Flying Diamonds FDX1: A Fin Developed With Midlengths in Mind
Developed by the man behind Thunderbolt construction to answer midlength riders' fin questions.
Quick Answer
The Flying Diamonds FDX1 was developed to answer a question from midlength riders: which fins should I use? Designed by Yu Sumitomo, the man behind Thunderbolt construction, it combines a balanced outline with carefully tuned flex for everyday surfing.
It comes in three-fin Thruster and five-fin Tri-Quad sets, with separate versions for FCS II and Futures boxes. Midlength riders helped drive its development, and Flying Diamonds also recommends it for compatible shortboards.
What's in this guide
- A Bigger Board Raises a Fin Question
- Months of Scanning and Hand-Tracing Shaped the FDX1
- The Experience Behind the Design
- Designed for Speed Early in the Wave
- AirFlex Construction Tunes the Flex
- Which Midlength Boards Can Use the FDX1?
- Three-Fin or Five-Fin Set?
- Do You Need to Size Up for a Midlength?
- A Close Fit Was Part of Yu-san's Plan
- Common Questions About the FDX1
- Choosing Your FDX1 Set
A Bigger Board Raises a Fin Question
At Hawaiian South Shore, we see riders move from a shortboard to a midlength and reconsider their fins. Someone who normally rides Medium fins on a shortboard may step up to Large for the bigger board.
As more riders picked up the midlengths built with Yu-san's Thunderbolt construction, they kept asking which fins to use. He wanted a dependable answer developed with those boards in mind.
That question led to months of work.
Months of Scanning and Hand-Tracing Shaped the FDX1
Yu-san bought popular fins from established brands and digitally scanned their outlines. He grouped them by size so he could compare similar fins, then overlaid 20 to 30 shapes.
Next came the paper and pencil.
He printed the overlapping outlines and traced them by hand, looking for the shape they shared. He repeated that work over several months, studying where upright designs and more swept-back designs came together.
That common outline became his starting point. He then refined it into the FDX1.
The finished outline sits between those extremes. Flying Diamonds describes it as a neutral, all-around template for shortboards and midlengths.
The Experience Behind the Design
Yu-san grew up working in his parents' surfboard factory, grinding different fin shapes by hand. He was also a competitive shortboarder.
He later developed Thunderbolt construction, used in boards from CJ Nelson Designs and the Harley Ingleby Series. Many of our customers have ridden his work without knowing the person behind it.
The FDX1 brings his experience with boards and composite construction into a fin. He developed its outline and tuned its internal fiberglass layers to work together.
Designed for Speed Early in the Wave
Yu-san's goal was a fin that builds speed early and stays easy to handle in everyday surfing. He was thinking about riders with jobs, families, and limited time in the water who want their board to feel good when they get out.
He gave the fin a slightly larger tip area. In his explanation, that helps resist sliding and contributes to forward drive when the rider puts pressure on the board.
He also wanted to control how the fin responds under that pressure. He asked the factory to adjust the fiberglass layers until the fin could twist slightly, using a sail twisting open as his comparison.
These are the designer's intended results. The feel you get also depends on your board, the waves, and how you surf.
AirFlex Construction Tunes the Flex
The FDX1 uses Flying Diamonds' AirFlex construction: a polyurethane foam core surrounded by fiberglass and epoxy resin.
The fins are molded around that core. Yu-san explained that he adjusted the internal fiberglass layers to tune their stiffness without changing the fin's cross-sectional shape.
The finished design depends on both the outline you can see and the construction inside it.
Which Midlength Boards Can Use the FDX1?
The FDX1 suits compatible thruster and quad midlengths. Choose the fin-base version that matches your board: FCS II or Futures. Those versions are not interchangeable.
These board families are worth considering:
These are setup checks, not a claim that the board maker recommends the FDX1. Send us your board model, length, and a photo of the boxes, and we'll help confirm the set and size.
Three-Fin or Five-Fin Set?
The Tri-Quad set includes two front fins, a center fin, and two dedicated rear quad fins. Choose the combination for your board and the way you want to ride it.
Do You Need to Size Up for a Midlength?
Our Hawaiian South Shore recommendation for the FDX1 is to start with your weight, rather than automatically move up a size because you ride a midlength: Medium up to about 185 pounds, Large above that.
Under about 145 pounds, close to the dividing line, or choosing fins for a particularly large board? Send us your weight and board model so we can help.
This is our shop's FDX1 sizing advice. Individual board makers may recommend different fin sizes for their designs.
A Close Fit Was Part of Yu-san's Plan
One of our early sample fins was tight enough that David needed Yu-san to walk him through installation on a video call. Once seated, it was snug and didn't move.
Yu-san explained that he wanted very little movement in the box. He also asked the factory to ease the original fit slightly after some people struggled with the samples.
If your fin doesn't seat smoothly, don't force it. Contact us or bring the board into the shop.
Shop the FDX1
Common Questions About the FDX1
Was the FDX1 designed for midlengths?
Midlength riders' questions helped prompt Yu-san to develop it. He wanted an all-around fin for those boards, and Flying Diamonds also recommends the design for compatible shortboards.
Will the center fin fit a long center box?
No. The FDX1 center fin does not fit the long center box used in a traditional 2+1 setup. Send us a photo if you need help identifying your boxes.
Can I switch between thruster and quad?
Yes, with the Tri-Quad set and a board designed to accept both configurations.
Does a larger-looking tip mean I should choose a smaller size?
No. The tip shape is part of the design. Start with our weight-based recommendation above, then check with us if you need help matching it to your board.
Choosing Your FDX1 Set
The FDX1 began with a question from midlength riders, followed by months of studying shapes and tuning construction. That work is what makes its story worth knowing.
See the FDX1 sets at Hawaiian South Shore, or send us your board model, fin system, and weight. We'll help you choose the right version.
Product reference: Flying Diamonds' FDX1 design and construction description.
The fin for your midlength
Come by the shop, or message us your weight and your board, and we'll match you to the right set. Still choosing the board? Start with our midlengths.
Shop the FDX1Hawaiian South Shore · 320 Ward Avenue #111, Honolulu, HI 96814
Phone: (808) 597-9055 · Email: sales@hawaiiansouthshore.com · Instagram: @hwnsouthshore