Getting bounce in ski rope.

[dcpolasky]

I was pulling friends on kneeboards and skis last weekend and had a lot of trouble with ski rope bounce. I was planed out, at a speed of roughly 20 mph and the rope appeared to bounce in the middle causing the riders to be pulled forward off balance and then given slack.

The water was quite calm, very little in terms of waves, no other boats' wakes, and my motor was trimmed (according to the trim gauge).

This bouncing effect at times caused the boat to lurch (with heavier riders cutting in and out of the wake.)

I hope I explained this well enough for someone to know what I'm talking about...

The rope we were using was labeled for pulling tubes but had no elastic/bungee section. The boat is a 81 Glastron Carlson Ski Machine with a Evinrude 200 v6 and ski pylon. Is this a case of the wrong choice of rope for the activity?

 

[skibrain]

Re: Getting bounce in ski rope.

Nice boat! I've owned a couple of CVX-16s and always wanted to try a 20 ft Sprint or Ski Machine.

Some recreational ski ropes are very stretchy and can be frustrating to ski with. After you make a cut, they rebound a bit like a bungee, but not sure that would be the source of a "bounce".

What you are describing sounds more like slack in the rope. Slack is more of a skier technique issue. i.e. pulling hard outbound from wakes, generating too much speed and then a quick turn back causing slack and the rope to dip. As the slack comes out of the rope you get a big hit and the skier is bent over at the waist. And wakes up the next morning ready for 3-4 ibuprofen with a cup of coffee.

Generally, the fix technique-wise is to do your pull or acceleration going toward the wakes, and stop pulling by mid-wake or by the time you get to the second wake, then edge change and glide out, decelerate and do a more gradual turn-in. The turn can finish with a quick or harder cut, but you shouldn't rush into the turn. Done well, you can keep a tight line, smooth things out greatly and it is easier on the body.

 

[NewfieDan]

Re: Getting bounce in ski rope.

How big were your friends? If I remeber correctly 20mph may be alittle slow, I used to tow a little faster at about 25. If slaloming (one ski) it would be faster still at just slightly above 30. that might be part of the cause. I've never towed a knee board so I don't know about that.

 

[dcpolasky]

Re: Getting bounce in ski rope.

This bouncing of the ski rope occurred even while I was kneeboarding in a straight line (center of wake). I weigh 165 lbs. The person pulling me stated that they were having a difficult time maintaining a constant speed, either going too fast or too slow. This caused the boat to lose plane and forcing me to plow the wake until he could plane the boat again.

I do believe that I may be pulling with my arms before doing 360 spins and creating some slack when completing the spin causing some of the slack/bouncing.

It did seem that once the bounce started, it started a echo/repeat pattern that would not resolve because of the boats sympathetic lurching caused me to try to keep upright by pulling even more with my arms.

I will have a friend video me on knee board next time, post it to youtube and add a link to this thread. Maybe someone can spot the problem.

Thanks for the responses.

 

[dcpolasky]

Re: Getting bounce in ski rope.

This bouncing of the ski rope occurred even while I was kneeboarding in a straight line (center of wake). I weigh 165 lbs. The person pulling me stated that they were having a difficult time maintaining a constant speed, either going too fast or too slow. This caused the boat to lose plane and forcing me to plow the wake until he could plane the boat again.

I do believe that I may be pulling with my arms before doing 360 spins and creating some slack when completing the spin causing some of the slack/bouncing.

It did seem that once the bounce started, it started a echo/repeat pattern that would not resolve because of the boats sympathetic lurching caused me to try to keep upright by pulling even more with my arms.

I will have a friend video me on knee board next time, post it to youtube and add a link to this thread. Maybe someone can spot the problem.

Thanks for the responses.

 

[dcpolasky]

Re: Getting bounce in ski rope.

This bouncing of the ski rope occurred even while I was kneeboarding in a straight line (center of wake). I weigh 165 lbs. The person pulling me stated that they were having a difficult time maintaining a constant speed, either going too fast or too slow. This caused the boat to lose plane and forcing me to plow the wake until he could plane the boat again.

I do believe that I may be pulling with my arms before doing 360 spins and creating some slack when completing the spin causing some of the slack/bouncing.

It did seem that once the bounce started, it started a echo/repeat pattern that would not resolve because of the boats sympathetic lurching caused me to try to keep upright by pulling even more with my arms.

I will have a friend video me on knee board next time, post it to youtube and add a link to this thread. Maybe someone can spot the problem.

Thanks for the responses.

 

[dcpolasky]

Re: Getting bounce in ski rope.

Sorry for multiple posts... the posts weren't going through so I posted again and again...

 

[skibrain]

Re: Getting bounce in ski rope.

Hmmm. Sounds more like a driver or boat set up issue if you can't stay on plane at kneeboarding speeds of 20 mph.
Heavily loaded boat? Trim down? Too much prop pitch?

Your boat, if in good tune sure doesn't lack hp for it's hull weight (1050 lb?).
My CVX-16 would plane out with bow down at 14 mph.

 

[DaveM]

Re: Getting bounce in ski rope.

I too believe that this sounds more like a driver issue. It reminds me of the trouble I had keeping a guy up on trick skis. Those of us old enough will remember trick skis. Any who, they require a much slower speed than wakeboarding and the boat had trouble staying on plane. Check your pulling speed. For 2 ski skiers I start at 24 MPH and adjust for ability. For slalom, 30 MPH and adjust for ability.

 

[dcpolasky]

Re: Getting bounce in ski rope.

I too believe that this sounds more like a driver issue. It reminds me of the trouble I had keeping a guy up on trick skis. Those of us old enough will remember trick skis. Any who, they require a much slower speed than wakeboarding and the boat had trouble staying on plane. Check your pulling speed. For 2 ski skiers I start at 24 MPH and adjust for ability. For slalom, 30 MPH and adjust for ability.

I do remember trick skis, used to have a pair... I've only been pulling one skier at a time... Here's a step-by-step of my pulling

1. Floor it.
2. Once rider is up, drop speed to roughly 20-25
3. Trim till gauge says I'm trim.
4. Pull till they fall or drop out.

Could my trim gauge be off? It has a tendency to bounce around sometimes.

I also have had a full boat usually, and one of my friends weighs about 300 lbs. but the boat planes out.

Also, the boat is tuned up beautifully. If I floor it when people aren't ready, I snap necks.

 

[skibrain]

Re: Getting bounce in ski rope.

If your bow is bouncing while you are pulling, your trim is too high.
On my glastron w/ OMC outboards with power trim and tilt, for skiing I would start with trim full down and move it up only about 1/8 to 1/4 way up the trim gauge. Prefer to run bow-down a bit because the boat would track better with slalom skiers.

 

[dcpolasky]

Re: Getting bounce in ski rope.

Here's some video of me knee boarding (first time in years).... you can see the bounce in the line for most of my ride...

 

[dcpolasky]

Re: Getting bounce in ski rope.

If your bow is bouncing while you are pulling, your trim is too high.
On my glastron w/ OMC outboards with power trim and tilt, for skiing I would start with trim full down and move it up only about 1/8 to 1/4 way up the trim gauge. Prefer to run bow-down a bit because the boat would track better with slalom skiers.

Thanks for the tip! I'll try that tomorrow!

 

[skibrain]

Re: Getting bounce in ski rope.

The bouncing in the line in your video is just because their are waves and the rider's upper body is moving up and down. It's COMPLETELY NORMAL - it just looks exaggerated because the camera is looking right down the rope.

The driver isn't doing a very good job keeping speed steady. At that speed in the 18 - 22 mph range It can require constant attention and very small adjustments up and down every few seconds to stay right at a rider's desired speed. Running with the trim further down may make it easier to hold plane at that speed. Less load in the boat would sure make it easier to drive as well. Maybe a prop with a lower pitch? I'm guessing the boat has at least a 21" pitch. A 23" pitch it would still have plenty of pull and really give nice top speed (60 mph plus if motor is set up right). However for water sports a 19" pitch or 19" four or five blade may be the way to go.

 

[dcpolasky]

Re: Getting bounce in ski rope.

The bouncing in the line in your video is just because their are waves and the rider's upper body is moving up and down. It's COMPLETELY NORMAL - it just looks exaggerated because the camera is looking right down the rope.

The driver isn't doing a very good job keeping speed steady. At that speed in the 18 - 22 mph range It can require constant attention and very small adjustments up and down every few seconds to stay right at a rider's desired speed. Trim down further down may make it easier to hold plane at that speed. Less load in the boat would sure make it easier to drive. Maybe a prop with a lower pitch? I'm guessing the boat has at least a 21" pitch. A 23" pitch it would still have plenty of pull and really give nice top speed (60 mph plus if motor is set up right). However for water sports a 19" pitch or 19" four or five blade may be the way to go.

I'll check the prop tomorrow. I know it has three blades but I'm not even sure how to check the pitch.... I know the speedometer pegs at 50 so I was planning on bringing a GPS to get an accurate read of the top speed, since I hit 50 really quickly.

To recap: I want less pitch/more blades for pulling, more pitch for higher top end, correct? (for higher speed would I want more (4-5) blades or the 'standard' 3?

I am SO glad I found this website. I have a great boat (too good for me really) and I'm not much more than a novice operator...

 

[skibrain]

Re: Getting bounce in ski rope.

There is a bunch of info here:

http://www.iboats.com/basics/propeller_basics.html

Yes lower pitch - like a 19" - will act like a lower gear in a car. Giving more acceleration, and greater engine rpm for a given boat speed. More blades (4 or 5) will give you more bite, but are generally not as fast as a 3, but pitch is what you should look at first.

The diameter and pitch should be cast into the prop inside the hub around the prop nut. When you are out on the water, check the rpm at WOT throttle. That will help with getting the best set up for your boat. The first number is diameter, the second is pitch: Something like 14 1/2 " x 21"

A website for older glastron boats is www.classicglastron.com
There you can find original sales literature, resources for parts.

 

[dcpolasky]

Re: Getting bounce in ski rope.

Wow skibrain, thanks for the link to the propeller basics! There is way more to a prop than I had realized! I will be studying this page for a while....

 

[MRS]

Re: Getting bounce in ski rope.

Just a thought you said rope was for pulling tubes? The tube line I have is way thicker than the ski lines we use maybe tow line to thick for ski and knee boards. Try a regular ski rope.....

 

[dcpolasky]

Re: Getting bounce in ski rope.

Just a thought you said rope was for pulling tubes? The tube line I have is way thicker than the ski lines we use maybe tow line to thick for ski and knee boards. Try a regular ski rope.....

I'll try another rope... the boat came with a thinner rope, the one I've been using came with the tube... unfortunately tomorrow we have a 70-80% chance of thunderstorms for the whole day, but Sunday is supposed to be beautiful... I'll just have to wait for any breaks in the weather because I hate sitting in the camper with that boat just waiting for me.

 

[dcpolasky]

Re: Getting bounce in ski rope.

Ok! Now we're cooking!

Switched to a standard ski rope, both drivers took some time and practiced doing some runs w/o skier/boarder. We focused on:
1. boat up to 32 for knee-boarders
2. maintained speed while trimming up 1/8 (huge difference)
3. kept boat planed out, maintained bow down, speed consistent

overall, I would say that the combination of serious driver practice and switching out of that tube rope made the whole weekend 80% more fun and productive to getting back into shape ski/board wise.

Thank you for all the help everyone!

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