https://www.facebook.com/groups/paipobe ... 375660080/
At the time I was also following the typical Aussie KB fin-placement, which pushes the fin cluster forward about 4 compared to a standard shortboard.. I dubbed the first KB based upon the G4 as the MPH which stands for modern planning hull , and it was essentially the G4 stretched out to 5-10 x 23-1/2 (coming from a non-Kneelo perspective, I was shocked at the time by what appeared to me as an excessive width. But who was I to argue with an experienced Kneelo?) I tweaked the outline to accommodate his requested Aussie-style fin placement, placing a wing/flyer just behind the leading fin box.
Here's what I’ve learned: Rider position on a kneeboard is very different from both surfboards and prone board (obviously!) but especially with regard to turning. Surfboard and prone boards are turned by weighing the tail and simultaneously shifting weight in the direction of the turn. It is much more difficult for a kneeling rider to shift weight far enough back to sink the tail. This was not an issue for the original Lis-style kneeboards (precursor of the fish) which had a relatively straight rail-line and were surfed in a more flowing, drawn-out turn style. As surfing style progressed and shorter-radiused turns became more in demand, kneeboards had to adapt. The adaptation was (1) increase curve in the outline and (2) move the fin array forward. The primary way to increase curve in the outline is to widen the center, hence the 23 + width of contemporary KBs. As a board is tilted over onto its rail, rail curve reduces the amount of contact that the rail has with the water.
Yaw is the term for the horizontal rotation of an airplane or ship around an axis that intersects its center-of-gravity (COG). Yaw is controlled by the rudder . Surfcraft typically don’t have moveable rudders, but their fins act as static rudders. Moving the fin array forward places the fins closer to the board’s COG, allowing for quicker changes in yaw. It also places the fin array where the kneeling rider can apply maximum pressure. In general, I find that turns on a kneeboard feel much flatter and pivot-y than turns on other surfcraft. (Not to say that full rail turns don’t happen or can’t occur.) So, I see the forward location of the fins combined with the curvy outline as a compensation for the rider’s inability to shift weight back far enough due to his static kneeling position. I find it important to also have the wide-point behind center, shortboard-esque , and the combination of fin location and WP location creates a pivot point for turns that is close to the rider’s position. You can see the same dynamic in the shape of surf skis , surf kayaks and other butt boards , where the rider has a fixed position on the deck. These adaptations are all done in service of shorter-radius turns. And, while you can kneeboard successfully on the old style parallel-rail, fins back fish-shape, the contemporary shape accommodates a wider range of surfing styles.
More volume forward of center may be helpful for paddling, but then the question becomes how much and how do you add volume? Increase width? Increase thickness? And how does the thickness flow impact the board’s performance. Less volume forward of center reduces the swing weight; it’s like swinging a baseball bat from the fat end. This distribution favors turning over paddling, although only slightly if not done in the extreme.
Attached are a couple of photos. The yellow board is my current ride 6-0 x 23 x 2-5/8 37L. The other is the board I shouldn’t have sold MPH 5-9 x 23 38L. Lastly, I use the fin setting specs from Hanalei Fin."
Assuming a finned shape, I still put as much curve in the outline as I can, and I push the wide-point even further behind center. Then I align the fin array just below the "hip". Trailing edge of quad rear fin usually lands about 6" up from tail. Twin fins a couple of inches more. All of the turning action takes place in the rear quarter. Finless requires as much rail line as possible for hold, so I keep a relatively straight rail for finless.
28 July 2023
https://www.facebook.com/groups/paipobe ... 822020080/
Bob, Love that vid! Nice bit of surfing, too. On a board that length (56", right?) you might want to push the fin cluster forward a bit, maybe 2-3". I would guess that about 2/3 of your body is on the board. Identify where you place the most weight/pressure when turning and that is where your fin's leading edge should go. This was the solution kneeboarders discovered for solving the same problem presented by the Lis fish. A little more curve in the outline would also help...maybe on your next board
-tpDamian Coase
I like that you are willing to experiment with your boards. Lots of experience in your decisions. The fins need a story all of their own. Again experimentation and improvement.
Bob Green
I'll travel down this road for awhile, then back to finless. I've borrowed a 5' twin fin, rounded pin. I'll post it after I surfed it.
Bob Green
Thanks Thomas. In the board below, it originally only had the forward fin slots. I didn't like the board and asked the shaper to put another set in further back (I just realised this is probably the first board modification so that makes 5 boards tweaked). The board went much better. Obviously a different design etc. The other thing about kneeboards, the centre of gravity is further forward. I'll soon try a curvier board. I'll post some photos of it. The next board I was thinking of wasn't going to be curvier, but more flat bottomed (I thought I posted some of Larry Goddard's design sheets but couldn't find them) . The curved board may change my thinking.
Thomas Haugh
On the red and blue board, the fin plugs appear to be parallel with the stringer, Is that so, or just an optics thing? I can see the toe-in on the yellow board. I use 1/4" toe-in on the front a 1/8" toe on the rear, unless I set the rear more towards the stringer a la McKee. Then only 1/16" or straight.
- BG_redHuie.jpg (9.04 KiB) Viewed 929 times
Bob Green
I don't have the board anymore. It was made for me to test out and eventually a friend of the shaper (Huie) took it to ride. The actual plugs look a little angled though placement seems parallel (if that makes sense).
Martin Hallen
Bob, it is possible the extra 2 plugs were placed in line with the existing ones to allow 3 fin positions as a twin fin - old (front), half back using the centre 2 plugs, or back, using the rear plugs. Or as a quad with a canted front pair so they sit out of line with the rear fins and do not disturb the flow......
Bob Green
I only used it as a twin fin, using the rear plugs. I was happy with the new setup, so never explored any further.
Thomas Years ago you recommended a Wayne Rich hatchet fin. It was just too much fin for my liking and I've never used it. I was thinking of giving them a spin on this board. Looking at the rear nubsters underneath it looks like overkill. WOuld you keep them in or take them out?
Thomas Haugh
Yes, the WR Nightmare Twin was the best twin fin set-up that I ran on a G7. It had the hold that a quad set has on the same shape, but it wasn't quite as loose as the quad. Nubsters are usually added to a quad that feels too loose, especialy in that transition from one rail turn to the another. I think that is more of an issue for a stand up surfer with a high center-of-gravity than a prone or kneeling surfer. That little bit of drift becomes part of the fun. Its not like its gonna cause a prone rider to lose balance and fall off.
Bob Green
Thanks. I don't mind a bit of drift.
Alan Bruce
You need a set of my leaf fins Bob. Turn tight & draw nice lines.
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Experimentation is still the name of the game for larger prone boards. I've moved fins, swapped fins, modified fins, modified boards, ordered new boards (4 so far) tried new ways to ride, etc., over the last few years. One conclusion that seems general is, that if there's too much volume, or rails are too fat, you may never be completely satisfied with swapping out fins. Regarding placement, I've felt that having the fins forward puts them under the heaviest part of my body (the soft middle). But I've been working on making it intuitive to bend the inside knee during a turn. That lifts the fin out of the water and applies pressure on the inside rail near the tail. Still working on that, but the results are promising.
Bob Green
Finless is my preference, this is a tangent.
John Morris
All my boards up until now have somewhat high volume to allow for switching off between kicking and paddling. I need to be able to get around in the line up. My most recent board is low volume, including much thinner rails, but I'm waiting for some energy before putting it to the test. I can imagine the new board being less reliant on the fins to hold a line steep and deep. No way would my previous boards do that. I do sometimes ride a boogie board or an airmat, so I am familiar with finless sliding.
29 July 2023
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There seems to be a d interest in both kneeboards and prone boards in this group, and rightly so. There is a natural common ground between the two types of craft due to the rider assuming a non-standing position in each case, and relying on arm paddling and/or kick paddling for propulsion when not riding an actual wave. What I wanted to present today was an example of how my design thinking on prone boards was successfully transferred to kneeboards. The images below are scaled photos of my 5’9” MPH (modern planning hull} kneeboard and my 49” T-Belly G5 (fifth generation). Both shapes have a similar outline, deck concave, rail shape and belly-to-flat-to-double exit concave bottom contour. Likewise, both shapes are quad-finned, although I have built twin-fin versions of both. The tail configuration differs between the two due to rider location when surfing, and width of tail (wider tails benefit from a split-tail design). Both shapes have similar performance characteristics; speed and hold on steep faces. Likewise, they are both best suited for smaller waves, in that they tend to develop too much lift in larger waves resulting in a loss of control.
Sean Catlin
Wow love them
Damian Coase
I like your thinking.
Ryan Titilah
Looks great for Emma Wood
Harlan Fujioka
I am/was a kneeboarder but am using some of my kbs as I call them gun paipo. Many of my boards are 6’0” but having an issue with one of my knees I just paipo them. Some work better than others.
Tom Newton
So what changes do you suggest for larger waves. Have already ridden mine in some fairly solid peaks. Can handle getting slightly airborne. It's any amount of chop in the wave face that can bring me undone.
Thomas Haugh
My shapes and most prone boards are basically planing hulls, made to generate lift. Lift increases with speed, and speed is mostly a function of gravity (of course there are other factors , e.g. surface conditions, wave shape, etc) So, sliding down a big wave generates more speed than sliding down a small wave. But the wave is also moving towards the beach and there is significant water flow up the face, so there is a vector of forces which impact speed. "Bigger" is such a relative term, but I find wave size in the "overhead+" range to be the strating point, The craft must be in contact with the water to allow control. What I do to compensate for the excess speed and accompanying lift is de-tune the shape. I go narrower, reduce volume, use bigger fins. In other words, increase form drag. I would also use a flat to slightly convex bottom; no lifting bottom concaves.
Bob Green
I think Damian Coase in another thread posted about nose vee reducing the chop effect.
Damian Coase
yes both Don Boland and I have gone with a vee in the nose, in Dons case combined with an edge bottom, to help with the board chatter created by chop. For larger waves we have longer, narrower and heavier PU boards that seem to cut through the chop. Don is healthier and fitter than me and still charges 8 foot plus waves on some of the heavier reef breaks around here. This is my 5 9 edge bottom PU board.
Thomas Haugh
This is a good graphic showing what I believe are the critical design elements. This applies to both my kneeboard and my prone board. In other words, I took the prone board design and enlarged it to accommodate a kneeling rider.
- Haugh29July23graphic.jpg (8.03 KiB) Viewed 948 times
Did you ever fine tune a finless board? I know you dabbled.
Thomas Haugh
First and only finless attempt...TBFX Eventually added fins....
...worked much better, of course
Ryan Titilah
Is there a way to order 1 from you? Are you building customs? Do you have any paipo T-Belly G5 available to look at. I’m in Ventura?
Thomas Haugh
unfortunately, I'm no longer shaping. You might want to try Tasha at Island Stream Surfboards. She has glassed several of my prone boards, and is a good shaper in her own right. I'd be happy to consult with her on the shape, if that helps.
John Morris
With experience prone and kneeling I wonder if you’ve pondered this comparison. Both types are able to tuck into tight spots nicely I reckon. But the combination of short hull length and low vantage point seems to limit the ability of paipos to look down the line and run out into the flats when needed to get past broken sections and set up for sections down the line. Anyone else notice this?
Bob Green
I think it depends where you are. If you are high up the face, I don't think the view would be much different. There are points doing a bottom turn, where vision can be more restricted.
Thomas Haugh
I think the visibility from the kneeling position is better than from a prone position. Riding prone has some advantages though over kneeboard; more fun in smaller surf, heightened sensation of speed, easier to duck dive in larger surf. Prone boards are especially good in super fast-breaking waves; no wasting time getting to feet or knees, just drop in and go. Bottomline: I'll have fun on my prone board regardless of wave size or speed. My keeboard needs chest-high face before the fun starts, but its 39L volume makes duck diving a chore for me at head-high or above. I keep both in my car at all times.
John Morris
my aim is usually to trim high, but also climb and drop, come hard off the bottom and the top. I know fins dragging in the water likely slow things down at times. But I feel like I’m usually spotting opportunities a little later than I did when I was standing. Maybe anatomy/neck mobility is also an issue. Rotating the head while upright provides a wider range of movement than bending the neck while prone.
1 August 2023
https://www.facebook.com/groups/paipobe ... 347700080/
Goddard was my first inspiration when I started shaping prone boards. I was more influenced by his incremental design process than his actual shapes. And, yes, his boards were finned...
Focusing volume in the rear-half of a prone board was another lesson I learned from Larry Goddard’s work. I keep 58% of the volume behind the mid-point. Drawing shows volume distribution (red line is profile out at the rail, black line is the profile along the center line) of the G5 and G7.
https://www.facebook.com/groups/paipobe ... 025090080/
Thomas Patrick Surfboards
I just posted this on MyPaipo: Man, I've always wanted to build a wooden version of my T-Bellys. I considered the chambered approach, but didn't/don't have access to a band saw. I've collaborated several times with a local Intermediate school shop teacher who had his woodshop students building HWS mini-Simmons. I would use Aku to design the shape and then a seperate application to to convert the Aku BRD file to create templates for the ribs. His class must have built a dozen or so. I'd be really interested in hearing the details of your "T-Belly" clone build. -tp
11 August 2023
https://www.facebook.com/groups/paipobe ... 042640080/
Thomas Patrick Surfboards
I’ve spent a lot of time thinking about what I call the “skipping stone” phenomenon and how to counter it. About 7 years ago actually designed a prone board with a deep v-to-flat bottom, but never built it. Long discussions on the MyPaipo forum led me to abandon this design. Then, I came across a video of a bodyboard rider on a wave taken from beneath the surface of the wave. It was clear from the video that only about the last 1/2 to 1/3 of the tail was in contact with the water (that and the rider’s thighs). Back to the drawing board…
I also once built a prone board using a tri-plane hull design, specifically for California winter waves. It rode very smoothly, i.e., no “skipping stone” if I could control my speed. I named that board the “Manta” because of its horned outline shape. Likewise, I built a couple of “Hull-style” displacement prone boards but never got a chance to ride them. One was a single fin a la Greenough, and the other was a 2+1 if memory serves me. Ride reports for both echoed the “smooth, cruise-y” feel in larger waves. So, for larger waves, switching from a planning-hull to a displacement-hull might be the way to go.
20 August 2023
https://www.facebook.com/groups/paipobe ... 305420080/
You can fix the "expansion" problem by installing an air vent, which is the same size as a leash plug and installs the same way. I have one on my black carbon-fiber prone board for exactly that reason. The vent has a one-way Gortex valve that allows air to escape but won't allow water to enter. The actual valve threads into an outer casing and can be removed with hex socket if necessary for drainage. Available online at most surfboard supply outlets, e.g. Fiberglass Hawaii, for a few bucks. Mine has lasted 6 yrs without any problems.
28 September 2023
https://www.facebook.com/groups/paipobe ... 534225080/
Bill Wurts
I have no idea how Thomas determines lehgth and width. If you know length and width, in general, volume should give you an estimate of thickness. Among other things, length affects spin radius. Aspect ratio is an important factor. The benefits of a Lindsay Lord 0.4 Aspect Ratio are decreased resistance, increased load capacity and reduced percent wetted surface. One primary benefit is speed.
John Morris
yep, familiar with the planing hulls L and W versus drag formula. But recall that the test conditions were very controlled and did not take into account the dimensions of a human body. One thing I can claim based on a few years trading off between mat, 42" boogie board, and paipos between 59 and 64 inches, is that the paipos allow for the sort of moves I know from my days standing. Running out onto the flat before bottom turning, floating across the top of a collapsing section are just two maneuvers the longer boards make possible.
Thomas Patrick Surfboards
Bill Wurts let me add some clarification...From longboards to cafeteria trays to handplanes, every prone rider choses his/her own vehicle with which to ride waves. Every prone-ridden shape has its own set of riding characteristics that are a function of shape and size. These characteristics interact with similar characteristics of the rider to produce the experience of prone riding. Choosing a specific shape will in many ways define the rider’s experience; choosing an inflated mat will yield a much different surfing experience than choosing a plywood paipo board. Notice I said “different” not “better”. Having spent years riding Tom Morey’s invention, the “Boogie”, I chose this shape as my preferred prone-riding basic shape when I embarked on producing prone boards. I was so familiar with the fit and performance of the boogie, but, then I was exposed to the designs of Larry Goddard. I quickly saw the advantages of foam core & fiberglass shell construction, and those FINS! I was hooked.
My first prone board was handshaped from a polyester-foam “fish” blank and using Goddard’s published dimensions and outline. After riding this board, I made another board incorporating changes I felt would improve performance. Thus began my journey of trial-and-error development which culminated 40-50 prone boards later in the T-Belly Generation 7. My basic design goals were (1) a length that would allow me to kick-paddle the board while remaining in max trim position and simultaneously able to keep my elbows on the deck and still reach the nose. I wanted to be able to go from a kicking position to a riding position with little or no movement on the deck. And, (2) I wanted the width to be just great enough that my body from hips to head and from side-to-side rode on the deck without over-hanging and causing drag. And (3) I also wanted enough volume to enhance paddling but still be easy to duck dive and I wanted the volume to be in the right place. These requirements lent themselves to being derived from the rider’s dimensions, i.e. height and weight. After determining through trial-and-error what I found to be ultimate length and volume for the shape for me, I determined numeric ratios so that I could design the most appropriate T-Belly shape for any rider’s given height and weight. Key to this process is the availability of the CAD program Aku. It allowed me to tweak volume flow and make minor adjustments to width and thickness while holding length constant, and maintaining all of the bottom and deck contours.