Some projects demonstrate what a shipyard can build. Others demonstrate what a shipyard can engineer.

This project represents one of Highmark Marine Group's most comprehensive vessel modification programs to date—a complete in-house engineering, structural, mechanical, and systems integration project that transformed an already capable aluminum landing craft into a faster, more efficient, and more versatile commercial vessel.

From the initial engineering calculations through final sea trials, every aspect of this project was designed, engineered, fabricated, installed, and commissioned by the Highmark Marine Group team. The result was a vessel that not only met its projected performance targets but exceeded many of our original expectations during sea trials.

The project began with a commercial aluminum landing craft featuring:

• 45.5-foot hull length
• 66-foot overall length
• 16-foot beam
• Semi-V aluminum hull
• Twin Caterpillar C12 diesel engines (1,400 HP total)
• Twin Arneson ASD-11 Surface Drives
• 
  

• Cruise Speed: 24 knots
• Engine RPM: 1,950 RPM
• Engine Load: Approximately 90%
• Fuel Burn: 32–34 gallons per hour per engine
• Top Speed: 30 knots

Although the vessel performed well, the owner wanted significantly greater operational capability without replacing the existing propulsion package.

The owner's vision extended well beyond a simple hull modification.

Primary project goals included:

• Increase internal machinery space
• Improve serviceability
• Add crew accommodations and dive support capability
• Increase fuel capacity and operating range
• Reduce regulatory vessel tonnage through admeasurement
• Improve cruise efficiency
• Increase overall vessel performance
• Retain the existing propulsion system

Achieving all of these objectives simultaneously required careful engineering, structural analysis, and complete integration between hull design and machinery systems.

Unlike projects built from customer-supplied drawings, this modification was engineered entirely in-house.

Highmark Marine Group performed:

• Structural engineering
• Hull modification design
• Weight and balance analysis
• Draft predictions
• Buoyancy calculations
• Machinery layout
• Systems integration
• Construction planning
• Fabrication detailing
• Final commissioning

Every major engineering prediction—including vessel trim, draft, weight distribution, and expected performance—closely matched the finished vessel during launch and sea trials.

The most significant structural change was a five-foot extension of the engine room and aft hull.

This modification was carefully engineered to become an integral part of the vessel rather than simply adding length. The additional hull volume increased buoyancy, improved weight distribution, and created valuable interior volume while maintaining the vessel's structural integrity.

The project also included:

• Complete structural aluminum fabrication
• Hull framing modifications
• New engine room construction
• Machinery space expansion
• Dive suite integration
• Crew accommodations
• Vessel admeasurement reducing regulatory tonnage to 14 tons

While many projects rely on larger engines to improve performance, this vessel retained its original propulsion package.

Existing machinery retained:

• Twin Caterpillar C12 main engines
• Twin Disc reduction gears
• Twin Arneson ASD-11 surface drives

New systems included:

• Additional 200 gallons of fuel capacity, increasing total fuel capacity to 1,100 gallons
• Engine-driven high-pressure breathing air compressor
• Dedicated diesel-powered hydraulic power unit replacing the original engine PTO hydraulic system
• Expanded machinery space for greatly improved serviceability
• New dive support facilities
• Crew accommodations
• Zipwake interceptor trim control system

Following completion, the vessel underwent extensive sea trials.

The engineering objectives were achieved, and overall performance exceeded expectations.

PerformanceResultCruise Speed24–26 knotsCruise RPM1,850 RPMEngine Load80–83%Fuel Burn25–27 GPH per engineTop Speed36 knots

Additional sea trials demonstrated the vessel maintained excellent performance under increased displacement.

With approximately 400 gallons of fuel and approximately 1,000 pounds of equipment positioned on the bow, the vessel cruised comfortably at 25–26 knots while maintaining only 82–85% engine load.

An additional 400 gallons of fuel—bringing total onboard fuel to approximately 800 gallons during testing—resulted in less than one knot reduction in cruise speed, demonstrating the effectiveness of the new hull geometry and increased buoyancy.

The vessel now transitions onto plane at approximately 1,800 RPM without requiring full-throttle acceleration, improving drivability and reducing engine loading during acceleration.

OriginalModifiedCruise RPM1,9501,850Cruise Load~90%80–83%Cruise Fuel Burn32–34 GPH/engine25–27 GPH/engineFuel Capacity900 gallons1,100 gallonsTop Speed30 knots36 knots

The completed vessel now carries more fuel, offers significantly greater interior volume, provides improved crew functionality, and delivers substantially better performance while utilizing the original propulsion package.

This project highlights what distinguishes Highmark Marine Group.

Every phase of this project—from concept development through engineering, structural fabrication, machinery installation, systems integration, coatings, launch, and sea trials—was completed by our own team.

Rather than relying on outside engineering firms or multiple subcontractors, Highmark Marine Group managed the project from initial concept through final commissioning, ensuring every system worked together as a cohesive design.

This integrated approach allows us to solve complex marine challenges while delivering practical, reliable, and high-performing vessels tailored to our customers' operational needs.

Whether extending an existing hull, repowering a commercial vessel, modernizing machinery spaces, or completing a full custom aluminum build, Highmark Marine Group delivers turnkey marine solutions backed by practical engineering, skilled craftsmanship, and proven results.

This landing craft project demonstrates what is possible when engineering, fabrication, and operational experience come together under one roof.

If you're considering a vessel modification, repower, structural conversion, or custom marine fabrication project, we'd welcome the opportunity to discuss how Highmark Marine Group can help bring your vision to life.