Water Movement From Behind (pic)

nj_surfer · April 29, 2010, 10:27pm

Thicker rails create more suction if the shape is the same. But… it’s incremental. A drastically thinner rail starts to release water by nature of the radius of the rail… tighter radius becomes harder and more release occurs. That means less suction. But if you’re talking about a small increment of volume reduction, with the same shape, I believe the lower volume rail creates less suction.

And by the way, it’s not really suction… but that’s another thread. We all know what we mean when we say, “suction,” so let’s just leave it at that for now.

deanbonkovich · April 30, 2010, 4:14am

Any chance of some dims on the board?

Surffoils · April 30, 2010, 8:06am

All understood TaylorO.

I was playing Devils Advocate by initially promoting the wrapping theory, explaining how its possible. Proving that it does exist. ( Drawing the reader in to establish the credibility of the theory.)

But then IF it does exist, why doesnt it have any effect on surfboard performance ?

Is it a magical force that draws constant volumes of water around inside rails but has no measureable effect or variation between different rail shapes ? Or just a visual furphy?

Like a magician cutting a woman in half, did you see what you saw ?

or what you think you saw ?

I agree that theres a lot going on but wrapping doesnt occur out on the face (because the angles are wrong) but begins when the water rises more vertically back towards the tube. When it does occur , its still of little effect or use because of the erratic surface texture, cavitation and minimal contact area.

The proof is to ask people that believe in wrapping " What effect does wrapping produce ?"

.

Surely it does something ? And if it has no effect , then does it actually exist beyond mis-attributing other flow forces and a 50 year old myth ?

And if it does exert a powerful force or effect in any direction,.... then why arent we all talking about how its influencing design ?

The unanswerable question stands..... what effect does wrapping produce ?

nj_surfer · April 30, 2010, 11:08am

Water wrapping around a soft, edgeless rail produces drag. Enough to be discernable. This drag reduces the top end speed of all boards, and provides a sense of stability. That’s why they work great on noseriders, letting you get out to the tip even in the smallest of surf. They’re used on big wave boards, too, for the same reason… stability and control. Although I must admit I’ve never turned around to look and see what’s happening behind me on a bomb. But on a longboard, I do it all the time.

MrJ · May 1, 2010, 2:44am

[quote="$1"] ... Surely it does something ? And if it has no effect , then does it actually exist beyond mis-attributing other flow forces and a 50 year old myth ?

And if it does exert a powerful force or effect in any direction,.... then why arent we all talking about how its influencing design ?

The unanswerable question stands..... what effect does wrapping produce ?

[/quote]

I don't think its unanswerable. My answer is the same as NJ's - stability and drag. The drag speeds up turning, but at times is unwanted so thats when hard release edges are used.

I think the concept of wrap has hugely influenced rail design. If water always sheared off cleanly as soon as the hull started to turn the corner around the rail then we wouldn't bother with release edges and would have a rounded rail from nose to tail. All HP boards have down rails nowadays - to tighten up the rail curve making it easier to release water in order to make it more responsive from rail to rail. Regarding your other question about why isn't a chunky railed McCoy Nugget much slower I think I have the answer. I have ridden a nugget and its chunky rails are more resistant to burying. A rail that is buried shallow has less drag than a deeply buried rail which helps moderate the wrapping effect.

Surffoils · May 1, 2010, 4:01am

[quote="$1"]

Water wrapping around a soft, edgeless rail produces drag. Enough to be discernable. This drag reduces the top end speed of all boards, and provides a sense of stability. That's why they work great on noseriders, letting you get out to the tip even in the smallest of surf. They're used on big wave boards, too, for the same reason... stability and control. Although I must admit I've never turned around to look and see what's happening behind me on a bomb. But on a longboard, I do it all the time.

[/quote]

I think this is whats possible rather than actually occurring.

From the photos above you can see that in the 1st pic the board is angled into the face and rotating up the wave, and theres lots of water over the inside rail.

In the 2nd pic, less angle and less rotation, appreciably less water. The board is sunk into the face and turning /pushing up into the water making the water run over the rail.

If anything the water should wrap on the outside rail as the water moves away from the rail and it could be pulled up the rail. But it doesnt do that.

Water does wrap around a spoon because the flow and the direction of the curve are aligned or parrallel, but on a wave the water is stationary, the board moves forward.

How does water takes a 90 degreee vertical turn and gets pulled up a rail against the direction of flow and gravity...?

On the inside of any turn the water is pushing against the rail and sheeting off the outside rail.

And its the same under and over the board...

[IMG]http://i153.photobucket.com/albums/s225/SURFFOILS/deck.jpg[/IMG]

[IMG]http://i153.photobucket.com/albums/s225/SURFFOILS/bottom.jpg[/IMG]

[IMG]http://i153.photobucket.com/albums/s225/SURFFOILS/bottom2.jpg[/IMG]

[IMG]http://i153.photobucket.com/albums/s225/SURFFOILS/bottom3.jpg[/IMG]

Its clearer to me that water should wrap around a rail in the direction of the flow (below) .. just like the spoon example.

[IMG]http://i153.photobucket.com/albums/s225/SURFFOILS/me1wr.jpg[/IMG]

But longboards are different, Ive seen water spilling over the deck from the inside rail but I believe thats more about the board slowing the surface of the wave as it rises vertically near the top of the wave and it slows enough to break up and fall onto the board. That fall happens behind all boards but its more pronounced with longboards.You can see it beginning to crumble and fall in the 2nd pic of the 1st post as well here..

[IMG]http://i153.photobucket.com/albums/s225/SURFFOILS/03032008420559.jpg[/IMG]

[IMG]http://i153.photobucket.com/albums/s225/SURFFOILS/fall2.jpg[/IMG]

dpicton · May 1, 2010, 3:12am

cool pic and over my head speculations. But I like reading the farout interpretations… C’mon, post the 5 pics before and after this one…or lets make love to this one photo like dude was teleported there without any other wave face interaction configuration? . I like this peculiar arena where people say almost anything they like to virtually the entire computer-accessing world…seriously though, I have this hangup but I think the less interesting photos say things, edit, sorry took me a while to type. somebody already made it obselete

obproud · May 1, 2010, 4:14am

WRONG

MrJ · May 1, 2010, 4:26am

edit--> damn IE give small pics, I'll fix it later

Surffoils · May 1, 2010, 4:41am

[quote="$1"]

but on a wave the water is stationary, the board moves forward.

[/quote]

WRONG

[/quote]

What, the water moves forward and the board is stationary ?

obproud · May 1, 2010, 4:55am

The water moves up and the board moves where the surfer turns it.

Surffoils · May 1, 2010, 5:38am

Looking at the picture when its level...

[IMG]http://i153.photobucket.com/albums/s225/SURFFOILS/me2tmsBMP.jpg[/IMG]

What sort of vertical or 'up' component is happening at this position on the wave ?

[IMG]http://i153.photobucket.com/albums/s225/SURFFOILS/me2tmsBMP2.jpg[/IMG]

The water looks almost flat in front of the board.

obproud · May 1, 2010, 6:15am

In front of the board the water is flat because that is the trough of the wave. That water is not moving up, there, yet. It will be a few moments after this image was taken.

See that bulge in the wave on the toe side? That is from the water being deflected and displaced by the surfboard hull. The extra, upward moving water, that has been deflected by the hull, is being forced there, creating that bulge.

MrJ · May 1, 2010, 9:34am

this experiment inspired by Crafty

hose is on the left directing water down hull. Deck on the right side

[img]http://www2.swaylocks.com/files/images/2010/04/wrap2.preview.jpg[/img]

hose on right directing water off hard edge of tail

[img]http://www2.swaylocks.com/files/images/2010/04/release.preview.jpg[/img]

reverb · May 1, 2010, 3:56pm

…in my opinion you re debating with not so much data

I mean, we need 2, 3 more pict, at least

remember that pict not always say the “true”

With these only 2 pict I see a board that surf mostly with the bottom and not with the rails

and that is not so good

That water is not grabbing the outside rail beacuse of the board speed and convex or rolled bottom in that precise moment the pict were taken

that is why we need the other pict

and I bet that we ll see the rail grabbing the water (if the rider use it more of it)

-I think many in Swaylocks practice too much “coach surfing” and not the real deal

or barely can surf good waves.

surferguy80 · May 1, 2010, 8:03pm

ill take a grab from the bottom turn, but unfortunately there is absoultely no board in it…just my upper torsoe, i took those from the rare moment that the board is 100% visible.

this doesn’t help much, but it was the next bottom turn which was identical to the first, just to show the angle that i was turning at; nothing extreme, just a decently full railed bottom turn;

nj_surfer · May 1, 2010, 9:11pm

The hose experiment is valid only at the velocity of the water coming out of the hose. In reality, the water may flow along, under, and into the rail at velicities much greater or much less than the hose. Still… it shows us something, and we need to consider it. A tucked hard edge only releases water cleanly at higher velocities. At lower velocities, the boundary layer and the rest of the water act differently… the boundary layer wants to release, but the rest wraps around. So you get low pressure along the rail, along the boundary layer, but you still get the Coanda effect… but to a lesser degree than the full, round rail.

Surffoils · May 1, 2010, 9:32pm

[quote="$1"]

In front of the board the water is flat because that is the trough of the wave. That water is not moving up, there, yet. It will be a few moments after this image was taken.

[/quote]

If you agree that the water in the pic is not moving up and thats what Im talking about. Theres little movement either vertical or lateral at that instant.

Not whats going to happen later.

[quote="$1"]

See that bulge in the wave on the toe side? That is from the water being deflected and displaced by the surfboard hull. The extra, upward moving water, that has been deflected by the hull, is being forced there, creating that bulge.

[/quote]

And thats exactly what I said in my first post, that the bulge on the inside rail is deflected and displaced water.

Its not from wrapping.

Cool pics MrJ.

But I wonder how often the flow is at 90 deg to the rail ? If its possible, could you do some more with the flow angled at 45 deg to the stringer ?

tblank · May 2, 2010, 7:34pm

Remember, We are talking about a “HULL” shape. They push water differently than the average bottom. Instead of riding on top of the surface, they are IN the wave DISPLACING water,

ps. This is not shouting…I’m just too thick to figure out how to use italics. I’m not a computer wonk.

MrJ · May 3, 2010, 9:17am

Coolest pics are the ones from Surferguy. Also good observations from UPSurfboards. As NJ said the experiment is not a perfect simulation. I got the idea from Crafty’s old experiment which illustrated diagonal flow. I realise its not the same as a surfing situation but it does illustrate release Vs wrap. I played with the hose at 45 - there is more wrap - particularly on tail hard edge region.

Pics from the same angle as before sprayed my camera! For what its worth here is a 45 degree flow viewed from the front - flow directed away - previous pics were with the hose full on but a plain nozzle. This one is a high pressure nozzle which would eject the water at a higher speed. The higher speed overcomes the extra wrapping effect of the diagonal flow.