TBXL

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TBXL

Unread postby nomastomas » Sat Feb 24, 2018 11:53 pm

After discussions on the G5 thread, I decided to start another post specifically documenting my attempts to design a better “big wave” belly board. “Big wave” is a relative term, and for me it means waves with face heights in excess of 6 feet, more typically in the 8’-10’ range, which I occasionally see at my local break. On rare occasions, my local surf heights will push into the triple-overhead range, but I’m always content to watch from the beach on these days. I’m hoping that this thread will generate more discussion, and to that end I would invite everyone’s opinion.

The key design concerns I have gleaned from the G5 thread is the need to mange the impact of less than ideal surface conditions, and the need to control the speed and consequent lift that comes into play when surfing larger, more powerful waves. To this end my first attempt has a spear-like outline, with peaked nose, wide-point forward of center about 2”, and a winged square tail. In laying out the dimensions, I wanted only enough deck area to keep my body from contacting the water. Essential, I wanted the deck to mirror the outline of my body, but with roughly an inch margin all the way around. The intended deep V bottom entry made my preferred diamond nose shape impossible. A peaked nose was just more suitable. My new goal dimensions reduced the the size of the outline as compared to the G5, but it is still a wide tail. Tail width impacts turning radius. A wide tail is harder to turn than a narrow tail. One way to compensate for a wide tail is to increase tail rocker (conversely, flat rockered boards are made more responsive by narrowing the tail, e.g. big wave guns). Another way is by adding “bumps” or “wings” in the outline to rapidly reduce tail width. With this shape I did both, increasing tail rocker from zero to ¾” and by adding the wing 10” up from the tail (which is also where the trailing edge of the front quad fins will be located) The combination of the toed-in fin and the bump in the outline serves as a pivot point for turns when on rail. The tail was left square to maintain efficient water flow along the bottom for as long as possible (which is when it encounters my trailing legs) The width of the tail at the wing is almost 17” while the tailblock is 13.5”. Wide point is 20” and the nose at 6” down is 13.5”. I increased the length from 49” to 52” primarily to compensate for the loss of volume when I narrowed the outline. The pulled-in nose will allow me to grab the rail 2-3” below the nose but still have my elbows on the deck.

The shape incorporates an extreme “V” nose-to-flat bottom design, with wide-point forward and thickness flow (or foil) skewed towards the front. I want the front of the board to cut through chop and to resist lifting. At the same time, I don’t want the nose to be prone to pearling, so I have set the nose rocker to 3.25”. The bottom transition from deep V to essentially flat is in about the middle of the board, with a corresponding change in the rail shape from a tightly pinched (almost up-rail) shape in the nose to a softer, 70/30 rail mid-section and then an almost hard down-rail in the last couple of inches. Gone are the concaves to minimize lift and speed; the flat bottom will be fast enough.

Questions? Comments?
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TBX1c.jpg
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Re: TBXL

Unread postby jbw4600 » Sun Feb 25, 2018 2:04 am

Looks good. I'll take 5. Can you show a better outline shot?
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Re: TBXL

Unread postby nomastomas » Sun Feb 25, 2018 2:48 am

Outline looking down on deck.
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Re: TBXL

Unread postby krusher74 » Sun Feb 25, 2018 6:52 am

The one thing I found from bodyboarding over the years is the the bigger the wave the smaller the board I prefer.

In smaller waves the extra planing area and rail volume of the board helps both catch waves and generate speed on them, in big waves these attributes are a hindrance. Too much rail volume and the board wants to pop out of the face and loose traction, you cant sink it in the face and get it to bit hard.

I'm lucky that the magic board you CNC modeled for me works better than another board I've have in good waves from 1ft to 12ft. The only time any other board i have performs better is in very soft small waves and that just the fact that the fat bodyboard I would use had a large gain in volume.

I really enjoy the up-rail at the front of my board.

Lots of interesting ideas on your design.
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Re: TBXL

Unread postby nomastomas » Sun Feb 25, 2018 8:06 am

I agree with you Keith about the up-rail nose. I think I started going full up-rail nose on the G3. Its very forgiving and adds a little more rocker out at the rail. What's been your experience with the" skipping stone" phenomenom?

Here's a head-on view of the nose:
TBX1e.jpg
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Re: TBXL

Unread postby rodndtube » Sun Feb 25, 2018 2:00 pm

nomastomas wrote:After discussions on the G5 thread, <snip, snip>
Questions? Comments?

Nice discipline and articulation in trying to pull together many of the theories and comments in the 6-12 ft. mitigating chop hop discussion.

My only comments as I mull things around the wetwear is that the diagrams present very sharp rails throughout the board. The "V" also appears to extend half way through the board. Challenging to visualize some of this stuff!

Looking forward :)
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Re: TBXL

Unread postby nomastomas » Sun Feb 25, 2018 8:27 pm

You need to keep in mind that what you see is what the blank will look like after machining. The process of finish-sanding the blank will dull the sharp edges in the nose, as will the lamination. The rails are pinched but soft until the last 6" of the tail. Here the edge turns down but with a slight tucked edge. Edges release water, but down hard rails with sharp edges don't offer enough hold. I always want a little water to wrap around the rail before it releases, even at the tail. But, I always want the tailblock to have a firm, down edge so that the water is forced to let go. Water is actually very sticky, and wants to adhere to smooth surfaces. In the "Slices" view below, notice how there is no hard edge after the first 4"-6" in the nose.

TBX1f.jpg
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I have the extreme V deepest where the bottom enters the water when in a normal, planing position. It becomes progressively less deep and more flat as it moves rearward from the "entry" location, and becomes completely flat in the last third of the bottom where most of the action takes place. When paddling or moving down the wave face at less than planing speed, most of the bottom is in contact with the water. But at a certain speed, the board begins to lift out of the water, typically the nose first and then the rest of the bottom. Very much like a power boat, at planing speed the front third or more of the hull is out of the water and the rear third remains at or close to the water surface, which is why I say that is where the hydrodynamic action occurs. Of course, shifting over onto the rail completely changes this dynamic due to the loss of planing surface. As speed increases lift increases but much faster. Rough water or chop can act as a ramp, which also increases lift. Deep V entry serves to slice through this ramp instead of riding up it. So, I'm hoping that the shape, with speed, will lift and ride on the rear flat, and that the entry V will come into play whenever the water surface becomes uneven. (It occurs to me that the analogy to power boats is weak, in that power boats rarely go "downhill". At least not typically)
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Re: TBXL

Unread postby bgreen » Tue Feb 27, 2018 6:01 am

Nomas,

A couple of comments.

Regarding wide tails - my boards have tails varying from 20" to 15". I've never had trouble turning these.

One potential issue with the new board, is that so many variables are being changed it may be difficult to know what aspects of the new design make a difference.

I had a wave today where there was a significant skipping. When we talk about skipping, there probably are a few varieties - high speed propelled skipping and the bumpy, less forward propelled bounce. The type of chop is probably a variable. Today, it was more the bumpy, less forward propelled type, where just hanging on is an issue. The difficulty dealing with this is that the focus becomes hanging on, making it difficult to get too fancy in trying things to reduce bounce.

Then there is the issue of big waves versus choppy big waves.
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Re: TBXL

Unread postby nomastomas » Tue Feb 27, 2018 3:06 pm

“Regarding wide tails - my boards have tails varying from 20" to 15". I've never had trouble turning these. “
Just to clarify, I’m not saying that wide-tailed boards can’t be turned or even that they are difficult to turn. I’m only saying that with all other things being equal, e.g. rocker, volume, fins, length, etc, a narrow-tail board will have a shorter turning radius and will be experienced as more responsive (quicker turning) than a wide-tail board, an admitted generalization widely accepted by most shapers and riders. The same is true for board length; in general, shorter boards turn easier/quicker than longer boards. And finally, one of my favorites, fins offer more directional control than no fins.

“One potential issue with the new board, is that so many variables are being changed it may be difficult to know what aspects of the new design make a difference. “

A surfcraft’s performance is more than the sum of its parts. It’s difficult if not impossible to determine the contribution of any one particular design feature outside the context of the integrated whole. Surfcraft designers are accustomed to considering the integrative impacts of multiple design features. For example, how tail width, outline curve, fin placement and rocker all combine to impact turning. The proposed design is purposely quite simple; deep-V-to-flat bottom, relatively narrow, wide-point-forward outline. Volume has been maintained at 23L. The simplicity of the new design will help to identify those features that have an impact. My money is on the deep-V.

Lots of wave condition possibilities to be sure. My local point break is relatively slow and sloping, even at size. And yes, there is speed-generated lift, and lift caused by “ramping”, which can be due to surface anomalies (chop) or from striking the surface at a less than optimal angle, typically on take-off. And of course, a combination of the two, which is what I usually encounter and will be the conditions I’ll be testing in.
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Re: TBXL

Unread postby krusher74 » Wed Feb 28, 2018 12:36 pm

[quote="nomastomas"]. What's been your experience with the" skipping stone" phenomenom?

I think i've missed if some other thread what were talking about here :?

If were talking about what I think we are, then my design does not do it unless there is a lot of chop on the water, with a smooth to fair wave surface (and wales clean waves are what I think you guys would call choppy) then either it does not happen with my board or i dont notice it.

I think coming from bodyboarding I am always putting weight through my elbow into the rail, I think maybe use my shoulder as a shock absorbed to cushion shock/skipping.
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