Castoldi

• Category: marine waterjet propulsion systems and jet tenders
• Founded: 1962
• Based: Albairate, Lombardy, west of Milan
• Site: 18,000 square metres, including 8,000 square metres of production sheds and offices, a test basin and a helicopter landing area
• Waterjets: nine Turbodrive models, from the Turbodrive 224 D.D. to the Turbodrive 600 H.C.T.
• Jet tenders: fourteen models, from the JT 14 to the JT 34 LIMO
• Size range: 14 to 34 feet, roughly 4.3 m to 10.4 m
• Rescue variants: JT 14, JT 18 and JT 19 offered in RB/SOLAS form
• Quality system: ISO 9001 certified
• Class approvals: ABS, BV, DNV, RINA, RMRS and RRR
• Markets: superyachts, coast guard and military
• Published data: Castoldi does not put weights, speeds or prices on its public model pages

The company that made the waterjet work

Castoldi started research into waterjet propulsion in 1962 and describes itself as the innovator of the system. The claim is defensible in the sense that the company was working on jets for small craft when almost nobody else was, and it has stayed on the same problem for more than sixty years. A waterjet takes water in beneath the hull, accelerates it through a pump and pushes it out astern.

The engineering that makes it useful on a tender is the steering and reversing arrangement. Castoldi builds reversible thrust deflectors and a system that can hold vertical neutral thrust independently of pump speed, which means the boat can sit still with the engine running and then move in any direction without a gear change. That is what makes a jet tender easy for a guest to handle alongside.

Albairate

The plant sits at Albairate in Lombardy, west of Milan, on a site of 18,000 square metres with 8,000 square metres of production sheds and offices. There is a water basin for testing on site, which is unusual and says something about how the company develops product. There is also a helicopter landing area, which says something about who visits.

The operation is certified to ISO 9001 and holds approvals from the major classification registers, including ABS, Bureau Veritas, DNV, RINA, the Russian Maritime Register and the Russian River Register. Those approvals exist because the jets go into commercial and naval craft as well as yacht tenders, and they are the reason a builder specifying a Castoldi drive does not have to justify it to a surveyor.

The drive that lets a tender idle among swimmers, usually wearing somebody else's badge.

Why an owner should care about jet drive

The practical case is swimmers. A tender with an exposed propeller cannot safely idle among people in the water, cannot nose onto a sandbar, and cannot be handed to a guest to take to the beach without a conversation. A waterjet removes all three problems, because there is nothing turning outside the hull. This is why so many superyacht tenders are jet driven.

The second case is draft. A jet boat draws less than a shaft or sterndrive boat of the same size and will run into shallow water that would destroy a propeller. The costs are real. A jet is less efficient than a propeller at low speeds, it will ingest weed and plastic bags through the intake grille, and the impeller is a wear item.

The Turbodrive range

Nine Turbodrive models cover the range, from the Turbodrive 224 D.D. at the small end up through the 240 and 284 in both H.C.T. and L.V.T. forms, the 340 H.C., the 400 and 490 H.C.T., and the 600 H.C.T. at the top. These are sold to boatbuilders, so most owners meet a Castoldi drive inside somebody else's tender.

That is the important commercial fact about the company. A Castoldi waterjet may be under a tender built by an Italian, British or Dutch yard, and the badge on the transom is not Castoldi. Owners choosing a tender should ask which drive is fitted, because the drive determines the service parts, the impeller availability and the handling more than the hull does.

The jet tenders

Castoldi also builds complete boats. Fourteen jet tender models run from the JT 14 at about 4.3 m to the JT 34 LIMO at about 10.4 m, taking in the JT 15, 16, 17, 18, 19, 21, 23, 25 and 28 in between. They are rigid inflatable boats with diesel engines and Castoldi's own jet drives, which is an unusual combination in a yacht tender of that size.

Diesel matters aboard. A yacht that runs diesel machinery and does not want petrol on the swim platform can specify a diesel jet tender and avoid a second fuel entirely. The step from a 4.3 m boat to a 10.4 m limousine covers most of what a yacht from 30 m upwards actually needs, and the naming steps through the sizes in single feet, which suggests how closely these boats are matched to garages.

The SOLAS rescue variants

The JT 14, JT 18 and JT 19 are offered in RB/SOLAS form, built as rescue boats to the international convention standard. That is a different product from a guest tender. A SOLAS rescue boat has to be launchable and recoverable in defined sea states, has to self-right or stay stable when swamped, and has to be maintained and inspected on a schedule.

For a large yacht this matters directly, because commercially registered vessels above a certain size are required to carry a compliant rescue boat. Being able to buy that boat from the same maker as the guest tender simplifies training, spares and service. It is also a reminder that Castoldi's engineering is validated in a market where a failure is not an inconvenience.

What Castoldi does not publish

The company publishes no weights, speeds, capacities or prices on its public model pages. Specifications are supplied on request through the yard, the dealer or the boatbuilder. That is normal for a company whose customers are mostly other manufacturers, and it is inconvenient for an owner trying to compare a Castoldi tender with a Williams or a Novurania on a screen.

The practical consequence is that the comparison has to be done through the captain or the build manager. The figures that decide the outcome are lifting weight with fuel aboard, length and beam against the garage, and the number of guests the boat will actually carry. Anyone shortlisting tenders should insist on those three numbers in writing before the decision is made.

Service and parts

The service position is a consequence of the customer base. Because Castoldi drives are fitted by many builders and by commercial and naval operators, jet components and impellers move through an established supply chain, and Italian marine engineers know the product. In the Mediterranean this is about as good as it gets for a specialist drive.

The Caribbean is thinner and the practical answer there is to carry a spare impeller and wear ring aboard. The common in-season faults on any waterjet are intake blockage and impeller damage from ingesting debris, both of which are dealt with locally by a diver or a haul-out. Serious pump work goes back to a specialist.

Against outboards, sterndrives and Williams

For a small tender the comparison is with Williams Jet Tenders, which built its business on petrol jet tenders sized for yacht garages and is specified as standard by many yards. Williams is the volume answer. Castoldi's tenders are heavier, diesel and closer to a working boat, and its real reach is through the drives fitted inside other builders' hulls.

Against an outboard, a jet gives up efficiency and simplicity and buys safety around swimmers and access to shallow water. Against a sterndrive it gives up low-speed thrust and buys the absence of anything vulnerable under the hull. On a yacht where guests swim off the platform and the tender comes and goes all day, that trade usually settles in favour of the jet.

Who it is for: Owners who want a diesel tender with nothing turning under the hull, and anyone specifying a tender who should be asking which waterjet is inside it.