Not legal 1 class
Aftermarket hulls prohibited.
- Ski Stock · SSK
IJSBA · Hull and handling
Aftermarket hull or top deck, IJSBA
The highest-stakes eligibility question in the book.
This page is IJSBA only, and the bodies do not agree. The same part under IHRA and UIM. Which one applies to you is decided by whoever sanctions the race you enter.
Where it stands, class by class
20 classes, grouped where the same rule gives the same answer rather than listed one by one, because an answer that holds for a class usually holds for every class that borrows its rules.
What each answer below means
- Not legal
- This comes off. The rules refuse it in this class.
- Not permitted, not listed in the rules
- Treat it as coming off. The class requires the craft to stay stock except where the rules allow otherwise, and this part is not on the list, so this is our reading rather than a rule we can quote at you.
- Legal, with conditions
- Keep it, but measure it: the rules permit this part only inside stated limits.
Not legal 1 class
Hull and top deck must remain as originally furnished.
- Vintage Ski Limited · VSKL
Not legal 1 class
No allowance for aftermarket hulls.
- Sport Spec · section headings, no numbered rules
Not legal 1 class
The class description controls build costs by prohibiting aftermarket hulls, and deck repairs may change the original shape by no more than 2.00mm (0.08 in.). · SKSS.1, SKSS.2.2
Not legal 1 class
Exclusively the 1991 OEM SC hull.
- Vintage SC · VSC
Not legal 1 class
Upper deck substitution only by IJSBA WRITTEN approval, and the replacement deck must have historical approval in 550 competition.
- Vintage Ski · VSK
Not permitted, not listed in the rules 8 classes
No aftermarket hull is listed, the craft must remain strictly stock, and a deck repair may not alter the original configuration by more than 2.00mm (0.08 in.).
- Fixed Steering Ski Stock · FSSK.1.1, FSSK.2.2
- Runabout Rec Lites · RRL.1.1, RRL.2.2
- Four Stroke Ski Lites · FSKL.1.1, FSKL.2.2
- Runabout Naturally Aspirated · RNA.1.1, RNA.2.2
- Runabout Stock · RAS.1.1, RAS.2.2
- Ski Lites · SKL.1.1, SKL.2.2
- Runabout Limited · RAL.1.1, RAL.2.2
- Runabout Superstock · RSS.1.1, RSS.2.2
Legal, with conditions 1 class
IJSBA-approved aftermarket hulls and top decks permitted, must display IJSBA-recognised hull identification. · SKM.1.1
Legal, with conditions 1 class
An aftermarket hull may be fitted while the top deck stays as the manufacturer furnished it, provided the hull is no longer than the top deck. The class's requirement for the 1986-1995 OEM X2 sits beside its allowance for 2006 X2 engine cases, so the 2006 cases do not bring the 2006 hull with them. · VX2.1, VX2.2.2
Legal, with conditions 1 class
Legal if it does not exceed OEM upper-deck length/width. Max 165.1mm (6.5 in) shorter than OEM length, within 50.8mm (2.0 in) of OEM width. Ski deck absolute minimums 193cm x 68.5cm x 53.3cm.
- Freestyle · FREST
Legal, with conditions 1 class
Permitted via the Aftermarket Hull Homologation Process; the top deck must resemble the generic look of existing homologated Ski watercraft. EXCEPTION: the 1500cc Kawasaki SX-R must use the OEM hull and top deck.
- Ski Grand Prix · SKGP
Legal, with conditions 1 class
Permitted only on watercraft homologated in numbers of 500 or higher, and the hulls themselves must be IJSBA-approved and homologated. · SPGP.3.2
Legal, with conditions 1 class
Permitted if homologated at 500 or higher units and IJSBA-approved. Upper decks must be an exact OEM replica judged by a silhouette test. From Jan 1 2025 the engine block must be from the same manufacturer as the originating top deck.
- Runabout Open / GP · ROP
What we corrected here, and when
- Vintage X2. Corrected 2026-10-06: the IJSBA Vintage X2 row said prohibited, from the OEM-hull sentence alone; VX2.2.2 allows a modified or aftermarket hull under the original top deck.
Aftermarket hull or top deck: if the rule your class applies reads differently to you, or the rulebook has changed since this was read, ask. We answer with the section we read it from, or that we have not read it. Ask a rules question.
Every IJSBA class · where the rulebooks differ · checks on parts the shop sells · how this site reads a rulebook.
Hull and handling · two and four stroke · legal in 6 of 20 answered, all with conditions