Hydrofoil Paddlewheel Catamaran Concept: Lift, Power, and Performance Analysis for a 60 Foot Electric Vessel

A hybrid propulsion concept combines paddlewheels for low-speed efficiency with hydrofoils for high-speed lift. This article evaluates whether a 20,000 lb, ultra-slender catamaran can sustain hydrofoil operation at 20 knots using 4 ft by 2 ft foils and 80 total horsepower, and explains where physics supports the idea and where it imposes hard limits.

Concept Overview

The proposed vessel is a 60 foot long by 30 foot wide power catamaran with very slender hulls, each measuring approximately 2 feet in width to minimize wetted surface and wave-making drag. At each of the four corners of the catamaran is a modular propulsion unit consisting of:

• A 12 foot diameter paddlewheel driven by a 10 HP electric motor for low-speed operation.

• One paddle per wheel shaped as a hydrofoil, measuring 2 feet in chord and 4 feet in span.

• Two 5 HP electric motors with propellers mounted on the hydrofoil paddle for propulsion in hydrofoil mode.

Total installed power is 80 HP. The design intent is to operate in paddlewheel mode at 5 knots and transition to hydrofoil mode at 20 knots, with the hydrofoils providing lift and the foil-mounted propellers providing thrust.

Hydrofoil Geometry and Lift Capability

Each hydrofoil paddle has:

• Chord: 2 feet

• Span: 4 feet

• Area: 8 square feet, equivalent to 0.743 square meters

• Aspect ratio: span squared divided by area, equal to 2.0

This is a low aspect ratio foil, which can generate substantial lift but incurs relatively high induced drag.

At 20 knots, the vessel speed is 10.29 meters per second. Using seawater density of 1025 kilograms per cubic meter, the dynamic pressure is approximately 54,000 newtons per square meter.

To support the full vessel weight of 20,000 lb using four foils, each foil must carry 5,000 lb of lift, equivalent to about 22,240 newtons.

The required lift coefficient per foil is calculated as:

Lift coefficient equals lift divided by dynamic pressure times foil area

This results in a required lift coefficient of approximately 0.55 per foil, which is a realistic and controllable operating point for an optimized hydrofoil section operating below stall.

At this condition, each foil is capable of producing the required lift at 20 knots.

Induced Drag and Power Requirement

While lift capability is sufficient, the dominant limiting factor is induced drag due to the low aspect ratio.

Using the standard induced drag relation:

Induced drag coefficient equals lift coefficient squared divided by pi times aspect ratio times efficiency factor

With:

• Lift coefficient of 0.55

• Aspect ratio of 2.0

• Efficiency factor of 0.8

The induced drag coefficient is approximately 0.060.

The induced drag force per foil is then:

Induced drag equals dynamic pressure times foil area times induced drag coefficient

This yields approximately 2,440 newtons, or about 550 lb of drag per foil.

Across four foils, total induced drag is roughly 2,200 lb.

The power required to overcome this drag at 20 knots is:

Power equals force times velocity

This results in approximately 100,000 watts, or about 135 horsepower, required solely to overcome induced drag and sustain lift.

This number excludes:

• Foil profile drag

• Strut and mounting drag

• Motor pod and propeller hub drag

• Propulsive inefficiencies

• Residual hull drag in real sea states

As a result, the true installed power required for full hydrofoil flight at 20 knots would be substantially higher than 135 HP.

Performance Implications

Low-Speed Operation (5 knots)

At 5 knots, hydrofoil lift is minimal and induced drag is small. Paddlewheel propulsion is well-suited to this regime and offers:

• Good thrust at low speed

• Debris tolerance

• Excellent maneuverability

• High thrust per unit power in displacement mode

This operating point is well within the capability of the installed 40 HP allocated to paddlewheels.

High-Speed Operation (20 knots)

At 20 knots, the foils can theoretically lift the vessel, but the induced drag power alone exceeds the total installed power of 80 HP.

Therefore:

• Sustained full hydrofoil flight at 20 knots is not achievable with the current foil span and power level.

• Partial lift assistance is feasible and likely beneficial.

• A lift fraction of 20 to 40 percent could meaningfully reduce hull drag and wake while remaining within the available power budget.

Advantages of the Concept

1. Dual-mode propulsion

Efficient low-speed paddle operation combined with lift-assisted higher-speed operation.

2. Very low displacement

A 20,000 lb, 60 foot catamaran with 2 foot hulls is exceptionally slender and hydrodynamically efficient.

3. Distributed propulsion and lift

Four corner modules provide redundancy, maneuvering authority, and load sharing.

4. Electric architecture

Enables precise control, modularity, and compatibility with batteries or hybrid energy sources.

Engineering Challenges and Constraints

1. Induced drag from low aspect ratio foils

The 4 foot span fundamentally limits hydrofoil efficiency at high lift.

2. Insufficient installed power for full foiling

Full lift at 20 knots requires significantly more than 80 HP once real-world losses are included.

3. Structural loads

Each foil must carry approximately 5,000 lb of lift, resulting in high bending moments at the foil root and hull interface.

4. Control complexity

Four lifting foils require active control of ride height, pitch, and roll to avoid instability and ventilation.

5. Near-surface operation risks

Foils operating 4 feet below the surface are vulnerable to ventilation and lift loss in waves.

Practical Path Forward

From an engineering standpoint, the concept becomes viable if one or more of the following changes are made:

• Increase foil span to improve aspect ratio and reduce induced drag.

• Target lift-assisted operation rather than full hydrofoil flight at 20 knots.

• Increase total installed power if full foiling is a firm requirement.

• Separate paddlewheel and hydrofoil functions mechanically to reduce drag and control complexity at speed.

Conclusion

The hydrofoil paddlewheel catamaran concept is grounded in valid hydrodynamic principles and offers meaningful advantages at low and moderate speeds. The hydrofoils, as sized, are capable of generating the required lift at 20 knots, but physics imposes a clear constraint: induced drag power exceeds the available horsepower.

As a lift-assisted, ultra-efficient electric catamaran, the concept is technically sound. As a fully flying hydrofoil vessel at 20 knots using 80 HP and low aspect ratio foils, it is not power-feasible without significant design changes.

This analysis highlights not a failure of the idea, but the importance of aligning foil geometry, lift fraction, and installed power with the immutable laws of hydrodynamics.

TEL: 1-608-238-6001 Email: greg@infinityturbine.com

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