Going straight at low speed?

[dingbat]

Deadrise and weight distribution plays a huge role on how a boat tracks as well.

I have continuously variable deadrise hull. I literately can stand at the stern and maintain course all day long by simply shifting my weight relative to the keel, akin to the "Chesapeake Waltz"

 

[Mc Tool]

It's akin to riding a bicycle real slow. If you don't keep turning the front wheel to compensate for balance you'll fall. Going fast problem is greatly reduced.

Yes ,when on a bicycle or motorbike , when travelling in a straight line its actually a slow weave continually correcting an out of balance situation . If you tried to ride in an actual straight line you'd fall over .

 

[Mc Tool]

Deadrise and weight distribution plays a huge role on how a boat tracks as well.

I have continuously variable deadrise hull. I literately can stand at the stern and maintain course all day long by simply shifting my weight relative to the keel.

Oh yeah , wanna give us a clue what sort of weight we are talking here ?
Im 265 lb's, you'd think moving that lot from side to side would turn the boat fast enough to run over the skier being towed

 

[cyclops222]

S D wander is cured with a Duo Prop lower unit as a option. All the ones I have driven. 3

 

[Mc Tool]

S D wander is cured with a Duo Prop lower unit as a option. All the ones I have driven. 3

I did wonder about that

 

[04fxdwgi25]

Duo pro will fix, but so will the correct trim tabs deployed all the way down.
My old Chaparral 2550 SX (7.4L w/ B1 drive) wandered like a drunk. Added the tabs (12 x 16 sport tabs), then straight as an arrow at head speed when deployed.

 

[charliedaubitz1]

Ha ha yeah , my friend Pierre bought a jet boat ( we all fell about laughing coz hes a blimmin ***** ) any how come Monday and he looks like he got beaten up ( all jokes aside he looked bloody awful ) . He had got all gung ho with the throttle ............until he gets to a sharp bend .... chickens out and lifts his foot and ploughed into overhanging willows .

Sounds like the first time I took mine out. I didn't have a rudder on it, we were cruising down the Brazos on the first run after a total rebuild, following behind a ski boat about 300 yards about 50 MPH. All of a sudden the boat we were following cut the gas and threw out ski's. I cut the throttle and turned the wheel, it did nothing, then I remembered about the gas steering it, I prayed the motor was still running, it was and we turned. Big deep breath.

 

[cyclops222]

Baaahh HUMBUG !!

 

[dingbat]

Oh yeah , wanna give us a clue what sort of weight we are talking here ?
Im 265 lb's, you'd think moving that lot from side to side would turn the boat fast enough to run over the skier being towed

I vary between #230-238 depending on if I'm slacking on my diet or not.

It’s not the weight. The hull pretty much steers itself. All have to do is stand over the center line of the boat and shift my weight from one leg to the other to maintain course.

Anything “skiing” behind the boat is “bait” for the local inhabitants

A performance review of my hull design

 

[airshot]

Years back when I had my Islander, we had a long canal ride out to the big lake. The canal was very protected, idle speed only and no wind or waves. When taking folks for their first ride on my boat, I would find that sweet spot and allow the boat to wander from side to side without touching the wheel and standing still. Always told my guests that ghosts were driving the boat!
Kids always got a big kick out if that as well as a few adults!

 

[04fxdwgi25]

Duo pro will fix, but so will the correct trim tabs deployed all the way down.
My old Chaparral 2550 SX (7.4L w/ B1 drive) wandered like a drunk. Added the tabs (12 x 16 sport tabs), then straight as an arrow at head speed when deployed.

Meant to say "B3 Dual Prop", but somehow can't edit.

 

[a70eliminator]

Learn to anticipate the wander with minimal steering input corected before it happens, sounds dumb but it works and not difficult

 

[airshot]

Finding that sweet spot takes small adjustments and no moving around, but when you find it.....the boat will wag from one side to the other all by itself, look me a ghost is doing the steering !

 

[JonBoat55]

Assuming you’ve got an I/O, you can check the gimbal ring. Mine had gotten a tad loose and once tightened to spec (carefully) it improved the wander at slow speeds greatly for me.

 

[Grub54891]

Assuming you’ve got an I/O, you can check the gimbal ring. Mine had gotten a tad loose and once tightened to spec (carefully) it improved the wander at slow speeds greatly for me.

This is true, can’t tell you how many I’ve snugged up when they came in for service. If it’s left to long it ruins the ginble ring and you end up with an expensive repair.

 

[Stinnett21]

Is it not true however, that when in gear prop torque keeps the outdrive pressed hard to one side? I don't think it's free to flop around so to speak. This would mean the wear on the steering components, gimbal ring/steering lever, etc. is mostly on one side. Unless of course you drive in reverse all the time. Maybe I'm wrong in this.

 

[04fxdwgi25]

Is it not true however, that when in gear prop torque keeps the outdrive pressed hard to one side? I don't think it's free to flop around so to speak. This would mean the wear on the steering components, gimbal ring/steering lever, etc. is mostly on one side. Unless of course you drive in reverse all the time. Maybe I'm wrong in this.

All Deep V's with single prop I/O's wander to some extent, even brand new, unless mods have been made. Nature of the beast

 

[Grub54891]

Is it not true however, that when in gear prop torque keeps the outdrive pressed hard to one side? I don't think it's free to flop around so to speak. This would mean the wear on the steering components, gimbal ring/steering lever, etc. is mostly on one side. Unless of course you drive in reverse all the time. Maybe I'm wrong in this.

Under low idle, there isn’t much, Torque, besides the gimbal moves with th drive.

 

[Riredale]

Some interesting notions on the source of the yawing effect, but have to say that anyone who has raced sailboats intuitively knows the real cause--vortex shedding.

Basically, if you're flying a spinnaker dead downwind, it's acting like a giant parachute, with wind spilling over both edges. A little vortex is created at the edge, which quickly grows and eventually breaks off and spreads to the center of the spinnaker backside. A vortex breaking off the starboard edge will spin to the center rear and the friction against the back side of the spinnaker will pull the spinnaker to starboard. But then after a few seconds the vortex will break away, to be replaced by a similar vortex, this time from the port edge, which then pulls the spinnaker to port, and so on. This back and forth rolling effect can become so strong that it makes the boat heel strongly back and forth as it continues downwind.

A ski boat has a very blunt edge separation to water flow on port and starboard stern sides at low speeds, and similar vortices are formed in the water. One vortex current will shove the stern in one direction, followed by another vortex pushing in the opposite direction. And the boat wanders like a drunken sailor.

If you try, you can make minor steering changes in anticipation of the effect and minimize the yaw.

Good YouTube videos showing Vortex Shedding.