Leech 38 ‘TJ’ – Twin STEYR SE286E40 New-Build

A First for a Dan Leech Catamaran

TJ is a Leech 38 foil-assisted power catamaran designed by New Zealand naval architect Dan Leech and built as a high-specification recreational vessel for owners James and John.

The project represented something particularly significant: TJ was the first Dan Leech-designed power catamaran to be built with inboard diesel propulsion, with previous vessels across the Leech range using outboard power.

James and John had originally been considering a pair of approximately 190 hp diesel engines, but after seeing STEYR engines installed in a similar Ron Given-designed T9 catamaran, they approached Marine Power Systems to discuss whether STEYR could provide a suitable alternative.

From those initial conversations, we became closely involved with the project, working with Dan Leech and our specialist suppliers to develop a complete propulsion package for a vessel where there was no previous inboard installation to follow.

The result would ultimately become one of the most technically involved new-build projects we have undertaken.

Selecting the Twin STEYR SE286E40 Package

One of the major considerations when selecting engines for the Leech 38 was the extremely narrow hull design. Engine width, overall dimensions and weight were therefore critical, making the compact STEYR monoblock diesel particularly well suited to the application.

We initially proposed the STEYR SE236E40, however the 279 hp SE286E40 offered several advantages while retaining essentially the same physical dimensions and weight as the lower-output STEYR options.

With twin SE286E40 engines providing 558 hp combined, there was considerably more power available than the vessel required for normal cruising. Importantly, this did not come with the normal weight or packaging penalty associated with installing larger engines.

The additional power also allowed the propulsion system to be matched with a larger, more heavily loaded propeller. At any given cruise speed, the SE286E40 could therefore deliver the required propulsion power at a lower engine rpm than the smaller engine package.

For a lightweight cruising catamaran, this provided a useful combination of performance reserve, relaxed cruising rpm and the opportunity to optimise propulsive efficiency without compromising the narrow hull design.

Each engine was paired with a ZF 68A down-angle marine transmission and Marex electronic engine controls.

Developing a First-of-Class Propulsion System

Because TJ was the first inboard-powered Dan Leech catamaran, there was no existing installation from which the complete machinery and auxiliary systems could be replicated.

Apart from the initial driveline arrangement, which we helped develop, many of the propulsion and vessel systems had to be specified and engineered as the project progressed.

Marine Power Systems worked with the designer and our suppliers on the engine installation, transmissions, shaftlines, propellers, shaft seals, couplings, P-brackets, fuel systems, seawater systems, exhausts, electronic controls, steering, charging systems, hot-water systems and helm layout.

Our previous experience working with catamarans over the preceding decade proved particularly valuable. We had previously been involved with vessels from designers including Roger Hill, Ron Given and Voodoo, giving our team a strong practical understanding of the challenges involved in packaging propulsion and auxiliary systems into narrow, lightweight multihull designs.

That experience allowed us to take what was effectively a largely blank sheet and turn it into a complete, practical propulsion system.

Shaftlines, Propellers and Steering

TJ uses a conventional twin-shaft propulsion arrangement.

The 2-inch shaftlines were manufactured by Chatfield Engineering, with the driveline calculations developed in conjunction with Marine Power Systems and our specialist suppliers. The completed installation uses 21.5-inch diameter propellers, manufactured by Briski Propellers.

The shaftline installation was carried out by our team in August 2024, well ahead of the final engine installation. This required accurate positioning of the shafting, bearings, P-brackets, seals and engine driveline components to ensure the complete system could later be aligned correctly.

Steering presented another important part of the installation. Hy-Drive designed and supplied the hydraulic steering system, including hydraulic power assistance for the twin-rudder arrangement. Marine Power Systems installed the steering components and integrated them into the finished vessel.

During final commissioning, the propellers were found to be very slightly over-pitched. They were re-pitched from 25 inches to 24.75 inches of pitch, allowing the engines to achieve their designated maximum operating rpm.

The final propeller specification was therefore approximately 21.5 × 24.75 inches.

Complete Systems Integration

Our involvement extended well beyond the engines and shaftlines.

Marine Power Systems supplied and installed virtually all of the equipment associated with the propulsion, control and steering systems. This included the engines and transmissions, electronic engine controls, fuel supply systems, seawater cooling, exhaust systems, steering, rudders and helm instrumentation.

STEYR CAN displays were installed at the vessel's single helm station, together with the Marex electronic controls.

The electrical system also presented an unusual requirement. TJ was designed with a substantial lithium-ion house electrical system, requiring considerably more charging capacity than the standard engine alternators were intended to provide.

Working with our colleagues at STEYR Australia, we developed a secondary alternator installation for each engine. Each SE286E40 was fitted with an additional 170-amp, 12-volt alternator, giving the vessel a high-capacity engine-driven charging solution without compromising the standard STEYR electrical system.

Two hot-water cylinders were also incorporated into the installation, with one heated from the coolant circuit of each engine.

Bringing all of these systems together in the confined machinery spaces of a 38-foot performance catamaran required careful planning throughout the build.

Completing and Commissioning TJ

The project ultimately spanned approximately two and a half years from the initial planning stages through to launch and final commissioning.

During the build, the vessel was relocated from Kopu to Pine Harbour Boat Builders, who completed the boat to an exceptionally high standard. Pine Harbour Painters carried out the fairing and paintwork, producing an equally impressive finish.

The relocation created an additional logistical challenge for our team. Much of the remaining installation work now had to be completed well away from our Kopu workshop, requiring technicians, tooling, components and equipment to be transported between Kopu and Pine Harbour as the build progressed.

The engines were finally installed and aligned during late 2025, followed by completion of the auxiliary systems, controls, steering and helm installation.

TJ was launched in March 2026, allowing final engine commissioning, driveline checks and sea trials to begin.

James and John were heavily involved throughout the project and were a pleasure to work with. Their patience and understanding throughout what became a particularly demanding build contributed greatly to achieving the finished result.

Sea Trials and Final Performance

Sea trials confirmed both the performance of the finished vessel and the advantages of matching the lightweight Leech hull with the compact twin STEYR package.

TJ's foil-assisted design incorporates a wing between the hulls which generates lift as vessel speed increases. This reduces the effective load carried by the hulls and assists both cruising performance and efficiency.

The final performance figures were:

The figures show a particularly economical cruise range around 2500–2750 rpm, where TJ achieves approximately 16.4–18.4 knots while consuming only 2.37–2.38 litres per nautical mile combined.

At wide-open throttle, the twin SE286E40s reached their specified 4000 rpm, confirming the final propeller loading following the small pitch adjustment carried out during commissioning.

TJ was a challenging project and one that required a considerable amount of collaboration, engineering and problem-solving over its two-and-a-half-year duration. As the first inboard-powered Dan Leech catamaran, there was no established template to follow.

The finished vessel is something that Marine Power Systems, the owners and everyone involved in the project can be extremely proud of — and a strong demonstration of what can be achieved when good design, specialist suppliers and practical marine engineering experience are brought together.

Related Diesel Inboard Projects:

• Leech 38 New-Build with Twin STEYR Inboards
• AMF Repower with FPT N67
• Marlborough Launch Repower with VOLVO D4-230/DPH
• Rayglass 730 Repower with STEYR
• Bladerunner Repower with twin STEYR
• Mustang 3200 Repower with twin STEYR
• Repower Centre
• View all Projects