Engineering comparison
Model Steam Engine Comparison: V2 vs L2 vs V4
Compare cylinder geometry, displacement, torque delivery, Stephenson valve gear, and hull sizing across the Rocking Whale live-steam range. Match the mechanical layout to your model boat hull or bench installation.
| Model | Layout & Type | Cylinders | Displacement | Bore × Stroke | Max. Torque | Working Pressure | Recommended Boat | Propeller Range | Valve Gear |
| RW-BL1K | Single-Cylinder Plant | 1 (Single) | 3 cc | 12.2 × 12.7 mm | 600 gf·cm | 0.5–2 bar | 50–80 cm | 35–45 mm | Fixed eccentric D-slide |
| RW-V2 | 90° Twin-Cylinder | 2 (Twin) | 6 cc | 12.2 × 12.7 mm | 1,200 gf·cm | 0.5–2 bar | 70–130 cm | 45–60 mm | Dual Stephenson reversing gear |
| RW-L2 | Inline Twin-Cylinder | 2 (Twin) | 6 cc | 12.2 × 12.7 mm | 1,200 gf·cm | 0.5–2 bar | 70–130 cm | 45–60 mm | Dual Stephenson reversing gear |
| RW-V4 | V4 Four-Cylinder | 4 (Quad) | 12 cc | 12.2 × 12.7 mm | 2,000 gf·cm | 0.5–2 bar | 90–150 cm | 60–80 mm | Quad Stephenson reversing gear |
| RW-BL2 | Twin Steam Plant | 2 (Twin) | 6 cc | 12.2 × 12.7 mm | Continuous | Specification on request | Tabletop base | Bench display | Slide valve mechanism |
| RW-BC2 | Tabletop Steam Plant | 1 (Single) | Compact | Miniature | Tabletop | Specification on request | Tabletop base | Bench display | Single slide valve |
| RW-B2 | Compact Steam Boiler | — | — | — | — | Specification on request | 50–100 cm match | — | Safety valve & regulator |
RW-V2 vs RW-L2: 90° V-Twin vs. Inline Twin
Both the RW-V2 and RW-L2 share a 6 cc displacement (1.5 cc × 2 × 2) double-acting cylinder architecture delivering 1,200 gf·cm of peak torque and equipped with full Stephenson reversing links. The choice between them depends entirely on hull architecture and visual preference.
RW-V2: 90° V-Twin Layout
Arranging the two cylinder banks at 90° creates a compact longitudinal footprint that lowers the overall centre of gravity in the hull. Perfect for beamier steam launches, pinnaces, and runabouts where engine bay length is constrained.
RW-L2: Inline Twin Layout
The classic inline arrangement offers an exceptionally narrow lateral profile supported by a rigid six-bearing crankshaft bed. Ideal for long, slender hulls (such as scale torpedo craft and river steamers) where authentic open-crank machinery is showcased.
RW-V2 vs RW-V4: Twin-Cylinder vs. Four-Cylinder Power
Stepping from the 6 cc twin-cylinder to the 12 cc flagship RW-V4 doubles the total swept volume and delivers 2,000 gf·cm of maximum torque. The V4 is built specifically for large-scale vessels requiring authority in rough water or heavy displacement.
Torque Continuity & Dead-Centre Elimination
With four double-acting cylinders phased across two 90° banks, the RW-V4 delivers eight distinct power impulses per revolution. There is zero possibility of a dead-centre stop, guaranteeing instantaneous radio-controlled self-starting in forward or reverse.
Propeller Authority in 90–150 cm Craft
While the V2 handles 45–60 mm propellers in 70–130 cm boats, the V4 easily turns large 60–80 mm multi-blade scale marine propellers, making it the definitive choice for working steam tugs and scale naval models.
RW-BL1K vs RW-V2: Complete Marine Plant vs. Independent Engine
The difference between the BL1K and the V2 reflects two distinct approaches to live-steam boat building: all-in-one drop-in integration versus custom bespoke engineering.
RW-BL1K: Complete Marine Propulsion Plant
Includes the single-cylinder 3 cc engine, 200 ml copper boiler, ceramic alcohol burner, pressure gauge, safety valve, and piping pre-mounted on an aluminium base. It drops directly into a 50–80 cm hull with minimal fabrication.
RW-V2: Standalone Machinery
Supplied as an independent engine with Stephenson reversing gear. Builders select their own steam source (such as the RW-B2 boiler or workshop steam plant), throttle valves, and displacement lubricators for custom installations.
Single-Cylinder vs. Twin-Cylinder Steam Principles
The transition from single-cylinder (BL1K) to twin-cylinder (V2/L2) fundamentally transforms control and operational characteristics under live steam.
Single-Cylinder Dynamics
Single-cylinder engines require an initial flywheel flick to clear dead centres, but offer maximum thermal efficiency and low steam consumption from compact boilers. Ideal for sustained, steady cruising in lightweight hulls.
90° Phased Twin Dynamics
Setting cranks at 90° phasing ensures continuous starting torque from rest. When one piston is at the stroke limit, the partner piston is mid-stroke at peak crank leverage, enabling precision low-speed docking maneuvers.
50–80 cm Small Craft & Launches
Lightweight steam pinnaces, tender launches, and classic open dinghies where total plant weight must remain below 1.8 kg.
- Recommended engine
- RW-BL1K (3 cc)
- Propeller diameter
- 35–45 mm (2–3 blades)
- Displacement range
- 1.5–4.0 kg hull
- Operating speed
- 800–1,500 RPM
70–130 cm Medium Scale Steam Boats
Cabin cruisers, river launches, steam yachts, and scale naval patrol craft requiring bidirectional maneuvering and steady torque.
- Recommended engine
- RW-V2 or RW-L2 (6 cc)
- Propeller diameter
- 45–60 mm (3–4 blades)
- Displacement range
- 4.0–10.0 kg hull
- Operating speed
- 600–2,000 RPM
90–150 cm Large Scale & Heavy Workboats
Harbour tugs, ocean-going steamships, warships, and heavy scale models demanding immense bollard pull and authority.
- Recommended engine
- RW-V4 (12 cc)
- Propeller diameter
- 60–80 mm (3–5 blades)
- Displacement range
- 8.0–25.0 kg hull
- Operating speed
- 500–2,200 RPM
Selection guidance
Frequently Asked Questions
What is the key difference between the RW-V2 and RW-L2 steam engines?
Both engines share identical cylinder dimensions (12.2 mm bore × 12.7 mm stroke, 6 cc displacement) and produce 1,200 gf·cm of maximum torque with reversible Stephenson valve gear. The distinction lies in architecture: the RW-V2 arranges cylinders in a 90° V bank for a low, compact envelope ideal for beamier hulls and launches, whereas the RW-L2 uses an inline configuration with a six-bearing crankshaft bed that fits long, slender hulls such as vintage torpedo craft or river steamers.
How do I choose between a twin-cylinder (V2/L2) and a four-cylinder (V4) engine?
Choose a twin-cylinder (V2 or L2) for model boats between 70 and 130 cm where moderate steam consumption and compact machinery installation are paramount. Choose the flagship RW-V4 (12 cc displacement, 2,000 gf·cm torque) for boats between 90 and 150 cm, heavy-displacement workboats, scale tugs, or multi-propeller naval models requiring large 60–80 mm marine propellers and guaranteed dead-centre-free self-starting from any stop position.
Is the RW-BL1K better than the RW-V2 for a beginner live-steam project?
Yes. The RW-BL1K is supplied as a complete, pre-engineered live-steam plant with an integrated copper boiler, alcohol burner, pressure gauge, and steam piping mounted on a common baseplate. It is designed as a drop-in installation for 50–80 cm model boats. The RW-V2 is a standalone marine engine requiring a separate steam boiler (such as the RW-B2) or compressed-air supply, making it better suited to builders who wish to engineer their own plumbing circuit.
Why do twin-cylinder steam engines start more reliably than single-cylinder engines?
A single-cylinder engine has two dead centres (top and bottom of piston travel) where steam pressure on the piston cannot exert rotational leverage on the crankshaft. A twin-cylinder engine with cranks phased at 90° ensures that whenever one cylinder is at a dead centre, the other cylinder is positioned at maximum connecting-rod angularity, allowing the engine to start under steam in either direction without hand-turning the flywheel.
Can all Rocking Whale miniature steam engines run on compressed air?
Yes. Every Rocking Whale model steam engine operates smoothly on 0.5–2 bar (7–30 psi) regulated workshop compressed air for bench testing, timing verification, and indoor demonstration without lighting a boiler or consuming fuel.
