_andrew007
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    firth_andrew007 Junior Member

    sorry guys for the terrible photos!!!!!

    i took some better more reveling shots thanks alot for all your imput i really appreciate it : )



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  13. Village_Idiot
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    Village_Idiot Senior Member

    So the idea is to have less wetted surface area / friction by having the hull planing on the 'sponsons' at speed?

    I'm not sure that the reduced buoyancy from the tunnel is worth the reduced wetted surface. As buoyancy is lost at the stern, the attitude of the hull will have a higher AoA, especially with two 300hp engines hung off the stern. Thus, the hull will set deeper in the water at the rear and have more wetted surface along the sides, although that may be a moot point at high speeds.

    It will be a question of whether your AoA is reduced sufficiently at speed to negate the loss of buoyancy at the stern. If it ends up being too great, the addition of trim tabs may help, although I don't know where you would mount them.

    If possible, I would reproduce the hull in two forms. One with the tunnel, and one without (i.e. - filled). Then see which one performs better in the real world.
     
  14. SamSam
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    SamSam Senior Member

    You might have to vent the tunnel to break the suction.
     

  15. firth_andrew007
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    firth_andrew007 Junior Member

    re

    samsam thanks for your advice!
    i will deffinently look into this subject thank god its such an easy thing to induce air into the tunnel.. several skin fittings two inlet lines and ball valves.

    villageidot cheers for your imput! that is a great idea i could do it in a way where i skip lamination on the tunnel and fair in the new shape after the release : )
     
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