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Article 501.05 · 502.04 · 503.05 · 504.05 · 505.04
Fins
In 6 of the 8 MotoSurf classes the fin system is named in the rules and nothing else is accepted. Most of those classes also run a closed permission list, so the fin is one of a handful of parts a rider is allowed to change at all.
Why a fin is worth this much attention here
Three of the technical articles run a closed permission model: anything the rulebook does not name is prohibited, and the lists run to 6 or 7 items. Fins are on every one of them. A rider who wants to change how the machine behaves has almost nowhere else to go, which makes the fin the most consequential part on the board.
Limits and requirements, with no list
Art. 501 and 505: each article states limits a board must stay inside and requirements it must meet.
-
A change that keeps every limit and requirement
goes through
- Meets the article
-
A change past a limit, or breaking a requirement
stops
- Does not meet the article
A closed list of changes
Art. 502, 503 and 504: each article lists 6 or 7 changes a rider may make, and carries the clause at Art. 502.02 a), 503.02 a) and 504.02 a).
-
A change the list or another section allows
goes through
- Allowed
-
A change no section of the rulebook allows
stops
- Prohibited
The clause each list article carries reads "Features not allowed by sections of this rulebook are prohibited." It refuses only what no section of the rulebook allows, and the sections together can allow more than a list names. Art. 501 and 505 carry no such clause: they state limits and requirements and are silent on a change none of their sections touches. Art. 503 and 504 also cap the board's length and mass, so a list class is measured as well. Art. 501, 502, 503, 504 and 505 all cap the main fin at 230 mm high and 340 mm long, and Art. 502, 503 and 504 accept only FCS side fins, while Art. 505.04 d) allows only officially certified FCS fins.
How we know: The 2026 MotoSurf Rulebook, read article by article: Art. 502.01 a), 503.01 d) and 504.01 d) hold each list class's board to its standard specification and point it to its list of allowed modifications, the clause sits under each list article's engine requirements, Art. 501 and 505 hold the limits and requirements, and each article's heading names the classes it covers.
Every distinct sentence about which fins a board may carry, once, word for word, with the classes that carry it. The shared size limits follow.
| Clause | Elite Men | Elite Women | Stock Men | Masters Men | Masters Women | Juniors Boys | Juniors Girls | Electric Challenge |
|---|---|---|---|---|---|---|---|---|
| The allowed side fins for the Elite Women… | Not in this article | 503.05 d) | Not in this article | Not in this article | 503.05 d) | Not in this article | Not in this article | Not in this article |
| No other fins will be… | Not in this article | 503.05 d) | 502.04 d) | Not in this article | 503.05 d) | 504.05 d) | 504.05 d) | Not in this article |
| Only officially certified FCS fins are… | Not in this article | 503.05 d) | Not in this article | Not in this article | 503.05 d) | 504.05 d) | 504.05 d) | 505.04 (Fins requirements) d) |
| Side fins for the Stock Men category must… | Not in this article | Not in this article | 502.04 d) | Not in this article | Not in this article | Not in this article | Not in this article | Not in this article |
| The allowed side fins for the Juniors categories… | Not in this article | Not in this article | Not in this article | Not in this article | Not in this article | 504.05 d) | 504.05 d) | Not in this article |
| Side and central fin configuration of each surfboard… | Not in this article | Not in this article | Not in this article | Not in this article | Not in this article | Not in this article | Not in this article | 505.04 (Hull requirements) e) |
| Maximum number of the fins on the board… | Not in this article | Not in this article | Not in this article | Not in this article | Not in this article | Not in this article | Not in this article | 505.04 (Hull requirements) h) |
| Elite Men and Masters Men: Art. 501.05 sets fin integrity, shape and dimensions, and names no fin system. | ||||||||
The allowed side fins for the Elite Women and Masters Women categories are all the FCS fins compatible with provided adjustors.
Art. 503.05 d)
No other fins will be accepted.
Art. 503.05 d), 502.04 d), 504.05 d)
Only officially certified FCS fins are allowed.
Art. 503.05 d), 504.05 d), 505.04 (Fins requirements) d)
Side fins for the Stock Men category must be FCS fins compatible with approved adjusters.
Art. 502.04 d)
The allowed side fins for the Juniors categories are all the FCS fins compatible with provided adjustors.
Art. 504.05 d)
Electric Challenge has two more fin clauses in its hull article. The rulebook prints two articles numbered 505.04, so citations here name the heading too.
Side and central fin configuration of each surfboard has to be compliant with standard configuration and specification of the manufacturer.
Art. 505.04 (Hull requirements) e)
Maximum number of the fins on the board must correspond with the production standards of each manufacturer.
Art. 505.04 (Hull requirements) h)
The remaining 2 classes name no fin system at all. Their article regulates fin dimensions and shape and stops there, so a rider in Elite Men or Masters Men is not required to run any particular brand.
Fin size limits: all the sanctioning body publishes on geometry
- Main fin, maximum height
- 230 mm
- Main fin, maximum length
- 340 mm
- Shape
- Shape of each fin shall be without any toothed shape larger than 1 cm.
That is the complete list. The measuring scheme is a silhouette with two arrows: no scale, datum, fin box type, plug spacing, cant or toe angle, tolerance or extension lines, so it does not say where height is measured from.
Where the fin specification is not
- Not in the two technical appendices. Their titles name two boards and read like board specifications, but both are UIM homologation forms for the engine, exhaust, jet pump and electronics. Across their 40 pages the word "fin" does not appear once, and neither form states a board dimension or a board mass either.
- Not in the manufacturer's owner manual, which gives no fin screw size, no fin torque and no fin dimension beyond the seven inches in a product name. It says the centre fin is held by four screws and stops.
- Not in the definition the rulebook does give. Its glossary describes the named system as having two tabs secured with set screws, which is the original generation, while the manufacturer ships the second generation with a tool free locking mechanism. Neither rulebook ever writes the second generation's name.
So a rider reading only the rulebook would buy the wrong generation of fin; no rulebook specifies a fin box standard.
| Board | Side fin | Code | Centre fin | Code |
|---|---|---|---|---|
| JetSurf Race DFI SL | FCS II Performer Black Medium - Side fin | R06Z083 | FCS II Connect GF 7" - Center fin | R06Z082 |
| JetSurf Race DFI SKI | FCS II Performer Black Medium - Side fin | R06Z083 | FCS II Connect GF 7" - Center fin | R06Z082 |
| JetSurf Titanium DFI SL | FCS II Power Twin JS PG Retail Fins | R06Z085 | Center fin L200 | P004463 |
| JetSurf Titanium DFI SKI | FCS II Power Twin JS PG Retail Fins | R06Z085 | Center fin L200 | P004463 |
| JetSurf Cruiser DFI | FCS II Performer Black Medium - Side fin | R06Z083 | FCS II Connect GF 7" - Center fin | R06Z082 |
| JetSurf Adventure DFI | FCS Accelerator Large Neo Glass - Side fin | R06Z081 | FCS II Connect GF 7" - Center fin | R06Z082 |
Codes from the maker's equipment tables, not a retailer. One side fin, on the JetSurf Adventure DFI, is named without the II: do not assume one part fits the range.
The centre fin is not a surfboard fin box
Only the side fins sit in a fin box. The centre fin bolts to a maker's own flange with four screws, and 2 of the 6 models list a differently named centre fin with no flange. The surfboard overlap is the side fins, not the mounting.
One asymmetry to know before buying adjusters
The side fin rules for Elite Women, Masters Women and both Juniors classes tie the fin to the adjustors provided (Art. 503.05 d) and 504.05 d)). Yet neither permitted changes list for those classes, Art. 503.07 or 504.07, names fin adjusters, while the Stock Men list at Art. 502.06 does. So the rulebook leaves open whether a rider in those four classes may swap the adjusters on her or his board.
These fins are not a jet ski part
Withdrawn September 2026: an earlier version called them a cross discipline part. IJSBA's stand-up ski rules mention fins only to bar hazardous ones (SSK.2.3, SSK.2.5: "Fins, rudders, skegs and other appendages that may create a hazard will not be allowed."), and we found nothing the fin maker publishes on powered craft, for or against. The two sports share riders, not parts.
This page carries no prices. What it offers is the legality and fitment reference above, read from the rulebook and the manufacturer's own equipment lists.