T-Belly Gen 4x

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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T-Belly Gen 4x

Unread post by nomastomas » Thu Mar 12, 2015 4:36 am

The 4th generation T-Belly is now ready for surfing trials. Keep in mind that similar to the G2 and G3, the G4 is not a one-size-fits-all belly board. Rather, it is designed to “fit” the rider based upon rider height and weight. This G4 was built for me (5-10/190) The TBG4 is similar to its predecessor, the TBG3, with these exceptions: (1) the overall length has been increased by 3”, with the wide-point and the fin array both moved up from the tail that same distance. (2) The single, open tail concave has been replaced by dual open concaves, one on each side of the centerline, (3) there is now a small amount of “V” exiting the tail, (4) there is now a shallow single concave in the mid-third, between the entry and the exit contours, and (5) the shallow deck concave has returned. In an effort to maintain the same board-volume-to-rider-bodyweight ratio, I reduced both the thickness and the width. Thickness is now about 2" and width is 22-1/4". Volume is 23L.

Feedback from riders of the TBG3 as well as my own experience in riding the G3, suggested that a slightly longer outline (relative to rider length) might help to lessen the drag introduced by the rider’s thighs and knees. The longer length places the tailblock closer to mid-thigh when riding in the maximum planing efficient position. The extra length necessitated the movement of the wide-point/hip and adjacent fins to a point further forward. I place the wide-point and fins in the location close to the rider’s hip, where it serves as a pivot point for turning.

The exit single-concave concept was abandoned in favor of a dual-concave design. There were a couple of reasons for this. It is apparent to me, that when riding a wave prone (as opposed to paddling prone on a flat surface) the rear corner of the board closest to the wave face is the area of the bottom most in contact with the water. An open concave in this area serves to manage water flow, and increases “bite” at the rail by altering the rail profile. The single-concave in the middle of the bottom also provides lift in much the same manner, but is most effective when the rider’s weight is forward. Lastly, the performance gained by the hard-edged single concave did not justify the labor required to shape it.

The V added to the tail simply facilitates turning by making rail-to-rail transitions quicker. V also increases the rocker curve out at the rail. The end result of adding V is that the rocker along the stringer or centerline remains flat (for speed), while rocker at the rail increases (for turning on rail).

I eliminated the shallow deck concave on the TBG3, replacing it with a flat deck but found that when doing abrupt turns at speed I would sometimes slide off the deck in the opposite direction. During a turn in more powerful waves, the beach-side fins engage with authority, yielding an immediate change of direction. At such times, the centrifugal force is strong enough to pull my body off center. I’m hoping that the concave will help to keep me centered.

I plan to begin trials with my now standard quad fin set-up: Front Fins - True Ames Side Bites 3.7”, Rear Fins – TA SB 3.25”. Anybody in the Ventura-SB-LA area is welcome to sign up for a demo ride. I would appreciate the feedback.
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Re: T-Belly Gen 4x

Unread post by soulglider » Thu Mar 12, 2015 11:01 am

cleanest version yet. looks like a lotta fin? wutta the rails look like?
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Re: T-Belly Gen 4x

Unread post by nomastomas » Thu Mar 12, 2015 1:51 pm

Thanks, SG, I would agree. I use the same rail shape as G2-3, which is primarily a sloped, tucked-edge rail, progressing quickly from an up-rail shape in the nose to a down-rail shape in the tail. As can be seen, I've tried to keep the outer 2" of the rail as thin as possible. I believe that a pinched rail offers superior wave penetration, providing excellent hold, which is then converted into forward speed. The tucked edge offers a release point for water flow, preventing drag from water wrap. (Water is actually very sticky stuff, and once it attaches to a surface, it doesn't want to let go. Edges encourage water to let go.) The foil and toe-in of the fins creates lift in the direction of the wave face (not in the direction of the deck), pulling the rail into the wave. This helps to keep the rail engaged.

I've done extensive testing with different fin configs and I've found this set-up to work best for a light-heavyweight rider (yours truly) in chest-high or better conditions. There are trade-offs in all surfcraft design, and of course fins are no exceptions. Fins create drag, plain and simple. But, if their use allows the rider to capture more speed, and/or better control, then that drag is an acceptable trade-off. I know from experience that the fin area of these fins fails to earn its keep when wave size drops below 3.5ft, and I down-size fin area accordingly, either by using smaller fins front and rear (in quad set-up) or removing the rear fins altogether and converting to a twin-fin set-up. That's the advantage of having removable fin boxes.
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Front view
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Re: T-Belly Gen 4x

Unread post by krusher74 » Thu Mar 12, 2015 3:07 pm

The evolution continues! :D

With the deck concave do you find you stay in the same place and just lean.

When I ride, my hip and elbow is on the edge of the rail, i'm only in the center of the board if i am going straight. (or middle of a cut back) I find I move around a lot. :?

I think I ride 23L also (found 25L to much) I am 5.10 170lbs

So this is EPS/epoxy again?

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Re: T-Belly Gen 4x

Unread post by nomastomas » Thu Mar 12, 2015 3:20 pm

Deck concave actually helps a lot, but doesn't eliminate all movement. I'm trying to eliminate the "half-on-half-off" predicament.

Everyone should get to know their preferred volume. There's really no right or wrong here, just what works for you. Thanks to CNC, I can dial in volume for each rider, while maintaining the integrity of the shape.

EPS/Epoxy..."the only way to fly!" (you youngster may not recognize the reference to the old Western Airlines motto) Double 4oz E-cloth deck/single 4oz E-cloth bottom.
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Re: T-Belly Gen 4x

Unread post by krusher74 » Thu Mar 12, 2015 5:37 pm

nomastomas wrote:Deck concave actually helps a lot, but doesn't eliminate all movement. I'm trying to eliminate the "half-on-half-off" predicament.

Everyone should get to know their preferred volume. There's really no right or wrong here, just what works for you. Thanks to CNC, I can dial in volume for each rider, while maintaining the integrity of the shape.

EPS/Epoxy..."the only way to fly!" (you youngster may not recognize the reference to the old Western Airlines motto) Double 4oz E-cloth deck/single 4oz E-cloth bottom.

Heard and used the same quote, but had no idea of its origin :oops:

I was recently looking at marko EPS recycled foan and supersap eco resin, that would be towards a eco board.

I did not get onn with my first EPS board, but i think it not enough dencity on the EPS and to much glass and epoxy giving that pop out feel. Hopefully I will get to try one of yours someday.. :D

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Re: T-Belly Gen 4x

Unread post by ClanB » Sat Mar 14, 2015 9:03 pm

T-Belly has come a long way...and it started out pretty good in the 1st place. The rails look like they would stick to a steep wall well.

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Re: T-Belly Gen 4x

Unread post by Daryl D » Sun Mar 15, 2015 8:02 pm

Nice board Thomas. I've really enjoyed the G2 I have, but I think the changes you've made are all good. I think you're right on about the length. I also like the channels. Let me know when you're ready to sell it. I know I out weigh you 30 lbs, but after riding wood paipos, buoyancy is relative.

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Re: T-Belly Gen 4x

Unread post by nomastomas » Mon Mar 16, 2015 4:37 pm

ClanB - yes, that's the idea. I'm in Tucson until next week, so I haven't been able to take it for test ride yet. Looks like we have some waves coming next weekend, so...

Daryl - Yes, buoyancy is relative. Everyone has a different comfort zone. I don't foresee any major design changes over the next year, so this one is a keeper. I'm a little concerned about the the extra 3" of length, and how it will impact my paddling position. I've got another solution to this problem in mind.
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Re: T-Belly Gen 4x

Unread post by bgreen » Tue Mar 17, 2015 6:03 am

Thomas,

If you'd like the interview updated let me know. Just send photos and text and we can go from there.

Bob

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Re: T-Belly Gen 4x

Unread post by Sparx45 » Mon Mar 23, 2015 6:33 am

I love this thread...really interesting to see the evolution and thought behind it all...I just finished shaping a "rabbits foot" style finless and had similar thoughts about rails and concaves which gave me a real headache thinking about "correctness".... ended up with pinched chines in areas and some pretty radical concaves and transition areas on the hull.

Made a few mistakes i'm sure but the thing I learned most about all this is that building these smaller craft (as with the bigger stuff) is a serious learning process which is not mastered easily or without some very hard work indeed....It's a journey for sure.....love it though !!

Spx

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Re: T-Belly Gen 4x

Unread post by nomastomas » Wed Mar 25, 2015 10:37 pm

I finally had a chance to take out the TBG4x, and to put it simply, I wouldn’t change a thing. Conditions were a peaky combo swell, running 3’-4’on a rising tide at my local point. The type of wave that stays soft, until the last second when it suddenly jacks up. Not the best conditions for my new 9-6 noserider, on which I started the session, but pure fun for the T-Belly. So, back to the truck to switch out boards. On the way I ran into two guys from the shop who had been shortboarding. Both complained about the “crappy conditions” and low wave-counts. I just smiled, and headed back to the water with fins and the G4.

The length at 48” is just right for me at 5’10”. I can comfortably place my hands and forearms on the deck while kick paddling. If I need/want to execute a more powerful kick, I slide off the tail about 3”. This frees my legs for a full length kick stroke. Pressing down on the nose a little helps to keep the board in trim position. The extra length really shows its value once in the wave. With the tailblock now about mid-thigh, it’s much easier to keep thighs and knees out of the water, minimizing drag. A few times, I forgot I was on a longer board, and pulled myself too far forward with predictable results; an impromptu duck dive :o

After I sold my personal G3, I was without a belly board for over almost 6weeks (yes, shapers have to wait for new boards, too). This forced me to go back to my old Morey Mach 7-7. This was a good opportunity to re-acquaint myself with finless, wide-point forward prone craft. I was reminded how much the forward rail is used for control on those boards. With the G4 and similar finned, wide-point back shapes, the focus is on using the rail fins and the rear rail for control. Also, I find that there is little need to grab the opposite rail for leverage to keep the rail engaged with the wave face. When I lengthened the G4, I also moved the widepoint and the fin cluster forward 3”, keeping the pivot point close to the rider’s hips. I found the G4 to have even better control and turning response than the G3. But most apparent performance-wise, was the effectiveness of the dual open concave bottom. The board seemed to leap out of turns.

Since I kept the same volume, and volume distribution, I found duck-diving to be un-changed. A narrow, thin nose is key , in my book. Also, I didn’t notice a significant increase in speed, but then the conditions did not allow for long, speed runs. So, overall I would say that most of the performance improvements noted were in turning response, particularly in ease of turning. The G4 has a nice, flowing feel,loose and smooth. Although, it can still turn on a dime. To illustrate, I paddled into one wave, and after my first turn of the top, I spotted a longborder about 15’ away paddling for the wave I was already on. As I rapidly approached, I could see that he was focused on catching the wave, and hadn’t seen me (giving benefit of the doubt here). As he was just pushing himself up to a standing position, he glanced to his left and suddenly we came eye-to-eye. Seeing me rapidly approaching, he clumsily sat up, pulling out of the wave as I cranked a cutback throwing spray in his direction. Smiling to myself, I continued on my merry way. Throwing spray is fun :twisted:
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Re: T-Belly Gen 4x

Unread post by nomastomas » Sun Aug 23, 2015 1:48 pm

Here's the latest TBG4. This one is for a rider 6-2/220. Although I recommended a 50" length, this rider was reluctant to go over 49" (having never ridden a TBG4). Volume is 23L. This board is also a twin, so it is a good model for how I locate twin fin set-ups.
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The nose of the TBG4 gets narrower as the length increases in order to maintain a good curve in the outline. While there are no major changes in the design, subtle refinements can be seen in the tail, where I've thinned the foill. The rail shape progresses from an up-rail in the nose to a down-rail in the tail. A tucked edge appears about mid-way down, with just a slight still seen in the rail at the tailblock. The rear view shows clearly how the concave changes the rail shape.
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Re: T-Belly Gen 4x

Unread post by Uncle Grumpy » Mon Aug 24, 2015 8:03 pm

Very nice.
I'd like to try one like that some time.
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Re: T-Belly Gen 4x

Unread post by nomastomas » Wed May 18, 2016 2:11 pm

Its been almost a year since I built the first TBG4, and its still my goto prone-board in waves up to 6'. I've built about a dozen of these in that time, and some have gone to early adopters of the G2 and G3 like SJB. Here he is recently enjoying the warm water of Mexico on his G4.
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Re: T-Belly Gen 4x

Unread post by krusher74 » Sat May 21, 2016 11:05 am

nomastomas wrote:Its been almost a year since I built the first TBG4, and its still my goto prone-board in waves up to 6'. I've built about a dozen of these in that time, and some have gone to early adopters of the G2 and G3 like SJB. Here he is recently enjoying the warm water of Mexico on his G4.
Unless i'm seeing it wrong he looks to have inside hand on the rail and outside on the nose :? , looks like it working though :D

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Re: T-Belly Gen 4x

Unread post by nomastomas » Sat May 21, 2016 11:09 am

To many California right-point waves...
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Re: T-Belly Gen 4x

Unread post by SJB » Sat May 21, 2016 5:11 pm

Probably....might also have something to do with my being left handed and stand up goofy foot. :idea: Color me upside down and out of the box.....but it does seem to work fine. 8-)

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Re: T-Belly Gen 4x

Unread post by nomastomas » Sat May 21, 2016 7:19 pm

Beautiful wave, though...I'm jealous1
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Re: T-Belly Gen 4x

Unread post by nomastomas » Sat May 28, 2016 1:02 am

It had to happen sooner or later...the first carbon fiber TBG4 is headed to Oregon. This one was also fitted with a vent plug (like the Manta). The black Futures boxes were a no brainer...
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