With Moomba fast approaching I was curious about who undersatands currents and how they affect the ski. I’ve skied Moomba several times, but have never managed to stay out on the water very long. The river level fluctuates quite a bit, and the current can be moving right along some times.
Which direction is easier to ski? Is a head current like a head wind, or is it the opposite with the water moving faster relative to the ski?
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Not a pro by any standard but my main ski site is on the river which is a controlled body of water and varies from 0.6 mph right up to 4 or 5 mph which is a challenge
My 2 cents.
There are actually two effects to the skiing.
First it’s the actual speed through the water.
Boat speed is set by gps, so fixed or over ground as you will.
Let’s make it easy and say, you have a current of 2mph. Boat travels at exactly 34mph (over ground).
Skiing downstream, the skier will ski @ 34mph above ground, but only 32mph through the water.
The opposite is true when skiing upstream. Boat - again pulls @ 34mph above ground - skier though will get pulled through the water @ 36mph. Feels quite weird and very different from the last pass!
Secondly, due to the current flowing in one direction through the course, the distance between the buoys feels totally different going upstream vs going downstream. Not side to side of course, but almost like the whole course is shorter (clenched?) downstream vs longer (stretched) upstream. That greatly effects your timing!
I always found it quite challenging and always skied my best going against the current (upstream).
In theory if the entire volume of water was moving uniformily the only difference would be apparent wind speed +\- speed of current. I suspect reality is that across the width of the course, the flow in the middle of the river could be different than edges, or there is complicating turbulence. Cue the experts...
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I would suppose only practicing on a river can solve the problem. What of a head wind downstream vs a tail wind downstream and vice versa
We need a Moomba skier to tell us if the water flowing under the ski feels faster /harder one way than the other.
As far as the skier goes, I found it to be like skiing wind, but with glass water. I personally find it easier to ski upwind, and also found it easier to ski up current. Against the current, generating the same lateral vector, which is what is required to reach the line of the turn balls before actually reaching the turn ball, will generate increased lateral velocity compared to with the current. This gets us to the width of the ball earlier, with more set up time for the turn, on the up current pass. Like skiing with wind, one does need to pull longer going up current than down. I found that time pulling and slack issues were similar to skiing in wind.
The other issue is the ideal speed for which the ski is designed. I've always used a 36 mph ski and skied at 34.2. Naturally, the ski performs ideally at a faster speed, relative to the water. So, on the upstream pass, I felt the ski to be more responsive. That said, the smoothest, easiest short line pass I ever completed on the river was a downstream 32 off pass. Can't really explain that.
With higher relative speed through the water cross course is quicker, but decel in pre-turn is more dramatic and angle better off of the ball.
Downstream goes more downcourse thru the pull and less converted to cross course, less decel in pre-turn like a tailwind in that respect, and harder to finish as well.
Sorry not very technical, and not backed with data...so I guess these are opinions (everyone's got one) from experience.
Up to 28 off I am think that skiing against the current is likely better.
For skiers at 35 off and shorter it seems like it could be a bit of a puzzle.
At 36 mph, if there is a 2 mph current and you are skiing against the current then the boat is moving at 38 mph across the water. If you were to free ski at 38 that would be the feel and I bet it does not feel comfortable for most skiers. On the other hand the course would feel long as the current would help you make speed into the wakes and help you slow down. At the ball things are going to be frantic as the boat is going to pick you up fast.
In the other direction the boat is going across the water at 34 mph. The feel of the water might be awesome but you would make less speed into the wakes and you are going to carry what speed you have better than normal. Slowing down might be an issue. The balls are going to come up fast but it is going to be easier to ski technical.
My guess is you want a tail current for your hard pass but this is all a guess.
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If there is a 2mph head current, there will be more resistance (call it drag) on the ski that will make it more difficult to accelerate out of the buoy and slow the ski down quicker coming into the next buoy and potentially making the skier more narrow. In this regard, it would be very similar to a headwind.
Similarly in a 2mph tail current, the water will be “pushing” you downcourse in the exact way a tailwind would push you downcourse out of the buoy and have the skier hauling ass into the next buoy if control is not maintained.
Now whether a 2mph current is comparable to a 5mph wind or 30mph wind, IDK, but the effect is very similar – the difference is that in a current the drag/push is exerted on the ski whereas in a wind the drag/push is exerted on the skier’s body.
JMO, and also based on the posts of the several skiers who actually have skied in current, you have it bass-ackwards. Again.
BTW, your initial post in this thread was one of the better ones you have made!
But there are also added factors with rivers. Depth changes are huge in slalom wakes. We have a stretch of water we ski where sandy flats go out then drop off. Going straight down the lake you'll have wake crossings in 5 feet and then in 50 feet. Huge difference in firmness.
Currents can eddy around things, pillars can cause turbulent zones behind them for hundreds of feet.
@Bruce_Butterfield @twhisper
Do we agree that if we are free skiing in a 2 mph current going against the current - the boat "water speed" is 2 mph faster than the GPS speed? The inverse if downstream?
If the above is true then the mind bender the impact of balls being attached to anchors and not moving with the water.
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