“Our mission is to radically rethink, through R&D, modern surfboard fin design and materials; to contribute to the advancement of surfboard fin manufacture; to enhance the surfing experience; and to be adopted by shapers and surfers of all disciplines.” – Phil Todd, Founder, Caudal Fins.

Cau•dal | \ ˈkȯ-dᵊl \ (adjective)

1: of, relating to, or being a tail
2: directed toward or situated in or near the tail

A Caudal Fin is removable handmade polycarbonate surfboard fin with a flexible arm or ‘stem’, that is fastened using fin plugs to the back of the underside of a surfboard, typically on a traditional three-fin set up, but is adaptable for all kinds of surfboards, kiteboards, foilboards and more.

Introducing Caudal Fins

Australian inventor and surfer Phil Todd has devised a potentially breakthrough surfboard fin concept, one that replicates the sweeping flexible motion of the back fin of a fish: the Caudal Fin.

In nature, the caudal fin or tail fin is situated at the rear end of a fish or ocean mammal. Connected to the vertebrae; it provides the power to propel the creature forward and also acts like a rudder to help it change direction.

Following a long-established pattern of ‘biomimicry’ in surfboard shaping – most notably by American surfing design eccentric George Greenough in fin design – Phil’s concept was born from what he calls a “light bulb moment” while surfing and windsurfing in his native South Africa in the late 1980s.

Though Phil made and tested a single prototype back then, he shelved the idea to revisit later. After a long break from the water to pursue twin careers in geology and plastics technology, Phil recently returned to surfing, surprised to discover that surfboard fin design remained largely unchanged.

Armed with extensive experience in plastics manufacture – and emboldened by new materials and manufacturing technologies such as CNC that did not exist a few decades ago – Phil resumed research and development on his ‘Caudal Fin’ concept.

“Having COVID time on my hands and the availability of cheap 3D printing and table routers acted as the catalyst for me to revive the project,” says Phil, who has since churned out scores of his unique handcrafted Caudal Fins, made from both polycarbonate and other durable plastic hybrids.

Always on a quest to perfect his original idea, Phil’s fins have been well-received by test pilots in the surfing community in Australia and South Africa, keen to explore the potential of this new fin. Their feedback has resulted in a fin that has the potential to change the way we have always looked at the good old surfboard ‘skeg’ – the Caudal Fin.

Tech Specs

The main theory behind the Caudal Fin is that the flexible rearward mounting of the fin – far behind the trailing edge of a conventional surfboard fin – will allow a certain amount of side-to-side movement or play. This in turn would allow the fin to automatically adjust to the optimal angle to suit the water flowing over it, thus reducing the inherent drag found in normal surfboard fins.

The flex in Caudal Fins also creates incredible potential for the loading and release of energy by the surfer during turns, its recoil propelling them forward and potentially enabling them to gain extra speed. It widens the possibilities for the surfer to turn his or her surfboard and recover from these manoeuvres in a myriad of interesting new ways.

Caudal Fins and stems are constructed from 10mm thick panels of high-performance plastic known as Lexan or polycarbonate. Phil starts the process for each fin on his bench-top CNC milling machine and has made more than 50 different shaped prototypes to date.

“The CNC machine cuts the fins from 10mm sheet to a 90% completed shape and they are hand finished to tune the flex to the exact requirement. Each one is developed from the previous and they are still mostly experimental,” he says.

Incorporating feedback from his own surfing and that of the test riders, Phil is continually trying out various fin templates, foils, flex patterns, and stem lengths for both conventional shortboards and longboard surfboards. 

Phil expects it will take another two to three years to properly explore the possibilities of the concept and to arrive at a few performance-optimised variants. “I feel like up until now we have discovered only a small amount, perhaps 10% of what may be possible so far,” he says.

Most of the important fin design elements of the Caudal Fin concept have been under the protection of Australian and USA patent applications since September 28, 2021.

Read more about the technical aspects of Caudal Fins here.

Manufacturing Process

Phil begins the manufacture process for each version of the Caudal Fin with a CAD design model, then cuts the preform on his bench-top CNC milling machine and finishes them with old school hand foiling methods borrowed from woodworking, which he found requires a different method to fibreglass.

“I load the computer g-code to the CNC machine,” he explains, “which cuts the fin preforms from 10mm, much like CNC machines shape blanks. Similarly, I shape the preforms by hand to the final thickness and I tune the flex to the exact requirement. Each Caudal fin component developed with design inputs flowing from the previous. With rider feedback, the designs are evolving rapidly.”

After a long break, Phil is surfing more than ever surfing and is frothing like a grom now that he has discovered the ideal board size, volume and fin size to take his 100kg frame back to the board feel of his younger days.

Incorporating feedback from his own surfing and that of the test riders, Phil is continually trying out various fin templates, foils, flex patterns, and stem lengths for conventional shortboards, mid-lengths and longboards. Phil is also passionate about seeing surfers ride with the correct fin for their size and weight and as such is also making right sized Grom Fins and Big Guy fins in between his prototypes (see products below).

Phil expects it will take more experimentation to thoroughly explore the possibilities of the Caudal Fin and to arrive at a few performance-optimised variants in a variety of surf conditions. “I feel that up until now we have only uncovered the tip of the iceberg in terms of possibilities. It is really exciting to imagine where this could go.”

Read more about the technical aspects of Caudal Fins – here.

A Quick History of Surfboard Fins


Surfboard fins have both come a long way since original Californian surfboard innovator Tom Blake slapped an old speed boat keel on one of his patented wooden hollow boards, and literally altered the direction of surfing forever (see timeline below). In reality though, fin fundamentals have mostly remained the same since then. While surfboard fins are now made in a variety of shapes, they all have one thing in common: they are attached along their baseline to the surfboard – although that too may be about to change.

Caudal Fins Products and Services


While creating Caudal Fin products, company founder Phil Todd realised the amazing flexibility of the process. “I discovered it is possible to design and make nearly any fin imaginable using poly panels and the CNC router method,” explains Phil. “Flexibility is the key word. The process is flexible and the fins can be too. Along the way, test pilots have asked for specific requirements and I have worked out a design for them, shown them the computer model, made the tweaks and then manufactured the fin. As Hawaiian legend Larry Bertlemann once said – ‘anything is possible’.”

Prototypes & Research

Phil believes there is an exciting phase of discovery ahead for Caudal Fins, including making custom fins. “You may have some fun ideas of your own and want to turn them into reality,” he says. “Please contact me via the site to discuss your needs, as well as for an estimate of price and waiting time. If required, your idea will remain confidential. I have Patent Pending status on both caudal fin variants, for example, the flex stem model on the Energy model which has the super flexible trailing edge and tip.”

Caudal Right Sized Fins – Big Guy and Microgrom

Phil doesn’t don’t believe it is possible to make a meaningful contribution to fin or board designs without actually surf testing those designs yourself. “Yes, the test riders give excellent and enthusiastic feedback, but there is no substitute for personal experience,” he says. This led Phil to become inspired to design two types of specialist fins for surfers who fall outside of the ‘normal’ fin users – which he calls ‘Right Size Fins’ – one for bigger guys like himself and one for lightweight grommets. “Big blokes need big fins and groms need small fins. It’s that simple. Imagine shoe shops offering only three sizes, Small, Medium and large for everyone from Kids to adults,” he says.

Big Guy Fins

“For twenty years, I diversified my pursuit of adrenaline into motocross, hang gliding and sailboard racing. With my recent move to the Sunshine Coast of Queensland, Australia, surfing has again taken its place as my top priority. I’m now 40% heavier than I was in my heyday and catching waves on a 6’6” board wasn’t working out well for me. I tried a 9’6” mal, but it’s just not my thing so I thought it through and scaled up my board dimensions by 40% and I’m having a good time again. I now make my own 150mm ‘scaled up ‘Big Guy’ fins and everything is working just as before, if not better.”

Microgrom Fins

“Early in 2021, I noticed a six -year-old ‘microgrom’ surfing amazing at Noosa Point early in 2021 and saw on the beach that the standard issue fins in her 4’10” board looked way oversized. I did the scale down calculation and made her a smaller scaled down ‘right-sized’ ‘Microgrom’ set of fins and she rewarded me and stunned the guys in the line-up by riding a half kilometre, 55 second wave until the beach close-out. She is super stoked and said the board now is so much looser and responsive than before.”

Caudal Fins will be available to purchase online in the near future. Until then, please contact Phil directly to order from his specialist fin selection.

Testimonials from the Pit: Caudal Test Pilots


Caudal Fins inventor and founder Phil Todd has enlisted a crew of surfers on the Sunshine Coast and Newcastle, NSW, and in his native South Africa to try his fins out and provide valuable feedback. “From testing so far,” says Phil, “the team has talked about Caudal as a surfing experience rather than simply a new piece of hardware. It just feels very different. We welcome any surfer to join us in a journey, which may turn out to be just a design curiosity or might go on to enhance the scope of board design.”

“I was sceptical of the long-stem prototypes at first and asked Phil if they would throw me off the board and he said ‘no way, they will smooth your ride’. In the surf, I hardly felt the fins were there, but I was amazed when they helped me to pull off moves that haven’t often worked for me before.”

Sam Wills –

Neighbour and weekend surfer, Sunshine Coast, Australia, Quad set up, performance shortboard. Two long-stemmed Caudals behind the front fins. Surf: 2-3 foot beach (first ever Caudal Fins working prototype test ride in Australia)

“I have had some really good surfs on those new fins, really good. As long as I get a bit of speed up, they kick in and are insane. I’m so stoked with these fins, I wanna send a pair to you know who… no wait, let’s do some more testing!”

Dean Geraghty –

Shaper and former pro surfer, originator of the 4-Way Fin System, Sunshine Coast, Australia, Quad set up on a @geraghtyshapes performance short board. Pair of rear Caudal fins designed by Dean. Surf: 3-6 foot beach breaks.

“The fins are pretty good. Can I get another three sets? I’m sending some of your fins overseas!”

Jamie Carvell –

About as good a surfer as you can get while holding down a daytime job, a man of few words. A board and fin design deep thinker, Custom template fins, with big flexi-overhang, fitting the 4-Way Fin System box, performance quad. Caudal fins trailing the rigid front pair.

“Mate, I’ve found they are super responsive, particularly in the small stuff. They also work great in the barrel. Super keen to work on this some more.”

Kyle O’Donnell –

uni student and standout surfer at the beach breaks around Kawana, Queensland. , Speed and air specialist, always in the tele-lens frame. Caudal fin as trailing fin in a thruster set up.

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