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Class Legality

IJSBA · vintage

Vintage Ski

IJSBA 2025, VSK. A closed-list class. The craft must stay stock except where the rules allow otherwise, so anything unlisted is not permitted.

  • 2Not legal
  • 1OEM part required
  • 1Not permitted, not listed in the rules
  • 16Legal, with conditions
  • 31Legal

Read out of the published IJSBA rulebook on 2026-09-07, so confirm anything that decides a purchase. The full note is at the foot of the page.

Running the class

Eligible craft
Designed for the original Kawasaki 550 Ski. ORIGINAL KAWASAKI 550 ENGINE CASES MUST BE USED (VSK.3.2). Original manufacturer hull and top deck configuration required, OE lower deck required. Upper deck replacement only with IJSBA written approval, and the replacement deck must have historical approval in 550 competition.
Displacement limit
600cc (VSK.3.1). VSK.3.1 permits the engine to be bored and requires the displacement not to exceed the class designation, and records 600cc as the maximum allowed at the IJSBA World Finals, where the default Vintage Ski class is for the 550 Kawasaki.
Licence or tier
Not stated.
Minimum weight
Not stated in this document.

Read from the same class section as the part answers. The rider side of the sport, tiers, ages, licences and what gets inspected, is set out across the bodies at Racing.

Open questions on this class (5)

Places where the rulebook contradicts itself, or where a figure could not be settled. Nothing in this list is decided, and it sits here rather than in a footnote because it is what you would want before spending money.

  • Titanium pump parts ALLOWED here but explicitly PROHIBITED in Vintage X2 and Vintage SC. Confirmed on re-fetch but worth verifying.
  • Pump/nozzle limit expressed as 139.7mm (5.5 in) from the transom, an absolute distance, where every other class uses 50.00mm over OEM.
  • No model-year cutoff exists anywhere in the document.
  • No seat-height limit surfaced, unlike X2 and SC.
  • Whether non-Kawasaki craft may enter at all is not addressed.

What the rules say (51 parts)

31 permitted outright, 16 permitted with stated conditions, 2 refused by a rule we can quote, 1 held to the original part by a rule we can quote and 1 refused by our reading of the class rather than by a quoted rule. Grouped where the same rule gives the same answer, so two "Not legal" groups can sit side by side under different rules.

What each answer below means

Not legal
This comes off. The rules refuse it in this class.
OEM part required
This comes off. Only the part the manufacturer fitted is allowed here.
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.
Legal
Keep it. The rules permit this part in this class.

Read the refusals as a list of work. Anything below marked Not legal, OEM part required, or Not permitted has to come off the machine, or go back to the standard part, before it races in this class.

Not legal1 part

Upper deck substitution only by IJSBA WRITTEN approval, and the replacement deck must have historical approval in 550 competition.

OEM part required1 part

The hull stays as the manufacturer furnished it, and the one change listed is cutting or modifying the hull liner while the full hull thickness moves by no more than 2.0mm (.079 in). VSK.2.2

Not permitted, not listed in the rules1 part

VSK.5.1 lists the ignition changes it allows, the CDI unit, timing, the pickup mount and a total loss system, then allows no other, so the flywheel itself stays as supplied while VSK.5.3 lets its cover be modified or aftermarket. VSK.1.1, VSK.5.1, VSK.5.3

Legal, with conditions1 part

The exhaust system, which this clause names as the manifold, head pipe, expansion chamber, waterbox and mufflers, may be modified or aftermarket, and an insert in the stinger is part of it. No tuned portion of the exhaust may protrude outside the hull. VSK.3.7

Legal, with conditions1 part

An unmodified tank from another homologated PWC; a non-homologated aftermarket tank only by race director approval meeting or exceeding OEM strength and safety. VSK.4.4

Legal, with conditions1 part

Must fit the OEM battery box and be securely fastened. GP/Open/Freestyle/Sport GP additionally allow an additional battery, a new box and relocation.

Legal, with conditions1 part

The impeller housing may be modified or aftermarket, and the wear ring is the liner inside that housing rather than a part the document names on its own. VSK.6.1

Legal, with conditions1 part

Extension may not be wider than the OEM plate, sides must be connected and radiused, and no fins, rudders or skegs. Max extension beyond the OEM plate: 100.00mm (3.94 in) Ski and Sport, 177.80mm (7.00 in) Runabout.

Legal, with conditions1 part

Full-length type with at least one bar parallel to the drive shaft, all leading edges radiused, extending no more than 12.00mm (0.47 in) below the flat plane of the pump intake area.

Legal, with conditions1 part

Up to FOUR: two traditional bladed plus two Tubbie-type convex appendages. Max 63.5mm drop.

Legal, with conditions1 part

Padding and/or mat kits may be added in every class. Where footwells exist they must be BLOCKED OFF during competition with no indentation into the footwell sides.

Legal, with conditions1 part

Replacement bumpers allowed provided no hazard is created. A soft flexible water-spray deflector may attach to the hull sides or bond flange, not extending beyond the perimeter of the OE bumper or side moldings as measured by plumb line. A permanently affixed IJSBA-approved nose bumper is REQUIRED under GEN.8.12.

Legal, with conditions1 part

Allowed in essentially every class. Universal prohibitions: no manually controlled devices that alter cooling water flow during operation, no electronically controlled valves or water injection unless original equipment, and in most stock classes no NEW fittings added to the cylinder head, cylinder or crankcase.

Legal, with conditions1 part

Constant mass only, within the normally exposed areas of the hull, creating no hazard and requiring no modification or relocation of other parts. Water and any other fluid ballast is prohibited in every class.

Legal, with conditions1 part

An extension mounted on the transom counts as a trim tab, so it must be fixed in position, no wider than the planing surface and no more than 100.00mm (3.94 in.) past the end of the original planing surface, as on the fixed trim tab row. VSK.2.7

Legal1 part

Carburetors may be modified or aftermarket if they do not vent or spill fuel, with no more venturis than cylinders and no slide-type carburetors. VSK.4.1

Legal1 part

The carburetor may be modified or aftermarket provided it cannot vent or spill fuel at any attitude, which covers its jets, needle valves and needle valve springs. VSK.4.1

Legal1 part

Must meet USCG, SAE J-1928 Marine or UL-1111 Marine backfire flame arrester standards.

Legal1 part

Modified or aftermarket filler cap allowed provided no hazard is created. The FILLER and RELIEF VALVE themselves must stay OEM.

Legal1 part

Engines may be bored and aftermarket piston assemblies are allowed, with displacement kept within the class limit. VSK.3.1

Legal1 part

The crankshaft assembly may be modified or aftermarket and rod length may be changed, which covers the connecting rods. VSK.3.4

Legal1 part

The impeller housing, stator vane assembly, pump mounting plate and pump shoe may be modified or aftermarket, titanium included; the overall length sentence is misprinted and appears to cap the pump and nozzle assembly at 139.7mm (5.5 in.) from the transom. VSK.6.1

Legal1 part

Modified or aftermarket handlepole and mounting bracket, provided it functions as originally designed. Attaching point may be reinforced. VSK.2.9

Legal1 part

An aftermarket hood may be used. The ventilation tube clause still allows no other modification to the hood, so the original hood cannot be reworked beyond its vents. VSK.2.3, VSK.2.13

Legal1 part

The original bilge pump may be modified or disconnected and aftermarket bilge draining systems are allowed, provided no hazard is created.

Legal1 part

Replacement engine mounts are allowed in every class that addresses them. Ski GP, Vintage and Freestyle additionally allow a modified or aftermarket ENGINE BED with the engine repositioned in the hull.

IJSBA 2025, VSK, read from the rulebook on 2026-09-07. Read the rule yourself. Every IJSBA class · where the rulebooks differ · how this site reads a rulebook.

This is one class. Every part below also has a page of its own showing where it stands across every class this body runs, and legality by part is the index of them.

What we corrected here, and when

  • Replacement wear ring. Corrected 2026-10-01: this row read as unanswered until VSK.6.1 was read against it, and the clause opens the housing the ring sits in.
  • Stinger reducer insert + cooling line. Corrected 2026-10-01: this row read as unanswered until VSK.3.7 was read against it, and the clause opens the whole exhaust system.
Cite this page

“Vintage Ski, IJSBA class rules”, BaddJet archive, https://baddjetarchive.com/legality/ijsba/vintage-ski/

Add the date you read it.

51 parts read · 31 permitted, 16 with conditions · 2025 rulebook

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