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Class Legality

IJSBA · ski

Ski Modified

IJSBA 2024, SKM. A closed-list class. The craft must stay stock except where the rules allow otherwise, so anything unlisted is not permitted.

  • 3Not legal
  • 3OEM part required
  • 12Not permitted, not listed in the rules
  • 5The rules do not say
  • 19Legal, with conditions
  • 11Legal

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
OEM homologated naturally aspirated four-stroke engines only.
Displacement limit
1500cc. The class runs in ranges, 0-1100cc (SKM.3) and 1101-1500cc (SKM.4). SKM.3.1 and SKM.4.1 permit the engine to be bored and require the displacement not to exceed the class designation, one clause for each of the two ranges.
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.

  • Document year conflict - filename 2024, body reads 2023.
  • SKM.6, SKM.7 and SKM.8 do not exist. There is NO ignition/ECU section, NO dedicated exhaust-system section and NO flame arrester rule in this class document.
  • The document gives no port-chamfering allowance, unlike the stock classes.
  • Sponson drop 63.5mm here vs 38.00mm in the stock classes it says Kawasaki hulls inherit from.
  • Deck height figure printed as ".155mm (.06in)" - almost certainly a decimal typo for 1.55mm.

What the rules say (53 parts)

11 permitted outright, 19 permitted with stated conditions, 3 refused by a rule we can quote, 3 held to the original part by a rule we can quote, 12 refused by our reading of the class rather than by a quoted rule and 5 the rules do not settle. 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.
The rules do not say
Unanswered. The rules do not settle this, so ask the club before you rely on it.
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.

OEM part required1 part

Throttle bodies must remain stock. No throttle plate angle change, no housing modification, NO PHENOLIC OR ALUMINIUM SPACERS behind the throttle body. SKM.5.2

OEM part required1 part

Camshaft stock. Timing may be changed and adjustable sprockets fitted in the 1101-1500cc category.

Not permitted, not listed in the rules10 parts

Not listed in this class document. Illegal under the closed-list principle.

Not permitted, not listed in the rules1 part

SKM.3.9 and SKM.4.9 list no aftermarket manifold or head pipe and allow only an exhaust manifold previously drilled or tapped, once its holes are filled or capped. SKM.1.1, SKM.3.9, SKM.4.9

Not permitted, not listed in the rules1 part

No waterbox allowance in SKM.

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

Aftermarket springs and retainers in the 0-1100cc category ONLY. In 1101-1500cc, springs and retainers must be OEM. SKM.4.5

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

Max TWO, 63.5mm drop per SKM.2.4, BUT the class also says Kawasaki hulls follow Ski Stock rules and Yamaha hulls follow Four Stroke Ski Lites rules. Unresolved conflict.

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

IJSBA-approved aftermarket hulls and top decks permitted, must display IJSBA-recognised hull identification. SKM.1.1

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

Separating the bond flange is the only work on the OEM hull the class lists: it must be rejoined by the original method, such as high-strength adhesive, and nothing else on the OEM hull may change. SKM.1.1, SKM.2.2

Legal, with conditions1 part

A bow appendage that diverts spray and stabilises handling may be fixed to the top deck only as an approved design listed on IJSBA's website. At the stern, SKM.2.7 counts an extension mounted on the transom as a fixed trim tab, no wider than the planing surface and no more than 100.00mm (3.94 in.) past its end. SKM.2.2, SKM.2.7

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

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

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 2024, SKM, 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.

Cite this page

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

Add the date you read it.

53 parts read · 11 permitted, 19 with conditions · 2024 rulebook

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