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Thread: Tunnel Hull Necessary?

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    Default Tunnel Hull Necessary?

    Is a tunnel hull absolutely necessary for an outboard jet? I guess what I mean is, are the benefits so much more that it would be crazy to run a jet on a flat bottom without a tunnel? Clear as mud?

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    No not at all, I don't care for tunnels because they tend to cause more cavitation, and less performance. I'll run any flat bottom boat anywhere a tunnel can go.

    There are benefits for new boaters that are learning to run rivers, if they run a tunnel there's less chance of damaging the foot.

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    Default I have run a few tunnel hulls

    But with sturn drive I/O.
    I don't care for them . they are very wind sensitive
    they are very hard to turn at speed, unless it is a speed boat , even then the flight on the water is touch and go. But ,
    as a party boat or for fishing , very much like a pontoon boat very nice that way.a lot more deck space to roam around than conventional deepVhulls or tri hulls. Flat bottom boats whie they don't hold course well and will beat you to death in rough water are good for shallow conditions. beware though all that flexing is fatige. The worst issue though I've had with most of them is the inability to do service on them . often simple operations such as changing the spark plugs is a major ordeal . changing the starter would require engine removal ;no joke.
    use it or not, boats require service, keep that in mind as a part of the cost of the boat. Also keep in mind how your going to haul the boat out and around .very few marinas have a trailor capable of fiting a tunnel hull. Don't talk to a sales man talk to several area boat mechanics, that are not part of the sales force, about the better combinations that are successful in the areas you plan on using the boat.
    B reak
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    Boat= hole in the water you throw money in to.
    sucking up rocks in a jet pump is not pretty, replacing it in the middle of no where is major .
    Sturn drives props can be replaced in a few muinets.
    I prefir out board motors ,they have the most versatility.

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    I've not owned a tunnel yet, just flat bottoms. There are advantages to a tunnel, when you do run aground your jet foot is still 1-2" up off the bottom. They still suck gravel, maybe not as much. I think a properly designed tunnel will handle a bit better in corners than without, but my flat bottom jon has done fine. I know up in one village I visit they don't run tunnels. The theory is when grounded on sandy bars, a tunnel causes suction and makes it harder to get the boat floating. I obviously don't think they are necessary as I just bought another flat bottom boat without a tunnel.

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    They cause your boat to sit lower in the water when at rest, therefor when at the bank or approaching it (not the $ bank either!) you have a greater tendency to swamp over the stern from a following wake... be aware of it.

    You have to run faster to get the boat to plane as high as it will with a full bottom under it... coming downstream that can bring some additional challenges with it. again, be aware of it.

    It will track better in a corner, or rather it wont slide out in a corner as quickly as a flat bottom will... thats a good thing.

    You can run shallower and not necessarily foul your jet... thats a good thing... if the tradeoff is worth it to you, just be aware of the other limitations it brings with you.

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    The only tunnels I have run are on Lunds. They performed far better with a short shaft prop than they did with a jet. Normal flat bottomed Lunds worked much better with the jets. I ran the hell out of a propped tunnel Lund on the Yukon and Kuskokwim and they worked really well..even in the side rivers with rocks. When we tried jets on them we had lots of issues with cavitation.
    Bunny Boots and Bearcats: Utility Sled Mayhem

  7. #7

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    i have had both and i have 18 foot alumweld that i built the tunnel in it and it will run shallower than you will want to go with it. it over come the need to go faster on step issue you just need to ad some extra bottem the stern when you built the tunnel also helps keeps the jet spray down. and as far as siting lower in the water i build my transome full height all the way accrose the boat. if you balance your boat as you should any jet boat it will sit flat in the water at rest. i would never own anything but proper built tunnel hull.

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    Quote Originally Posted by jtm9 View Post
    Is a tunnel hull absolutely necessary for an outboard jet? I guess what I mean is, are the benefits so much more that it would be crazy to run a jet on a flat bottom without a tunnel? Clear as mud?
    Absolutley neccessary.NO, but I think the benefits outweight any drawbacks, w/o a tunnel the foot will be below the bottom of the boat, ~3". If you like running shallow water sooner or later you will cross something that is shallower than your boat will run and drag the bottom, if its short enough you can skip across with out the foot digging in, I am not advocating anyone do this but sooner or later it will happen.
    In the two tunnel hulled boats I have owned, cavatation was not a issue.
    The tunnel causing more suction??? how can this be?
    A tunnel hulled boat when drifiting will sit lower in the water, particuarily so if its a narrow bottom (60" or less) w/ a heavy motor, this is simply a matter of hull displacement and any tunnel will provide less displacement. and I think thats why a lot of boats have gone to a wider hull (72" or more).
    If you are on step when crossing a shallow spot you will feel the boat raise up when you start getting really thin (6" or less, I think?).
    Any boat, wide narrow, tunnel or no tunnel will do this, its physics, water is almost 800 times denser than air and doesnt compress very well.
    Personally I dont believe there are drawbacks that outweigh the posistive qualities of a boat with a properly designed tunnel.
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    Thanks for the info guys.

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    Quote Originally Posted by Captain T View Post
    I'll run any flat bottom boat anywhere a tunnel can go.
    really?...wow....
    ------------------------------------------------
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    Quote:
    Originally Posted by Captain T
    I'll run any flat bottom boat anywhere a tunnel can go.



    Quote Originally Posted by tjm View Post
    really?...wow....
    At least to its firmly planted.........................
    “Nothing worth doing is easy”
    TR

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    Quote Originally Posted by AKDoug View Post
    The only tunnels I have run are on Lunds. They performed far better with a short shaft prop than they did with a jet. Normal flat bottomed Lunds worked much better with the jets. I ran the hell out of a propped tunnel Lund on the Yukon and Kuskokwim and they worked really well..even in the side rivers with rocks. When we tried jets on them we had lots of issues with cavitation.
    Were your Lunds prop or jet tunneled?
    Lund stopped offering tunnels a few years back and I am not familar with Lund tunnels?
    Alumacraft use to offer jet tunnels and discontinued them a few years ago also, just didnt sell enough of them apperently.
    They still offer prop tunnels and there are some unscruplous delaers that will install a jet on a prop tunnel. some say it works, most say they are prone to cavitate.
    “Nothing worth doing is easy”
    TR

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    Quote Originally Posted by fishslayer View Post
    I've not owned a tunnel yet, just flat bottoms. There are advantages to a tunnel, when you do run aground your jet foot is still 1-2" up off the bottom. They still suck gravel, maybe not as much. I think a properly designed tunnel will handle a bit better in corners than without, but my flat bottom jon has done fine. I know up in one village I visit they don't run tunnels. The theory is when grounded on sandy bars, a tunnel causes suction and makes it harder to get the boat floating. I obviously don't think they are necessary as I just bought another flat bottom boat without a tunnel.
    I dont know about the suction theory, but certainly when at rest it will take more water to float a tunnel than a flat bottom, thus it seems it would take more effort to get unstuck if you have a tunnel. Anybody doubts this theory is welcome to meet me at the Talkeetna boat launch and if Kelsey will share his boat, we can shut them both down in deep water, and drift them towards shore... his straight bottom will drift in closer than mine with the tunnels.

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    Quote Originally Posted by Akgramps View Post
    Quote:
    Originally Posted by Captain T
    I'll run any flat bottom boat anywhere a tunnel can go.





    At least to its firmly planted.........................
    If a flat bottom is planted so will a tunnel hull.

    The tunnels are better for the inexperienced. but will not run any shallower then a flat bottom. That was my point.

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    Quote Originally Posted by Captain T View Post
    The tunnels will not run any shallower then a flat bottom.
    I am assuming you are talking inboards....can't see how that is the case with an outboard....please correct me if I'm wrong...

    the original poster asked about outboards...if the foot is hanging down below the bottom, wouldn't it hit before the bottom would?....I'm trying, but am having a hard time picturing how one boat with a couple inches hanging down can go "Anywhere" a boat that doesn't have a couple inches hanging down....perhaps im just dense....

    if you're frequently running very shallow water, wouldn't the boat with a tunnel be less prone to getting clogged up?....it would seem that one good bump without a tunnel and you'd have something in your grate....not the case with a tunnel....again, please correct me if Im wrong...

    I am in the process of deciding on a new boat to order....the tunnel debate is currently part of the process for me too...

    Quote Originally Posted by Captain T View Post
    The tunnels are better for the inexperienced.
    in what way?....if they don't allow you to run shallower?...
    ------------------------------------------------
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  16. #16

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    I have many years running outboad jets with and without tunnels. A tunnel will run in a shade less water but you tend to bang up the bottom of you boat and are always fixing leaks. So in genral a flat bottom will run any where that a tunnel will and will usually handle better.

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    Quote Originally Posted by SkwentnaMan View Post
    I have many years running outboad jets with and without tunnels. A tunnel will run in a shade less water but you tend to bang up the bottom of you boat and are always fixing leaks. So in genral a flat bottom will run any where that a tunnel will and will usually handle better.
    Why do you bang up the bottom more on a "tunneled" boat?
    “Nothing worth doing is easy”
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  18. #18

    Default tunnell

    Here is a 17 alaskan wooldridge foot tucked up in the tunnell

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    Quote Originally Posted by SkwentnaMan View Post
    I have many years running outboad jets with and without tunnels. A tunnel will run in a shade less water but you tend to bang up the bottom of you boat and are always fixing leaks. So in genral a flat bottom will run any where that a tunnel will and will usually handle better.

    wouldn't you rather bang up the bottom than bang up your foot?
    ------------------------------------------------
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  20. #20
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    Default I honestly think that its going to more be the operator than the tunnel

    When it comes to running shallow there are so many variables that come into play. Finding that perfect slot to keep your jet in being a crucial one, along with manuevering corners with the minimum loss of step as is possible, and a host of other minutia that all combined together make for the "perfect" shallow water run. I'd venture to guess that the skills and aptitude of the operator, and probably local knowledge of the river will have far more to do with shallow water performance than does having or not having a tunnel.

    In a full bottomed boat, the hull will ride higher on the water at the same speeds as compared to a tunnel. So, if it's your hull dragging thats keeping you from running shallower than you can at present, I'd recommend a full bottom. If you're one of these guys who have this uncanny ability to keep your jet perfectly positioned in the center of a 6 inch wide path thats still got an inch and a half of water in it, and most of your hull is over dry ground because you're heeled over and lining up for the next transition... well, you'll probably outdoo the results you could acheive with a tunnel.

    If your jet foot is typically the thing to touch first and it fouled and thus you get stuck... then probably a tunnel will be of more benefit to you.

    If you worry about damaging your jet unit or transom, then probably a tunnel is for you.

    For comparision, forget about the outboard for a minute and visualise two identical 19 foot inboards, one with tunnels, one without. The one with the tunnels tracks better, holds better in the turns, and sticks easier and sooner in the shallows. In fact, in order to run with the other boat with the full bottom, I've oftern got to run several knots faster than him to get the same amount of lift from the hull and make it through the shallows.

    The one without the tunnels can run slower through the identical shallows than the tunnel boat, it also tends to slide out in a corner more readily. It doesnt track quite as well in a straightaway, but it steps quicker (a huge advantage in shallow water running)

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