TBG5

What works and what doesn't. Share design ideas, references and contacts for paipo board builders.
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nomastomas
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Re: TBG5

#71

Unread post by nomastomas »

Go to the FX thread for an update....
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nomastomas
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Re: TBG5

#72

Unread post by nomastomas »

The G5 has become my goto board on OH+ days. Ease of duck-diving is the primary reason, and, with no need to get to my feet, steep and/or late take-offs are much more manageable. In the past, I've been plague by excessive lift in larger surf, but I think I've discovered a solution. It occurred to me that the planing efficiency of this shape, while beneficial in small waves, becomes detrimental in larger, more powerful waves. The mini-Simmons stand-up shape has the same issues. So, with this in mind, I decided to introduce more drag to the shape by increasing the fin size. I'm currently using True Ames Twin Fins (5.25"x5") placed in the read quad boxes of my G5, with a small 1" canard fin placed in the rear slot of the front fin box. My research showed no precise location for the canard fin, other than forward of the big fin and maybe an inch or so away. The idea remains the same: the canard cleans up the flow of water across the foiled side of the larger fin, reducing cavitation and loss of hold.
Twinzer-esque setup
Twinzer-esque setup
Twinzer.JPG (104.35 KiB) Viewed 166416 times
My experience has been that the fin set up reduces skipping, almost eliminating it. It also reduces speed, bringing it down to a more manageable and controlled level. Instead of losing sight of every thing watery speed blur, punctuated by body slams, I was able to enjoy the ride. Turns are very pivoty and precise, as would be expected from the larger fin, set in the rear corner. Hold was excellent, allowing me to go anywhere on the wave face, for as long as I wanted. I also found that it was easier to get around any whitewater. Usually, if the wave breaks in front of me, I get stuck being pushed side-ways by the whitewater (really bad on the finless GFX) There was more opportunity to get back on the face with the large twin fins.
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rodndtube
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Re: TBG5

#73

Unread post by rodndtube »

Thank you for sharing the update.
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Re: TBG5

#74

Unread post by nomastomas »

Here's the latest G5...it boasts a whopping 40L volume to accommodate a 300# rider. I had to exceed the prescribed length by 2 in in order to achieve the desired volume. Dimensions are 52" length, 23.5" width and 2.5" thick at centerline (thickness at rail is close to 3") Using Aku allows me to shape to very specific dimensions, including volume, while maintaining the G5's basic design features. While there is some distortion caused by the camera angle, the impact of increasing thickness does cause an increase in the depth of the beveled-rail concave. I don't beleive this will have any negative impact on performance.
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G5_BB_40L_2.JPG
G5_BB_40L_2.JPG (130.5 KiB) Viewed 166257 times
G5_BB_40L_1.JPG
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krusher74
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Re: TBG5

#75

Unread post by krusher74 »

It's hard to tell from the pictures but with those tail concaves does the G5 have a lot of tail rocker?
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nomastomas
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Re: TBG5

#76

Unread post by nomastomas »

Not an easy question to answer....about 1" at the centerline. But, then there is a great deal of "V" in the tail, so there is a lot more rocker out at the rail. A board with no rocker is fast, but resists turning. The rider has to weigh the tail to bring the rail out of the water in order to turn. Weighing the tail causes the board to stall and loose speed. Rocker makes the board easier to turn because the curve automatically frees the nose rail. Some would argue that V isn't needed in such a small shape, but I've found that it really shortens the turning radius. With a board that has no V, the rocker out at the rail is identical to the rocker at the centerline. But, what V does is to progressively increase the rocker at the rail so that the farther the board goes over on rail, the more rocker curve and the tighter the turnin. The concaves become progressively deeper as they extend through the tail. I'm sure this would also change the rocker curve as the board is rolled over onto the rail.
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Re: TBG5

#77

Unread post by bgreen »

Here's another approach to riding choppy waves:

https://www.swellnet.com/news/design-ou ... -stop-four
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Re: TBG5

#78

Unread post by krusher74 »

Tomas: was just trying to compare rocker to my own designs seeing mine have about 1/4" yours at 1" would be a lot to me, I wonder how much tail rocker a bodyboard bends to from its static 0.

I can't say I have really noticed the chop/skipping think at all, either my boards don't do it, I dampen it with my shoulder or I just don't perceive it.
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Re: TBG5

#79

Unread post by nomastomas »

I don't believe that rocker has anything directly to do with lift. If anything, rocker slows a board down when going in a straight line. Your shapes tend to be smaller (less planing area) than mine. You may have come upon a combination of volume and planing area for your weight that, while fast, doesn't generate enough speed to lift the board and you out of the water. That's what I'm trying to achieve with the G6. I suspect that your new groveler will skip in larger waves.
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krusher74
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Re: TBG5

#80

Unread post by krusher74 »

nomastomas wrote: Thu May 16, 2019 11:43 am I don't believe that rocker has anything directly to do with lift. If anything, rocker slows a board down when going in a straight line. Your shapes tend to be smaller (less planing area) than mine. You may have come upon a combination of volume and planing area for your weight that, while fast, doesn't generate enough speed to lift the board and you out of the water. That's what I'm trying to achieve with the G6. I suspect that your new groveler will skip in larger waves.
So do stand up boards skip (larger planning area), or Is that dampened with bending of the knees? i feel if you flowing along on rail you are not on a lrge enough flat area to skip, I have seen video of Greenough skipping horribly on his spoon. its looked like the large amount of nose belly just made that think rear up like a boat and take off,like when you try to go fast in a speed boat in choppy seas
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Re: TBG5

#81

Unread post by rodndtube »

Knees do act like natural shock absorbers. But, I have also noticed that cross-chop/cross-swell tends to create a special scenario when moving at speed in an open ocean wave (meaning one several, several hundred yards out where I have encountered this happening). My body/belly can't do what my knees and legs can do in a standing position.
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nomastomas
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Re: TBG5

#82

Unread post by nomastomas »

So much for trying to keep a complicated subject simple. So, its not the amount of planing surface per se, but more the characteristics of the planing surface, particularly the relationship of the length of the hull to the width of the hull. Naval architect, Lindsay Lord referred to this as the “aspect ratio” (AR) of the hull. Writing in “The Naval Architecture of Planing Hulls” (a must-read for any budding surfcraft designer. Also, a pretty good sleep-aide) he states:

“The lift and the drag, or the carrying power and the resistance, of a simple plane are combined functions of the effective planing angle, together with those characteristics inherent in the particular plane’s beam (to) length proportion or aspect ratio…In other words, while increasing speeds require the displacement hull to become progressively narrower, the planing hull moving at high speed requires the widest possible beam. To simplify still further, the displacement hull can improve speed only with added length; the planing hull requires added beam. The beam-length proportion is fundamental as a controlling factor in (planing) hull performance. This relationship, as indicated by the aspect ratio, is basic in the estimate of potential lifting power…” Lord found that an aspect ratio of 0.40 was the best, and that an aspect ratio around 0.20 “..compared with wider bottoms, is inferior on every count. The resistance is higher at all speeds, the lift is low, the stability poor, the longitudinal moment excessive and the wetted surface reduction almost zero.”

So, to answer your question, consider the aspect ratio of a 9’6”L x 23” W longboard, and the aspect ratio of a 49” L x 23” W prone-board. The AR for the longboard is 0.20 (23/114), while the AR for the prone-board is 0.47 (23/49). According to Lord, the prone-board is better at generating lift than the longboard. It is for this reason that big wave guns opt for an aspect ratio of 0.16 (19.5/120). In waves of consequence, lift is a quality to be avoided.
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Re: TBG5

#83

Unread post by rodndtube »

So, my 50 inch board would need to be 10 inches wide to avoid all that lift and skipping as a planning. LOL, at 10 inches wide it would no longer be a planning hull but a displacement hull ;)
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Re: TBG5

#84

Unread post by GeoffreyLevens »

Can't remember who said/where I read, but quite a few years back I remember reading that GG style hulls, at very high speeds, will plain up on smaller and smaller area along the midline and lift out of the water. Not likely in continental US type waves, think Sunset, HI beach West swell type power.

Stand-up boards, I have rocked (small amount) rail to rail to "calm" bounce or skip in choppy surf and it seemed to help quite a bit at maintaining control
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Re: TBG5

#85

Unread post by GeoffreyLevens »

Rod your theoretical 50" X 10" board would make a good weapon for hunting/spearing small game. Just make sure the nose has a nice, sharp point
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Re: TBG5

#86

Unread post by nomastomas »

The load must also be taken into consideration as well as its counterpart buoyancy. And speed, too. Then, of course, there is the impact of form drag produced, not just by the legs but by other body parts, arms, hips, etc, that may be hanging over the outline. I thought all that was obvious? And, while I'm sure there is a mathematical way to take all of these variables into account and determine the ultimate aspect ratio for a given length at a given speed with a given load, I am no mathematician nor engineer.

What I take away from Lord's work is that, with a planing hull, the 0.40 aspect ratio provides the highest potential for lift for a given length. A decrease in aspect ratio from 0.40 results in a decrease in planing efficiency and lift. Therefore, one way to reduce lift is to decrease the aspect ratio by narrowing the width. Without benefit of a trained engineer, I'll have to utilize a trial-and-error approach to determine the ultimate aspect ratio, reducing width while knowing that I will need to maintain a specific volume for my body weight and a minimum width (the width of my shoulders and hips). Reducing the aspect ratio reduces the hull's efficiency of planing which increases drag, reduces speed and the resultant lift. But there are other ways of reducing speed which in turn will reduce lift. I can introduce drag, for example, by increasing fin area, dragging my legs or by introducing drag producing features to the bottom contour, e.g. increase rocker.
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Re: TBG5

#87

Unread post by krusher74 »

rodndtube wrote: Thu May 16, 2019 2:42 pm Knees do act like natural shock absorbers. My body/belly can't do what my knees and legs can do in a standing position.
one reason I'm such a proponent of boards shorter than most people seem to ride it that I like to ride with about a 90 degree angle on my rail arm elbow while holding the nose. This I feel is the most optimum position for up and down shock absorption through your shoulder and lifts your chest/belly much further off the board. I see guys outstretched for the nose look very static and unable vary there position quickly to maneuver the board.

You can feel this effect my lying on the floor with both forearms on the floor in front of you propping you up and elbows at 90 degrees. Feel how easy it is to move up and down etc , now slide your hands further and further forward and you will feel how much less mobility you have and the more your chest/stomach makes you immobile. This immobility makes it much harder to dampen chop.
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Re: TBG5

#88

Unread post by nomastomas »

I totally agree with your arm position/location, but I design my boards to provide a little support for the upper thigh when ridden in this position. The tailblock is about 6" below the natural break at the hip when ridden in the position you describe. It requires a slight shift forward to go from kick-paddling position to riding position. I know I'm in the correct position when my hands are on the nose and my elbows/forearms are on the deck. The bit of support by the tailblock makes it easier for me to keep my legs from dragging.
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nomastomas
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Re: TBG5

#89

Unread post by nomastomas »

Here are five G5s that are headed to Florida. This photo shows the scalability of the G5 design. Intended riders range in height from 6'2" to 5'6", and in weight from 230lb to 140lbs. Lengths are 52", 50", 46" and 45".
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Re: TBG5

#90

Unread post by CHRISPI »

Very nice boards. Keel V bottom is the way to go.
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