Foil-assisted catamarans: a third path between conventional hulls and full hydrofoils
An EnviroCat newbuild delivers up to 50% lower drag than a conventional diesel catamaran of comparable size. Combined with electric propulsion, energy consumption drops by over 80%. For operators that can’t replace their fleet today, our retrofit packages cut cruise-speed drag on existing high-speed catamarans by 14–28%.
This page explains how — and why we made the design choices we did.
Forty years of high-speed catamaran design
EnviroCat is not version 1.0 of foil-assisted catamarans. The hull platform draws on more than four decades of high-speed catamaran naval architecture by our CTO and chief designer, Ola Lilloe-Olsen.
Since the early 1980s, Ola has realised 130+ vessels — high-speed catamarans, electric and hybrid ferries among them — and established Norway’s first private marine test tank as part of that practice. The design choices in EnviroCat reflect this history: which problems are worth solving with foils, which aren’t; what catamaran operators actually need; what happens to a foil at sea state 4 versus sea state 5. The foil is an addition to a working high-speed catamaran, not the design itself. The catamaran behaviour buyers and crews rely on is intact.
Four ways to lift a hull, one we settled on
There are four established approaches to reducing wave-making drag on a fast-water catamaran. Each solves a different problem.
1. Conventional catamaran, no foils. The default. Two slim hulls provide stability and crew comfort. Drag reduction comes only from hull shape — limited at higher speeds, where the planing transition is energy-hungry. Most commercial fast-ferry operators run on conventional cats today. Reference platforms include Brødrene Aa’s carbon-composite hull.
2. Surface effect ships (SES). An air cushion contained by rigid side walls and flexible fore-and-aft seals lifts the vessel partially. A continuous fan pushes air under the hull to maintain the cushion, transferring part of the vessel’s weight from buoyancy to the cushion and reducing wetted surface. Drag reduction can reach 30–50% at design speed. The trade-offs are structural and operational: the fan is a continuous parasitic energy draw that partially offsets the drag saving; the flexible seals are consumables that wear and require regular replacement; cushion stability is sensitive to sea state; SES hulls require custom geometry with integrated side walls (retrofit to a conventional catamaran is not practical); and conventional propulsion is constrained (typically waterjet-driven, with limited options for pods or CPPs). These platforms can work well for protected-water passenger and crew transport where the operating environment matches the technology’s strengths.
3. Full hydrofoils. Vessels like Candela P-12, Artemis EF-12 and EF-24, Vessev VS-9 and VS-12, and Boundary Layer Electra lift the entire hull out of the water. Drag reduction reaches 40–60%. The trade-offs are real: active ride-control is required at all times, strut mechanics are sensitive to debris and wear, the platform is sensitive to weight variation, conventional propulsion (pods, propellers, waterjets) is not compatible with the foil-strut geometry, and retrofit is not possible. These platforms are well suited to new-build, low-sea-state passenger services in protected water. They are less suited to commercial crew and ferry catamarans above 20 metres in open-water service.
4. Foil-assisted catamaran — the EnviroCat approach. A passive lifting foil between the hulls partially raises the vessel — enough to deliver up to 50% lower drag, but the catamaran hulls still carry stability across all degrees of freedom. No active ride-control is required; the foil system cannot fail catastrophically because the hulls remain in the water. Conventional propulsion remains compatible across multiple supplier options — controllable-pitch propellers (Kumera Helseth, Servogear), pod systems (Volvo Penta IPS Electric), or waterjet propulsion. Retrofit on existing catamaran hulls is possible.
We sit in the middle of this landscape — durable, retrofittable drag reduction without active control surfaces, without consumable seals, and without a continuously powered cushion. Full hydrofoils and SES platforms each maximise a particular axis at the cost of complexity and operating constraints; we solve for commercial catamarans in open-water service with conventional-propulsion compatibility and passive safety.
How we arrived at the current foil configuration
The current foil configuration is the fifth in a development sequence begun in 2017. Earlier iterations explored strut-supported foil arrangements at different positions before we converged on the present strut-less between-hull configuration. Each step taught us something specific about the trade-offs between hydrodynamic lift, structural load, foil immersion, and reliability in commercial service.
We didn’t arrive here by accident; we arrived here by working through configurations that didn’t meet the bar first. The detailed design history, the failure-mode analysis from each iteration, and the selection rationale for the current configuration are available to qualified buyers under NDA.
A configurable platform, not a single product
EnviroCat is a platform that adapts to operator and route requirements rather than a fixed vessel with a fixed configuration. The platform is configurable across five axes:
- Vessel size — 15 to 50 metres LOA, across standard models (EC16.5, EC18, EC22, EC34) and Custom variants.
- Propulsion type — fully electric, hybrid, or ICE-powered.
- Propulsion supplier — mechanical propulsion from controllable-pitch propellers (Kumera Helseth, Servogear), pod systems (Volvo Penta IPS Electric), or waterjet propulsion (multiple compatible suppliers); electric drive systems from Brunvoll Mar-El, ZEM, or other compatible suppliers. The platform is propulsion-agnostic at both layers.
- Energy storage architecture — installed battery capacity and configuration sized to route requirements.
- Use case — passenger ferry, crew transfer, pilot, patrol, SAR, ambulance, fire, tourism, excursion, workboat, taxi boat.
The configurability is deliberate. Operators and procurement agencies face distinct route, energy-budget, and regulatory environments. A platform that adapts to those — rather than asking the operator to adapt to the vessel — is a better commercial proposition. For more on how that adaptation actually works in practice, see Approach.
Norwegian heritage in marine electrification
EnviroCat sits at the intersection of two Norwegian leadership areas: high-speed catamaran naval architecture and marine electrification. The team and technology partners are part of this heritage, not adjacent to it.
Norway has deployed more than 120 electric ferries, workboats, and tourism vessels since 2015 — the largest such fleet globally. Road-ferry electrification reached approximately 40% of connections by 2025, reducing annual CO₂ emissions from the road-ferry segment from around 300,000 tonnes in 2015 to approximately 149,000 tonnes in 2025. The platform’s design choices, propulsion architecture, and partner integration draw directly on this body of work:
- Ola Lilloe-Olsen has designed electric and hybrid ferries alongside his broader high-speed catamaran practice over four decades.
- Bjørn Utgård (CEO) has 20+ years in zero-emission marine technology, including design, build, and commercialisation of all-electric vessels and charging infrastructure.
- ZEM — battery systems and electric drive systems; active supplier in Norwegian marine electrification.
- Brunvoll and Brunvoll Mar-El — thrusters and manoeuvring systems (Brunvoll’s traditional product line) and electric drive systems (Brunvoll Mar-El); grounded in extensive Norwegian electric-vessel work.
- Mechanical propulsion partners — Kumera Helseth (controllable-pitch propellers, with collaboration on foil-plus-propulsion hull integration), Servogear (controllable-pitch propellers), and Volvo Penta (IPS Electric pods) have each been active suppliers across the Norwegian electric and high-speed ferry fleet. Waterjet propulsion from multiple suppliers is similarly supported.
This is not a Norwegian-electrification credit list. It is the operational supply chain EnviroCat draws on every day.
Validation, classification, and partners
The current foil configuration has been validated through tank-testing at Stadt Towing Tank in Måløy — one of Northern Europe’s leading independent hydrodynamic facilities — and through CFD analysis run against the tank results. The foil-assisted catamaran solution was selected as one of four entrants in Fremtidens Hurtigbåt, a competitive innovation programme run jointly by the counties of Nordland, Trøndelag, and Vestland to identify zero-emission high-speed ferry designs.
EnviroCat vessels are designed to DNV HSLC notation. Full validation reports, performance curves, and detailed weight breakdowns are available to qualified buyers under NDA.
Technology and validation partners:
| Partner | Role |
|---|---|
| Kumera Helseth | Controllable-pitch propellers; foil-plus-propulsion hull integration; complete vessel designs |
| Servogear | Controllable-pitch propellers |
| Volvo Penta | IPS Electric pods (integrated mechanical and electric) |
| Multiple waterjet suppliers | Waterjet propulsion (selection per operator requirement) |
| Brunvoll Mar-El | Electric drive systems for marine propulsion |
| ZEM | Battery systems and electric drive systems |
| Brunvoll | Thrusters and manoeuvring systems |
| Maritime Engineering | Engineering and integration partner; foil-hydrodynamics specialty via Audun Yrke (inventor and co-founder of Wavefoil AS) |
| Stadt Towing Tank | Hull validation and tank testing |
| DNV | Classification |
Where this platform fits
Three paths from where you are, depending on what you operate today:
You operate diesel catamarans today. Our foil retrofit packages cut cruise-speed drag by 14–28% on existing high-speed catamarans (mid-point estimate 21%). The retrofit service is full-scope: feasibility analysis on your host vessel and route, complete foil-kit production, installation in cooperation with partner yards, and performance monitoring and optimisation post-install. Availability is subject to case-by-case feasibility analysis. [See retrofit offering →]
You are planning a newbuild without electrification yet. Our EnviroCat newbuilds in diesel or hybrid configuration deliver up to 50% lower drag than a conventional diesel catamaran of comparable size, with proportional fuel and emissions savings expected. [See newbuild offering →]
You are ready to electrify. Our foil-assisted electric EnviroCat newbuilds reduce energy consumption by over 80% versus a conventional diesel catamaran of comparable size. [See foil-assisted electric →]
For configurations beyond our standard range (15 to 50 metres), custom design programs are available on request. [See custom →]
Talk to us about your route, duty cycle, and fleet renewal timeline.
[Download the platform technical overview (PDF)] [Book a 30-minute technical briefing]