Author Topic: Will it Plane?  (Read 15442 times)

PonoBill

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Re: Will it Plane?
« Reply #30 on: June 30, 2016, 04:55:34 PM »

I have been thinking more about the text I linked to earlier and how he says that lift is always created by both displacement and hydrostatic lift, even when you are planing.  Basically the weight of the rider still pushes down the water and displaces water even when you are planing on the surface.  When you look at the skim boarder he is clearly creating a big hole in the water, displacing the water.  So even though we can agree that he is planing, he is also displacing water, right?

Yeah, but he's not doing it with bouyancy.
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PonoBill

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Re: Will it Plane?
« Reply #31 on: June 30, 2016, 04:58:38 PM »
Some interesting stuff here.  I like the curve/push theory.  However we have omitted the 'Inclined Plane' and what this does to the physics as the wave builds and the ability to PLANE efficiently or not (remember the term 'plane' just means FLAT something we would all agree helps to plane). The surging wave actually lifts us UP causing an incline for us to FALL DOWN and move horizontally.  We can never outrun this source of power as long as the wave provides the incline. 

Realizing that there is a massive difference between a sailboat, downwinding and wave riding.  Bill suggested that you might tap out the energy of a wave.  I would suggest otherwise (you could be talking about downwinding where I suppose you could crush the wave).  Look at the picture below and imagine how you could tap this out.  Also note the angles involved.  Nothing like an extreme to make the point.

Someone suggested running the numbers, I have taken the opportunity to show what happens with a 10 degree incline.  For every 100 lbs you weigh there will 17 lbs of Gravity Pulling you vs. just 98.5 lbs of Force normal to the face of the wave.

When the angle increases to 45 degrees, like where Jamie Mitchell is running over Haley, the vector of the board + rider normal to the face of the wave is equal to the horizontal pull down the face.  Think 1:1 Weight to thrust ratio like a Tesla in insane mode.  100 lbs of weight --> 71 lbs of Pull vs. 71 lbs of support (lift) from the water.

2 Observations:
1) As the incline increase our available THRUST increases delivering speed used to counteract drag whether displacement or hyrdrostatic
2) As the incline increases our Normal vector (effective weight on the water) DECREASES lowering the necessary displacement or hyrdrostatic lift.

More exciting are the implications to FOILS.  Because foils have an even lower drag profile than a displacement or planing hulls.  The challenge is binary rather than the transition from displacement to planing.  A 'wing' with a 10:1 lift to drag ratio would be considered pretty antiquated.  BUT it only takes a 6 degree incline to provide the necessary Lift to Thrust ratio.  Starts to explain those crazy small, unbroken waves those kids are riding in other posts.

Nice insight, and of course there's a gravity component, but remember that gravity applies an acceleration of 32 feet per second After one second a surfer in a wave moving 30 feet per second is going 16 feet per second. Goodbye wave.
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TeachSB

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Re: Will it Plane?
« Reply #32 on: June 30, 2016, 05:15:46 PM »
Uh, Bill. The acceleration's only 32 fps in freefall. People sliding down wave faces aren't in freefall so that doesn't apply. Sorry to be a nag, but that post was too well written to be so easily dismissed. Also, you can't say "he's not doing it with buoyancy."  Bouyancy is a force created by displacement. If an object displaces water, then it has buoyancy. Maybe think of it like this, if a skimboarder is dropped straight down into the water, then he begins to experience a buoyant force from the first moment that he touches water, and that force increases as more of the boarder enters the water. Moving horizontally doesn't change that. Any water displaced creates a buoyant force that acts along with "dynamic lift" to support the rider.

I honestly think Bill and Robert are both saying 98% of the same thing and using different words.
« Last Edit: June 30, 2016, 05:19:31 PM by TeachSB »
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PonoBill

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Re: Will it Plane?
« Reply #33 on: June 30, 2016, 06:17:30 PM »
What?!? The downward acceleration is the same for a surfer, a skier on a hill, a satellite in ordit (a timy bit less, but the change is negligible) or a feely falling object, the resultant velocity is calculated using acceleration from gravity times the sine of the angle. The velocity you can achieve falling from the top to the bottom of a wave is substantially less, but easitly calculated. I used the highest velocity case (90 degrees and a sine of 1) to make the point.

Swell energy is trasferred to a surfer if the surfer has a similar velocity to the wave. The energy is a combination of skin friction (drag) interacting with the circular motion of water on the wave face, and kinetic energy transferred by the velocity of the wave face--no different than a skateboarder being pushed by a car. A surfer starting off catching the wave and staying at exactly the same height in the wave face has no velocity imparted by gravity (no change in height) but still has enough energy transferred to him to overcome drag and propel him at least as fast as the wave face.

I didn't say anything about bouyancy. You mean the skimboarder question? How much bouyancy does a skimboard have? Two pounds? I don't understand what you are trying to say.

Please tell me you don't teach physics.
« Last Edit: June 30, 2016, 06:20:51 PM by PonoBill »
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Weasels wake

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Re: Will it Plane?
« Reply #34 on: June 30, 2016, 07:00:21 PM »
Just cut to the chase, no tail rocker with hard rails back there for maximum planning, done, out, next?
It takes a quiver to do that.

PonoBill

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Re: Will it Plane?
« Reply #35 on: June 30, 2016, 07:06:09 PM »
Bill suggested that you might tap out the energy of a wave.  I would suggest otherwise (you could be talking about downwinding where I suppose you could crush the wave).  Look at the picture below and imagine how you could tap this out.  Also note the angles involved.  Nothing like an extreme to make the point.

Someone suggested running the numbers, I have taken the opportunity to show what happens with a 10 degree incline.  For every 100 lbs you weigh there will 17 lbs of Gravity Pulling you vs. just 98.5 lbs of Force normal to the face of the wave.

When the angle increases to 45 degrees, like where Jamie Mitchell is running over Haley, the vector of the board + rider normal to the face of the wave is equal to the horizontal pull down the face.  Think 1:1 Weight to thrust ratio like a Tesla in insane mode.  100 lbs of weight --> 71 lbs of Pull vs. 71 lbs of support (lift) from the water.

2 Observations:
1) As the incline increase our available THRUST increases delivering speed used to counteract drag whether displacement or hyrdrostatic
2) As the incline increases our Normal vector (effective weight on the water) DECREASES lowering the necessary displacement or hyrdrostatic lift.


I don't think I said any such thing. Perhaps you're talking about my comment that transitioning a rockered hull to a plane means  the area for the wave to push against decreases? But whenever you talk about energy from gravity you have to include some component of movement in the Y direction. Simply having the force of gravity applied to something does not mean any energy is transferred or expended, and therefore any velocity achieved. The rocks in your garden have the full force of gravity applied, and no velocity change--because there is no movement in the Y direction (I'm avoiding saying displacement in this context). If a surfer stays at the same height in a wave, how much force has been expended by gravity, how much energy expended? If you move from the top to the bottom of a five foot wave, converting five feet of potential energy into kinetic energy, how fast are you going and how much of that velocity could be attributed to gravity. I leave the answers to readers as an exercise.
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TallDude

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Re: Will it Plane?
« Reply #36 on: June 30, 2016, 09:46:59 PM »
I like this guys explanation of what happens with planing hulls and how they work. I read it last night. Worth reading.

http://bluejacketboats.com/planing-boat-theory/

It's not overhead to me!
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PonoBill

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Re: Will it Plane?
« Reply #37 on: June 30, 2016, 10:13:01 PM »
Interesting article. Quite a bit of it relevant to this discussion. I particularly like the comments about flow. Whenever people talk about water flowing over a hull I wonder "what do they think is making the water move?"
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surfshaver

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Re: Will it Plane?
« Reply #38 on: June 30, 2016, 10:20:34 PM »
Bill, you probably know about this already but years ago a movement started among surfers in San Diego, led by Richard Kenvin, to rediscover planing hull design from Bob Simmons roots.  This led to innovative surfers such as Ryan Burch riding the most minimal surfboards imaginable, literally a square piece of Unglassed foam with a leading edge shaped to form a hull edge.  The videos are mesmerizing.


PonoBill

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Re: Will it Plane?
« Reply #39 on: June 30, 2016, 10:33:44 PM »
Wow, Nice. I wasn't aware that was going on. I've read everything I could find about Bob Simmons. He had some great ideas. A tragedy that he died so young. I found the hydrodynamica website some time ago, but didn't know that people are using and mastering something like the Lord boards. I haven't built a sufboard from scratch yet, which is kind of odd given the extreme stuff I've been involved with, but I think my first board will be a mini Simms in a traditional fashion, with two glassed in fins, but sized for me to paddle.
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surfshaver

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Re: Will it Plane?
« Reply #40 on: June 30, 2016, 10:43:51 PM »
Ryan Burch, the surfer in that video, has gone on to become an extremely creative shaper and rider of a his own variety of innovative boards, most of which are asymmetric.  Of course it doesn't hurt that he is as talented or more than your average world tour surfer. 

https://m.youtube.com/watch?v=SJpEHK6VjcA

TeachSB

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Re: Will it Plane?
« Reply #41 on: June 30, 2016, 10:51:40 PM »
Bill, I'm going to assume that since you've never bee one to make personal attacks you meant no offense by your previous comment to me. Yes, I teach physics. It is precisely because I teach physics that I was able to identify the small (probably insignificant to most) flaw in your comment. So, I will try to explain but I am well aware that the Internet is a horrible place for this type of discussion and I have no interest in a debate so I will not continue past this post. Feel free to have the last word.

You made two contradictory claims in your comment:

1 - all objects (skiers in a hill, surfers on a wave, and satellites in orbit) have the same downward acceleration.

2 - the "resulting velocity" from that acceleration is dependant on the sine of the angle of the slope the object is on.

Those statements contradict because two objects with the same acceleration (assuming they start from the same velocity) will have the exact same velocity at all times. They cannot have different "resulting velocities" and still have the same acceleration. If they gain 32 fps every second they will be going 320 fps ten seconds later no matter what. That's what acceleration means.

So which statement is wrong? As others have correctly identified, statement 2 is correct. The acceleration down an slope is related to the sine of the angle (and other factors probably not important to this discussion). Statement 1 is the incorrect one.

Why is that wrong?  In physics class, you learned the term "acceleration of gravity" and that the value was the same for all objects. This value, usually represented with the symbol "g," is derived from Newton's Law of Universal Gravitation and is only a theoretical value. Literally nothing has ever fallen and accelerated at this rate. Why? In order to have this acceleration the object must be at "the Earth's surface" and be opposed by absolutely no other forces. That means there must be a perfect vacuum as well as nothing touching the object. A surfer doesn't accelerate at that rate because as Beasho said there would be a normal force opposing at least some of the force of gravity. So no, not everything accelerates at that rate. It is just a theoretical value used in calculations. I hope that makes my argument more clear and if not well... Cheers anyway.

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blueplanetsurf

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Re: Will it Plane?
« Reply #42 on: June 30, 2016, 11:33:39 PM »
I like this guys explanation of what happens with planing hulls and how they work. I read it last night. Worth reading.

http://bluejacketboats.com/planing-boat-theory/
Good explanation, I like how he defines planing:

That term, “dynamic lift”, is all-important and, to be called planing, a boat should be getting a significant portion of its lifting force from dynamic sources in addition to the buoyancy force.  Just what portion of lift should be dynamic in order to define a boat as planing, I don’t know, but if the percentage is greater than 50%, we should be safe in saying that the boat is in the planing mode.  I think the planing mode definition should hold well below 50% but don’t know where, or even if, a specific percentage should be chosen.  In any event, such a definition would be far more satisfying than the usual ones of speed/length ratio, etc.  We should not care a fig what it is called anyway, but rather expend our efforts in improving the planing ability of a boat intended for that service.
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PonoBill

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Re: Will it Plane?
« Reply #43 on: July 01, 2016, 12:27:21 AM »
Yes, I mis-spoke--or at least mistyped. I should have said the same gravitational force per unit of mass applied instead of the same acceleration. Typing before I thought.

But what I think Beasho is inferring is that gravity is what we use to play in a wave--that we're basically just sliding down a hill. The maximum speed attainable by dropping from the height of a wave is the square root of (2*gh), where h is the vertical height. All other factors associated with the surfer just falling reduces this speed. So for a head high wave (6 feet) that's at most 19 feet per second, and actually more like 13. The further point that a surfer does not have to travel from top to bottom of a wave to travel at the wave's speed should make this point obvious. Without vertical displacement there is no change in velocity due to gravity. Surfing would be a very dull sport if we relied on the acceleration down a six foot slope.

Obviously gravity partially holds that vertically stationary surfer in place, since the force of the wave has a vertical component, a vector determined by the wave face angle--a surfer trying to catch a wave has to go as fast as he can to minimize the energy transferred by the vertical component or he's up and out--but it's primarily kinetic energy transfered from the mass and velocity of the wave, that keeps a surfer moving. Gravity isn't the only force that holds the surfer in place--it's a dynamic environment, and velocity can be gained by transiting up the face of the wave, moving to a more favorable geometry. Most surfers have experienced the acceleration of moving up and down the face, gaining speed in both directions. Clearly we're not just rolling down a hill.

That great Ryan Burch video makes all this particularly obvious.

Sorry about the dig.
« Last Edit: July 01, 2016, 12:39:50 AM by PonoBill »
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PonoBill

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Re: Will it Plane?
« Reply #44 on: July 01, 2016, 12:28:36 AM »
We give a little more of a fig, Robert, since we are dealing with slow speeds, long skinny hulls, and a really weak power plant.
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