Tunnel hull design questions
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Tunnel hull design questions

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    Senior Member lbhsbz's Avatar
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    Default Tunnel hull design questions

    I'm in the market for a tunnel boat, but not exactly sure what to look for.

    I've heard that the CP tunnels like to hook on a hard shutdown...what makes them do that? I looked at a Wildercraft the other day and it had a very strange bottom on it...the tunnels were rounded, as were the running surfaces (sponsons?) outside of the tunnels...each sponson was like it's own little V-hull. Advantages/Disadvantages?

    Basically, what makes one tunnel hook on shutdown while another is nice and safe? What makes one tunnel perform better than others?

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    Senior Member bp298's Avatar
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    do you want a race boat, or a river boat??

    Quote Originally Posted by lbhsbz
    I've heard that the CP tunnels like to hook on a hard shutdown...what makes them do that? I looked at a Wildercraft the other day and it had a very strange bottom on it...the tunnels were rounded, as were the running surfaces (sponsons?) outside of the tunnels...each sponson was like it's own little V-hull. Advantages/Disadvantages?
    look under the bow of a cp sometime - there is nothing there for the bow to land on. the add-on sponsons help a lot, but even with those a person can get tossed. they are very hi-strung, finicky boats that are pretty much best suited for racing only.
    there are differing theorys about coving the tunnels and rounding everything. some people believed that would enhance flow, most don't. i've seen coved tunnels on pretty much everything - doesn't seem to matter a whole lot.

    Quote Originally Posted by lbhsbz
    Basically, what makes one tunnel hook on shutdown while another is nice and safe?
    there's a littany of attributes that can cause a tunnel to hook, and pretty much any model tunnel can hook on shutdown, depending on setup. last year in marble falls, watched a guy in a stealth, of all things, lose power at about 113, hook and spit him out. a lot of it has to do with the way it's setup.

    Quote Originally Posted by lbhsbz
    What makes one tunnel perform better than others?
    that's a fairly broad, loaded question, and really depends on what you mean by "perform better". pretty much any of 'em perform well, just depends what you're trying to do, just depends how much time, energy and expertise you want to throw at it. same model boats are different weights, have different modifications, different power applied, etc., etc., to the point it's almost impossible to make objective comparisons. examples could be given that might indicate a capps cheyenne performs best compared to a daytona, but when you really dissect the examples, there are so many differences inside the boats that it makes the hull comparison moot. there are daytona examples that could show the same thing. then there's the stealth that's the current fastest and quickest jet in the country - i've watched that boat lose power 3 times in the traps, at over 150, settle right in straight as a string, slide to a stop. pretty much a different result than the boat, out of the same mold, at marble falls. then there's the topless tunell and placecraft and the "other" cheyenne.
    Last edited by bp298; 07-18-2010 at 06:37 PM.

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    Senior Member Futs's Avatar
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    Are we talking Mod V's here? I will give my .02 On the SWTD the keel is deeper all the way through the transition so when the boat sets down it sets down on the keel first rather than the outer "sponsons" for a lack of a better word. They can still bite you if it comes down hard to one side as any boat can, but for the most part it settles down straight.
    Now on the placecrafts, the outer sponsons are deeper and can bite and hook because the transition of the keel and outer sponsons are almost the same.
    On the CP Kinda the same deal, there is a lack of center keel vrs. the outer sponson.

    Im sure someone could explain it better, but thats kinda the idea.....

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    Senior Member lbhsbz's Avatar
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    Quote Originally Posted by bp298 View Post
    do you want a race boat, or a river boat??

    no santioned events for me....rules take all the fun out of it.

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    Senior Member lbhsbz's Avatar
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    Quote Originally Posted by Futs View Post
    Are we talking Mod V's here? I will give my .02 On the SWTD the keel is deeper all the way through the transition so when the boat sets down it sets down on the keel first rather than the outer "sponsons" for a lack of a better word. They can still bite you if it comes down hard to one side as any boat can, but for the most part it settles down straight.
    Now on the placecrafts, the outer sponsons are deeper and can bite and hook because the transition of the keel and outer sponsons are almost the same.
    On the CP Kinda the same deal, there is a lack of center keel vrs. the outer sponson.

    Im sure someone could explain it better, but thats kinda the idea.....
    Cool, that's about what I had come up with looking at pictures of different designs. Thanks for the lesson.

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    Senior Member bp298's Avatar
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    Quote Originally Posted by Futs View Post
    Are we talking Mod V's here? I will give my .02 On the SWTD the keel is deeper all the way through the transition so when the boat sets down it sets down on the keel first rather than the outer "sponsons" for a lack of a better word. They can still bite you if it comes down hard to one side as any boat can, but for the most part it settles down straight.
    Now on the placecrafts, the outer sponsons are deeper and can bite and hook because the transition of the keel and outer sponsons are almost the same.
    On the CP Kinda the same deal, there is a lack of center keel vrs. the outer sponson.

    Im sure someone could explain it better, but thats kinda the idea.....
    crusaders are the same way. the pc, sw, crusader, wilder, etc., all have center keels extending several feet forward from the front of the outter sponsons. that helps, but if the boat is running with a lot of attitude, which is the way a lot of people run them, and slams down at 100+, it's still gonna dig in.

    so lb, are you looking to get an old used hull? are you thinking about a new blank at all? seems like you'd have everything you'd need, except a hull - perfect scenario for a new blank.

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    SAVE YOURSELF a lot of problems give GS MARINE a call and buy a 19 ' stealth great ride and with small amount of hp ( 700 ) it will go 100 mph or better. and they have done ALL the home work so when you feel the need for more its only a phone call away. the champ. ( just the facts )

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    Quote Originally Posted by lbhsbz View Post
    Basically, what makes one tunnel hook on shutdown while another is nice and safe? What makes one tunnel perform better than others?
    When at higher speeds, a tunnel hull is supported by a 'balanced' combination of aerodynamic lift and drag (mostly from aerofoil formed by upper deck surface and tunnel roof surface) and hydrodynamic lift and drag (mostly from sponsons) and the hull weight distribution. At higher speeds, all of the surfaces (including drive appendages, etc) that contact the water have a huge influence on the dynamic balance of the hull - so changes to any contacts need quick correction (driver input) to re-balance the hull. The balance is different at every speed. The location of the 'dynamic center of gravity' of a hull can change by 80% throughout the operating velocity range of the hull.

    Some hull designs are more 'foregiving' to this 'correction' than others are - and it depends on how the hull surfaces are designed to 'balance' all of these the different forces at different speeds. This 'balance of forces' is important for the hull to remain stable. A high performance vee hull or vee-pad hull has similar 'balance of stability' issues as speed changes.

    A tunnel hull (or performance vee) can be designed to maximize stability at any speed, but not all speeds. Driver input is usually required to adjust the balance and stability of the hull as speed changes - and same is required during a 'shutdown' of power...if this happens quickly, then the hull's inherent 'dynamic stabilty' will determine how much of a 'handful' the hull will be for the driver to make the adjustments fast enough to stay in control. Some boat designs and setups are more forgiving in these situations than others.

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    Junior Member Bert's Avatar
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    My dad just loaned me his 19' Southwind Tunnel Dragster. The boat just ran (Thursday) 76.1mph GPS at 5400rpm with a 454 w/ about 550HP. I'm really impressed with the way the boat rides. With the diverter down you can putt at 3K and it feels safe. Put the diverter slightly passed half way and bump up to 4K and the boat rides on top of the water-very nice. Here are a few pictures. The back seat however was built for small children
    Bert
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    Quote Originally Posted by bob fry View Post
    SAVE YOURSELF a lot of problems give GS MARINE a call and buy a 19 ' stealth great ride and with small amount of hp ( 700 ) it will go 100 mph or better. and they have done ALL the home work so when you feel the need for more its only a phone call away. the champ. ( just the facts )
    Can't afford a new boat, but thanks.

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    TRG
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    seems to be quite a few gullwings available these days, I was just noticing over in the spam area.

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    Senior Member wizard612's Avatar
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    It's getting a bit conflicted here. Futs your saying a deeper center keel running further forward is more stable. Yet a CP is more stable with Bennett's outside sponson add ons per bp298. I look at it as how much hull is out there to hold the bow up and what angles are involved to keep it tracking straight on shut down. As far as tunnels go I've always like the Daytona types even though they can catch a chine if you turn them too hard and blow over if the weight is too far back. But then again these are performance boats and you have to drive them knowing that. If you want "the best hull" look to current records within the type of motor you want to run, double check it's safety record, then go shopping.

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    Senior Member lbhsbz's Avatar
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    Here's my dilema....I got tossed from my boat on the 4th...it wasn't fun. I dunno what happened first...I see evidence in the remains that one of the cav plate braces went through the hull, maybe that influenced the roll, but who knows.

    I need a new boat. I like to go fast. I know that anything can be made fast with enough effort/work. I also have a 2 month old son, and I'd like to be around for him. Part of me wants to get a nice slow safe boat, but I know that I won't be happy with it, and I'll try and make it faster...and it will get dangerous. This is just for hot rodding around on the river. I'd be perfectly happy with high 90s / low triple digits, but I don't want a boat that is inherently unstable. I know that "safe" and "triple digits" are not 2 words that belong in the same sentence, but I'd like to improve my odds the best I can. I will be purchasing a lifeline and most likely dusting off the old road race helmet for any high speed runs...call me paranoid, but getting tossed sucked, and I was lucky it turned out as well as it did. Maybe I'm just still a bit gunshy. Maybe it can't be done...in which case I'll turn boring like my dad and buy a little outboard ski boat, take up collecting stamps for fun, and spend my weekends manicuring the lawn. That would suck though and I'd sooner shoot myself in the head..LOL.

    Wingers are too expensive. I've got about $5K to spend. All I need is the fiberglass part...I've got a motor/pump/rigging/etc...sitting on a shelf waiting for something to bolt it into. I know I can find a nice tunnel in my pricerange....the question is simply which one. I don't need the fastest hull out there...I'm just running it on the river, but I would like a hull that has a decent track record of not getting funny on shutdown.

    I like the SWTD and the crusaders....the Wildercraft I looked at had way to busy of a bottom on it and I didn't really know what to think...wasn't a straight line on the bottom of the boat. There were some other aspects of the boat that didn't sit well with me as far as rigging went, so I didn't buy it. I figured this time I'll do my research before I buy something rather than research what I just bought like I usually do.

    One question about the crusaders...I see a lot of these with shorty stringers. I imagine the side of the keel act as stringers to keep the bottom ridgid so that stringers are only really needed to bolt the motor too...But it's rare that I see fast boats w/ shorty stringers, so this kinda scared me a bit. Any input on this? Can 4 foot long 1x4 stringers hold down a 700hp motor?
    Last edited by lbhsbz; 07-19-2010 at 11:35 AM.

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    Senior Member bigblock68's Avatar
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    big A has a new gullwing hull i thank you could get for close to that but its in tn

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