Jet Tenders

A jet tender uses a waterjet instead of a propeller, spanning from the 2.85m Williams DieselJet to 14m Castoldi platforms. No exposed prop and a flat underbelly make it the default for tight, height-constrained garages under 60m.

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A jet tender uses a waterjet drive instead of a propeller. The category covers a wide spread, from the compact Williams DieselJet 285 used as a sub-3m garage tender on yachts down to 35m, through to 8m+ jet-driven RIBs running as guest tenders on 80m flagships. The shared property is the drive: water drawn through an inlet under the hull, accelerated through a pump, expelled through a steerable nozzle.

Why operators choose jet

Three reasons dominate:

  • No exposed prop. The intake sits flush under the hull. Safer around swimmers, water-toy operations, and beach landings; tolerant of shallow water that would foul a propeller drive.
  • Manoeuvrability. Reverse-bucket steering gives almost on-the-spot turning at low speed and clean docking control once the helmsman has learned the boat.
  • Garage compatibility. The flat underbelly and absence of running gear below the keel line keeps depth to a minimum, which matters in the height-constrained tender garages on most superyachts under 60m.

Where jet drives have trade-offs

  • Fuel efficiency. Jets are typically less efficient than a sterndrive or shaft-driven boat at cruise, especially in the diesel-jet sizes. The hit is biggest at displacement speeds and shrinks at planing speeds.
  • Low-speed control in cross-wind. A jet has no thrust below the helm-input threshold; in tight marina manoeuvres in a cross-wind, sterndrive owners often prefer the always-on prop bite.
  • Maintenance. Jet impellers are vulnerable to debris ingestion (rope, weed, plastic). Annual inspection is mandatory; replacement is not free.

Categories within jet tenders

Three sub-categories show up in superyacht briefs:

  1. Williams DieselJet range. Compact garage tenders, 2.85m to 7.5m. The volume player in the segment; almost every yacht garage built since 2010 has a Williams in mind. Diesel-powered (Yanmar 4LV most commonly), low fire risk, easy yard-side fuelling.
  2. Castoldi Jet range. Italian-built, larger than Williams (5m to 14m), often specified as guest limousines or beach landers with the Castoldi 320 jet.
  3. Custom RIB or hard-bottom jet builds. SACS, Pirelli, Novamarine, ZAR, and increasingly Brabus building 8m to 12m guest tenders with twin or triple Mercury jet outboards. These are sport tenders dressed for chase duty.

How to spec a jet tender

Three questions front-load the decision:

  • What's the garage envelope? Length, beam, and headroom. Williams sizes most commonly map to 30m to 50m yachts; the larger Castoldi jets to 50m+. Beyond 7m the jet category narrows quickly.
  • Diesel or petrol? Diesel for compliance with mothership fuel storage rules (almost universal above ~50m); petrol acceptable on smaller yachts where fire-safety regulations are looser.
  • Single or twin? Single jet works for the smaller Williams-class boats. Twin jets, more controllable for guest-facing duty, are standard on the larger Castoldi and custom platforms.

Where it sits against alternatives

If the brief is "smallest possible tender that fits a tight garage and runs safely around the swim platform", a Williams DieselJet wins almost every time. If the brief is "guest day boat with serious range and a more refined ride", a sterndrive or outboard platform usually wins on fuel and on cruise comfort. The tender vs chase boat comparison covers the broader category split.

See also

Sources

  1. Williams official site — Williams
  2. Castoldi official site — Castoldi
  3. Brabus official site — Brabus
  4. Novamarine official site — Novamarine
  5. Pirelli official site — Pirelli
  6. Strider 10 | Sacs Marine — SACS (retrieved May 2026)
  7. Rebel 40, Sacs Marine — SACS (retrieved May 2026)
  8. Strider 13, Sacs Marine — SACS (retrieved May 2026)
Why do so many yachts under 60m end up with a jet tender?
Because a waterjet keeps depth to a minimum. The intake sits flush under the hull, so there is no running gear below the keel line and the flat underbelly slots into the height-constrained garages found on most superyachts under 60m. The same absence of an exposed prop makes the boat safer around swimmers, water-toy operations and beach landings, and more tolerant of shallow water that would foul a propeller drive. Reverse-bucket steering adds near on-the-spot turning at low speed.
What are the real downsides of a waterjet compared with a sterndrive?
Three: fuel, low-speed bite and impeller maintenance. Jets are typically less efficient than a sterndrive or shaft-driven boat at cruise, with the biggest hit at displacement speeds and a smaller one once planing. A jet also produces no thrust below the helm-input threshold, so in tight marina manoeuvres in a cross-wind sterndrive owners often prefer the always-on prop bite. Impellers are vulnerable to rope, weed and plastic ingestion; annual inspection is mandatory and replacement is not free.
Should we specify diesel or petrol for the garage tender?
Diesel, almost universally, once you are above roughly 50m. Diesel keeps the tender compliant with mothership fuel storage rules and carries low fire risk, with easy yard-side fuelling. The Williams DieselJet range is built around that logic, most commonly on Yanmar 4LV power. Petrol remains acceptable on smaller yachts where fire-safety regulations are looser. It is one of three questions we front-load, alongside the garage envelope and whether the boat runs single or twin jets.
Where does Williams stop and Castoldi start on size?
Williams covers 2.85m to 7.5m, Castoldi 5m to 14m. Williams is the volume player in compact garage tenders, and sizes map most commonly to 30m to 50m yachts; almost every yacht garage built since 2010 has a Williams in mind. The larger Castoldi jets, often with the Castoldi 320 jet, suit 50m+ programmes and are frequently specified as guest limousines or beach landers. Beyond 7m the jet category narrows quickly.
Do we need twin jets, or will a single do?
Single jet works for the smaller Williams-class boats; twin jets are standard on the larger Castoldi and custom platforms. The argument for twin is controllability, which matters when the boat is guest-facing rather than a utility run. Above that, the custom RIB and hard-bottom segment, SACS, Pirelli, Novamarine, ZAR and increasingly Brabus, builds 8m to 12m guest tenders on twin or triple Mercury jet outboards. Those are sport tenders dressed for chase duty.

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