Sharp Turns

[jmarty10]

When I am pulling the kids on the tube, alot of times we will reverse direction by making sharp turns (360 turns) to spin them pretty hard. I'm usually going about 30 MPH or about 3k RPM. I would imagine this is probably not good for the outdrive. When i make that hard turn the boat slows unless I give it more throttle and when I do that I can feel some vibation and growling going on. Anybody who has an I/O experience this or do this? By the way when we are cruising along at that speed and turn left or right (not a 360) I'm not getting any vibration or growling so I dont think there is anything wrong with drive.

 

[kailec00]

Re: Sharp Turns

I do the same when pulling the tube. I do not get the vibration, but the boat does slow down, I just give it more throttle if needed. However I am pulling a 7 year old and not going 30MPH.

 

[QC]

Re: Sharp Turns

Sounds like time for a u-joint replacement . . . I often argue here that hard turns are the same as trimming up too high. I am not one to baby my stuff though, so I would just be proactive with the maintenance.

 

[Fireman431]

Re: Sharp Turns

When I am pulling the kids on the tube, alot of times we will reverse direction by making sharp turns (360 turns)

When I want to change direction, I usually do 180-degree turns. 360-degrees usually puts me right back in the same direction!!

(Sorry...couldn't resist!)

 

[jmarty10]

Re: Sharp Turns

I should have read some other posts on this topic. I think I learned what cavitation is. It seems the prop is slipping or out of the water on these sharp turns at high speed. I'm going to trim down and slow down on the turns. Joints have about 60 hours on them, I hope they dont need to be replaced. Mechanic inspects them every year during winterization.

 

[jmarty10]

Re: Sharp Turns

When I want to change direction, I usually do 180-degree turns. 360-degrees usually puts me right back in the same direction!!

Good catch! I'm a little foggy this Monday am! But man, being able to do a full 360 in a boat would be crazy!

 

[Home Cookin']

Re: Sharp Turns

jet skis can....

 

[QC]

Re: Sharp Turns

vibation and growling going on.

This is what prompted the U-joint comment.

I think I learned what cavitation is. It seems the prop is slipping or out of the water on these sharp turns at high speed.

What you describe is actually called ventilation, but is often mistakenly called cavitation which is very different. Ventilation is the prop grabbing air off the hull or other disturbance. Very common in hard turns especially with trim up. Buuuuutttt . . . what you should hear is a revving up of the engine and a feeling that you're not going anywhere. Maybe that's what you meant by "growl"? Trimming in before and during turns can make all of the difference in the world and different props can too. Adding cup to an existing one help too.

 

[ScotWithOne_t]

Re: Sharp Turns

I could be wrong, but as an engineer, I would never design something like a u-joint that would be outside of its safe range of usage when the steering wheel is turned at full lock. That's what the mechanical stops are for. I suppose if you're trimmed up past the first limit stop and turned full lock, you might be hurting something.

Again, I can't verify this from anything in print from Mercruiser, but I have to believe that they would not hire such an imbecile of an engineer to design something like that.

 

[QC]

Re: Sharp Turns

Don't take my comment wrong. Those u-joints are very much a weak link, but required to get the trimming and turning range we have. My point was only that looking at them, when they are turned hard over, it seems that the deflection is easily more than typical trim range. With that said, I can't find the specs for turning angle vs. trim angle. I usually use this as an argument against those who flip out over high trim/tilt angles and full power. In this case I am suggesting that it may explain the "growl". Still looking for those specs if anyone has them: steering angle max, trim down max, trim up max, vs. straight out (no trim and no turn).

BTW, I agree with you about the engineer, but I also think I/Os are engineering abortions and yes I own one . . .

 

[reelfishin]

Re: Sharp Turns

I could be wrong, but as an engineer, I would never design something like a u-joint that would be outside of its safe range of usage when the steering wheel is turned at full lock. That's what the mechanical stops are for. I suppose if you're trimmed up past the first limit stop and turned full lock, you might be hurting something.

Again, I can't verify this from anything in print from Mercruiser, but I have to believe that they would not hire such an imbecile of an engineer to design something like that.

As someone who gave up on dealing with I/O drives for these reasons, I would have thought that they would have used a better coupler, maybe a constant velocity joint or something. Even a ball type gear system or something that doesn't have so many limitations.

 

[superbenk]

Re: Sharp Turns

As someone who gave up on dealing with I/O drives for these reasons, I would have thought that they would have used a better coupler, maybe a constant velocity joint or something. Even a ball type gear system or something that doesn't have so many limitations.

Ok, +1 for the OMC Stringer, finally!!! We can do all sorts of crazy turns (with a significantly tighter radius even!) without worrying about U-Joints

So, that's Stringer 1, everything else a lot-more

 

[extreme76]

Re: Sharp Turns

Mine does the same on high load full turns and that is with brand new gimbal bearing and u-joints. They do not do it at lower speeds and it only seems to be noticeable when tubing (i.e. accelerating at full turn) Last year it did it all the time (which prompted the new parts). I have seen Don over at the I/O forum write several times that a full turn under power will cause some u-joint noise even with brand new joints.
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So I think you maybe fine. I do think full turns while towing are probably hard on em.

 

[Moody Blue]

Re: Sharp Turns

When I am pulling the kids on the tube, alot of times we will reverse direction by making sharp turns (360 turns) to spin them pretty hard. I'm usually going about 30 MPH or about 3k RPM.

Wow, that's pretty fast to be pulling a tube. When you spin the tube around like that, it is traveling alot faster than 30mph .

 

[jmarty10]

Re: Sharp Turns

Wow, that's pretty fast to be pulling a tube. When you spin the tube around like that, it is traveling alot faster than 30mph .

Have to get them to fall off somehow

 

[Lucraft]

Re: Sharp Turns

As someone who gave up on dealing with I/O drives for these reasons, I would have thought that they would have used a better coupler, maybe a constant velocity joint or something. Even a ball type gear system or something that doesn't have so many limitations.

Guess the marine industry hasn't discovered the Birfield joint yet?

 

[H20Rat]

Re: Sharp Turns

I could be wrong, but as an engineer, I would never design something like a u-joint that would be outside of its safe range of usage when the steering wheel is turned at full lock. That's what the mechanical stops are for. I suppose if you're trimmed up past the first limit stop and turned full lock, you might be hurting something.

Again, I can't verify this from anything in print from Mercruiser, but I have to believe that they would not hire such an imbecile of an engineer to design something like that.

all u joints have a specific range of rpm and angle that is considered within limits. (etc 20 degress at 1000 rpm, 10 degrees at 4000 rpm...) So full stop turns are within the range while at lower rpm, at full throttle it most likely is well outside the limit.

 

[QMAZIGGY]

Re: Sharp Turns

One of the important things to remember is that a u joint by design is not a constant velocity joint, that is to say that the velocity of the output shaft varies throughout each revolution. If the input shaft and output shaft are exactly paralell with each other, even if on different planes, the center section of the drive will cycle back and forth if the two u joints are correctly phased with each other. This cycling generates a very small vibration, but goes largely unnoticed because the output shaft speed runs virtually identical to the input shaft. In the case of turn or tilt as in a final drive, the output shaft is no longer parallel with the input shaft and the unavoidable speed variations in the center shaft are now transferred to the output shaft causing noise, vibration, growling and the like. These observations are even more noticeable under heavy load and can be somewhat unsettling to the untrained ear. Constant vigilance as far as u joint condition and gimbal bearings are a must. If everything is in good condition, hammer down and enjoy, rest assured that the design engineers are well aware of these issues and the drive system is capable of full deflection under full power.

 

[Overkill82k5]

Re: Sharp Turns

Whipping a tube around that fast does put a very high strain on the drivetrain. Your motor might be "talking to you" too. Most marine engines dont see those high loads at higher RPM's, or very often.

On a side note, I wonder how many people have "adapted" a better joint system in place of the typical outdrive joint? It sure does seem like it wouldn't be that hard, but then again, if it was easy, why isn't everyone already doing it... haha

K, google time...