physics question: surf and river current

[formulaben]

So BS, if someone videos just the wake you'll easily be able to distinguish which one was upstream and downstream?

[gorilla]

When we are over in Entiat, we pretty much only see the Foil guys riding upstream. Never down.

That's because we are headed upriver to the area between Daroga and Sun Cove. That area usually has the least amount of people and milfoil. The area between Entiat and Lincoln Rock gets busy and we try to avoid it.

[Lance B. Johnson]

So BS, if someone videos just the wake you'll easily be able to distinguish which one was upstream and downstream?

Ben,

Its a feeling while surfing. Pics mean very little when it comes to surf waves, video barely means more.

[rennis]

That's because we are headed upriver to the area between Daroga and Sun Cove. That area usually has the least amount of people and milfoil. The area between Entiat and Lincoln Rock gets busy and we try to avoid it.

that too, but I typically only see other foilers riding upstream as they tow past us at the Orondo campground.

[formulaben]

Ben,

Its a feeling while surfing. Pics mean very little when it comes to surf waves, video barely means more.

The word you're looking for is "illusion."

[wakebrdr94]

We boat on the river a lot, and the wake and wave always seem a bit nicer heading up river. It appears more firm while wakeboarding and it appears to have more push while surfing. I'm no engineer, but when everyone i ride with prefers upriver, I have to feel there is something to it, not all of us are crazy

[Lance B. Johnson]

The word you're looking for is "illusion."

No, there is a difference

[augie09]

I believe the key is momentum. Although the boat, with a paddle wheel speed control, is going the same speed relative to water speed in all scenarios (up stream, down stream, stationary lake), the water it is going through has momentum if there is current. The wave might be identical the instant it leaves the boat's hull because of the paddle wheel controlled speed, but immediately after that the momentum comes into play. An object in motion tends to stay in motion, at rest tends to stay at rest.

looking at wave shearing, it makes sense that going against the current would make your wave slightly steeper.

Edited September 16, 2014 by augie09

[WakeGirl]

....

And while a discussion surrounding the physics of why there is a difference could be an interesting one (with the right people's input).......the debate on whether there is a difference or not is just plain dumb. There is. Period. Not debatable.

.....

Ooooo, that would be fun! Can we can we can we!?! (and no, that's not sarcasm)

[Lance B. Johnson]

^^ Oh boy.

[formulaben]

Nope. That's like taking a picture of a ski run and asking me to give you snow conditions for that given day. Uhhhh......'snowy'?......i guess?

Like I said; the wave will be firmer and faster (more poppy) going into the current. Not sure how I'm supposed to determine either of those from a photo.

And while a discussion surrounding the physics of why there is a difference could be an interesting one (with the right people's input).......the debate on whether there is a difference or not is just plain dumb. There is. Period. Not debatable.

and I should say: Sorry if that comes off a bit prickly. It's not directed at you by any means. Just a bit frustrating to constantly listen to the new-school-2-year-professionals around here dominate surfing conversations with bad information..........(again). A note to those guys: You ARE allowed to just read and learn...........you don't have to post an "answer" in every thread you read.

So you're absolutely certain there is a difference but can't offer any quantifiable or definable evidence of it...except that to disagree "is just plain dumb. There is. Period. Not debatable." Yeah, that's not douchey at all. Sorry if that comes off prickly.

[Lance B. Johnson]

So you're absolutely certain there is a difference but can't offer any quantifiable or definable evidence of it...except that to disagree "is just plain dumb. There is. Period. Not debatable." Yeah, that's not douchey at all. Sorry if that comes off prickly.

Ben,

It is clear that you A) Don't ride in a river or B) Don't ride enough to know the difference or C) Are just trying to pick a fight? Almost all of our riding is done in a river and there absolutely is a difference. Just read the posts from others that agree.

I will leave it to you to quantify the descriptive words, poppy, firmer and faster cause I don't know how to do it. But thats just what riding upstream is, faster, firmer, poppy.

Edited September 17, 2014 by Lance B. Johnson

[formulaben]

Not try to pick a fight at all, Lance. Maybe you should go back and read the posts. I'm not arguing that it's different...I asked a question and that's where I screwed up. What I had a issue with is the response. I bid you good day.

[REW]

Ooooo, that would be fun! Can we can we can we!?! (and no, that's not sarcasm)

have to talk Wifey into registering, she is the physics person.

[Lance B. Johnson]

Not try to pick a fight at all, Lance. Maybe you should go back and read the posts. I'm not arguing that it's different...I asked a question and that's where I screwed up. What I had a issue with is the response. I bid you good day.

Ok I get that. All we are saying is that it is what it is, we won't pretend to know why.

[bunji169]

I have a headache.

Surfin USA

[justgary]

Holy cow. Speaking of just reading and not posting.... I have answered this question twice now. Once on the other thread in July, and once on this one (after referring to the other answer once).

The short answer is doppler. The distance between the waves of the wake changes because of the flow speed of the water vs the flow speed of the waves.

Why? A wave in water wants to propagate at a specific speed (its phase velocity) related to several things, including the density and viscosity of the water. Asking the wave to move at a different speed (because it is propagating in a moving medium) causes its frequency to change.

Frequency is the inverse of period, and by changing the period, you change the physical space between the waves. If the waves are closer together but have the same height, the slope will be steeper. More slope turns into words like snap, pop, push, crackle, fizz, duuude, gnaaaaarly, and so forth.

For more information, please see the Wikipedia pages:

http://en.m.wikipedia.org/wiki/Dispersion_(water_waves)

http://en.m.wikipedia.org/wiki/Phase_velocity

[smooth as glass]

Discussion closed. Thanks justgary......I've been wondering bout this for slalom for sometime. River skiing up or down does seem to make a difference, always attributed it to wind or boat driver. But this seems to make sense.

 

[dielawn]

I ride on a river with a pretty hefty current. The only thing i changed on the boat was switched from GPS to paddle wheel, this gives me a better/more accurate read when wakesurfing. There is a about a 3 Mph variance going down river compared to up. Wakeboarding, there is no speed issues. 

[Lees23]

On 9/12/2014 at 3:25 PM, martinarcher said:

I don't know the hydrodynamic reason why, but I've spent enough time on a surf board in the river and lake to tell you current certainly makes a difference. I can also tell you if there is a significant amount of wind on our lake that running with the wind will produce a better wave for us. My boat speed is controlled by GPS on the lake so yes, into and with the wind speeds are consistent.

YMMV but that's my experience.

Are you sure that it’s just not the effect of running against the wind slows you down making you feel like your wake isn’t as good/not as much push as opposed to the wind at your back or decreased headwind creating the sensation of a wake with more push?  I have noticed this too but always just chalked it up to the wind creating more resistance when going against it. 

[Falko]

If I were surfing on Mars, would I need more or less weight in the bow to get the proper wave due to the change in gravity? I was just reading Elon Musk's plans for populating Mars and he left that part out. Major oversight....

[Raimie]

10 hours ago, Lees23 said:

Are you sure that it’s just not the effect of running against the wind slows you down making you feel like your wake isn’t as good/not as much push as opposed to the wind at your back or decreased headwind creating the sensation of a wake with more push?  I have noticed this too but always just chalked it up to the wind creating more resistance when going against it. 

It's not the wind. It's just as noticeable to me on a glassy day.

[martinarcher]

I agree with Raimie, even on smooth water it seems to make a difference.  I will say I do notice what you're talking about on our lake when it's windy.  You can certainly get a bit more greedy in the back of the pocket with the wind to your back.   

[Jmcclain01]

It has to make a difference, just thinking in my very basic mind.  Otherwise if you had a river flowing at say 11 MPH, or close to surf speed, you would be able to point the boat in the upstream direction, set the cruise at river current speed, 11 MPH, and not move the boat relative to land but be able to surf behind it.  Thinking very similar to the surf pools they have now where the water moves but the surfer really doesn't?

[kerpluxal]

6 minutes ago, Jmcclain01 said:

It has to make a difference, just thinking in my very basic mind.  Otherwise if you had a river flowing at say 11 MPH, or close to surf speed, you would be able to point the boat in the upstream direction, set the cruise at river current speed, 11 MPH, and not move the boat relative to land but be able to surf behind it.  Thinking very similar to the surf pools they have now where the water moves but the surfer really doesn't?

exactly... ask me how I know.. lol... Not my boat.. but on a M235 in the Trinity River after a flood... river current was 6 mph... once boat was in gear.. I was standing up.. boat was on GPS and had to be set for 6 or the wave was washed out... The wave is formed from the movement of the water over the hull... If you are going downstream you have to increase your speed to have the same speed of water over the hull...

Same for wind... it is resistance... if it is at your back.. it will push you forward.. If it is at your front.. it will push you backward... Put your hand out the window of a moving car... same principle

Lets see the arguments on this... it still applies as it uses the  Bernoulli's principle... If an airplane requires 60 mph wind speed to take off and it is on tread mill going 60 mph in the reverse direction.. will it fly?