T-Belly Generation 2

What works and what doesn't. Share design ideas, references and contacts for paipo board builders.
soulglider
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Re: T-Belly Generation 2

#21

Unread post by soulglider »

cool board tomas. have some fin fun! since you live right in the heart of the displacement hull. i would take a look at what it is about those boards that make them ride so high and in my opinion one of the best toob riders i've ever ridden. the biggest thing i've found by making my own foam/glass boards and comparing them with countless ones i've bought from real board shapers is that a lot of what the experts say works and doesnt isnt necessarily true about prone surfing. Having been a kneerider for 40 years prior to full-on prone surfing i had to toss out almost everything i was looking for in a kneeboard. its a plastastic journey!
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Re: T-Belly Generation 2

#22

Unread post by nomastomas »

Poobah - the concave bottom at the tail is designed to aid the release of water through the tail. Lindsay Lord found that with planing hulls (not displacement hulls) there is a high-pressure area on the bottom, in the back third of the tail while the hull is on plane. Bob Simmons applied this information to the design of hid boards in the late-40s/early-50s, adding a concave in this area to help relieve pressure and increase speed. All of my belly boards have been designed with this feature (as well as my mini-simmons shape, the Mini-Widgtet) The concave goes from 0" depth just in front of the fins, becoming wider and deeper until it exits the tail block at 14" wide x 3/16" deep. I wanted to the concave to have a defined, hard edge to encourage water release even more, but this would increase the degree of difficulty in sanding the board, and I don't believe the performance gains would warrant the extra time and labor.

Cuttlefish - Personally, I don't consider the rails "full" although I can see how the "sloped-rail" design can appear to be thicker in photos depending upon camera angle. At the center the rail is only 1-1/4"" thick @ 1/2" in from the rail edge, 1-1/2" thick @ 1" in from edge, 2" thick at 2" in from edge. Finally, at about 3" in from edge, the rail peaks at 2-1/4". Thickness then decreases as you move towards the center of the concave deck, where thickness s 2-1/8". This sloped-rail design was my attempt to maximize volume while maintaining a thinner rail. The design produces a rail, which is very similar to a shortboard rail along the 1"-2" perimeter of the outline. Since building and riding the G2, I'm not as concerned with maintaining volume when using an EPS core. I foresee an iteration of the TB with a normal crowned deck in the future. BTW, whatever came of the Aku file I sent you back in 09/12?

SoulGlider - I enjoy the organic look of your hullish belly boards. I don't have any personal experience with Hulls, but I believe in principal that they hold into the wave face much better than hard edge, down-railed boards. From what I've read and the vids I've seen, hulls don't offer the short-radius turning I like. I think it may be more a function of the fin set-up. That being said, I do like the feel of a thinly-foiled rail. Its a direction I may take when I move to a crowned deck. (wheels turning here...)

Og-nzn - I do plan to try the board finless, and in fact noticed that I could break the bonzer fins loose when I pulled myself far enough forward, and do 360s. Personally, I'm just not excited by the finless riding experience as demonstrated by Derek Hynde, side-slipping paipo riders and, of course, countless boogie board riders. Regarding flex, the blank was really flexy before it was glassed. However, after doing the bottom with the VectorNet, the board lost most of it flex. The original plan to use VectorNet on the deck was abandoned. I completed a second G2 shortly after the prototype, but this one with a 3/16" bass stringer. Glassed with 4+4+4 S-cloth deck and 4+4 S-cloth bottom, the two boards seem to have similar stiffness. VectorNet provides equal stiffness as stringer in my mind. I would like the board to have a little more flex for "livelier" feel, although not like a Boogie board. Next board will be stringeless, no VectorNet, 4+4S-glass deck and 4+4 S-glass bottom.

RodNTube - Sorry, but I don't understand your first question. Core material, with or without stringer(s) has no impact on volume. Buoyancy, is directly related to mass/weight. Object with greater mass tend to displace more water (sink) than object with lesser mass. Perhaps you can clarify?

The G2 weighs 5lbs 4oz without fins. The second G2 with stringer and S-cloth weighs 5lbs 10oz. I don't consider this to be a significant difference.

The G2 NR=2.75", but appears more due to belly in nose. Belly cuts through chop but also combines with rocker and pulled-in nose curve to help prevent pearling on late drops and re-entries.

Yes, less floaty than the 7-7.

Got to spend time with the family, but will get back to all the interesting questions later. -tp
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Re: T-Belly Generation 2

#23

Unread post by rodndtube »

Generally the EPS cores tend to provide a lot more float than poly. I don't know the relative weights of resins used on poly and EPS. A stringer probably adds more weight than foam for the mass but again that is my guess -- and provides more stiffness. The G2 would appear to me to be a more difficult board to duck dive with all that float in the aft half of the board -- a real consideration for those of us that paddle out into sand bar breaks like Ocean Beach/SF or the East Coast south of Long Island.

The VectorNet is intriguing. So, it is something you lay over the cloth before applying the resin. Sounds like it does not weigh much. Is it expensive? What is the tradeoff between VectorNet and 4+4+4S-cloth in terms of overall durability and ding resistance?
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Re: T-Belly Generation 2

#24

Unread post by nomastomas »

On his website, Austin advertises that his standard "Paipo" is 4'2" (50") x 20-1/2" x 2-1/2" which Aku determines to be 28 Liters of volume. The G2 is substantially smaller at 3'7" (43") 22-1/2" x 2-3/8" 21 Liters. At 7 Liters less volume, I'm not sure how the G2 would be more difficult to duck dive. But, maybe I'm missing something...
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Re: T-Belly Generation 2

#25

Unread post by rodndtube »

Does the volume estimator differentiate by foam type? My reasoning is being driven by the characteristics of EPS vice Poly foam.

The duck diving was based upon the distribution of float in the board and the newest board having more float aft. That has just been my personal experience and may not be so for others.

Below are rough volume counts. Obviously, this isn't as sophisticated as the machine calculator but provides some relative volumes. The S&S RPM has a more domed deck so is thinner towards the rail.

Code: Select all

50 x 20.5 x 2.5     = 2,563  Austin baseline
43 x 22.5 x 2.375   = 2,298  G2
50 x 20.0 x 2.0     = 2,000  Austin S&S RPM Tropical
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Re: T-Belly Generation 2

#26

Unread post by krusher74 »

Austin are on the right track going 43. 22.5, but they need to get volume back int he middle of the board and go nearly 3" to get back to 28ish litres. for the rider of weight and height those dimensions would suit.
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Re: T-Belly Generation 2

#27

Unread post by Cuttlefish »

Hi Tomas,
Still have the file but didn't have a board made from it as I had the modifications done to the current board and left it at that.
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Re: T-Belly Generation 2

#28

Unread post by bgreen »

Larry's boards have the bulk of the foam in the rear - I've found duckdiving can sometimes be difficult as a result of this.

Bob
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Re: T-Belly Generation 2

#29

Unread post by nomastomas »

Shortboards have the bulk of foam behind center and duckdiving is no problem. I have found that nose width, thickness of nose and overall volume of board have more impact on duck diving than center of mass, regardless of board length. A board with a narrow nose will duck dive better than a board with a wide nose. A low-volume board will duck-dive better than a high volume board. Furthermore, a heavier rider will duck dive any given board easier than a lighter rider. Boards with the center of buoyancy forward of center are harder to duck dive because the forward buoyancy creates more resistance to act of forcing the nose under water.
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Re: T-Belly Generation 2

#30

Unread post by bgreen »

Thomas,

Larry's board has an S -deck with nothing much up front all the foam is way down the back.

Bob
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Re: T-Belly Generation 2

#31

Unread post by rodndtube »

I generally agree with what Thomas is saying about the design principles that affect of duck diving. What is different, based upon empirical experience, is that those low volume short boards are longer than our paipos (generally, 6 ft vs. 3 to 4 ft) and one can not use a foot to drive the rear of the board in the duck diving evolution. That is about all I can say on the subject.

Still interested in whether the volume estimating machines use density of foams in calculating liters of displacement. And also my questions on the VectorNet fabric.

I am not crazy about super light boards. A friend has wanted to build me an EPS/epoxy board for many years... and we have talked about ways to distribute the weight. The fabric would also open up opportunities.
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Re: T-Belly Generation 2

#32

Unread post by nomastomas »

Believe it or not, this is the short answer...

The density of an object, or weight per measure of volume, e.g. cubic ft, liters, etc, has no bearing on its volume. A liter of air weighs less than a liter of lead because it is less "dense". For our purposes, a 2"x6"x8'redwood board weighs more than a 2x6x8 balsa board because redwood is more dense that balsa. (BTW, if you were paying attention in your Physics class and not doodling epic waves, you'll remeber that weight is actually a measure of the force of gravity on an object, where the force of gravity is a constant and the density of the object is the variable, and that measure of gravity is expressed in "pounds" or "kilos".) What's interesting is that both boards "float" despite the weight difference.Hmmmmm....

So why doesn't a large steel ship sink when a small pebble does? The answer is buoyancy. Buoyancy is also the reason that both redwood and balsawood float despite their different densities. Buoyancy is a force that counters the force exerted on an object by gravity in a liquid medium. All objects have buoyancy, some more and some less. An object will sink into water until the force of its buoyancy equals the opposing force of gravity or what some would call homeostatic balance. When an object is fully submerged in a body of water, it displaces an amount of water equal to but not greater than the "volume" of that object. This is commonly referred to as "displacement". A ships "displacement" is typically the amount of water it displaces at the point of homeostatic balance. Increase the cargo/passenger load (increase the density) and the ship will displace more water as it sinks lower.

Finally, to your question. EPS foam is more buoyant than polyurethane foam. A cubic foot (block 12"x12"x12") of EPS foam will float higher (displace less water) than a cubic foot of PU foam. Notice that in this example the volume remains the same. Given two belly boards of identical size and shape, but one is EPS and the other is PU, the EPS board will float higher in the water. It is this difference in buoyancy that allows the shaper to reduce volume when going from PU to EPS while maintaining the same "float".

VectorNet fabric is extremely light, maybe 1/3 or 1/4 the weight of 4oz e-cloth. It is used to increase tensile strength without adding much weight. Has wide application in high-performance racing sails. Not meant to add "crush" strength, so won't improve ding resistance. I just finished my second G2, this one for a customer in Oregon. Shape basic shape, EPS but 2" longer and slightly wider nose, so a little more volume, and a 3/16" bass stringer. This board was done in S-cloth (4+4+4 deck, 4+4 bottom) Weight without fins is 5lb 10oz. My original G2 is 5lb 8oz. I was surprised that the stringer had such little impact on overall weight. Equally, amazed that both boards "feel" to have about the same flex. Next G2 will have no stringer and no VectorNet, s-cloth 4x4x4 deck, 4x4 bottom.I don't like the feel of heavy boards, that may go back to the 35lb'ers we use to tote in the mid-60s. Buoyancy is what's key to me, because of my size. I don't like thick boards and I believe "thinner is better" when it comes to surfcraft.
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Re: T-Belly Generation 2

#33

Unread post by Poobah »

Okay, so the tail concave is more subtle than it appears in the photos.

I got to thinking about the little stepped corners, and how that might be given a hard edge. That got me to thinking about interchangable horizontal fins at the corners...some flexy...some not. Maybe I'm remembering something that Mr. Surfoils tinkered with.

That led me to thinking about gluing blocks of paulownia or redood into the stepped corners. Then you could experiment with different edges and chines. Simply sand and varnish for each change. We typically think of tailblocks as something under the fiberglass...a done deal. So anyway...my wierd thought for the day, is that varnished wooden tailblocks could be a dynamic design feature on a fiberglass bellyboard. Something that most people could modify.
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Re: T-Belly Generation 2

#34

Unread post by rodndtube »

Thomas, thank you for the short answer! I did begin to chuckle midway through the second paragraph, laughing at myself mostly, but thoroughly enjoyed reading the entire response. Your comment about the various metrics used -- mass, float, liters... hell, even inches as in 54 in long, 22.5 inches wide, all help guide the discussion but also need context and definition! Rocker, bottom contour, rails!!!

I am with you on "heavy" boards... recall all too well lugging around those waterlogged longboards in the mid- to late-1960s. So much lighter down in the 5 to 10 lb range.

My newest two boards, a replacement S&S Checkered RPM Austin for Puerto Rico, is 7-1/2 lbs without fins, 50x20x 2.25 dome/1.75 at the wax line. The yet to be ridden bonzer S&S Diamond RPM CB paipo is 7 lbs w/o fins, 7.8 lbs with the full 5-fin load (weighed with the 6" center fin). That board is 50 x 20-3/8 x 1-7/8. The tails and pods, respectively are 18-1/4 & 12@1in and 19 & 15-1/2. Both boards are a little heavier in the cloth and resin to increase survivability during travel and reef knocks.

P.S. When riding down in FL or along much of the East Coast in typical <6 ft conditions, I use my baseline Austin -- it has more float. The S&S just can't get into the waves unless there is some punch and steepness. The S&S on the other hand is more fun for skimming along the waves where there is more juice.
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Re: T-Belly Generation 2

#35

Unread post by soulglider »

check this out if you dare. design theory made fact through one guy as close to the little yellow haired surf idol, GG. its why my boards are under 21" wide, more interesting things too.http://surfmatters.blogspot.com/2014/05 ... aw_26.html
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Re: T-Belly Generation 2

#36

Unread post by rodndtube »

Interesting article. Didn't make the connection between the article and why your boards are under 21 inches. (Mine are also under 21 inches, usually around the 19.875 to 20.5 inch mark, for a range of reasons.)
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Re: T-Belly Generation 2

#37

Unread post by jbw4600 »

The rails on my new board came out a lot rounder than I had planned. I was worried that it might not hold well on a steep wave. But I was surprised, I have no problem holding on a steep waves and it is a lot looser. I don't think I will go narrower than 21 inches. Possibly I will go narrower, when I build a longer board.

Also, EPS is great. My eps board is very lively and a lot lighter than my PU board even though it has 3 layers of 4 oz cloth on both sides with a heavy gloss coat.
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Re: T-Belly Generation 2

#38

Unread post by krusher74 »

so with EPS having more float that poly (I realize both can have different density's).

If you had a tipical 30L poly board and a tactical EPS 30L board how much more float roughly would the EPS board have 10%?
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Re: T-Belly Generation 2

#39

Unread post by Poobah »

I'm not sure what a tactical board is, but I bet the difference in bouyancy is greater than ten percent. I think I'd rather have a litre comparison, like a 30 liter PU foam is equivelent to XX litres of EPS foam (maintaining a similar bottom surface area.) A sort of approxomate multiplier. Then you could tweak the design to hit your target in litres. I think that's sort of the question that Rod was trying to ask.

ON the US Blanks website they compare their (several) PU densities relative to eachother in percentages of lightness, but compare their EPS blanks to eachother by texture and pounds per cubic foot. There doesn't seem to be a calculator for comparing the apples to oranges. Part of the problem is the density of the PU foam varies with depth. I suppose the density for a particular PU blank could also vary during production. Still...it would be nice to have an approximate multiplier.

http://www.usblanks.com/catalog/about-o ... omparison/
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Re: T-Belly Generation 2

#40

Unread post by jbw4600 »

My board is made from 2lb EPS. I think that EPS is 15-20% more bouyant. I guess the increased bouancy with less volume and lightness makes it feel lively.
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