Question for Shapers...

Hey guys, I had something bouncing around in my head for adding speed to a surfboard was wondering about having an empty space near the tail, bottom side of the board. it would basically be a carved out area that might act as a vacuum to suck water into maybe increasing the speed? Here is a picture... any shapers or like minded people have thought reguarding this? has it already been tried/done? (obviously I am not a shaper and every part of the 3d image is just for conveying the thoughts)

Attachment 5099

I think that would cause turbulence. the easier the water enters under the board and exits the board the faster it will be I believe.

Hey Mfitz,

From the image such a large concave would actually probably slow down the board on east coast. In my opinion you need more juice for larger concave to work properly, subtle concave are my choice for east coast norm. It would probably create more lift and reduce speed from my experience. also from my experience concave which run out the tail cause more maneuverability but also create a reduction in speed. Hopefully LBcrew chimes in. Also in my opinion a flat surface is always fastest, less resistance but also it is dependent on waves. For instances Hulls are crazy fast but not on beach breaks, you need straight faces to reach the speed required to hydroplane which is where a hull really works. hope my .02 helps a bit.

Hey guys, thanks for the thoughts. Im not suggesting Im going to get a custom with something like this built into it.. but if the idea seemed reasonable maybe down the road with some spare cash I might get it built...
But I def. would like to hear the thoughts people might have.
thanks!

What's your theory based on? Explain what you believe the correlation is between water being "sucked into the void" and an increase in board speed?

In an effort to distill everything down to the most basic principles, let me suggest this... the two primary forces acting on a surfboard that translate into board speed are thrust and drag (a forward force, and a rearward force). The other two forces, lift and gravity (an upward force and a downward force), create thrust through translation: gravity tries to pull the board down the face, and the board's bottom and fins create lift. Lift reduces drag, while the constant pull of gravity, working opposite the force of the water rising up the face of the wave, increases thrust - the board is constantly riding "downhill," like walking down an up escalator. Because these forces are not balanced and equal, the result is acceleration until a sort of "terminal velocity" is reached - max board speed.

What I mean by all this is, if you want a board to go faster (raise it's "terminal velocity"), you have to decrease drag or increase thrust. You can do this all kinds of ways. How does your design do either one?

Quote:

---

Originally Posted by LBCrew

What's your theory based on? Explain what you believe the correlation is between water being "sucked into the void" and an increase in board speed?

In an effort to distill everything down to the most basic principles, let me suggest this... the two primary forces acting on a surfboard that translate into board speed are thrust and drag (a forward force, and a rearward force). The other two forces, lift and gravity (an upward force and a downward force), create thrust through translation: gravity tries to pull the board down the face, and the board's bottom and fins create lift. Lift reduces drag, while the constant pull of gravity, working opposite the force of the water rising up the face of the wave, increases thrust - the board is constantly riding "downhill," like walking down an up escalator. Because these forces are not balanced and equal, the result is acceleration until a sort of "terminal velocity" is reached - max board speed.

What I mean by all this is, if you want a board to go faster (raise it's "terminal velocity"), you have to decrease drag or increase thrust. You can do this all kinds of ways. How does your design do either one?

---

LBCrew, thanks for the quick summary. In short I don't have any real reason why this could possibly work. My thought process was that if one has a concave down the bottom of the board, water is getting somewhat squished in the slight channel of a standard concave... as far as I know water can not be compressed so it is being forced down the standard concave on board and it is more then happy to be released out the back of the board. So I was thinking that if you increase the release area by a large amount, the water would be filling that void, with force. the entry into that void in the picture, I was trying to get the effect of an airplane wing (upside down mind you) which might aid in amount of water that is pulled into the cavity space. But after reading your response... perhaps that void would only serve to pull the board down onto the surface of the water, creating more drag? I suppose my theory could be based on a ram jet, which from what I understand is forcing such a huge amount of air into a chamber that at a certain speed the air coming out the back is exiting with more force required to pull the air in....
I dont know... Im not physicist lol.

I'm no physicist either!

But my guess would be that yes... you're creating "suction" through low pressure under that concaved area, along with turbulence. Remember that lift is created by lower pressure above the wing. If you create lower pressure under and behind the leading edge of the concave, you create a lift force pulling the board down and back. Recall, too, that turbulence creates turbulent drag... another speed-reducing force.

Remember that a ram jet requires fuel... an outside source of energy that's added to the system. I'm not sure the same theories would apply to surfboards and wave energy.

But this is all guessing... and I'd be interested to hear what others have to say. Of course, the only true way to see what happens is but build it and test it. From there, who knows where the ideas will go!

Quote:

---

Originally Posted by LBCrew

If you create lower pressure under and behind the leading edge of the concave, you create a lift force pulling the board down and back. Recall, too, that turbulence creates turbulent drag... another speed-reducing force.

---

hmmm "down and back"... that seems like this design would be counter productive to speed. lol. thanks for the insight it very interesting to hear what you and others think...

The other part of it where you mention having a larger release are to increase force is not right. You have a decent idea but it's somewhat backwards. Having a larger release area will actually decrease the velocity of the water. You'd what to start with a larger area and filter it down into smaller channels to increase the speed of water flow.
Check out Bernoulli's principle and the Venturi effect for more in depth info.
There is a pretty cool interactive animation that demonstrates this here.

Quote:

---

Originally Posted by Driftingalong

The other part of it where you mention having a larger release are to increase force is not right. You have a decent idea but it's somewhat backwards. Having a larger release area will actually decrease the velocity of the water. You'd what to start with a larger area and filter it down into smaller channels to increase the speed of water flow.
Check out Bernoulli's principle and the Venturi effect for more in depth info.
There is a pretty cool interactive animation that demonstrates this here.

---

Hey Drift... that is an interesting demonstration.... I cant for the life of me explain what my thought process is other then my missunderstanding or my lack of knowledge on the actual physics. lol.
But my initial thought is that the pipe animation wouldnt necessarily be the same as the flow on the bottom of the surfboard... as the opening pressure could hypotheticaly be the entire ocean, or perhaps the size of the wave, which would make every channel and contour under the board smaller then the opening flow, just by width of board compared to the ocean or wave surface.... but now I have easily ventured into an area which I dont fully understand.... lol.