custom tunnel hull additions mods adding to traditional hull

Discussion in 'Boat Modification Journal' started by Goldenshinner, Dec 24, 2007.

  1. Goldenshinner

    Goldenshinner New Member

    wondering if anyone has successfully added a tunnel hull to a regular traditional flat bottom. I poked around for info and talked to one custom hull repair shop that installed one.they said that they would never do another one. they would not tell me any more info other than that if i could get my hands on a factory original tunnel that they would install that. im woundering were the problem comes in. and if this addition improperly installed could crack the floor???

    also how difficult would it be to build this piece, any reinforcement of surrounding area, i realize that you would need new drain holes on either side, and that the placement of this piece would have to perfectly allign in between the folds in the aluminum.
  2. metalman

    metalman Well-Known Member

    That is a loaded question.
    It would depend on the skills of the person doing the job and the equipment / material at their disposal. A good fabrication shop should be able to reverse engineer a tunnel if they have one to copy or detailed photographs and measurements. The danger is that although it's easy to copy what someone else did it's not so easy to know WHY they did it and that may lead to problems. Fab' shop rates, especially those with the skill to do this modification, will be pretty salty.
    I would suggest inquiring with the manufacturer of the boat if a tunnel hull version of your boat is available. If it is then you should be able to buy the tunnel insert. You may want to prepare yourself for sticker shock. I don't know but I suspect it will be quite expensive and again the shop rate to have it fitted may make you want to reconsider...W

  3. RivrLivn

    RivrLivn Member

    From my understanding of building a tunnel design is actually getting the water to flow "smooth" through the tunnel. This is especially important when putting a jet behind the tunnel.
    If not done correctly the water is very aireated (spelling?) so the jet looses a lot of thrust.
  4. Mark J

    Mark J New Member

    Four Oaks, NC
    Building a tunnel would be the easy part.
    The biggest thing is what you are wanting to tunnel.
    A tunnel will destabilize a boat so you need plenty of stable in the bank before you take on a tunnel.
    Saw a builder build one into a hull and the designer explicitely advised against it telling what would happen.

    It happened. Brand new boat did a one point snap roll out of nowhere.

    Tunnel boats are often flat bottom, and wide.
    This particular designer doesnt recomend one on anything he designs smaller then his 20x8 garvey that I am aware of.

    The guy who had the problem may not be having a problem with getting the right shape or size for the tunnel. He may just be trying to tunnel the wrong boat and dont know it.
  5. cantstopgrandma

    cantstopgrandma New Member

    Something to think about with the fab shop that did it: Maybe they did an outstanding job, maybe if looked like it came from the factory that way. Even with all that, some people are never satisfied. They may have wanted their tunnel hull boat for a specific reason, and after the shop did all that work, it didn't live up to the customer's expectations. This could cause grief for the shop in many ways (lawsuits, bad publicity) making them not want to build another (or in this case refusing to build another). What i'm getting at here, is that the difficulty (or lack thereof) may not be the reason the shop wont do another one.
  6. Mark J

    Mark J New Member

    Four Oaks, NC
    Its not the difficulty, its the outcome.
    There is more to a tunnel then the appearance of it. It has to be sized and shaped properly.
    True, the owner may not have been satisifed with reason.
    That reason could could range from the man doing the job without rhyme or reason to a boat owner that thought he wanted a tunnel to a tunnel being put on a boat that a tunnel had no business being put on because of the destabilizing factor involved.

    If he dont want to talk about it and would only do it again with a factory tunnel in his hand leads me to believe the fabricator is operating out of his realm because anybody that welds can fabricate something as simple as a tunnel shell. What he did leads him to believe it was the tunnel he built wasnt up to par.
    Maybe nothing was wrong with the tunnel at all but the boat he put it on.
    If this is the case he is still lost in thinking a factory tunnel will be the difference.

    A tunnel will destabilize a narrow beam boat enough to flip it in a hurry. Snap roll with no warning. Tunnels are for the big beamy boats if you want predictable stability.

    1st and most important consideration of tunneling a boat is the hull.
    2nd would be the science of building a tunnel to achieve what a tunnel is supposed to. Many factory tunnels have little to no science behind them until you get up into the high priced machines where the tunnel is designed specifically to a hull and its nuances.
  7. Goldenshinner

    Goldenshinner New Member

    wow, thanks for the imput, i was gone too long from this site.

    the shop i talked to, specializes in hull repairs and customizations, they are well known and respected. ive seen their work and consider them excellent quality.(i will not post their company name, as i dont know if they would like that). i think you are right, their problems probably were with the design of the actual tunnel. the boat itself was a standard JOhn boat, probably an alumicraft(as they are the most comon in my area). the tunnel is a standard option on these boats, and as far as i can tell they dont change the hull design on those that are "tunnel" options. ive studdied them and i could see that the placement and spacing of the install would probably be extreamly critical as far as strength goes. also i would mention that they are welded and not rivited. so i think it would have to be a first class install all the way to make it work. i am still interested, as ive got a particular flattie(boat) that ive got a love affair with and would rather modify than upgrade. i cant expain it better, as i know id be better off upgrading. thanks any more comments would help.
  8. Goldenshinner

    Goldenshinner New Member

    oh one more comment on this thought. i believe that the shape of the particular tunnel is not only matched to the boat, but also to intended speed. as im sure they have a design plaining speed,angle,depth etc for typical running. i am wondering if such a mod could be dangerious if coppied on to an identical hull otherwise. especialy if at plaining speed??and if it is dangerous would reducing the depth of the tunnel to make it slightly less agressive, if that might make it a safer gamble.
  9. Mark J

    Mark J New Member

    Four Oaks, NC
    Thats what naval architects and engineers are for.
    Personally, I wouldnt sit down and design a tunnel for my boat or your boat.

    Like I wouldn't call a plumber to fix the flood light.
    I've read enough about tunnel hulls to get myself in trouble with designing one for an application.
    I personally dont have the need to run in 2 or 3 inches of water but if I was going to tunnel a boat I wouldnt stop there. You'll never utilize the tunnel until you install a hydraulic jack plate too.
    The way a tunnel works almost mandates it have a hydraulic jack plate.
    The tunnel is operating at low speed so the motor needs to come down.
    At higher speeds the water column rises and allows for the engine to be raised as well.
  10. Ketch

    Ketch New Member

    Glad to see you pop in again Stephen. Hadn't seen you for awhile.

    Mark has given you some great advice. Adding a custom tunnel is not something just anyone should do. You need to find someone who knows what they are doing, and there are very few of them. If you are thinking of getting a tunnel put on your boat, and there is one available, I would suggest getting something from the factory.

    Yes, other people could design them to perform better, but one thing marine engineers do is try to minimize lawsuits by making them as stable as possible, even at a slight reduction of performance.

    I know a guy who has a custom one on his boat. I can try to see who did his and how it performed. I think it was in the south metro so it might not be too far for you.
  11. rgmatt

    rgmatt New Member

    Delaware River,Pa
    Jet or prop tunnel? Big difference and neither performs well when used in place of the other. As far as jet tunnels go there are a few guys here in Pa. that do them often , but these guys are custom jet boat builders. One of them, I believe, used to do prop tunnels also but I don't think he still does, but I doubt you want to travel to Pa for this anyway.

    Shot in the dark, but try contacting Kevin Turner from River Pro boats. He's out of MO but I believe he gets up your way to run his inboard jet boats. He may be able to direct you to someone from your neck of the woods who deals w/ tunnel fabricating.