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Class Legality

IJSBA · ski

Ski Grand Prix

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

  • 21Legal, with conditions
  • 39Legal

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
Start from a stock OEM watercraft. Aftermarket or modified hulls and top decks permitted but must be IJSBA-approved through the Aftermarket Hull Homologation Process, and the top deck must resemble the generic look of existing homologated Ski watercraft.
Displacement limit
1300cc two-stroke, 1500cc naturally aspirated four-stroke and 1100cc forced-induction four-stroke. Forced induction: boost relief valve required, and this rulebook gives three different figures for what it must be set to. The class intro requires release above 11 psi at 900cc or less and above 9 psi above 900cc, while SKGP.9.3 requires release above 12.00 PSI with a 1 psi tolerance and never testing above 13.00 PSI. Three ceilings in one document, recorded 2026-09-10 and unresolved. No single figure is stored, because storing one would invent a rule the document does not settle.
Licence or tier
Expert or Pro recommended.
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.

  • The boost limits contradict each other, since SKGP.9.3 gives three incompatible sets, so this site quotes no Ski GP boost number.
  • Sponson vertical channel printed as 63.00mm here vs 63.5mm elsewhere.
  • The hood rule inside the Ski GP document references "the Ski Modified Class" - possibly a cut-and-paste artefact in the PDF.
  • Sub-numbering under SKGP.2 is unreliable.
  • The "97 inches" aftermarket hull length cap for the SX-R sits oddly beside the rule that the SX-R may not use an aftermarket hull at all.

What the rules say (60 parts)

39 permitted outright and 21 permitted with stated conditions. 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

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.

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. SKGP.3.7

Legal, with conditions1 part

Original injectors may be modified to increase fuel flow; aftermarket injectors that increase FUEL flow only. Injectors that increase AIRFLOW are prohibited. SKGP.8.1

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

Allowed on engines up to 1100cc. Boost relief valve required. Turbo housing must be full circulating water-jacket type whenever the engine runs. The boost figures in SKGP.9.3 contradict each other, so none is quoted here.

Legal, with conditions1 part

Couplers, bearing housing and driveshaft may be modified or aftermarket provided they keep a 1:1 drive ratio between the engine and the pump. The clause names no material, so a titanium shaft is covered by it. SKGP.10.2

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

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

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.

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

The hull may be modified within the length and width of the upper deck's bond flange by plumb bob, bumpers removed, with no hazardous fins, rudders or skegs, and a separated bond flange is rejoined by the original method. The 1500cc Kawasaki SX-R is the exception: it must keep exact OEM hull dimensions. SKGP.1, SKGP.2.2, SKGP.2.3

Legal, with conditions1 part

The class counts any extension mounted on the transom as a trim tab, which may be fixed, automatic or rider controlled but no wider than the planing surface and no more than 100mm (3.94 in.) past its end, as on the trim tab rows. SKGP.2.7

Legal1 part

The exhaust system may be modified or aftermarket on every engine, the two-stroke manifold and head pipe and the four-stroke manifold and connecting pipes included. SKGP.3.7, SKGP.6.8, SKGP.7.8

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. SKGP.4.1, SKGP.8.4

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. SKGP.3.1, SKGP.6.4, SKGP.7.4

Legal1 part

Aftermarket camshafts are allowed if the original number of camshafts, the original bearing type and dimensions and the original method of valve activation are kept, and cam timing may be changed. SKGP.6.3, SKGP.7.3

Legal1 part

Aftermarket valvetrain components, valve springs and retainers included, are allowed provided the original method of valve activation is kept. SKGP.6.3, SKGP.7.3

Legal1 part

Two-stroke cylinders may be modified or aftermarket, and four-stroke intake and exhaust ports may be changed in diameter and shape with runners and combustion chambers modified. SKGP.3.3, SKGP.6.2, SKGP.7.2

Legal1 part

Two-stroke cylinders may be modified or aftermarket and four-stroke ports may be changed in diameter and shape, so a chamfer within the appendix limit is covered. SKGP.3.3, SKGP.6.2, SKGP.7.2

Legal1 part

Forced induction is allowed only on four-stroke engines of 1100cc or less, and there the original turbocharger or supercharger may be modified or an aftermarket unit fitted, so its internals, clutch, belt and pulleys are open. SKGP.9, SKGP.9.1

Legal1 part

The document names no wear ring, but the impeller housing it lines may be modified or aftermarket within the 50.00mm (1.97 in.) overall pump and nozzle length limit. SKGP.10.1

Legal1 part

Modified or aftermarket handlepole and mounting bracket, provided it functions as originally designed. Attaching point may be reinforced. SKGP.2.11

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, SKGP, 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

  • Stinger reducer insert + cooling line. Corrected 2026-10-01: this row read as unanswered until SKGP.3.7 was read against it, and the clause opens the whole exhaust system.
  • Titanium driveshaft, impeller housing or stator vane assembly. Corrected 2026-10-01: this row read as unanswered until SKGP.10.2 was read against it.
Cite this page

“Ski Grand Prix, IJSBA class rules”, BaddJet archive, https://baddjetarchive.com/legality/ijsba/ski-grand-prix/

Add the date you read it.

60 parts read · 39 permitted, 21 with conditions · 2025 rulebook

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