"The results of the spoon/faucet test are in: Inconclusive!"
HAHA ... please post pics! Conceptually, I can't think of a better illustration. There are all kinds of ways to shape concaves in a board.
I did’t put fins on it though! To tell you the truth it wanted to suck the spoon into the flow of water. Is this the expected result?
That’s actually a force created by a low pressure area near the around the back and tip of the spoon caused by a combination of the adhesive properties of water, surface tension, and the Bernoulli Effect. A lot of people say is the Coanda Effect, but I don’t think that’s exactly true.
Correct me if I’m wrong.
Yeah it really just felt like spoon wanted to suck into the waterflow. Seemed like like ‘cohesion’ to the waterflow.
Turn it over and try putting the other side in the flow. All you've done so far is verify what Skip Frye says about round bottoms... ("They suck...literally.")
I think a slightly rolled bottom works good. I’m playing with a variety of things that are the opposite of concaves. My latest board is 5’11" x 20 1/2" x 3" and it has a slightly rolled bottom. The middle third is flat but the outer edges are sightly rolled, or vee maybe a 1/8" or 3/16". The tail section from the center finbox has vee to the edge. Not sure if this is what they call a tri-plane bottom. It has standard tucked under rails. I guess if you were to look at the bottom rocker profile, the rail line runs an 1/8" higher than the center rocker line.
Previous boards have had about 1/4" up to 1/2" of bevel running along the bottom starting about 2’ in from the rail. I combined that with concave under the nose, but then flat about a third of the way in all the way to the fin and vee from there. I just changed from the bevel starting at 2" to having the bottom set as 3 sections with the middle being flat (except under the nose).
I like my concaves starting at the nose and flattening out where you stand. I like concaves like they have on nose rider boards, the big tear drop shapes. I can tell for sure that this gets the board moving when I stand on the nose. And this for boards in the 7’ to 8’ range. I think the concave adds a bit of air then it gets pushed under the board where it flattens out and adds lift. I’ve been adding the 3 planes after the tear drop on the last 2 8’ boards I did.
I have a shot of an old board that has the rolled bottom but the concave runs all the way through, and one of the newer boards where the concave is only up to the first third of the board.
I have several boards with the bonzer bottom. There is noticeable acceleration when you turn with your back foot in the right spot. If you are not ready for it, you might fall off the back of your board. I also have Greg Griffin 5 fin boards, which all have flat bottoms. These boards have a similar affect when turning, there is noticeable acceleration coming out of turns. The Griffin boards use the 5 fins to create lift under the tail of the board. You can feel that lift when the board is planing flat. I think the modern bonzers all use a 5 fin setup, but it’s the way the bottom channels the water flow that creates the lift. When you push down to turn you’re pushing against the lift and it results in more energy going into the turn. I don’t know if this acceleration is a result of “venturi effect” or something else, but it’s there.
You have to try these boards and stand in the right spot to feel the way they work. The bonzer design has credibility, but Greg has shown that you don’t need the complex bottom design to get similar results. Anyone with enough time on one of these boards will tell you they work.
hopefully this answers the infidels who are out to discredit the bonzer without trying it for themselves. hmmm lurker roy still can’t get over the campbells for some reason " )
cheers,
More food for thought.
Here’s what put the idea of the concaves up front going to flat towards the back in my head. One of these days, I’m going to put a mild version of this on a surfboard.
http://www.mshipco.com/mhull.html
Something else to look at is Jeff Alexander’s Gemini. It has a big concave running down the middle of the board. It’s about an inch of concave. I have one of those, and my brother has a couple. Those boards are fast. The only down side is the funky nose design.
Slater has a board with a hole running through it to send air under the bottom. In the 70’s that was something that people were playing with.
All these ideas are to get a faster short board that is also maneuverable.
I think on HPSB’s concave’s are mainly a feature to control flex; especially to give some “spring”.With super light foam an minimal glassing, thy would be to flumsy otherwise.
This is not based on experience just a thought.
For other boards i think they help keeping the fins work,as we ride up and down the wave which induces drastically changing AoA’s,which could result in stall , through “pre-directing” Water flow they keep the fins in a working range of AoAs.
Anyway,yet another thread worth following.
paging cjdboy! hehe any resolution yet ?
cheers,
Update:
Yup. Haven't been on for a while - just trying to fill orders for the models that I shaped off the back of this thread. Thanks guys.
I now have a website full of science and testimony as to the awesomeness of my new 'Venturi Spoon' model.
Check out the new yeam rider
[quote="$1"]
More food for thought.
Here's what put the idea of the concaves up front going to flat towards the back in my head. One of these days, I'm going to put a mild version of this on a surfboard.
http://www.mshipco.com/mhull.html
[/quote]
Thats a really interesting concept, I wonder if its applicable to surfcraft or only flat water craft.
Seems like theyre making a frothy air cushion for the back to ride on.??
here is my similar shape for wakesurf boards , built 40 of this type of hull this year, stable down the line and never seems to pearl. i just started to put a mild V out the back to quicken up the turns. Wakesurf boards like low rear rocker and fat tails to work good I keep center section flat and then a taper to the rail line.
Lakewaves, whats with the hand holds? And are they routed in or a plastic mould ?
And heres some back story to the M-Ship concept and its validity...
http://www.boatdesign.net/forums/boat-design/m-hull-m-hull-m-ship-5687.html
Futures box holes wetted out , to crisp up. This puts a thin shell coat in the box so resin don’t seep into core.I also wait till resin gets thick like honey then pour and set boxes. Use will be .5 oz .
