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hydrodynamics question !

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    Pro Gas Jet RedPearl's Avatar
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    Default hydrodynamics question !



    Im trying to figure out if this radius is giving me lift from the air pack or drag from the radius drag in the water ! any ideas ? Dallas my bottom guy said he tried filling this radius in back in the day on a wilder craft and it killed the boats performance.
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    Senior Member Mike D's Avatar
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    Quote Originally Posted by RedPearl View Post


    Im trying to figure out if this radius is giving me lift from the air pack or drag from the radius drag in the water ! any ideas ? Dallas my bottom guy said he tried filling this radius in back in the day on a wilder craft and it killed the boats performance.
    Thats a Bennet Question, He has played with a lot of tunnel bottoms, always said biggest area is the keel.

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    Amber Racing Services BUSBY's Avatar
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    So ... let me ask, does the radius extend all the way forward??? looks like it from the pic. If so, I would say that isn't needed and that I have never seen it.


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    Quote Originally Posted by BUSBY View Post
    So ... let me ask, does the radius extend all the way forward??? looks like it from the pic. If so, I would say that isn't needed and that I have never seen it.

    yes brian it does . im talking about the outside tunnel. theres been talk about the keel too we know it should'nt extend that far forward.
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    Amber Racing Services BUSBY's Avatar
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    Quote Originally Posted by RedPearl View Post
    yes brian it does . im talking about the outside tunnel. theres been talk about the keel too we know it should'nt extend that far forward.
    The outside radius shouldn't be in the water at all (in theory) ... and should be creating some sort of lift I would think.

    Mike is right, Bennett would be the guy to ask.

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    B1 Racing cs19's Avatar
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    Thats an interesting bottom. I wrote out a whole deal and my thoughts were that i didnt like the drop down pieces on the outer sponsons but the more I think about it that may not be a bad design. There is alot to be said about the relationship between the center and outer sponons, problem is its hard to make adjustments without hacking up the boat.

    If you want more lift you have tons of things you could do to the center sponson, generally this is where you would do work to get lift, not the outer sponons.

    could be a cool thread.
    Last edited by cs19; 12-12-2008 at 07:43 PM.
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    what about the size of the radius created in the corners of the tunnel?


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    I've seen one other Wildercraft bottom and it didn't look anything like this one.

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    Senior Member bp298's Avatar
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    Quote Originally Posted by RedPearl View Post


    Im trying to figure out if this radius is giving me lift from the air pack or drag from the radius drag in the water ! any ideas ? Dallas my bottom guy said he tried filling this radius in back in the day on a wilder craft and it killed the boats performance.
    there's been all types of things done over the years to either increase outter sponson depth, or increase depth of the inside edges. this was a different approach, but i do not believe there's any additional drag created by the radius. it's too difficult to tell from the pics, and would need more thought and consideration, but if anything, i'd think about deepening the inside edges of the outter sponsons (building them up so they are deeper in the water). i'd also think about thinning the inside edges (they look about 1" wide?) at the same time, especially the last 4' or so.

    and, there's nothing wrong with the center pod as it is. yeah, it doesn't have a giant air box like a cp, but you have something to land on. your boat seems to work real well; i wouldn't get to carried away with it...

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    The way i see it, the outer sponson's inside depth would be a starting point for too much drag, from the pic it looks to me to be as deep as the keel or real close, but im sure the radiused outer sponson should be adding some sort of lift.
    Rob, what are you looking to do?
    It would be real interesting to see how a small change to the outer sponson area would benefit or hinder the performance.
    Great thread so far.
    how deep is the relief at the transom, on the keel? looks to be damn near an inch?

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    I would'nt mind getting rid of a few radius's to help the effeciency of the bottom. As we all know its all about efficiency with jet boats. Its amazing how this boat likes a little wind and chop on the water. My last pass of the day with a little wind is usually better than the first pass with a good air. John and myself discuss a lot of improvements we could make on the hull design. It's great hearing your guy's imput.
    Don't be afraid to try something new. Remember, amateurs built the Ark...Professionals built the Titanic!

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    I have never seen a botton quite like this. I do build a 22' modified tunnel that is similar is very fast and works well. the diferance being the sponsons on my design are set up like a modified v hull with two lifting srtakes one on the inside at the tunnel edge and one on the outer edge of the sponson running surface. I believe that if you were to fill in the concave and use the existing outer surfaces for you lifting strakes this would have a better effect.thus allowing your tunnels to be more efficient and having less wetted surface.
    Last edited by Richcraft; 12-12-2008 at 03:53 PM. Reason: clicked to soon

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    Quote Originally Posted by Mike D View Post
    Thats a Bennet Question, He has played with a lot of tunnel bottoms, always said biggest area is the keel.
    Thanks Mike! I know the keel is good , I copied this boats keel. so i think im good there. I just may need to deepin my tunnel's a bit!

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    Last edited by RedPearl; 12-12-2008 at 06:33 PM.
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    Pro Gas Jet RedPearl's Avatar
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    Default more tunnel?

    I'm thinkin it would help to give the boat more tunnel too! what do you think?

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