TBG7

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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TBG7

#1

Unread post by nomastomas »

I've put a lot of thought into the G5 design over the past 7 months, removing features and adding features. With the return of my glasser, the door to eps shapes was re-opened, and I decided that it was time to settle on a new design, the "G7". Basically, I removed the bottom rail bevel/concave, because I don't believe it added that much to the overall performance, and it slowed both shaping and glassing in production. I maintained a shallower version of the deck concave. This required a lot of finagle-ing to get the concave in while keeping the rail profile thin and foiled, while all along trying to hit a specific volume target. I also made some adjustment in the location of the wide-point and a corresponding adjustment to the location of the fins. I also made tweaks to the foil, so that I now have almost 60% of the mass behind center. Most significantly, I'm going to focus on using a twin-fin configuration, as I've learned that twins favor turning more than the quad. For optimum twin-fin setting, you can't just use the front boxes on a quad. I mean, you can and I have, but it places the fin array a little to far forward. I sent an order for two G7s, a 48" and a 50", to Marko a few days ago, and will post pictures of the blanks maybe next week when I receive them.
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nomastomas
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Re: TBG7

#2

Unread post by nomastomas »

I just picked up this board from the glasser. It's the precursor of the new G7. It was the first PU/PE T-Belly that I've done in about 10 years. I forgot how much finishing the stringer can slow you down. I used the ultra-light "Red" density Millennium 5-0WS blank for this shape. Millenium foam is very white and shapes nicely. On this shape, I greatly reduced the depth of the deck concave, and eliminated the bottom rail bevel. I also shaped in a flat area on the bottom to make setting the fin boxes easier. Customer will take possession of this tomorrow.
TPSG57_PU_Deck.JPG
TPSG57_PU_Bot.JPG
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Re: TBG7

#3

Unread post by flojo »

Hey Thomas, nice looking board.

What are the dimensions?
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nomastomas
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Re: TBG7

#4

Unread post by nomastomas »

Hmmm....I posted a reply to this a couple of days ago...where'd it go?
Anyhow...thanks for the props...Dims are 48"x22-1/2"x2" 23L Rider is 6-0 170lb 60-ish. Twin fins are set 9-3/4" up, 1-1/4" from rail and 1/4" toe, 5-deg cant. Fins are set just behind "hip" which is turning pivot point.
Fin set relative to outline more important than a specific measurement. Wide-point forward boards, e.g. boogie boards, have relatively straight outline (parallel rails) in the rear-half of the board, so for those boards I place the fins on the rear corners, being sure tip doesn't overhang tail block. Fins on boogie boards help with hold but make the board stiffer, less easy to turn than without fins. For fins to be truly effective, all aspects of the design, including outline curves, bottom contours, foil, etc must be taken into consideration to determine if and where fins should be placed. Its naïve to think that you can just stick fins anywhere on any board and improve performance. Oftentimes, performance is worse due to conflicting design features. Something I had to learn the hard way...
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bgreen
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Re: TBG7

#5

Unread post by bgreen »

Out of curiosity, what is the volume target.

Are the fins further forward compared to your other boards. Modern kneeboards seem to have moved fins way forward compared to older boards.
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Re: TBG7

#6

Unread post by nomastomas »

On custom boards, the volume target varies with the weight of the rider. I use a formula I derived from pure trial-and-error going back to the G3. The formula produces the optimum volume for a particular rider when rider weight is known. Of course there is a +/- factor, such that a given volume will work satisfactorily for a range of body weights, with performance improving the closer the rider's weight approaches the optimum for a given volume. Differences can be subtle. Most riders with no T-Belly experience who weigh within 10-20lbs of a boards optimum volume would not notice a difference.

In general, I have not changed the location of the outline hip and the fin array for several years. I do place the twin-fin array, slightly rearward of the front fin position on the quad set up. In other words, I don't just use the quad front fin position for a twin set up.

To turn a stand-up surfboard, the rider steps on the tail. This raises the nose out of the water, and reduces the amount of wetted surface offering resistance to the change in direction. Then, the rider applies differential pressure to the rail on the inside of the turn. This action cause drag from both the rail, and the now fully engaged rail fin. Much like dragging a paddle or an oar, the board's direction is changed. When kneeboarders figured out that, for best turning, the fin array needed to be where the rider is best able to apply downward pressure, namely where the ankle/lower-shin is located, the fin array was moved forward. When I ride prone, I use my hip to apply pressure, so that's where I locate my fins.
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Re: TBG7

#7

Unread post by krusher74 »

Any side views to show rocker? are you using tail rocker or is the tail rocker just in the tail concaves?
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nomastomas
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Re: TBG7

#8

Unread post by nomastomas »

I still don't have the cut shapes back from Marko, but here's a drawing of the 48"er taken from Aku
G7_Profile_48in.jpg
Dark line is profile at centerline, while red line is profile at rail. As can be seen, centerline rocker is flatter than rail rocker. Tail concaves definitely flatten bottom rocker along centerline and 2"-3'" out from center. But then returns to the curve matching rocker curve out at the rail. Keep in mind that prone boards, like other surfcraft, are rolled over onto their rail when turning. The progressively increasing rocker curve out at the rail reduces the turning radius but also creates some drag. This drag is released as the board is rolled back onto the flat bottom and speed increases again. Drawing also shows distribution of volume by percentage.
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krusher74
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Re: TBG7

#9

Unread post by krusher74 »

it's interesting to compare to mine. I cant see the number but yours appear to have more nose rocker than mine if you cut your nose down to my 2 3/4" nose rocker how much length of the tip of the board would you lose?
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nomastomas
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Re: TBG7

#10

Unread post by nomastomas »

About 1/2"...although I will bring the bottom up to the deck when I finish shape it, which will add another 1/4" or so of rocker. Final rocker measurement not as important as the actual bottom curve. I like rocker that rises slowly for the first 6" or so, and then begins to accelerate (a la parabolic) until it hits the terminal number. Its called a "relaxed" entry. On a prone board, I like to have 0"-1/16" of rocker in the middle 12" of the bottom along the stringer. That's the gas pedal and coincides with where my chest, shoulders and upper stomach are on the deck.
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nomastomas
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Re: TBG7

#11

Unread post by nomastomas »

Actually, I just checked the numbers and the rocker is 1/16" @ 12" up from tail, goes to 0" at 16" up and stays there until 29" up where it goes to 1/16" until 32" up. So, for you Lindsay Lord fans, the "water plane" is 22.5"W x 40"L (Overall length Minus Start of bow rise to bow/2) for 0.56 aspect ratio.
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Re: TBG7

#12

Unread post by nomastomas »

Cut blanks have finally been delivered, but unfortunately, I'm still in Portland. Should be able to finish-shape them next week and and get a couple of photos posted.
FWIW, The surfing industry in the US is seriously backlogged. It took me 7 weeks to get blanks that normally take only 2 weeks to get delivered. I tried to order FCS II boxes for two G-7s and two kneeboards, and my local source was completely out, while a secondary source up in Washington state was only able to partially fill my order. I've heard that new orders for surfboards have an 8-10 week wait.
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bgreen
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Re: TBG7

#13

Unread post by bgreen »

Hello Nomas,

From the above dimensions, your boards are about 1" narrower than mine, 1/8" thicker and 6" shorter but have a bit more volume.

I'm considering a higher volume board, for bigger, fuller/flatter walled waves that are harder to get into.

When you want to increase volume for a BB, would you increase one of these dimensions or a bit of all three?

Bob
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nomastomas
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Re: TBG7

#14

Unread post by nomastomas »

Short answer...depends. I have a specific formula for length based upon the rider's height, so I always start with a specific length. Then I consider volume, which I normally base upon the rider's weight but might adjust up or down depending upon wave condition, rider experience, etc. The width of my T-Belly shapes vary between 22.25" and 23.5" depending upon volume. I try to keep the G7 as thin and narrow as possible, so I adjust thickness last. So, basically, my process is to set the length and then starting with an arbitrary width of 22.5" I fiddle with width and thickness until I hit the target volume.
In big, flat waves I want to maximize width to maximize planing area. For me, that's no more than 23". Then, I increase thickness to achieve target volume. Other considerations are deck shape (flat or crown) You can pack in more volume for a given length and width with a flat deck. Alternatively, you can focus extra volume along the stringer and keep the rails thinner with a crowned deck. Alternatively or additionally, you can increase thickness at both ends.
I shape almost entirely with Aku nowadays, which allows me to make frequent adjustments and re-adjustments, I like to shape LBs by hand because larger shapes aren't as critical when it comes to volume and planing area because they're huge! And, they're more fun to do by hand...
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Re: TBG7

#15

Unread post by bgreen »

Thanks Nomas.

Basically, whether flat faced or hollow, I wanted something that will get me into bigger waves earlier. The issue with fuller waves is there no barrel to pull into.

At this stage I may refine my current design or get something different - a discussion yet to be had.
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nomastomas
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Re: TBG7

#16

Unread post by nomastomas »

"Getting in earlier..." is always a tough one on a prone board. You could go "Mega", as some have, Skiff comes to mind. Problem for me with a Mega- design is paddling out on bigger days without the ability to duck-dive easily. I've just come to accept the air-drop and wear UDTs.
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Re: TBG7

#17

Unread post by bgreen »

I'm not planning on going too high volume but probably a bit more than the current 21-22 litres.

Where there is a nice peak or lump to launch from, this is less of an issue.

Burying the tail and launching can help sometimes, as well as bigger fins, but they can be a killer on the legs sometimes or a hazard if there is lots of rock hopping.
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nomastomas
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Re: TBG7

#18

Unread post by nomastomas »

Agreed...always compromises to be made. And, individual differences, e.g. experience, fitness, strength, etc, to take into consideration...
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nomastomas
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Re: TBG7

#19

Unread post by nomastomas »

The G7s have been finish-shaped and left with my glasser. I was really pleased with how they turned out. I'm especially happy with the rails. Looking at the rails from various 3-D views in Aku is very helpful, but no substitute for running your hand down the rail. Should be ready to surf in 4 weeks, which will allow my recent cataract surgery to heal. I'm very anxious to get the 48" twin G7 into the water.
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Re: TBG7

#20

Unread post by bgreen »

I'll be interested to see what the latest design looks like.
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