Great East Predictor - solid mounts is a great suggestion. I agree with you!
Fastcheckmate175 - chine walk is pretty common on performance vee-pad hulls like yours.
As the hull accelerates, lift increases and the wetted running surfaces that are required to support the hull are reduced (more Speed = more Lift = less Surface). As the speed increases throughout the velocity range, the hull often gets to a point where the lifting surfaces become very much reduced and the hull is now "balancing" on a small area of the vee-portion or the "vee-pad" of the hull. When that surface becomes sufficiently small, it becomes tricky to "balance" the hull on its vee or pad. The result is a rocking of the hull from side-to-side. This rocking can tend to get a little more extreme with each motion, and so the "balancing" must then be provided by additional driver (steering/throttle/trim) input in order to maintain the hull in a balanced state.
With some driver input, the condition can be stabilized. With changes to hull setup and/or changes to the driving technique the condition can be alleviated.
Chine walking is predominantly characteristic of vee-hulls with deeper Vees (more deadrise), or hulls with deep or narrow running pads and hulls, or with a Veed pad or no pad (straight vee). 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, putting an imbalance on a hull that is trying to balance on it's vee or pad, and ultimately initiates chine walking.
Setup of your hull and driver "seat-time" are the best solutions to the problem. Usually an alteration to the hull, or 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. You will be unable to achieve proper steering control for high-performance conditions with a single-cable steering system. 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 all parts of the 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. If you’re not sure of your hull design, you should check with the manufacturer to confirm if the original design had some hook or rocker designed into it for some performance reason (sometimes this is the case). Otherwise, rework your bottom running surfaces until they are very straight and very smooth.
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, but a manual jack plate will provide the same range of adjustment needed. 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 handling instabilities such as chine walking. Engine setback can also affect stability, although it is more difficult to test using the ‘trial and error" method.
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 forces that are generated at the aft-end of the hull. High-pitch propellers (lower RPM) can make the boat more difficult to drive and ultimately contribute to slower achieved top speed simply because they are more challenging to drive. Be sure to select a prop that allows you to stay within your manufacturer's recommended RPM range, though. Larger diameter props with lesser rake can improve handling situations like chine-walk. And more blades will usually improve handling (less prop-slap). 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 dynamic instability to occur earlier and with more drama (more surprises). Higher trim angles can also lead to onset of porpoising in some hulls. A high-flying attitude is also harder to balance. When chine walking starts, it is not likely that you can simply "drive through it" safely without first reducing trim slightly.
Summary: Optimize Hull Setup and Driver "seat-time"!
Here's some more details in an
article on "Chine Walking"
/Jimboat
AeroMarine Research
