Not legal1 part
The exhaust system must remain entirely of origin as delivered by the manufacturer, so the through-hull outlet flap may not be removed. 501.02.03.03
- Through-hull exhaust outlet flap removal · Exhaust
UIM · ski
Ski Juniors GP3.3
UIM 2026, 302.01. The rulebook does not state a governing principle for this class.
Read out of the published UIM rulebook on 2026-09-08, so confirm anything that decides a purchase. The full note is at the foot of the page.
Running the class
- Rider requirements
- Ages 13-15, reckoned at 31 December; Minor Release Form.
- Race duration
- 12 minutes + 1 lap.
- Riders on the grid
- 15.
- Entry fee
- Free; no proportional travel money paid.
- Championship status
- World Championship class.
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.
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.
- Same inference problem as GP3.2 - the technical link to 501.02 is not stated in any rule.
- The rulebook gives no rule distinguishing GP3.2 from GP3.3 on anything except rider age.
What the rules say (57 parts)
9 permitted outright, 19 permitted with stated conditions, 5 refused by a rule we can quote, 7 held to the original part by a rule we can quote and 17 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
Only replaceable-type jets, needle valves and needle valve springs, choke removal and an aftermarket primer. NO OTHER CARBURETTOR MODIFICATIONS. 501.02.04.01
Not legal1 part
No fuel-injection allowance exists for Ski GP3.
Not legal1 part
No internal modifications of any kind - grinding, surfacing, polishing, machining, shot peening. 501.02.03.02
Not legal1 part
Homologated production craft only - 50 specimens, marketed, conformity certificate. 500.02.01
- Aftermarket or prototype hull · Hull and handling
OEM part required1 part
The exhaust system must remain entirely of origin as delivered by the manufacturer, so the original expansion chamber is required under 501.02.03.03. 501.02.03.03
OEM part required1 part
The exhaust system must remain entirely of origin as delivered by the manufacturer, so the original water box is required under 501.02.03.03. 501.02.03.03
- Aftermarket waterbox · Exhaust
OEM part required1 part
Ski GP3 is a two-stroke class, and 501.02.03.03 keeps its whole exhaust system as the manufacturer delivered it, so the original manifold and head pipe are required. 501.02.01, 501.02.03.03
- Aftermarket exhaust manifold / head pipe · Exhaust
OEM part required1 part
OEM fuel tank, pickup, filler, filter, tap assembly and relief valve must be used and may not be modified. 501.02.04.02
OEM part required1 part
Ski GP3 keeps the original equipment charging system, allows no ignition change it does not list, and unlike GP2 prints no flywheel, alternator or flywheel cover allowance. 501.02.05.04, 501.02.05.05
OEM part required1 part
THE OEM CHARGING SYSTEM MUST BE USED. Stated for every production class in both divisions.
- Aftermarket charging system / stator · Ignition
OEM part required1 part
The hull may be repaired but not otherwise modified, and a repair may not alter the original configuration by more than 5 mm. 501.02.02-02
- Modification of the OEM hull · Hull and handling
Not permitted, not listed in the rules10 parts
Not listed in this class. Illegal under the class's own stock clause.
- Aftermarket or modified rotary valve · Fuel
- Long-distance fuel filling system (stopper and tank connection) · Fuel
- Aftermarket vapour / air separator · Fuel
- Aftermarket pump nozzle and directional nozzle · Driveline
- Aftermarket driveshaft, couplers, bearing housing · Driveline
- Titanium driveshaft, impeller housing or stator vane assembly · Driveline
- Aftermarket nozzle trim system (pump-mounted) · Driveline
- Aftermarket hull trim tabs · Hull and handling
- Ballast weight kits · Hull and handling
- Hull extension · Hull and handling
Not permitted, not listed in the rules1 part
No reed valve article exists for Ski GP3. Under the closed-list rule aftermarket reeds appear illegal here while explicitly legal in GP2, but the rulebook never says so directly.
Not permitted, not listed in the rules1 part
No intake manifold article.
- Aftermarket intake manifold · Fuel
Not permitted, not listed in the rules1 part
No pump allowance; only petcock bypass and additional filters.
Not permitted, not listed in the rules1 part
Ski GP3 lists replacement gaskets and interchangeable cylinders but no cylinder head allowance, and bars internal work on any engine component, so the original head stays. 501.02.03.02, 501.02.03.06
- Aftermarket cylinder head (2-stroke) · Engine
Not permitted, not listed in the rules1 part
Ski GP3 prints no starter motor or bendix clause, and that allowance first appears at GP2, so the original starter stays. 501.02-02
- Replacement starter motor and bendix · Electrical
Not permitted, not listed in the rules1 part
Nozzle, stator and pump housing are not listed as modifiable, so under the closed-list rule they must stay OEM.
Not permitted, not listed in the rules1 part
No hood article; ventilation tubes are covered separately.
- Aftermarket hood · Hull and handling
Legal, with conditions1 part
Aftermarket flame arresters meeting USCG, UL-1111 or SAE J-1928 Marine standards. 501.02.04.01
Legal, with conditions1 part
Must fit the OEM battery box and be securely fastened. GP2 additionally allows relocation of the battery, box or housing limited to the strict minimum needed to fit an aftermarket exhaust.
- Replacement battery · Electrical
Legal, with conditions1 part
Cylinders may be interchanged between homologated watercraft of the SAME MANUFACTURER. Engines may be bored. No internal modification of any kind. 501.02.03
- Aftermarket cylinder (2-stroke) · Engine
Legal, with conditions1 part
Must retain original port timing, compression ratio, dome profile, skirt length/shape and material type, and weigh within +/-25.00% of OEM. 501.02.03.04
- Aftermarket piston assemblies · Engine
Legal, with conditions1 part
Rebuild allowed. Stroke and rod length may NOT change. Bearings must keep original type and dimensions. Counterweights must resemble the original with no new holes or pockets. Total assembly weight within +/-5.00% of OEM. Non-ferrous counterweights, crank pins and connecting rods are prohibited. 501.02.03
Legal, with conditions1 part
Replacement gaskets of the same type as OEM, with the base gasket no thicker than 0.8 mm. 501.02.03.06
- Aftermarket head gasket · Engine
Legal, with conditions1 part
Chamfering of NON-ORIGINAL cylinder ports up to 1.00 mm at a maximum 30 degree angle. 501.02.03.04
- Port chamfering service · Engine
Legal, with conditions1 part
The FRONT ENGINE SUPPORT may be reinforced or replaced. 501.02.02.13
Legal, with conditions1 part
Original diameter maintained. 501.02.06.01
- Aftermarket impeller · Driveline
Legal, with conditions1 part
Permitted, subject to the limits UIM applies to every class, namely the sound ceiling, the hull repair tolerance, the fuel specification, and the intake grate, sponson and pump dimensions.
- Replacement wear ring · Driveline
Legal, with conditions1 part
Max 100 mm. 501.02.02.16
- Aftermarket pump cover plate / extension · Driveline
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 12.00 mm below the flat plane of the pump intake area. GP1 adds that the projecting member must be filed so as not to create a hazard.
- Aftermarket intake grate · Driveline
Legal, with conditions1 part
Max 2 per side. Max 126 cm each, 153 cm total with two sets. Max 100 mm lateral protrusion, 52 mm vertical channel, 50 mm below the hull side/bottom intersection, 50 mm below the lower bond flange. Minimum 6 mm thick if aftermarket. 501.02.02.04, 501.02.02.05, 501.02.02.06
- Aftermarket sponsons · Hull and handling
Legal, with conditions1 part
The pole and its mounting bracket may be modified or aftermarket if they work as originally designed, the attaching point may be reinforced and the spring changed, and the pole must sit in front of the engine compartment with at least 75 degrees of movement. 501.02.01.07, 501.02.02.10
- Aftermarket handle pole and mounting bracket · Hull and handling
Legal, with conditions1 part
Handlebar, throttle, throttle cable and grips may be modified or aftermarket, with padding at the mounting bracket or on the crossbar if one is fitted. 501.02.02.09
- Aftermarket handlebars, throttle, cable, grips · Hull and handling
Legal, with conditions1 part
The clause first says original switches must be used and then that aftermarket switches and switch housings may be used; housings may be aftermarket and switch positions changed under either reading. 501.02.02.09
- Aftermarket switches and switch housings · Electrical
Legal, with conditions1 part
Replacement bumpers allowed. A soft flexible water-spray deflector may attach to the hull sides or bond flange, not exceeding the perimeter of the original bumpers or the external hull edge measured with a plumb line. SAFETY BUMPERS ARE COMPULSORY in both GP1 classes.
- Replacement bumpers and water-spray deflectors · Hull and handling
Legal, with conditions1 part
Allowed; bypass fittings directed downward and/or rearward. 501.02.03.08
Legal, with conditions1 part
All cooling system valves must be of FIXED OR AUTOMATIC type - thermostats, pressure regulators, solenoids. Manually controlled devices that alter cooling water flow while under way are prohibited in every class, as are electronic water injection systems unless of origin.
Legal1 part
Replaceable-type jets, needle valves and needle valve springs may be changed; choke may be removed provided it creates no additional air intake. 501.02.04.01
Legal1 part
Ducting, support and adapter between flame arrester and carburettor. 501.02.04.01
Legal1 part
Filler cap may be modified or aftermarket if it creates no hazard. 501.02.04.02
- Aftermarket fuel filler cap · Fuel
Legal1 part
CDI unit may be modified or aftermarket; RPM limiter bypassed or eliminated; ignition timing may be changed. OEM charging system required. 501.02.05
- Aftermarket CDI / ignition box (2-stroke) · Ignition
Legal1 part
Aftermarket spark plugs of a different heat rating are allowed in every class that addresses them.
- Aftermarket spark plugs of a different heat rating · Electrical
Legal1 part
Plus quick-turn steering modifications. 501.02.02.09
- Aftermarket steering shaft, holder, handlebar holder, cables · Hull and handling
Legal1 part
Padding and mat kits may be added and custom painting is allowed. Metal components above the bond flange may be polished, shot peened or painted.
- Padding, mat kits and custom paint · Hull and handling
Legal1 part
The original bilge pump may be modified, disconnected or removed and aftermarket bilge draining systems are allowed if no hazard is created. 501.02.02.12
- Aftermarket bilge draining system · Hull and handling
Legal1 part
Cooling system flush kits are allowed in every class that addresses them.
- Engine flush / rinse kit · Cooling
UIM 2026, 302.01, read from the rulebook on 2026-09-08. Read the rule yourself, Ski Juniors GP3.3. Every UIM 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 Juniors GP3.3, UIM class rules”, BaddJet archive, https://baddjetarchive.com/legality/uim/ski-juniors-gp3-3/
Add the date you read it.
57 parts read · 9 permitted, 19 with conditions · 2026 rulebook