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 Post subject: Wandering 215
PostPosted: Thu Sep 28, 2017 12:44 pm 
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Minnow
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Location: Thumb of Michigan
I just purchased a new (to me) 1987 Sundowner 215. Most of my previous boating has been on the Great Lakes in boats set up for SCUBA diving ops. Yesterday I put the boat into the Black River in Port Huron, MI and motored out to the St. Clair river which separates the US and Canada. The Black is a 3 mile no-wake zone and I noticed the boat consistently wandered a bit from left to right, requiring correction. Out on the big river I had no problems at speed. I just wondered if those of you with more experience might have some insight into it's behavior.

Thanks!

Tim J

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Mercruiser 230/V8 - Alpha One Gen 1


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 Post subject: Re: Wandering 215
PostPosted: Thu Sep 28, 2017 1:12 pm 
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268 Vista

Joined: Tue May 16, 2006 10:49 am
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Location: West Michigan
All I/O driven boats wander. Some possibly more than others. Prop is RH rotation and will NEVER go straight and true at no wake speeds.
Every single prop I/O boat does this, always have, always will. A Duo prop, since the propellers are counter rotating,
will not "wander" like a single. So no worries, just go boating and enjoy.

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 Post subject: Re: Wandering 215
PostPosted: Thu Sep 28, 2017 2:53 pm 
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Location: West Palm Beach, FL
Cap'n Morgan wrote:
All I/O driven boats wander. Some possibly more than others. Prop is RH rotation and will NEVER go straight and true at no wake speeds.
Every single prop I/O boat does this, always have, always will. A Duo prop, since the propellers are counter rotating,
will not "wander" like a single. So no worries, just go boating and enjoy.

True, but some worse than others. My previous 19' cuddy wandered a lot! (short/wide v-hull) My Horizon 240 only wanders a little. (longer/deeper V)

I used to trim all the way down for No Wake zones to keep the bow down. However, trimming to a level position will have much less wander (such as all the way down, then up for ~2 secs)

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tow: 2017 Honda PILOT EXL-AWD
prev. boats:
'87 Chaparral 198CXL 4.3 OMC Cobra
'69 Jetstar 16ft Ski Boat, 115hp Yamaha
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 Post subject: Re: Wandering 215
PostPosted: Fri Sep 29, 2017 1:21 pm 
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Minnow
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Location: Thumb of Michigan
I suspected it was something like that. In prop airplanes you have to add rudder correction to offset turning forces generated by the propeller but once the correction is in, the plane stabilizes. I couldn't find any happy position of the stern drive where it wouldn't wander.

Thanks for your input!
Tim

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 Post subject: Re: Wandering 215
PostPosted: Fri Oct 06, 2017 1:34 pm 
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Trim tabs down or smart tabs will help with wandering as well as the outdrive trimmed all the way down.
I have smart tabs on my 13' rib to help with porpoising but it doesn't wander at all anymore. A boat that size is going to be right in the middle of needing hydraulic tabs vs smart tabs but smart tabs are easy to install and inexpensive, in relative boat money.
I would call Bennett or Nauticus to see what they say.

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--2002 3880 Regal Flybridge | Twin Merc 8.1HO **Seven**
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 Post subject: Re: Wandering 215
PostPosted: Fri Oct 06, 2017 7:51 pm 
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Location: Minneapolis, MN
Oldav8tor wrote:
I suspected it was something like that. In prop airplanes you have to add rudder correction to offset turning forces generated by the propeller but once the correction is in, the plane stabilizes. I couldn't find any happy position of the stern drive where it wouldn't wander.

Thanks for your input!
Tim


As one old airplane guy to another, the big difference here is speed. The boat is stable at cruising speed, just like the airplane. At no-wake speeds the boat is much more affected by the water flowing around the hull and other factors. Just like a baseball curves or a knuckle-ball moves unpredictably, the water flowing past the hull can have an unexpected effect. For example, to stop a yaw to the left, the wheel is turned to the right. The slight course correction yaws the boat to the right. Remember that it takes more of a steering input to stop a yaw and bring the boat back on course than to maintain the course. This course correction eventually will be too much. Just like air flowing over an airplane wing at different angles of attack or an aircraft fuselage in a slip, the water flowing by one side of the boat may behave differently than on the other side. This constantly changing difference in water flowing past the hull causes the boat to wander. The boat's thrust at the stern which means that you are always pushing the boat. If/when the bow strays off-course the stern has to get around behind the boat to push it back on course. This can cause the boat to move somewhat sideways until it re-establishes a new course. At this point you realize you have too much steering input and start to turn back the other way. Any wind, water current, wave, etc. can push the bow off course and require another steering correction. Unlike an airplane at cruise, the boat is not "dynamically stable" at idle. It's somewhat like trying to push a wheel barrow or back a trailer. There are many "hydro-dynamic" forces at work on a boat at any speed. Like with an airplane, slower speeds usually take more control input. Sorry for the long-winded explanation. Hope this helps. Gary

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Surface Interval: A scuba diving term for that time between dives to relax and prepare for life's next great adventure.

Current boat: '02 FW 268 Vista
Previous boat: '95 FW 190 Horizon


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 Post subject: Re: Wandering 215
PostPosted: Mon Oct 09, 2017 4:28 pm 
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Location: West Palm Beach, FL
Surface Interval wrote:
Oldav8tor wrote:
I suspected it was something like that. In prop airplanes you have to add rudder correction to offset turning forces generated by the propeller but once the correction is in, the plane stabilizes. I couldn't find any happy position of the stern drive where it wouldn't wander.

Thanks for your input!
Tim


As one old airplane guy to another, the big difference here is speed. The boat is stable at cruising speed, just like the airplane. At no-wake speeds the boat is much more affected by the water flowing around the hull and other factors. Just like a baseball curves or a knuckle-ball moves unpredictably, the water flowing past the hull can have an unexpected effect. For example, to stop a yaw to the left, the wheel is turned to the right. The slight course correction yaws the boat to the right. Remember that it takes more of a steering input to stop a yaw and bring the boat back on course than to maintain the course. This course correction eventually will be too much. Just like air flowing over an airplane wing at different angles of attack or an aircraft fuselage in a slip, the water flowing by one side of the boat may behave differently than on the other side. This constantly changing difference in water flowing past the hull causes the boat to wander. The boat's thrust at the stern which means that you are always pushing the boat. If/when the bow strays off-course the stern has to get around behind the boat to push it back on course. This can cause the boat to move somewhat sideways until it re-establishes a new course. At this point you realize you have too much steering input and start to turn back the other way. Any wind, water current, wave, etc. can push the bow off course and require another steering correction. Unlike an airplane at cruise, the boat is not "dynamically stable" at idle. It's somewhat like trying to push a wheel barrow or back a trailer. There are many "hydro-dynamic" forces at work on a boat at any speed. Like with an airplane, slower speeds usually take more control input. Sorry for the long-winded explanation. Hope this helps. Gary

This is as good of an explanation/theory as I have heard. But I take exception to a few parts:

1. Overcorrection: while it is easy to overcorrect for the wander, it does not explain the wander. You can leave the steering wheel in one position, and have the bow wander left to right to left to right to etc. The amount of turn stays about the same each time.
2. Some of the other differences in "water flowing by one side of the boat may behave differently than the other side" make sense, but these differences would be the same with an outboard engine as well as an I/O. However, outboards do not seem to have this wander, and I/O's do.

So here is one difference I can think of: Think of what happens when water passing below the hull reaches the transom. It is suddenly free to "pop back up" to surface level right at the transom. This rush of water UP the transom would also be angled towards the centerline of the boat (perpendicular to the V-Hull bottom). Water at the centerline of the transom would compete for position up the center. With an outboard, this Upward rush of water would be unimpeded. With an I/O, it would hit the transom bracket on the way up. Some of the water would be forced to port of the outdrive and some would be forced to starboard. My theory is that this upward flow of water up the transom may shift back and forth to the current side of least resistance. There is also the propeller interaction to make it more complicated, with the right side rotating down and the left side rotating up.

...just rambling on instead of getting my work done...

Ray (another old airplane guy)

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"Knot Easy" 2000 Horizon 240 Volvo 5.7GS /SX
tow: 2017 Honda PILOT EXL-AWD
prev. boats:
'87 Chaparral 198CXL 4.3 OMC Cobra
'69 Jetstar 16ft Ski Boat, 115hp Yamaha
'68 Aluminum Jon Boat, 3hp Sears
'64 Water Wings


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 Post subject: Re: Wandering 215
PostPosted: Mon Oct 09, 2017 8:18 pm 
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"Overcorrection: while it is easy to overcorrect for the wander, it does not explain the wander."

Well, just like pushing a wheel barrow or backing a trailer, sooner or later it wants to veer off course. Or..... maybe its just Neptune messing with all of us that are out boating and having a great time. 8) :lol: :wink:

Since I just winterized mine today, I'll have to do some philosophical analysis over the next several months and rely on those of you in warmer climates to continue doing the hard work of hands-on research. Thanks for the comments, Ray. And for our original poster, Tim, again welcome to the website and good luck with the "research". When it comes right down to it, there are a lot of theories but I am kinda leaning more toward the "Neptune" or maybe some other cosmic force in the universe..... :?

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Surface Interval: A scuba diving term for that time between dives to relax and prepare for life's next great adventure.

Current boat: '02 FW 268 Vista
Previous boat: '95 FW 190 Horizon


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 Post subject: Re: Wandering 215
PostPosted: Mon Oct 09, 2017 9:42 pm 
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Livin' the Dream
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Surface Interval wrote:

Since I just winterized mine today, I'll have to do some philosophical analysis over the next several months and rely on those of you in warmer climates to continue doing the hard work of hands-on research.


Sad for you, I have 2 more weekends left, then same will happen. Hoping for a light winter for all of us boaters that have to winterize

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 Post subject: Re: Wandering 215
PostPosted: Wed Oct 11, 2017 11:39 pm 
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Location: West Palm Beach, FL
Surface Interval wrote:
...Thanks for the comments, Ray. And for our original poster, Tim, again welcome to the website and good luck with the "research". When it comes right down to it, there are a lot of theories but I am kinda leaning more toward the "Neptune" or maybe some other cosmic force in the universe..... :?


I am now thinking it is caused by Underwater Gremlins:
.
.
.
Image
.
.
No, not that type of Gremlin.
.
.
This kind:
.
Image

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"Knot Easy" 2000 Horizon 240 Volvo 5.7GS /SX
tow: 2017 Honda PILOT EXL-AWD
prev. boats:
'87 Chaparral 198CXL 4.3 OMC Cobra
'69 Jetstar 16ft Ski Boat, 115hp Yamaha
'68 Aluminum Jon Boat, 3hp Sears
'64 Water Wings


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 Post subject: Re: Wandering 215
PostPosted: Sun Oct 15, 2017 3:15 pm 
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Minnow
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Joined: Tue Sep 26, 2017 12:51 am
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Location: Thumb of Michigan
Wow! I am impressed by the thoughtful answers to my question..... Thanks to all!

Another factor to consider is that it is difficult to determine the exact angle of the stern drive relative to the boat's forward motion when the boat is in motion. The ascending and descending prop blades generate different amounts of thrust thus applying a turning force which would add to the wandering tendency. The angle of the stern drive could exaggerate this effect. Obviously many factors are at play here.

I suspect that if a I/O boat like my 215 had a larger keel (like a sailboat) that said keel would act a little like the vertical and horizontal stabilizers of an aircraft and reduce the wandering tendency. Obviously that wouldn't be practical and is not warranted by the minor inconvenience of having keep making corrections as the boat creeps along. At higher speeds such a keel would add drag that would reduce the boat's overall performance.

After reading the above I'm sure you realize that my boat has been winterized leaving me too much time to ponder all those things that really don't matter......
Tim

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1987 Sundowner 215
Mercruiser 230/V8 - Alpha One Gen 1


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 Post subject: Re: Wandering 215
PostPosted: Sun Oct 15, 2017 5:08 pm 
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A person would like to apply logic and absolutely predictable principals to how a boat works as it moves through the water. On the other hand, just like the smoke from a cigarette eventually tends swirl or deviate from rising vertically forever, I believe the thrust from the prop at displacement speeds does pretty much the same thing. The prop is pushing water against the water that the boat just disturbed as it passed through/over. The hull displacing this water and the prop pushing water against this water that the hull disturbed is likely to be a contributing factor to the wandering. My experience is that bumping the throttle up a couple hundred rpm may actually make my boat wander a bit more. The sailboats have a huge advantage in slow speed maneuvering because their large keel fin and large rudder. But most sailboats are in big trouble above 10 or 15 knots. :shock:

As for Neptune or Ray's gremlins, I am not ruling anything out. Either water clarity (lack of) or being occupied driving or crewing on the boat keeps me busy to the extent that I cannot observe and positively verify the presence or effect of these forces. Even though some say "In God we trust, all others bring Data", not having seen something firsthand doesn't mean that it doesn't exist. My recommendation is to keep up the first hand "research" during the boating season and work on theory during the off-season. 8) :lol: :wink: Best regards.

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Surface Interval: A scuba diving term for that time between dives to relax and prepare for life's next great adventure.

Current boat: '02 FW 268 Vista
Previous boat: '95 FW 190 Horizon


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