chine walking

Discussion in 'Stability' started by mig74, May 17, 2007.

  1. mig74
    Joined: May 2007
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    mig74 Junior Member

    hi, im new to this site, but hopefully you guys can help me.
    i have an 18 foot speedboat v-hull with a very small pad that measures about 4 inches. ive got a 225 promax mercury (i know-overkill), and when the boat is -on the pad- at 65 mph, it has a violent chine walk. mind you the boat is a 1974 powercraftmarine which probably never intended to have so much power, but i would like to know what i could to eliminate this. i want to put trim tabs on it, but since the boat-airs out- is completely out of the water at high speed, the tabs would have to go on the very inside of the transom, interfering with the motor? ive even thought about having a custom hydrofoil fabricated under the damn boat. any info,rants and raves will be appreciated
    thanks.
    MB:confused:
     
  2. lazeyjack

    lazeyjack Guest

    try putting on a couple of stakes
     
  3. lazeyjack

    lazeyjack Guest

    strakes
     
  4. marshmat
    Joined: Apr 2005
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    marshmat Senior Member

    I believe jack means strakes....:p ;)
    A few small lifting strakes might cure the boat's trouble. (Key word is might.) The problem is figuring out how big they should be and where they should go. Just about all of the decent data on the design and placement of them is proprietary. I'm not sure a hydrofoil would help much if you're already coming nearly out of the water.
     
  5. Bergalia
    Joined: Aug 2005
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    Bergalia Senior Member

    No Stu, I prefer your first response...If I had my way I'd ram stakes through all those nasty, noisey smelly things which now seem to pass as 'boats'....:D :D :D :D :D :D :D :D
     
  6. redtech
    Joined: Feb 2007
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    redtech Senior Member

    mig74, first that there boat was only ment for what 150-175hp?
    know lets see jack plate (doesn't have to be hydrolic just in right area) my thought 6-10inch off set from transom.
    raise the motor but keep 11-20psi of water pressure if loosing water pressure get a bullet from bob's marine, this should calm down the chine walk if not strakes
    as you raise the motor you'll have to reprop but the speed of chine walk gos up when all is said and done chine walk is just short of blow-out
    go luck but remember above 70 the life jackets so they can find the body
     
  7. mig74
    Joined: May 2007
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    mig74 Junior Member

    strakes?

    thanks 4 all the responses guys. i wanted to know who could tell me more about strakes. i also wanted to answer about my setback. i have 12" of set back with my 4 inch hydraulic jackplate and 8" setback bracket. im gonna have to show u guys a picture of my boat which i think has alot of lifting strakes built into the hull. ill try to posts some pics later. thanks again!:idea:
     
  8. hmattos
    Joined: Jun 2004
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    hmattos Senior Member

    Hi Guys,
    We have tested plenty of boats from many manufacturers and some of them chine walk in a really dangerous manner.
    Our boats - www.explorermarine.co.uk - will show signs of chinewalking with the SPORTS model from 65 mph, but most customers can live with that.

    Our best solution is to get another boat to run alongside at speed on a calm day and video the action. You will then see how little of the boat is in the water at that speed - there is no point in fitting strakes if they will not touch the water!

    Having determined what will touch the water you need to modify the hull with strakes or trim tabs so that the restoring force is small enough to be self damping. Severe chinewalking is caused when the restoring force amplifies the angle of oscillation and thus the situation gets rapidly worse.

    It will also help if you can get more of the straight part of the keel into the water, to stablise the yawing action. Do this by reducing trim angle, or moving weight forward - most outboard boats are tail heavy..

    Note that on most boats at this speed the AERODYNAMIC forces are greater than the HYDRODYNAMIC, so the boat is really flying at this point. The Vee of the hull then needs to be stable in the air, which it rarely is. As the, say, starboard side of the boat goes down for some reason, the vee angle means that at the point of contact with the water, it will give massive aerodynamic and hydrodynamic lift to the now flat side and thus throw it over to the port side, even faster than it came down first time, which amplifies the problem for the next cycle.
    Ever wondered why really fast boats are catermarans?

    Good luck
     
  9. mig74
    Joined: May 2007
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    mig74 Junior Member

    Cool

    Thanks Hmattos
    Very Informative Stuff, I Think You Guys Have Shed Some Light On My Situation, This Is A Neat Site. Ive Only Been Registered Since Yesterday And You All Seem Really Helpfull. Again, Thanks.
     
  10. igo2c
    Joined: Jul 2007
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    Location: New England

    igo2c New Member

    Some suggestions

    Hi MB,

    Maybe you've solved your chine-walking issues by now. If not, here's some suggestions:
    There are a few modifications required to safely run an outboard-powered, modified v-pad style hull. Severe chine-walking on this type of hull is usually a result of engine oscillations. When the boat is "aired-out", with only a few square inches of flat hull surface in contact with the water, the propeller and skeg are the only thing "holding the boat to the water" (when you get the chine-walking sorted out, try a variety of wheels and you'll see what I mean). The engine oscillations have the same effect as rapidly jerking the steering wheel from side to side. A few mods will make a huge difference:

    1: On the engine, get rid of the mushy, rubber mounts which hold the mid-section to the mounting bracket. Aftermarket solid mounts are plentiful for V-6 Merc's, and you may be able to find them "over-the-counter". Land N' Sea in New Hampshire used to manufacture them. Eagle-One down there in FL may have them, as well.

    2: Install a dual-cable steering system. This may can become a bit costly, depending upon what brand of system you currently have. Sometimes, another rack/pinion can be added to the existing helm. When a dual-cable system is installed, the cables are adjusted so as to be slightly binding against one-another, removing any backlash and/or endplay.

    3: Any boat that's running at those kinds of speeds should have a spring-loaded foot throttle and trim controls mounted on the steering wheel. Two hands on the wheel is a "must" at high speeds. Don't forget the kill switch tether.

    Even with these mods you will most likely have to "work the wheel" to oppose the effects of the hull reacting to the prop torque, but you should notice a huge difference in high-speed stability.

    'Best of luck, and I hope you get her running straight and fast.

    Scott
     
  11. mig74
    Joined: May 2007
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    mig74 Junior Member

    Thanx!

    HEY SCOTT, THANKS ALOT FOR THE INFO. I DO HAVE SOLID MOUNTS, A HOT FOOT, STEERING WHEEL MOUNTED TRIM AND JACKPLATE, AND A LOW WATER PICKUP, BUT IM BEGGINGNG TO THINK THAT THIS HULL (1974 POWERCRAFT) MAY BE AT ITS LIMIT. SOME LOCALS DOWN HERE HAVE TOLD ME ABOUT A SORT OF ALUMINUN STABILIZER THAT WOULD MOUNT UNDER THE SETBACK BRACKET, BUT NO ONE SEEMS TO KNOW WHERE TO GET IT OR EVEN HOW IT LOOKS LIKE! RIGHT NOW IM RUNNING A 15X26 CHOPPER2 PROP, MAYBE I SHOULD TRY A 4 BLADE? ANYHOW, THANKS AGAIN FOR THE RESPONSE, BUT FOR NOW IM STILL BAFFLED:confused:
     
  12. mig74
    Joined: May 2007
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    mig74 Junior Member

  13. Jimboat
    Joined: Feb 2002
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    Jimboat Senior Member

    The 'cyclic' action that hmattos notes is often initiated by a chine-walking incidence that progresses into porpoising. (You may wish to check out an article that I wrote in HotBoat magazine April 2007 - "Hump Zone - Why Does Your Boat Porpoise?")

    Here is some more info, specific to chine walking...

    The chine walking experience refers to the situation occurring with high performance vee-hulls as the boat accelerates, lift increases and the running surfaces raise out of the water. As hull speed continues to increase, the wetted surfaces are sufficiently diminished on the vee-portion of the hull that it becomes challenging to “balance” the hull on its keel (either vee or pad). To counteract, additional driver steering input is necessary in order to maintain the hull in a balanced state.

    If left unchecked, the boat will rock from side to side with increasing motion and drama. The boat is now “inherently unstable” – this means that if left alone, the “imbalance” of the hull is more likely to get worse on it’s own, not better (the worse it gets, the worse it gets). So the hull will now start to rock from port chine to starboard chine – back and forth. This is called “chine-walk”.

    Chine walking is predominantly characteristic of vee-hulls, with deeper Vees (more deadrise), hulls with deep or narrow running pads and hulls with a Veed pad or hulls with no pad. These bottom designs are just more inherently difficult to balance at higher speeds. Another contribution to chine walking can be seen at higher speeds from "propeller slap" (usually seen more with props of fewer blades). As the prop turns, each blade enters the water and another exits the water. This irregular in/out of every blade, changes the dynamic forces at the location of the propshaft, repeatedly putting an imbalance on a hull that is trying to balance on it's vee or pad, and ultimately it creating chine walking.

    Setup of your hull and driver “seat-time” are the best solutions to the problem.


    The experience of chine walk can be only slightly bothersome on some hulls or can get to be out-and-out dangerous on others. The latter can ultimately result in catastrophic consequences if the condition is not corrected quickly. Usually an alteration to the hull setup and/or modification to your driving methods (read seat-time) will improve the problem.

    Here are some established steps toward minimizing chine walking:

    1. Check & adjust steering. There should be no play in the steering mechanism. And a dual-cable or dual-hydraulic setup should be used for high performance hull setups. For cable setups, be sure that you have all of the slack adjusted out of it, so the cables are slightly pre-loaded against each other. Same for hydraulic, ensure it's adjusted so there is no play in the wheel and carefully bleed the lines to remove all air from the entire system.

    2. Use solid mounts - Stock rubber motor mounts allow for too much slack movement between steering wheel and engine. Solid mounts are much tighter and provide much better steering control at high performance speeds.

    3. Clean Hull Lines – make sure that any non-designed irregularities such as hook, rocker, bumps or other notches in the running surfaces are removed or faired away. You can use a long straightedge to visually inspect your running surfaces and fair out the imperfections.

    4. Weight balance of hull – Although this is a tricky thing to optimize for all speeds (since the dynamic balance of a hull shifts significantly throughout the operating velocity range of the boat), the onset of the chine-walking phenomenon usually occurs at a particular speed for each hull and you can focus on correcting balance at that bothersome speed. Try to situate movable payloads close to the static center of gravity (CofG) – both longitudinally and laterally. This can often be a trial-and-error experience, but you’ll see the results of weight balance changes immediately in the handling of the boat. Optimize portable equipment, batteries, oil tank and fuel tank positions. Also situate passengers for the best weight balance. An equally balanced passenger/driver load will help allot, so if the driver’s seat is positioned much to one side, add weight to the passenger seat to help balance the load and make learning to drive the boat much easier.

    5. Motor height – You can adjust engine height to minimize the instability. This is easiest to do with a hydraulic jack plate. Remember that as you raise the engine height, a low water pickup may become necessary in order to ensure that the engine gets enough water pressure. Test your rig at different speeds, weight distributions and water conditions to find the best height for each. Often, as the engine is raised on the transom, the reduced lower unit drag can have an improved effect on instabilities such as chine walking. Engine setback can also affect stability, although it is more difficult to experiment with.

    6. Propeller selection - The right propeller design can change the balance of a hull as well as make or break its performance. Rake, diameter, pitch, cup and blade number, can all influence the Lift and drag generated at the aft-end of the hull. Most high performance vee-hulls will handle well using medium-rake, large-diameter propellers. High-pitch propellers can make the boat more difficult to drive and ultimately contribute to slower achieved top speed simply because they are more challenging to drive. More blades will also usually improve handling. Propeller testing is also time-consuming, but can really pay off in overall performance and stability.

    7. Seat time (experience) – Chine walk on a vee hull can usually be controlled by the driver as he gains more experience and skill with his setup. Unfortunately, there is just no substitute for experience! Drive your hull in different conditions at lower speeds until you are completely comfortable with your ability to “sense” and “correct” for motions of the hull to conditions and speed changes. Then gain more experience at a slightly faster speed, in the same way. Work you way up to higher velocities slowly, under good control. With familiarity, you will develop a sense to predict your hull’s motion and you’ll soon be able to react accordingly to correct it prior to it getting severe. The correct driver input to balance a vee-hull or a pad-vee hull at higher speeds is very minor if the adjustments are made quickly, immediately at the onset of motion (“timing is everything”).

    "Timing is everything" - When you sense the onset of chine walking, reduce engine trim and/or throttle. When the motion subsides, you can increase trim and throttle smoothly as the hull drives right through the previous chine-walk speed barrier. Steering adjustments need only be small, but should be made in a timely manner in the opposite direction of the hull bow movement. When the left bow drops or the bow moves left, steer slightly right. When the right bow drops or the bow moves right, steer left. This steering input is done swiftly and in short motions. With practice you will be able to make these small steering inputs "before" the motion actually occurs. Turning the steering wheel slightly into (against) the torque of the propeller as soon as you “sense” the onset of lateral imbalance (side-to-side rocking), can help drive through the chine walk stage too.

    8. Minimize Trim Angle - This was mentioned above, but worth saying again. Use as little positive trim as possible. More trim (higher running angle of attack) causes the onset of instability to occur earlier and with more drama. A high-flying attitude is harder to balance. When chine walking starts, it is not likely that you can simply "drive through it" without first reducing trim slightly.

    Summary: Hull setup and driver “seat-time”.
     
  14. messabout
    Joined: Jan 2006
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    messabout Senior Member

    Looks like Jimboat has it covered.

    At the risk of offending fast boat guys, I have an honest question. Why must you go so fast? That is a legitimate question made in good faith. There must be a good reason. If you are involved in organized racing the question is answered. The operative word is "organized". You are a professional bass fisherman trying to get to the sweet spot you discovered yesterday, before the competitors do. You are a dope runner hoping to outrun the Coast Guard. Aside from those reasons there may be others that I have not thought of. Running an unstable boat at speed seems like Russian Roulette to me.

    If it matters, I was in the past a long time hydro racer. I can recall some of the exhillaration of trying to turn the boat around the markers, skipping sideways, saying quick prayers, and then clamping the throttle again down the straight. What in hell was I thinking?

    Although off topic, a round table discussion about our "need for speed" and its motivation would be enlightening, perhaps instructive.
     

  15. Jimboat
    Joined: Feb 2002
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    Jimboat Senior Member

    messabout - as a long time hydro racer yourself, you've probably answered your own question. I know that competitive racing has given me the most appreciation for what can really be accomplished with a good powerboat design - and the recreational side brings all the same satisfactions - and BOTH are so much fun that I don't know what I'd do without them! Lot's of performance boat owners have a desire to experience the "fun" of getting the most out of their rig. That doesn't need to be going 100mph, but often merely means getting the most out of their 10hp rig. The fun is in the challenge. Running an unstable setup is just not necessary....the most of a boat's performance can be achieved by ensuring that the setup is dynamically stable...it just takes some homework, and some hard work and patience. And there is always that next 1mph!
     
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