Questions for Quad Riders ........

[KenM]

Zorro, Yes I feel the "quad boost".BUT, I also feel it on my twin keel fishes. How do I reckon it works? I would think it's a combination of what Willi said about a "sudden reduction of friction" as the outside fin (or fins) releases combined with the long based fin or two inside fins pushing water through the tail in the power spot of the wave.Feels like an afterburner kicks in. When do I feel it? Off the bottom turn coming up into the pocket on a bowly wave.
As for tris, not my cup o'tea as I prefer tail rider drivier boards.
Regarding the 5 fin discussion, my "secret source" says that the fin set up on Steve Lis' boards is larger fins forward smaller fins back like on his quads with a small center trailer behind that.These are closed tail boards like a round pin not on his fishes.Hope to find out if he has done any kb's with this set up.

[willli]

the problem with skeg pairs is they don't always support each other. Why I posed the question Do you feel boost all the time?
Do you have to surf them "heavy" or driven? to feel the effect?
really concerned with exess drag. No? they just fly in unison? slotted?
I understand the argument, and having never ridden a Parkes or Pavel, unqualified to comment on performance. but wonder if "boost" is really the ONE angle of attack where the skegs actually support each other, released from otherwise exess drag of interfering with each other, yet an improvement over keels in maneuverability.
From experience with sails, the “slot” requires a large degree of maintenance, adjustment and helm balance, but the diagram on paper is so damn attractive that the fact that surfboard skegs are fixed in relation to the hull is overlooked. The ship example is another movable system where one diagram looks like skeg placement and what might be happening in ideal conditions on a surfboard, but I’m sure the ship has computers solving the efficiency problem and moves the keel (skeg) accordingly.
So can the lead skeg affect the trailing skeg? Certainly. Even in a major negative way (like a poorly trimmed set of sails) And through trial and error a workable (surfable) system has been devised to overcome the flaws of keels?

http://surfermag.com/features/onlineexc ... ndex3.html
nice photo at the end.

[frankfqr]

It's near impossible for me to convey any theories in relation to true hydro or aerodynamics. I never could get past the fact that our medium is unique when you throw in the force of the flow on the wave face and our angular aproach. Wind tunnels and water tanks take into account the flow over the entire mass. But as a mere child I was always drawn to the beauty of the flow off the back end of any object in motion, and for some reason fixated on the negative vortex. In motor races you'll find cars on the lead cars tail looking to be pulled along by the, I think it's refered to as the slipstream, it's a negative vortex. We probably would only create this at the moment we drift straight down the face out into the flats with pure straight flow off both rails, and at the moment we crank up onto one rail we must be breaking that flow patern. As stated, I only thru it out as food for thought. The direction your going with the wind sails seems more related and to the point. Enjoying the post!!!!!!

[fooj]

Surfing perfect uncrowded 6-8" Backyards with Bud earlier this winter I confided in him, "There were some waves that my board was going so fast I didn't want to turn, I just wanted to go fast." THAT is the quad boost (to me at least). The board goes where you want it to go, fast. Hand on the rail, of course.

[zorro]

well the ideas are coming thick and fast,

much obliged

willli wrote:

but wonder if "boost" is really the ONE angle of attack where the skegs actually support each other, released from otherwise exess drag of interfering with each other, yet an improvement over keels in maneuverability.

great point. Imagine if we could harness that effect where there was more than one point where it came into play? Assuming the effect is not apocryphal...

This might be important, bare with me.

I rode a fish for a year or two as a tri. Just to give my surfing a boost I ordered a quad off a well known shaper. While I was waiting I took the tri that I knew very, very well and put some fcs plugs in it to make it a quad. Well I screwed up on the placement (put them too close to the rail and too far forward). The only way I could get it to work was to make some "delta" keel fins and place them in the fcs plugs. This gave a lot of overlap along the base of the two fins.

In the water the board went just as fast as it did when it was a tri. But it was then that I noticed this boost at certain parts of the turn that it certainly did not have as a tri.

Six months later I reversed the process on my new quad (turned it into a tri) and noticed that, though it went at the same speed, it lacked the sudden boost that occasionally happened when it was a quad.

Why is this important.

If the boards go just as fast as a tri as they do as a quad, you would have to conclude that the quad fins aren't interfering with each other (or that tris and quads have a similar degree of inter-fin interefernce ).

The thing that stood out was the sudden boost (occasional). The sweet spot, as you might term it.

willli asked:

Do you have to surf them "heavy" or driven? to feel the effect

?

answer: I don't know. I think it is when you drive them.

as Kenm and yourself suggest there would be a good argument for attaching the boost to the point where the outside fins come more out of the water. And yet if this were true then the sudden action would be more like dragging you arm in the water to make a turn, rather then the sudden

Feels like an afterburner kicks in.

(Kenm)

[zorro]

Frankfqr

good point about the slip stream. One of the references suggests that jib mainsails arrangement with the slott keeps the air flow more together. I wonder if this fits in there?

Jfooj

what you say brings to mind that I only surf less than eight feet. That personally I've only felt it in smaller waves. In bigger waves, as you say, you're going fast enough.



Looking at the poll I'm pretty stoked.
There's at least eight guys who have felt it and know what we are talking about.

And two quad riders who haven't felt it.

Any chance of those gentlemen/women describing their fin placements??

Out of interest:

http://www.kneeboardsurfing.co.uk/forum ... =1394#1394

pics of a similar board to the world champion's.
have a look at the fins nearest the photographer in the top pic.

can't you imagine how much drag they should apparently cause.


Trouble is.....

they don't

cheers again.

oh yeh

album_showpage.php?pic_id=6360

[T Hall]

Yes I have felt the "fin boost" feeling. I make my own boards, (quads and tri fins) and design my own fins. I'm always tinkering with fin placement. This is what I have now. The board that I find to be the most versitile is my 5'10" quad. The foreward fins are at 16" from the tail, 1.5" from the rail and have a toe angle of 3/8" over a fin base of 4.5". They are 4 3/4" tall. The rear fins are 9.5" from the tail, 2" from the rail and have a toe angle of 3/16" over a fin base of 4.5". They are 4" tall. So the tall fins are in front and the small fins are in the rear. The toe angles are slightly different and the fin sets are fairly close together that is what I think gives the board it's extra squirt. On the boards with the rear fins closer to the center of the board I don't notice this effect as much. This is just my experience with tinkering with kneeboards over the years. Hope it helps. T Hall.

[zorro]

T.Hall wrote

Yes I have felt the "fin boost" feeling. I make my own boards, (quads and tri fins) and design my own fins. I'm always tinkering with fin placement. (snip) The toe angles are slightly different and the fin sets are fairly close together that is what I think gives the board it's extra squirt. On the boards with the rear fins closer to the center of the board I don't notice this effect as much. (snip)...... Hope it helps. T Hall.

Helps amazingly thanks THall
Good because you make tris, quads and have variations on quads (how many variables are there!) And are qualified to describe the differences you feel.

Especially that of fin seperation from the rails.

Plenty of questions come to mind.

Just a few for the moment.

Have you tried a wider based fin in the back with a more narrow one of the same height in the front?

A low keel fin in the front with the larger fin in the back?

As far as cant, less or more in the front, or the same?

Do you always try and overlap part of the fins? Eg tip of rake?

Have you tried the same board with the toe in angles the same, then different?

And if so what differences did you feel as far as the "boost"?

Martinmurph and jfooj (that rail grabber )

Rhetorical question. I take it you ride blast?
How would you say the H2 would contribute?

cheers

(Happy Easter )

[zorro]

thought this was relevent

Stevea (sept 25 2005)

(snip) feel that flex can and does increase a boards performance via injections of squirt the FF provides at the moment you want without lag of plastic not that i can say ive felt lag but i have felt the squirt.

Guessing stevea is talking about his quads here.

Is flex part of the equation?

[ScottMac]

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[W.G. Facenda]

Retro?? Like the 26 yr old thruster design?

[ScottMac]

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[Beeline2.0]

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[ScottMac]

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[zorro]

thanks mm!

talked me into buying (borrowing ) a set.

life is good


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ah, 4 votes for el zorro está de sus tuercas!!!!

but 11 for the important one