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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TBG5

#1

Unread post by nomastomas »

After months of designing and re-designing, I've come up with the latest iteration of the T-Belly. This one is heavily influenced by a kneeboard I built for BellyRider, which in turn was influenced by a progressive SUP design I did for the guys at Melody Surfboards in Greece, and 7-8 Mid-size shape that I’m now riding. All the above would fall into the "modern planing hull" school of surfcraft design. Nothing that hasn't been done before, just my interpretation, in this case applied to a prone board. The dimensions of this G5 are 49" x 22-1/2” x 2”-2-3/8” 23.5L.
The most obvious (and only) change in the outline is the diamond nose. I normally ride a 48" G4, but for a variety of reasons, I found myself on a 49" G4 for the past several months. I enjoyed the added length of the 49"er but didn't like the stretched reach to the nose when in the paddling position. The diamond shape reduces the reach by a good 1-1/2” at the corners, so we’ll see.
TBG5_web.JPG
TBG5_web.JPG (19.74 KiB) Viewed 375729 times
The bottom has the more obvious changes. Adding a bevel to the rail has a similar effect of adding “V”, namely it changes the rocker curve out at the rail, and assists in getting a relatively wide board over on rail for turning. As I looked at the beveled rail in cross-section, it occurred to me that I might be able to make the rail shape more effective by making that bottom rail-band concave. Looking at the concave bottom rail-band in cross section I could see (in my mind’s eye) not only a better hold into the wave face, but also a means of channeling water flow towards the tail. This concave would also reduce the volume of the rail, producing a thinner rail for better wave-face penetration. (A more effective rail profile may lead to a reduction in the fin area needed to obtain the same hold properties as the G4).
TBG5_Bot01_Web.JPG
TBG5_Bot01_Web.JPG (35.03 KiB) Viewed 375729 times
TBG5_Bot03_web.JPG
TBG5_Bot03_web.JPG (61.3 KiB) Viewed 375729 times

The bottom is otherwise standard G4; convex nose, slight concave in mid-section and dual exhaust tail concaves. I’m starting to thin out the tail of my prone boards a little more. I believe this helps the tail sink on take-off, keeping the board (and rider) more parallel. The board will have quad fin-boxes (of, course) and I designed a small, relatively flat section in the bottom where the fins will be located as a courtesy to my glasser. The board will be finished in 5.7oz carbon fiber, one layer deck and bottom. At this point in the process shaper becomes surfer, and I begin to pester my glasser with “Is my board ready yet?”
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TBG5_Slices.jpg
TBG5_Rail01_web.JPG
TBG5_Rail01_web.JPG (52.11 KiB) Viewed 375729 times
Last edited by nomastomas on Wed Aug 09, 2017 1:30 am, edited 1 time in total.
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Re: TBG5

#2

Unread post by Pes78 »

That looks like a good time. What blank did you use?
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Re: TBG5

#3

Unread post by nomastomas »

Its 2lb eps from Marko, probably slab cut. Because its stringerless, its just easier to send the file, approximate dimensions and my density requirement, and they do the rest. That way I'm not paying for foam I don't need.
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Re: TBG5

#4

Unread post by bgreen »

Nomas,

When it's glassed I'd be interested to see a shot from the tail looking down.

How wide is the planning area before the concave - 18"?
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nomastomas
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Re: TBG5

#5

Unread post by nomastomas »

I presume you mean the single concave that runs down the center. It's 14" wide at the center. The nose belly starts to go concave at 3'4.74" up from the tail. The single starts to go double at the mid-point. All the transitions are very subtle and can be seen best with the CAD software. I forgot to mention that some of the inspiration for the bottom came from George Greenough's "Edge Boards".
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Re: TBG5

#6

Unread post by bgreen »

Thanks. It was the concave I was referring to.

The raised bottom did remind me of an edge board. Flatter where the single concave is and without the double concave/vee is one of many ideas I had been toying with.
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Re: TBG5

#7

Unread post by nomastomas »

So...after what seemed like an inordinate amount of waiting (speaking here as a surfer not a shaper ;) ), I picked up the G5 at my glasser's. All I can say is "well worth the wait". I opted for the red accent because the bottom contours, when sheathed in carbon fiber, reminded me of an F1 race car, and the red added to that aesthetic. But red also because I'm growing weary of getting dropped on because people just don't see me coming. The photos below don't do it justice, as the black seems to absorb the shadows necessary to reveal the contours. But, I'm stoked at how the board turned out and can't wait to get it in the water.
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IMG_3058.JPG
IMG_3056.JPG
IMG_3060.JPG
IMG_3064.JPG
IMG_3065.JPG
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Re: TBG5

#8

Unread post by SJB »

Very cool. If we ever get a swell again let me know where and when. Would love to test drive.
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Re: TBG5

#9

Unread post by CHRISPI »

Very nice love the rails
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Re: TBG5

#10

Unread post by bgreen »

Nomas,

Thanks. The black does make it hard to see the details. It will be interesting to hear how it rides.

Aesthetically, the style of nose doesn't appeal, but if it works, that's the real test. It looks like there is fair amount of rocker in this board.

Bob
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Re: TBG5

#11

Unread post by nomastomas »

Yeah, I boosted the nose to 3" and the tail to 7/8" at the stringer, but the V in the tail adding another 1/8" to the rail rocker. I also added more curve throughout the bottom, instead of the original, staged rocker. Intent here is to increase turning performance with a more continuous curve, since the board is already plenty fast. I think it will pay off more in larger surf. Although, I'd settle for some chest-high mush right about now.
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nomastomas
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Re: TBG5

#12

Unread post by nomastomas »

So...while I'm waiting for some decent waves to test this thing on, I thought I'd mention something I recently learned about carbon fiber. CF is about 5 times stiffer than S-cloth and 30% lighter. S-cloth actually has a slightly (6%) higher tensile strength-to-weight ratio and a slightly higher compression-strength-to-weight ratio. So, if you're looking for superior stiffness and lightest weight, carbon fiber is the way to go. But, if your looking for general toughness, S-cloth is the choice. S-cloth also cost about 60% less per yd. But, the "curb appeal" of carbon fiber is undeniable.
Here are some definitions:
Tensile Strength - Ability to resist a force before breaking
Elongation - Ability to stretch before breaking
Stiffness - Ability to resist deflection or deformation before breaking.
Density - weight/volume
"Toughness" - a combination of the first two stated above.

Here's a great video on a comparison between fiberglass, carbon fiber and kevlar https://www.youtube.com/watch?v=KHXVf0SaJpA
Last edited by nomastomas on Sat Sep 23, 2017 9:08 am, edited 1 time in total.
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Re: TBG5

#13

Unread post by belly rider »

Wow another beauty
FERRARI red that is. :lol: :lol: :lol:
See you soon
its all about the ride
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nomastomas
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Re: TBG5

#14

Unread post by nomastomas »

EXACTLY!
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Re: TBG5

#15

Unread post by krusher74 »

Very exciting design, Would love to try that finless. (maybe try again this winter :? )
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Re: TBG5

#16

Unread post by nomastomas »

After sitting in its new bag for over a month, I finally got a chance to ride my ne G5. Here are my first impressions:

Conditions: Glassy, 4ft-5ft beach break, mid-tide rising. SW groundswell, with a touch of NW windswell. Just a little crowded, with a dozen shortboarders of various skill levels competing for waves across two A-frame peaks about 50yds apart.
Performance: Almost identical to the G4 in paddling and duck-diving. Take-offs are the late drop-in variety, again similar to the G4. I thinned the tail on the G5 by moving the thick point forward, which allows the tail to sink more at the tail, providing a more forgiving take-off. (The G5 remains more parallel to the surface regardless of how steep the face on take-off.) Again, like the G4, the G5 immediately engages the wave face and holds. But unlike the G4 where the rider can feel this engagement primarily in the rear ¼ of the tail where the fins are, on the G5, the rider can feel the entire “wetted” rail engaged in the wave face. The G5 rail feels much more engaged to the point that I believe I can reduce fin area, perhaps significantly. (less fin area=less drag=more speed) While as tested (with my favorite quad fin set FCS H2) there was no significant increase in speed noted, but no loss of speed either, despite the fact that the G5 has more rocker on both ends. I did notice that turns were easier on the G5, which I attribute to the continuous rocker of the G5 compared to the staged-rocker of the G4. The ultimate test of the rail performance would be to ride the shape finless.

Summary: The G5 equals or exceed the performance of the G4 in every category. I need to do continued research to optimize ideal fin area for a given wave size.
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Re: TBG5

#17

Unread post by bgreen »

Hello Nomas,

I was interested in your comment: "I thinned the tail on the G5 by moving the thick point forward".

Do you have a comparative photo of the respective G4 and G5 foils? How far forward is the new version?

Bob
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nomastomas
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Re: TBG5

#18

Unread post by nomastomas »

Comparing foils is difficult because the thickness of the rail masks the centerline thickness. And rail thickness is oftentimes what I use to add or subtract overall volume, so there is no consistent rail thickness shape to shape. I had a 49" G4, but it was 1/2" wider at 22" and 1/4" less thick at 1.75". On this G4, max thickness starts at 15.82" up from the tail and ends at 27.5", while max thickness on the G5 starts at 17.67" up from the tail and ends at 25.81" up. So, about a 3" shift forward.
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Re: TBG5

#19

Unread post by bgreen »

Nomas,

Thanks. It's interesting to see the shift forward from the original Goddard models which had the thickness way back - now more like a modern standard board foil.
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Re: TBG5

#20

Unread post by nomastomas »

tb1.jpg
tb1.jpg (187.61 KiB) Viewed 374422 times
This was my first T-Belly based entirely upon Goddard's work. It was 51" long and almost 3" thick. I found it hard to catch waves and prone to pearling on steep take-offs. I also found that it was not very good at holding into the wave face. It essentially felt too big for me in every dimension. A heavier rider might have had a much different opinion.

Over the next 7 years I made progressive tweaks in the shape, primarily thinning and shortening, but also playing with bottom contours. In each case, these changes were in service of my own biases, creating what I, personally, like to ride. Much of my foil changes have come from observing the shortboarders, with whom I frequently share a peak. Until the moment they stand up, they are essentially prone surfing. So, yes, my foil is now very similar to the common shortboard, albeit in a much shorter length.
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