Official UIM Unlimited Displacement Rule

Rule No. 904 for the Unlimited Displacement Class was passed at the UIM General Assembly in Riccione Italy on the 26th October 2009 for Circuit Racing, this reads as follows.  If you have any questions with this rule please feel free to contact us to clarify.

Alternatively you may download the pdf version by clicking here.



[1] Classes:

RD ∞ cylinder capacity of motor to infinity

(More classes may be added, depending on Rules being accepted)



The hull shall be displacement or monoplane type in which the continuity of the portion of the hull immersed at rest. Hulls are permitted to be either mono V hulls or flat bottom hulls.

Cockpits [rule 509].All new hulls built after 1st January 2011 must be fitted with a reinforced cockpit with a minimum strength of 5000 newtons.

All existing hulls must have a reinforced cockpit to the above specification fitted by 1st. January 2011.

In racing trim with the driver on board shall not be interrupted longitudinally or transversely by any form of break, step or device of construction or hydrofoil, that would provide multiple planning surfaces.

The term hull shall include all additions and attachments below the waterline with the exception of the shaft, strut, propeller, rudder, fin and such that are usual and necessary. Cavitation plate, trim tabs and after planes that are fixed or adjustable whilst underway shall be permitted.

Lap strake or reverse lap strake construction may be used provided the immersed portion of the strakes (planks) be approximately parallel with the centre line of the hull and the depth of the strake (plank) be no greater than 35mm.


Planning strakes (planks) unless continuing to the tuck (transom) must finish on an angle being not less than 450mm from the point of commencement of the angle to flush with the hull bottom and the angles not to be concave to the hull bottom.

Non-trip chines with a rise of not less than 75mm in 300mm, vertical sided keels and skid fins shall be allowed.

At the option of the owner or the builder, that point where the planking meets the nontrip chine can be rounded or left square regardless of the thickness of the planking.

The depth (thickness) of the strake (plank) is to be taken by stretching a wire or similar material around the bottom of the bull, at right angles to the centre-line, on the point being measured.

The depth (thickness) is to be measured are right angles to the hull surface and this depth must not be more than 35mm at any point.


Only Infinity class hulls fitted with forced induction (blown/supercharged) engines are permitted to use wings.

Only single or dual plane wings are permitted.

All wings must be mounted directly to the engine or the engine bearers

The wing including the side fins/spill plates should be a maximum of 450mm higher than the highest point of the boat or engine and must not extend beyond the extremities of the hull at the mounting point.

The suitability and adequacy of the wing is the responsibility of the owner, who should be satisfied that it is competently designed, manufactured and fitted so as to remain fixed and operational at high speeds.

The wing may be adjustable while the boat is in motion.


CLASS Weight Length Reinforced Cockpit

RD ∞ TBA 5.1 M Mandatory 1st January 2011 [5,000N]

The length must be measured between perpendiculars at the foremost and atmost rigid part of the hull.

Any extending parts such as rubbing strakes, fenders, stabilising or trim tabs, rudder, skeg or cavitation plate, are not to be included in the length measurement.

The minimum weights mentioned here are the weight of a complete rig weighed directly after the race including driver, personal safety equipment, residual fuel but without residual water.



The motor is free.

The motor must be fixed inside the hull.

The power transmission train must pass through the structure of the hull.

All modifications are allowed.

All propelling forces must be directed in and against the water.

An electric starter and battery must be on board.

The transmission is free.


The type of fuel will be Gasoline or Methanol.

Nitrous oxide will be permitted will the exception of Nitro Methane and any other chemical supercharging.

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