Castoldi

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.

What the jet buys, and what it costs below 25 knots

The case for the jet is swimmers and draught, and both hold up. Castoldi describes the arrangement as eliminating all under keel protrusions, which is what lets a tender idle among people in the water, nose onto a sandbar and be handed to a guest for the run ashore. Thrust is set by the bucket rather than by a gearbox, so the boat holds station with the impeller still gripping the water and then moves in any direction without a shift. That is the handling a captain notices in the first ten minutes.

The cost lands exactly where a tender spends most of its life. Wartsila puts the crossover at 25 knots to 30 knots, above which a waterjet can beat a conventional propeller and below which it does not. A tender making five minute hops around an anchorage at displacement speed is working in the worst part of that curve, and the season's fuel figure shows it. A sterndrive of the same power will out-thrust it at low speed, and because astern thrust comes from deflecting the jet rather than reversing a propeller, it will also hold a heading better going backwards in a crosswind.

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.

Dry weight, and the crane that has to lift it

Castoldi publishes a complete weight ladder on its range page, and it is the first number to put against the yacht's deck plan. Dry weight runs from 790 kg for the Jet Tender 14 at 4.28 m, through 1,270 kg for the 19 and 1,580 kg for the 21 at 6.30 m, to between 3,740 kg and 4,100 kg for the 34 LIMO depending on the engine pair. A 4.28 m boat at 790 kg dry is heavy for its length, and the diesel engine and the jet unit are why.

Dry weight is not lifting weight, and the gap between them is where davits get specified wrong. A Jet Tender 21 carries 155 l of fuel, roughly 130 kg of diesel at a nominal 0.84 kg per litre, before water, ground tackle, fenders or the lifting frame. A crane rated at 1,600 kg safe working load does not lift a 1,580 kg boat with a full tank. The figure that belongs in the specification is dry weight plus fuel plus the sling arrangement, confirmed by the builder for the boat as fitted, and it should be settled before the passerelle crane or the garage davit is ordered.

Parts, and who actually holds them

Castoldi builds at Albairate and sells through distributors rather than through a published service network. The company shows a network map and invites distributor enquiries at a dedicated address, but it lists no service points by country, so the question to answer before signing is which named business holds impellers and wear rings for that specific drive in the cruising area. The one firm expansion the company has announced is Castoldi USA Inc. in Seattle, set up in October 2022 to handle American sales and after-sales.

In the Mediterranean the answer is usually an Italian marine engineer and a courier out of Lombardy, which is quick in June and slower in the middle of August when Italian industry takes its holiday, which is also the fortnight the tender is running hardest. The parts worth carrying aboard are an impeller and a wear ring for the fitted drive, because those are what an ingestion event damages and what a diver or a short haul-out can change. A Turbodrive 240 H.C.T. is 130 kg dry complete, which is a lift and a workshop rather than a pontoon and an afternoon.

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.

Weed, sand and what the crew does about it

Every waterjet shares one failure mode. The intake is an opening in the bottom of the boat, and sooner or later it takes in weed, a plastic bag, a trailing line or a load of sand off a beach, at which point thrust falls away and the tender is unusable until it is cleared. Castoldi fits a movable grid at the duct water inlet on its drives to keep debris out in the first place.

What matters more is the drill after something gets past the grid. The Clear-Duct system reverses the impeller and opens the intake grid together, back-flushing the duct from the helm, and it is not reserved for the large commercial units: the Turbodrive 240 H.C.T. fitted to a Jet Tender 21 carries it. The consequence for a crew is that routine clearance is a lever at the console rather than somebody in the water with a knife, and only a blockage that survives a back-flush needs a diver. In a weedy anchorage that is worth more than a knot of top speed.

Price, lead time and the three numbers to get in writing

Prices and lead times are the real omission. Castoldi publishes neither, dealers quote on request, and the specialist tender brokers list every current model as built to order with no figure attached. Brokerage asking prices for used boats cover a decade of model years across a wide band and are no guide to a new hull or a refit replacement. Cost cannot be shortlisted from the websites at all, which is an argument for making the enquiry before the garage dimensions are frozen.

Three numbers decide the outcome and all three should come back in writing: lifting weight for the boat as actually fitted, length and beam against the garage opening and its door, and the guest number the boat will really carry. The published capacities are CE design category figures, 12 people on a Jet Tender 21 and 16 on a 25, which is not the number who will sit in one with towels, a cooler and a crew member driving. The drive model belongs in the same document, because it sets the spares list for the next ten years.

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.