Speed/Chine Walk

[PaulO]

Well, now that the Donzi is back together with the new Alpha and a various other improvements, I have a question for you 70mph plus guys. I have not gotten the GPS readings yet but, I am certain that the new top speed is quite a bit higher than my old setup. My guesstimate is somwhere in the mid 60s. At top speed, it really chine walks. I am wondering if I am approaching the maximum speed this hull was designed for but, there are you guys ( RickR, Geoo, etc) who are doing mid 70s. Do you have a chine walking problem? At what speed does it begin? If it is spooky at 65 does that mean it is hair raising at 75? Just wondering if I really want to build that motor I have been thinking about.
Paul

[GEOO]

Paul,
Drive trim angle, prop style and speed create transom lift and cause chime walk. My X-18 with a 300hp Volvo 290 drive chimewalked at WOT 58mph (Full Trim). The more horse power you have the less trim you need to go the same speed. When I put the 383ci 400hp engine in the boat was rock solid at 60mph, however at WOT and full trim 66-68mph it chimewalked. I've found that a cleaver prop and or a prop with less surface area will give you less transom lift and better control. Donzi Classics need bow lift too loosen the hull up to get top speeds, these props may trade off some the the bow lift.
Last year with 400hp and the Arneson I could run near 80mph without chimewalk unless I hit cross waves. GEOO

[RickR,GroveCity]

PaulO
A little bit of chine walking does not bother me, but we need to err on the side of safety.
Does she track well? If the bow hunts be very carefull.
When you get above the upper 60s the hull does not have a platform to ride on because you get up above the outside strakes.
Trim tabs help, at WOT I ride on the prop and the port tab (which counteracts the prop torque). Mine chine walks when I am on the ragged edge with alot of trim.

If you don't have tabs I would install some.

Many times chine walking is caused by sloppy steering. The Merc steering on my 95 22Classic is not up to the task of high speed operation. I haven't spent much time on it yet but it looks like the PS actuator was designed with too much play in it.

Try less trim, if you still have a problem experiment with different props. You might also try a torque tab on the drive.


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RickR mailto:riggerb@aol.comriggerb@aol.com</A>

[This message has been edited by RickR,GroveCity (edited 05-22-2000).]

[This message has been edited by RickR,GroveCity (edited 05-22-2000).]

[GeneD]

Gee, I don't get any chine walk at all!
Why is that Forrest?

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GeneD
007
Melbourne, Florida

[Forrest]

Well Gene (LOL), as we know from some of the previous posts on this thread, there are a number of factors that contribute to chine walk. Most notably, propeller torque trying to pull the boat to one side while the water pressure against the hull is trying to return the boat to its designed running position. As GEOO noted above, less propeller-blade wetted surface area will reduce the torque effect. By running the Alpha SS drive, which puts the prop about 2-1/2" higher than that of the regular Alpha One drive, you have effectively reduced the propeller torque effect by reducing the wetted surface of the prop. That combined with the fact that you probably don't have much slop in the steering, chine walking is not that much of a problem for 'ol 007.

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Forrest

[AVickers]

Don't forget that by using an SS rig that you also reduce the leverage that the prop/foot combination has to try to lift the bow of the boat at all...

Shorter foot = shorter stick with which to pry the boat up in the air.

With the Arnesons, the lever is non-existant. The forward force of the prop is applied directly to the lower portion of the stern trying to push the stern up -- as opposed to trying to lift the bow...

My guess is that changes in these force levers and vectors play a powerful role in the boat's willingness to run straight and true or chine walk. Also, early 18s had a sharp V at the stern, later boats have a rounded V. From what I understand, the round V is less proned to walking around in that when up to speed, the rounded area serves as a pad whereas the sharp V more-or-less wants to flop to one side or the other when water pressure is forcing the boat up and out of the water...

[GEOO]

Paul, Here are your choices.
1) Trim the boat less, go slower.
2) Try different Prop. Less Diameter.
Less blade area.
Cleaver Style.
3) Raise your X-Dimension. (drive height)
4) More Horse Power, get same speeds with
less trim.
5) Alpha SS.
6) Trim Tabs. Will slow boat and stop the
wobble.
7) Try and drive out of the chimewalk with slight counter steering.
8) Move more weight to the stern of the boat.

What else can we come up with? GEOO

[Frank Civitano]

Paul
I had more chine walk at 62 with my old prop,then I have with my new prop at 77mph? My wheel is 6 sizes larger on the pitch and it seemed to make the boat run better, More control,Lab finishing helped to?


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Frank Civitano

[PaulO]

Thanks to all for the input. Actually, the chine walk is not that bad just something new for this boat. The boat is a 73 with the rounded bottom. The steering is tight and the bow does not seem to hunt. The reason I ask is that I have plans to build a stroker motor over the winter and while driving a full tilt I asked myself "will going faster increase the chine walk to the degree that it becomes dangerous". It appears from all the input that the answer to that question is "not neccessarily". Perhaps an investment in an SS drive or a stern jack would be a better first step than the stroker. The idea of trim tabs seems to be defeating the purpose. The purpose is, after all, speed.
Paul