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Re: TBG5

Posted: Thu May 16, 2019 2:42 pm
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.

Re: TBG5

Posted: Thu May 16, 2019 11:44 pm
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.

Re: TBG5

Posted: Fri May 17, 2019 10:21 am
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 ;)

Re: TBG5

Posted: Fri May 17, 2019 10:44 am
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

Re: TBG5

Posted: Fri May 17, 2019 10:48 am
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

Re: TBG5

Posted: Fri May 17, 2019 11:58 am
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.

Re: TBG5

Posted: Fri May 17, 2019 4:16 pm
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.

Re: TBG5

Posted: Fri May 17, 2019 7:56 pm
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.

Re: TBG5

Posted: Wed Oct 16, 2019 3:58 pm
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".

Re: TBG5

Posted: Mon Oct 21, 2019 8:38 am
by CHRISPI
Very nice boards. Keel V bottom is the way to go.

Re: TBG5

Posted: Wed Oct 23, 2019 8:22 am
by belly rider
great looking line up of Floridian boards

Re: TBG5

Posted: Thu Oct 24, 2019 6:20 am
by krusher74
Great to see plenty of interesting paipos and 5! being ordered.

Re: TBG5

Posted: Thu Oct 24, 2019 10:14 am
by rodndtube
Where in Florida are they headed?

Re: TBG5

Posted: Mon Oct 28, 2019 3:06 am
by krusher74
Just noticed they are all leg leash plugs, was that by order or you dont like arm leashes?

Re: TBG5

Posted: Mon Oct 28, 2019 5:36 am
by CHRISPI
Arm leashes specially elbow make boards with pointy bits come back to fast and hard.

Re: TBG5

Posted: Mon Oct 28, 2019 8:37 am
by nomastomas
Rod - After last minute discussion with customer, 3 went to Laguna, CA and 2 went to Oldsmar, FL

Krusher - It's what I recommend for hard surface boards with hard fins.

Re: TBG5

Posted: Wed Oct 30, 2019 4:33 pm
by krusher74
CHRISPI wrote:
Mon Oct 28, 2019 5:36 am
Arm leashes specially elbow make boards with pointy bits come back to fast and hard.
That's not my experience of using them, but I guess they work differently for everyone. Dragging a leg leash just sounds horrific! lol

Re: TBG5

Posted: Wed Oct 30, 2019 7:14 pm
by nomastomas
No...watching your board bounce around on the rocks is horrific. :o

Re: TBG5

Posted: Wed Oct 30, 2019 7:20 pm
by rodndtube
krusher74 wrote:
Wed Oct 30, 2019 4:33 pm
CHRISPI wrote:
Mon Oct 28, 2019 5:36 am
Arm leashes specially elbow make boards with pointy bits come back to fast and hard.
That's not my experience of using them, but I guess they work differently for everyone. Dragging a leg leash just sounds horrific! lol
I'm with Krusher on this one but it is a matter of preference. And, I'd rather untangle with my hands and arms in close proximity. There are pluses and minuses in each approach. I do tend to use a longer leash than many bodyboarders/paipo boarders, 5 ft in smaller surf, 6 ft in larger surf, and I don't like coil leashes as they seem to snap back more... I'd rather a leash stretch out even if it mean having to buy a new leash.

Re: TBG5

Posted: Fri Nov 01, 2019 2:08 pm
by belly rider
I premer leg leashes and buy the 5' COMPETITION extra thin one
Never really experienced tangling as I am tall 6'2" and my long legs probably keep the leash stretched enough to avoid wrapping around