chine walk

this afternoon, i rode in a buddies '75 20ft master angler with a closed transom and non flotation single armstrong bracket w/200hpdi. the boat ran great up to around 53mph, but when it trims out it really starts to dance- around 57mph it was uncontrollable and had to back off. no combination of tabs/motor trim helped. im in the process of building a '70 20ft SF that has already been enclosed with a hermco flotation bracket, and was curious about this chine walk. do all 20s have this problem over say 55mph or could it be a poor design with the enclosure and bracket? any input would be greatly appreciated!

[RUSTYNTABATHA]

NOT TO SEND YOU SOMEWHERE ELSE FOR INFO BUT SCREAMANDFLY.COM IS A SPEED SITE. BUT CHINE WALK OCCURS IN ANY BOAT WHEN YOU GO FAST. YOU CAN DRIVE THROUGH THE CHINE WALK BUT IT TAKES PRACTICE AND INSTRUCTION AND A CENTER CONSOLE FISHING BOAT THAT YOU ARE STANDING IN WOULD NOT BE GOOD PLACE TO LEARN THIS DRIVING SKILL. IT PRETTY TUFF EVEN IN A BASS BOAT IF YOUR JUST LEARNING. I HAVE A FRIEND THAT DRAG RACES IN ODBA DRAG BOAT ASS. AND HE COACHED ME THROUGH THIS DRIVING LEASON.
GOOD LUCK
AND HOPE THIS HELPS
RUSTY

its something that ive never really experienced though. ive been in 95mph in v-hulls, 135mph in cats and they will bounce from chine to chine, but still track straight. this gets squirrely going left to right, progressively more each time, and if you dont let off, it feels like the boat will dart to 1 direction, which would be very bad. i dont mind a little teeter from chine to chine, but the left to right stuff is scary...

[Bigshrimpin]

I don't think that there are too many 50+ mph 20 seacraft around. I know props made a big difference in the handling of my 20MA. Bow lifting props specifically the Michigan Rapture gave my boat really squirrelly handling characteristics (at 40mph). The Mirage Plus and the Highfive gave the boat entirely different handling characteristics . . . The boat was rock solid up to 52mph with the mirage plus. You might try changing props . . .

The bracket is another variable which effects performance. I'm very pleased with the performance of my 20 seafari with a bracket up to it's top speed 48mph. I don't even have trim tabs and the ride is stable (mirage plus 17P, 26" setback, and 1.87 gear ratio). The weight of the seafari is further forward . . . but the hull really lifts out of the water as you can see in this photo (@ 35mph). You might have hit the threshold where you need bigger tabs or wedges . . . I'm sure the bracket and the additional weight hanging off the transom offsets the engineered balance of the hull. . . but I think you're probably charting new territory for the board as far as the behavior of a bracketed 20 above 55mph. Good Luck!! I'm interested to see what you come up with . . .

[Bigshrimpin]

Is this the boat you're talking about . . .
http://www.classicseacraft.com/diver...0CC/index.html

[Bigshrimpin]

This is a good thread with some info about props and chinewalk.

http://www.classicseacraft.com/forum...r=52369&Forum=,All_Forums,&Words=&Searchpage=0&Limit=25&Main=520 69&Search=true&where=&Name=2409&daterange=&newerva l=&newertype=&olderval=&oldertype=&bodyprev=#Post5 2369

[doug7488]

Many time chine walk is caused by a motor that is to deep in the water - try raising it a bolt hole or two...

bigshrimpin, no that is not the boat. i have a feeling the bracket is mounted to high on this boat and the nonflotation really throws it off. at rest and trying to plane off, the exhaust is under water. but once up to speed, you can only trim so much before the motor cavitates.

[peterb]

last Friday I got my girl up to 58 MPH (new record for me) and I am fine at that speed providing that I keep a straight line and don't keep her there for too long

Besides at that speed I think that i am averaging less than 1 mile per gallon, whereas I get 1.7 to 1.8 at 40 MPH.

[Fr. Frank]

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.

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.