What makes the Castoldi waterjet drives different from all the other ones on the market ? Exclusive features and benefits.

Much more than simple pumps, they are complete, integrated marine propulsion systems


Integrated gear box:

The integrated gearbox with its wide range of transmission ratio options (No. 17 to N. 25 depending on the waterjet drive model) is the ultimate solution for engine coupling system with multiple advantages at one stroke:

A very fine r.p.m. matching for every selected engine. This means full power absorption without over- or under-loading the engine regardless of boat speed, resulting in extended engine life.

Less weight: The integrated Castoldi gearbox is very light and simple as it is contained in the waterjet casing. It does not require an oil heat exchanger because its lubrication oil is cooled through the waterjet surface contact with the surrounding water. Therefore, the propulsion system weight is lower, compared to that of competitors, where marine transmissions must be added to the engine.

The use of a single unique stainless steel cast impeller, designed with the best geometry ever tested, without the constraints of having to modify it for adaptation to the engine. The impeller has optimized efficiency and cavitation resistance under any operating conditions and meets high standards of quality production processes.

The lifting of the input flange allows for a shorter and better-aligned cardan shaft without the need to trim the unit, allowing a drastic reduction in the engine room length. This is a clear advantage, given that long transmissions and forward engine installations may reduce the top speed due to moving the boat’s centre of gravity forward.

The lowering of the impeller shaft and, consequently the centre of thrust, results in better manoeuvrability and boat running stability; moreover this allows the design of a flat, straight duct enabling the water stream to flow smoothly with minimum hydrodynamic losses at high speed.

The reduction of the propulsion package weight and consequentely of the boat resistance, as the marine transmission is eliminated. The consequent reduction of overall costs.

Hydraulic pump:

Directly splined to the input shaft, thus avoiding any vulnerable belts.


The Castoldi impeller is a true axial inducer type design and is recognized as having the best efficiency, cavitation resistance and lowest weight compared to any other type of pump.

It operates on a volume system with high flow rate and low pressure.

Because of its volume design, increased blade tip clearance due to wear, does not significantly compromise its efficiency. This can be contrasted to what happens to mixed flow impellers, operating with low flow rate and high pressure, which are much more vulnerable to this type of clearance issue, leading to fast and dramatic speed loss.

The lower number of impeller and stator blades allows an easier transmission and discharge of any ingested debris or weeds.

The impeller which, due to the integrated gearbox, is free from direct engine matching constraints and from the limited available ratios of commercial marine transmissions is available in one unique geometry which is the most efficient, as experimentally determined in the Castoldi water impeller tunnel and by the Castoldi laboratory boats.

Being unique, it is manufactured with the highest quality materials in micro-casting systems with fully balanced blades. This is why it has robust mechanics and strong corrosion/erosion resistance.

Being unique it is always available in stock at a fixed price.

Impeller rubber damper:

This item damps vibrations if any transitory cavitation occurs at the impeller. Because this device has no shaft bearing function, it can withstand a large degree of wear without affecting the waterjet integrity. In contrast, water lubricated tail seals installed on competitor waterjets, with impeller shaft bearing functions, can generate vibrations to the impeller shaft as it becomes worn by repeated use in sandy or muddy waters.

These vibrations can be even transferred to shafts, gearboxes, engines and hulls causing severe damage.

Disconnecting multi-disc hydraulic clutch (H.C. range):

This light weight and highly useful device enables full connection and disconnection of the waterjet to and from the main power source, whilst the engine is idling. Particularly useful in engine warm-up and control checks, it can be invaluable in operational circumstances requiring several daily boat stops while keeping the boat at a perfect standstill without ingesting debris or sand in dirty or shallow waters and without jet turbulence.

In conjunction with the movable inlet protection grid, it allows the quickest and most efficient cleaning operation of the waterjet intake.

It is operated by an electric control via an on-off switch.

All bearings oil lubricated:

All the bearings are lubricated by the same gearbox oil. They never come into contact with seawater and are sized for several thousand hours of life.

Input shaft and impeller shaft:

The integrated gear box allows the input shaft to be located at almost the same level as the engine shaft, allowing the cardan shaft to be shorter and to work in more favourable conditions. This enables the positioning of the impeller shaft and, thus the whole waterjet unit, to be horizontal (0°) so as to prevent trim problems caused by strong vertical thrust and allowing optimized exploitation of the created thrust.

The impeller shaft rotates safely inside the fin oil chamber; and is thus perfectly protected from any debris that might enter the duct and entwine around it.

Main water inlet:

The optimized Castoldi water intake is positioned very close to the transom. This prevents aeration in rough sea conditions and in fast operations and also increases performance by recovering the boundary layer stream.


This unique patented device provides an auxiliary water flow by-pass to the main water intake allowing an increase in the power operational range and thrust on low speed heavy boats, as well as a take-off improvement for middle speed heavy boats.

It never affects the full speed efficiency and can be easily retrofitted.

Movable protection grid on water intake:

The inlet grid protects the water intake from the suction of floating debris and performs self-cleaning operations by rejecting the same through the shift opening of the flush mounted hydrodinamically profiled set of bars. The helmsman can activate the system, when the pressure gauge indicates a pressure drop in the waterjet duct.

The flush mounted grid bars have a smooth hydrodynamic profile which controls water flow with minimal losses.

This is absolutely the most efficient anti-clogging system as it prevents debris from entering the waterjet duct rejecting it with a quick, simple operation.

Clear-Duct superior unclogging system:

The waterjet duct and intake cleaning system are assured through the synchronized simultaneous electrically controlled operations of impeller rotation reversing and the intake grid opening. This generates a back flushing, which is ejected through the water intake without any obstruction caused by the grid bars.

The whole operation is feasible using special parts, all included in the Castoldi integrated gearbox.

Full protection against marine corrosion:

The whole unit is protected by a hard anodizing treatment, plating all light-alloy components with 60 microns thickness of aluminum oxide (ceramic), three layers of special paint and cathodic protection by zinc anodes.

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