Thread: chine walk
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Old 10-09-2007, 12:52 PM
Fr. Frank Fr. Frank is offline
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Join Date: Oct 2003
Location: Shalimar, Florida
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Default Re: chine walk

Quote:
CHINE WALK OCCURS IN ANY BOAT WHEN YOU GO FAST
Well, yes and no. or, not exactly. An Allison XB or XTB rarely chine-walks, and it has fairly definite hard chines. But look at the hull and notice the small transitions at the center pad.

Chine walking is caused by the hull being in an unstable hydrodynamic state. This is usually caused when transitioning from one hydrodynamic state to another, generally when the hull lifts/is forced higher in the water, and the primary hydroplaning surface is changed from one surface or pair of surfaces to another, usually from a wider planing surface and narrower together, to the narrower alone.

During that transition, the hull is not yet fully able to achieve primary plane on the smaller surface, but is going too fast to maintain stability on the wider an the narrower at one time. So it tries to plane on just 1/2 the wider surface and the narrower. That creates a turning, out of trim hydroplaning situation. We should all remember that an object in motion will travel in a straight line unless acted upon by an outside force, and the P factor from the motor and propeller act like a slightly out of balance gyroscope. So when the hull falls off from the smaller, narrower planing surface alone, and begins to plane on it AND one of the wider surfaces, whereupon the gyroscopic effect and forward momentum cause it to begin to right itself. But remember, we don't have enough speed to plane on the narrower surface alone, yet, so, the righting motion which began continues, forcing the hull to try to plane on the narrower surface, and the wider surface on the other side, and the sequence begins to repeat itself.

At this point, you can only do one of four things: 1, You can accelerate to a speed at which the smaller, narrower surface is capable of supporting the hull as the primary planing surface (called pushing through or driving through)
2, you can counteract the oscillation with predictive steering input (a necessary part of pushing through),
3, you can reduce speed until the hull regains stability, or
4, you can bail out at very high speeds, either voluntarily or involuntarily.


Quote:
A CENTER CONSOLE FISHING BOAT THAT YOU ARE STANDING IN WOULD NOT BE GOOD PLACE TO LEARN THIS DRIVING SKILL.
Actually, a center console is the BEST place to learn to handle chine-walk, provided you have a stand-up wrap-around racing bolster. With your feet set about shoulder-width apart, you can feel and predict the hull oscillation much better than if you are seated. The danger with a chine-walking center-console is losing balance and/or grip on the controls as oscillation increases. If you are flung sideways, over you go. That danger is lessened quite a bit when you are seated in a wrap-around seat bolster.

I began racing hydroplanes 40 years ago as a boy, since the days of the spade-hulled "B" outboard "knee-boats" with a Mark 7 Merc. I've driven a wide variety of boats at great speeds, and crewed offshore racing powerboats of 22' and 30' as a throttleman and driver, and I've driven on the water at speeds greater than 100 mph. That's my credentials.

So, given the option, for learning or teaching purposes, I would choose a center console with stand-up racing bolsters.
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Fr. Frank says:
Jesus liked fishing, too. He even walked on water to get to the boat!

Currently without a SeaCraft
(2) Pompano 12' fishing kayaks
'73 Cobia 18' prototype "Casting Skiff", 70hp Mercury
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