Board outline, with and without fins

[nomastomas]

Great to have Larry G's input on this matter. However, I don’t understand what Larry means by his statement regarding WP back outlines “That makes the centerline of the board point inwards toward the wave face when you are in full trim going across a wave, BUT, when you lift the rail up in the air to carve a turn, the centerline of the board then points in the OPPOSITE direction of your intended curved path! It's dynamically UNSTABLE! It fights you when you want to change direction, as in a cutback. “ Can someone clarify for me?

[krusher74]

Great to have Larry G's input on this matter. However, I don’t understand what Larry means by his statement regarding WP back outlines “That makes the centerline of the board point inwards toward the wave face when you are in full trim going across a wave, BUT, when you lift the rail up in the air to carve a turn, the centerline of the board then points in the OPPOSITE direction of your intended curved path! It's dynamically UNSTABLE! It fights you when you want to change direction, as in a cutback. “ Can someone clarify for me?

When Larry is talking about WP back outlines I think he is being specific of these shapes only http://www.d-talks.com/wp-content/uploa ... Centre.jpg

[bgreen]

Nomatomas,

Here's Larry's comments:

" The Friday posting by "nomastomas" was actually already answered by "krusher74" in today's (Saturday, 25 July, 2015" posting. I was commenting
on the handling (turning) characteristics of boards that have the Wide Point (WP) located BEHIND the Mid-Point of the board. The most extreme
example is the original Paipo Nui from the early-mid-'60s, which used the traditional 'guitar pick' style outline shape or design: widest way back
in the TAIL area, as opposed to the more traditional "Tombstone" paipo board shape (round nose, more-or-less parallel rails, square tail), which
is not quite as fast, but is much easier to control and maneuver.

Take a look at the Paipo Nui, designed by John Waidelich, and produced by Val Valentine: Now, imagine laying this board down on the floor of your house. Line up
the centerline of the board with a line on the floor. If you then lift one side of the board so that the rail edge line is still on the floor, you
will notice that the direction that the centerline of the board is pointed has shifted and is NOW pointed a bit to the side OPPOSITE from the
direction you want to turn towards. All this means is that you need to turn on the corner of the TAIL, not on the rail of the board! You have to manhandle a BIG paipo to do that!

That's how Harry Akisada does it at Makaha in overhead surf. The nose is in the air... most of the board is in the air. He is carving
water-skier-size 'Rooster Tails' from the corner of the super-wide tail. But few paipo riders of that wide-tailed design do that, preferring to
just go as fast as they can. If you want an easy-turning board, then the outline of the board need to be narrower in the tail area that at the wide point, and the WP will end up a little forward of the mid-point of the board."

Bob

[krusher74]

Nomatomas,

Here's Larry's comments:

" If you want an easy-turning board, then the outline of the board need to be narrower in the tail area that at the wide point, and the WP will end up a little forward of the mid-point of the board."
Bob

I also notice that Larry's conclusion of the bullet points of a easy turning board are what bodyboards have been since there invention.

The second picture is the shape (at the extreme end of the scale) of a Drop knee bodyboard where the rider has all there weight on the back half of the board, these riders seem to prefer the wide point back from centre. Which I feel would suit a prone rider who likes to ride with the weight to the back corner of the board and maybe over a rear fin like in Nomas's designs.

Do the angles in these designs in context to this thread differ by more than a couple of degrees?

[rodndtube]

Now complement this discussion with the Vektor bodyboard fin system for dropknee riders.

[krusher74]

The BZ maligs board also had fins pretty far up in the 90's , hmmmmm totally confused now

[rodndtube]

The main point on the Vektor System's asymmetrical fin placement was placing the fins underneath the dropknee rider's weight (pressure) points for the foot and the knee. I might add that my Bonzer paipo has runners further forward on the board than my regular Austin placements.

[jbw4600]

Thomas, To answer your question about yaw angle. In very steep surf I think my yaw angle is minimal (0-5 degrees) when cutting across a wall. And with no fins it would be even less in steep waves. When ridding finless (which haven't done for a long while), I tend to dig the front rail in hard when cutting across a steep wall. But even with fins I tend ride the front rail quit a bit. That is why I like boards with the wide point forward of the midline. I always wear out the elbows of my wetsuits. When the wave angle goes down or the line of attack changes then I think the angle will increase. But everyone has a different style of ridding.

[davehahn]

Fascinating thread. I'm learning a lot.

I might just throw into the mix, if it matters, that the angle of yaw may well be 5-degrees or 12-degrees, but it's not positioned off the center line. The wave face hits a larger area on the board, as in the graphic attached. I think this difference is significant, as it brings much more of the B&R and outline into play.

Bodyboard_Mach_7_7.jpg (19.32 KiB) Viewed 3401 times

[nomastomas]

Your absolutely right, Dave. The Daniels video submitted by JJJ was quite revealing in this regard. I've been dealing with the summer rush and haven't taken the time to respond to all the great input here. I'm working on it, though...

[nomastomas]

There has been a lot of good information shared on this thread and it has taken me some time to digest it all. Most pertinent was the Sways thread on “Balance” that was supplied by Rod. It strikes to the heart of my question regarding the interplay between rail designs and fins…well, almost.

It’s very clear to me that regardless of outline shape, in prone riding all the action takes place in the back third of the board. The link to Gregg Daniels underwater video of body boarders submitted by JJJ is very revealing. With shots taken both above and below water, it seems pretty clear that the traditional “Boogie Board” shape is ridden more off the back, wave-side rail and corner. This video also shows how the riders of these finless, WP-forward (WPF) shapes rely heavily upon body weight placed on the wave-side rail to keep the board engage with the wave face. What interested me was that the yaw angle didn’t change too much, but the percentage of the board (and the riders body) actually penetrating the wave face increased as the steepness of the wave increased. In a couple of frames, the rider’s body has drifted completely off the board and into the wave face, with only the hands in contact with the deck, as if the body board has become a hand plane. In another frame of a drop-knee rider, only the rear, wave-side corner is in the water. This style of riding would be consistent with the need to keep the wave-side rail fully engaged in the absence of fins. The end result is that at times there is a lot more board in the water, than there is with a WP-back design (WPB). (not the extreme “guitar pick” shape, but shapes where the WP is only 6”-8” behind center. This extra “form drag” has got to slow things down. I noticed in Daniels’ video the riders seemed to be going fastest when just the rear corner was engaged.

As I see it, finless body boards rely primarily (but not entirely) upon the rail to hold position on the wave face. They probably perform better with a WPF outline, as this straightens the outline in the last half of the shape, which puts more rail in direct contact with the wave face for better hold. Unfortunately, this also creates more form drag (less than optimum speed), and ultimately is prone to failure in steeper parts of the wave, as the typically hard edge slips out, regaining hold in a less steep (less powerful) part of the wave. Expert riders are intuitively aware of this design flaw/feature and adjust their riding style in an attempt to compensate for it, e.g. drag wave-side leg, pull up on beach-side rail, do a spinner, etc. But the straighter rail and low rocker also has a wider turning radius, forcing the rider to pull up the nose to free the rail for sharper turns. Pulling up the nose causes the board to stall, which may or may not be desired outcome.

I agree with Larry that the extreme WPB shapes (guitar pick) don’t turn very easy. The rail line is too straight and must be lifted out of the water when turning sharply so as not to “catch” (much like a LB). I think the Boogie board outline suffers from the same problem, but in reverse. There, the rail line from WP to the tail is too straight. The combination of straight rail and flat rocker makes these shapes fast, but those two features also make them difficult to turn without raising the nose and pulling the rail out of the water, which I would call a stall. (Note: In DOH or larger waves, Larry’s frame of reference, where projection out of turns especially on the drop-in, is a must, the WPF design combined with additional length is the better choice. The wide turning radius of the longer, straighter rail line helps to project the rider down the line, away from the cascading lip. (This is essentially the difference in outline shape between a gun and a small wave shortboard.)

My design approach has been to capitalize on the fact that, with prone riding, all the action takes place in the rear third of the board. I place design elements, e.g. fins, rail curve, bottom contours in such a way as to leverage this naturally occurring relationship between rider, board and wave. What I like about the finned, WPB shape in OH or smaller waves is that it has a lot of curve where the outline engages the wave. With the fin(s) providing the necessary hold, this curve minimizes the amount of rail in contact with the wave, thus minimizing form drag. Currently, I locate the wide-point behind center a distance equal to 17% of the board's length. In the case of my personal board, that distance is 8", and it coincides with where my hips are located when riding. The leading edge of the fin(s) is/are located an inch behind this point. The "bump" or "hip" created by the WPB design provides a natural pivot point for a more carving turn, which again is enhanced by fin placement. Rocker curve and WPB outline negate the need to pull up on the nose to initiate a turn, so there is less loss of speed through turns. (This same outline shape is seen in contemporary shortboards, especially the Channel Islands Flyer.) The single most consistent report I get from owners of the TBG4 is how fast the board travels compared to other body boards they've ridden, both soft and hard. The speed comes from maximizing hold, allowing the board to stay in the wave's power band, and by minimizing form drag.

UnderwaterViewOfBoogieGoingRight.png (348.58 KiB) Viewed 2804 times

The above photo is a screen grab from a video posted on YouTube by “JJJ”. It shows a rider going right on a body board. The area of the bottom in contact with the water is clearly evident, as is the rider’s position, lying completely on his right side, on the wave-side rail.

TBG4vMach77small.jpg (60.5 KiB) Viewed 2804 times

In the above photo I’ve attempted to compare the outlines of the TBG4 and the Morey Mach 77. I’ve identified the WP of each with blue tape. Based upon videographic and photographic evidence, it appears that the yaw angle for the M77 is approximately 40° off the centerline. I used the same yaw angle for the TBG4 and based upon my experience I believe its pretty close to that of the Mach77. Notice (red arrows) that the Mach 77 presents significantly more rail to the wave face than the TBG4, especially in the tail. (This would be appropriate for a finless craft.) Also notice the conspicuous “hip” in the outline of the TBG4 and the location of the fins relative to it. The combination of rail shape, outline curve, rocker, fin position and bottom contours yield a "balanced" craft that is both very fast and very maneuverable for its intended wave-range.

Note: I highly recommend watching the video. Waves are far from linear, curving both horizontally and vertically, while constantly changing in steepness and speed. Seems folly to even attempt to understand how a surfcraft works. There are good reasons for the prominence of speculation and subjective report in world of surfcraft design.

[krusher74]

When I first went to indo it was the first time I had been in warm enough water to wear board shorts, in your picture that shows the riders thigh in the water off the back of the bodyboard I remember feeling the shorts flap and cause drag, especially both legs on take off, I soon moved to 2mm wetsuit shorts which greatly reduce the drag. I really dont know how all the warm water bodyboards put up with that flapping drag, maybe they never wear wetsuits and don't know any different.

Have you seen the shape of Toms very early boards

[nomastomas]

Interesting...WPB

[krusher74]

Looks like Tom might be in your local, would be cool to have a chat with him on your subject, crash his comp with your Tbelly.

[Uncle Grumpy]

Tom Morey's work was featured In a recent SHACC exhibit and one of the items was the very first "boogie" shown here. Somewhat larger than what finally ended up on the market.
For reference I'd guess Tom is about 5'10"