Steam-Powered Outrigger Hydroplane — Complete Design Research

Research compiled March 2026 — living document, updated as design decisions are made

Project Overview

1. Uniflow Steam Engine (32mm Bore × 28mm Stroke)

Operating Principle

A uniflow engine uses steam flowing in one direction only through the cylinder:

• Steam enters at the hot end (cylinder head) via the poppet valve
• Steam exhausts through ports at the centre of the cylinder, uncovered by the piston near the end of its stroke
• After ports close, residual steam is compressed by the returning piston, preheating the cylinder before the next admission

This temperature gradient along the cylinder wall means the hot end stays hot and the cool centre stays cool, giving better thermal efficiency than counterflow engines.

Displacement & Power Estimate

Bore:           32mm (radius = 16mm)
Stroke:         28mm
Swept volume:   π × 16² × 28 = 22,519 mm³ ≈ 22.5 cc

At 800 psi (~55 bar) working pressure:
  Mean effective pressure (est):  ~15-25 bar (with early cutoff)
  At 10,000 RPM: estimated ~1.5-2.5 HP mechanical output
  At 15,000 RPM: estimated ~2.0-3.5 HP mechanical output

At 800 psi with 12kW burner, this engine produces enough power to drive an outrigger hydroplane at 70+ mph.

Key Engine Considerations

• Cylinder, piston, and rings: High-strength ductile cast iron throughout. Ductile iron offers excellent wear resistance, good machinability, and more than adequate tensile strength (~60,000–80,000 psi) for 800 psi working pressure.
• Piston: Should be about 40–50% of cylinder length to properly cover the exhaust ports. At 28mm stroke, piston length ~25–30mm minimum.
• Exhaust ports: Ring of small holes or slots around the cylinder centre. Port timing is fixed by geometry — they uncover in the last ~15–20% of stroke.
• Flywheel: Needed to carry through compression stroke. Size depends on RPM target.
• Lubrication: Use a steam cylinder oil dispenser (displacement lubricator) feeding oil into the steam supply. Superheated steam at 500+ psi will strip ordinary lubricants.
• Starting: Not self-starting. Spin the flywheel by hand or with a starter cord before launch.

2. Cylinder Head & Cam-Operated Poppet Valve Design

Cylinder Head Design

                    ┌─────────────────────┐
                    │    STEAM INLET       │
                    │    (throttle valve   │
                    │     upstream)        │
                    └────────┬────────────┘
                             │
                    ┌────────▼────────────┐
                    │   POPPET VALVE      │
                    │   ┌──┐              │
                    │   │  │ Valve stem   │
                    │   │  │              │
                    │  ╔╧══╧╗             │
                    │  ║SEAT║  Conical    │
                    │  ╚════╝  sealing    │
                    │         face        │
                    ├─────────────────────┤ ← Cylinder head
                    │                     │    bolts to cylinder
                    │   CYLINDER          │
                    │   (32mm bore)       │

Poppet Valve Specifications

Spring Force Calculation

At 600 psi (41.4 bar) against a 12mm diameter valve head:

Pressure:    41.4 bar = 4.14 N/mm²
Valve area:  π × 6² = 113.1 mm²
Force:       4.14 × 113.1 = 468 N (~48 kgf / ~105 lbf)

Cam Mechanism

    Crankshaft
        │
        ├── DIRECT DRIVE 1:1 (gear or keyed coupling)
        │
        ▼
    ┌─────────┐
    │ CAMSHAFT │ ← Single lobe, direct-driven off crankshaft
    └────┬────┘
         │
    ┌────▼────┐
    │ FOLLOWER│ ← Roller or flat-face
    └────┬────┘
         │
    ┌────▼────┐
    │ PUSHROD │ ← If cam not directly on valve
    └────┬────┘
         │
    ┌────▼────┐
    │ VALVE   │ ← Opens against spring + steam pressure
    └─────────┘

Direct drive 1:1 off the crankshaft — the camshaft is directly coupled to or geared from the crankshaft at a 1:1 ratio. The valve opens once per revolution. Direct drive eliminates belt/chain slip and backlash.

Cam Profile & Cutoff

• Early cutoff (10–15%): Most efficient at high pressure. Steam enters briefly, then expands.
• Late cutoff (30–50%): More power, less efficient. Better for acceleration.
• For RC throttle control: Use a throttle valve in the steam line upstream. The cam timing is fixed, and the throttle valve limits steam flow.

Cylinder Head Bolting

6 bolts equally spaced around the bore:

Force = Pressure × Area = 41.4 bar × π × 16² = 33,294 N (~7,488 lbf)
Per bolt (6 bolts): ~5,549 N (~1,248 lbf)

M6 (grade 8.8) proof load: ~12,700N each — ample margin.
M5 also viable. Use high-tensile socket head cap screws.

3. Monotube (Flash) Boiler — 600+ PSI

Flash Boiler Principle

At 600+ psi, this is firmly in flash boiler territory. The tube walls store heat, water is injected in small metered amounts, and it flashes instantly to superheated steam. Very low water content at any time — a key safety advantage.

Tubing Selection

Barlow's Formula

P = (2 × S × t) / D

Where:
  P = burst pressure (psi)
  S = material tensile strength — 316SS = ~75,000 psi
  t = wall thickness (inches)
  D = outside diameter (inches)

Example for 3/8" OD, 0.049" wall, 316SS:
  P = (2 × 75,000 × 0.049) / 0.375
  P = 7,350 / 0.375
  P = 19,600 psi burst
  Safe working (4:1) = 4,900 psi  ✓ Well above 800 psi

Boiler Coil Layout

    ┌──────────────────┐
    │   EXHAUST GAS    │ ← Open top for gas exit
    │   ┌──────────┐   │
    │   │ ┌──────┐ │   │
    │   │ │      │ │   │  Multiple layers of
    │   │ │ FIRE │ │   │  coiled stainless tube
    │   │ │      │ │   │  wound concentrically
    │   │ └──────┘ │   │
    │   └──────────┘   │
    │                  │
    │  ══════════════  │ ← Fan + burner at bottom
    │  WATER IN (cold) │ ← Outer coils (preheater)
    │  STEAM OUT (hot) │ ← Inner coils (superheater)
    └──────────────────┘

Coil Parameters

Steam Output & Water

Steam consumption:  ~30-50 lbs/HP-hr (small non-condensing engine)
At 2 HP:            ~60-100 lbs/hr = ~500-800 g/min
Water for 5 min:    ~2.5-4 kg
Recommend:          ~2+ litres feedwater with margin

Feedwater Pump Options

1. Engine-driven piston pump (recommended): Plunger pump off crankshaft eccentric. Self-regulating — pumps more when engine runs faster.
2. Electric pump: High-pressure pump controlled by Arduino. More complex but independent control.
3. Pressurized tank: Pre-pressurize with compressed air. Simple but requires a pressure vessel.

4. Coleman Fuel Firing System

Burner Construction

     BOILER COIL
    ┌───────────────────┐
    │  ┌─────────────┐  │
    │  │  ┌───────┐  │  │
    │  │  │ FLAME │  │  │
    │  │  │       │  │  │
    │  │  └───────┘  │  │
    │  └─────────────┘  │
    ├───────────────────┤
    │  FLAME HOLDER     │ ← Stainless mesh or ceramic wool
    ├───────────────────┤
    │  MIXING CHAMBER   │ ← Fuel vapour + air
    │  ← Fuel jet       │
    │  ← Vaporiser coil │
    ├───────────────────┤
    │  FAN (brushless)  │ ← Blows air up through coil
    └───────────────────┘

Safety

• Fuel shutoff: RC-controlled solenoid valve to cut fuel remotely
• Pressure relief valve: On boiler output — set to ~960 psi (120% of 800 psi working pressure)
• Heat shields: Between fuel tank and boiler
• Ventilation: Open hull sections for air intake/exhaust

5. Arduino Control System

System Architecture

                                    ┌─────────────────┐
                                    │  RC TRANSMITTER  │
                                    │  (2.4 GHz, 3CH)  │
                                    │  Ch1: Steering   │
                                    │  Ch2: Throttle   │
                                    │  Ch3: Burner     │
                                    └────────┬─────────┘
                                             │ RF
                                    ┌────────▼─────────┐
                                    │   RC RECEIVER     │
                                    │  Ch1 → Arduino D2 │
                                    │  Ch2 → Arduino D3 │
                                    │  Ch3 → Arduino D4 │
                                    └───────────────────┘

┌──────────────────────────────────────────────────────────────────┐
│                        ARDUINO NANO                              │
│                                                                  │
│  INPUTS:                           OUTPUTS:                      │
│  ├─ D2: RC Ch1 (steering)          ├─ D9:  Rudder servo          │
│  ├─ D3: RC Ch2 (throttle)          ├─ D10: Throttle servo        │
│  ├─ D4: RC Ch3 (burner)            ├─ D11: Fan ESC (PWM)         │
│  ├─ A0: Pressure sensor            ├─ D6:  Fuel solenoid         │
│  ├─ A1: Thermocouple (MAX6675)     ├─ D7:  Water pump            │
│  ├─ A2: MAX6675 CS                 ├─ D13: Status LED            │
│  └─ A3: MAX6675 SO                 │                              │
│                                     │                              │
│  Power: 7.4V 2S LiPo via ESC BEC   │                              │
└──────────────────────────────────────────────────────────────────┘

Component List

PID Pressure Control

Control Loop Logic

┌─────────────────────────────────────────────────┐
│              MAIN CONTROL LOOP (50 Hz)           │
│                                                  │
│  1. Read RC channels (pulseIn)                   │
│  2. Read pressure sensor (A0)                    │
│  3. Safety checks:                               │
│     ├─ pressure ≥ MAX → close throttle           │
│     ├─ pressure ≥ EMERGENCY → full shutdown      │
│     └─ signal lost > 1s → failsafe              │
│  4. Map steering → rudder servo                  │
│  5. Map throttle → throttle servo (with limits)  │
│  6. PID fan control (auto pressure regulation)   │
│  7. Fuel solenoid control                        │
│  8. Serial telemetry (every 250ms)               │
└─────────────────────────────────────────────────┘

Wiring Diagram

                 7.4V LiPo
                    │
              ┌─────┴─────┐
              │    ESC     │──── Fan motor (brushless)
              │  (has BEC) │
              └─────┬─────┘
                    │ 5V BEC
              ┌─────┴─────┐
              │  Arduino   │
              │   Nano     │
   RC Rx Ch1 ─┤D2      D9 ├── Rudder servo
   RC Rx Ch2 ─┤D3     D10 ├── Throttle servo
   RC Rx Ch3 ─┤D4     D11 ├── Fan ESC signal
              │        D6 ├── Fuel solenoid (via MOSFET)
              │        D7 ├── Water pump (via MOSFET)
              │       D13 ├── Status LED
  Pressure   ─┤A0         │
  MAX6675    ─┤A1-A3      │
              └───────────┘

6. Outrigger Hydroplane Hull

Configuration

An outrigger hydroplane has a main hull (engine, boiler, electronics) with outrigger sponsons for stability. At speed, only the outrigger tips and propeller contact the water.

Plan View:
                      ┌───────────────────────┐
    ┌────────┐        │     MAIN HULL          │        ┌────────┐
    │OUTRIGGER├────────┤  (engine, boiler, RC)  ├────────┤OUTRIGGER│
    │ (port) │  arms  │                        │  arms  │(stbd)  │
    └────────┘        │   Propeller shaft ──→  │←rudder └────────┘
                      └───────────────────────┘

Side View:
                    ╔═══════════════════╗
    ═══╗            ║    MAIN HULL      ║
       ╚════════════╝                   ╚════►  prop
    outrigger                                   ▼
    (rides on tips)                           rudder

Hull Dimensions

Hull Construction

1. Fibreglass/carbon fibre: Lightest, strongest. Mould from foam plug. Ideal for a hydro.
2. Balsa/plywood planked: Traditional, can be glassed over.
3. 3D printed: Possible for outriggers and small parts.
4. ABS sheet: Heat-formable, cheap, reasonably light.

Internal Layout

    BOW ─────────────────────────────────────── STERN

    ┌──────┬──────────┬──────────┬──────────┬──────┐
    │      │  Water   │  BOILER  │  ENGINE  │Prop  │
    │ RC   │  Tank    │  + BURNER│  +       │shaft │
    │Equip │  (2 L)   │          │  Flywheel│  +   │
    │+Batt │          │  Fan     │          │Rudder│
    │      │  Fuel    │  below   │  Throttle│      │
    │      │  Tank    │          │  valve   │      │
    └──────┴──────────┴──────────┴──────────┴──────┘
     ▲ ~25% from bow (CG)                     ▲ ~15% from stern

7. System Integration

Weight Budget

Plumbing Schematic

                            ATMOSPHERE
                                ▲ exhaust
    ┌──────────┐          ┌─────┴─────┐
    │  WATER   │          │  ENGINE   │
    │  TANK    │          │ (uniflow) │
    │  (~2L)   │          │ 32×28mm   │
    └────┬─────┘          └─────▲─────┘
         │                      │ steam
    ┌────▼─────┐          ┌─────┴─────┐
    │ FEEDWATER│          │ THROTTLE  │←── Servo (Arduino)
    │  PUMP    │          │   VALVE   │
    └────┬─────┘          └─────▲─────┘
         │ high-pressure        │ steam
    ┌────▼──────────────────────┴──────┐
    │         MONOTUBE BOILER           │
    │    Water in → coil → Steam out   │
    │    ═══════════════════            │
    │          BURNER                   │
    │    ═══════════════════            │    PRESSURE
    │         ▲       ▲                 │    RELIEF → 960 psi
    │    fuel │       │ air             │    SENSOR → Arduino A0
    │    ┌────┘       └────┐            │
    │    │ JET       FAN   │            │
    └────┼─────────────┼───┼────────────┘
    FUEL TANK      ESC (Arduino D11)
    + SOLENOID (Arduino D6)

8. YouTube Videos & References

Flash Steam Boat Boiler Construction (3-part series)

1. Creating the flash steam boiler for Hydroplane — Part 1
2. Creating the flash steam boiler for Hydroplane — Part 2
3. Creating the flash steam boiler for Hydroplane — Part 3

These are cited in the Wikipedia article on Flash Boilers as references [5], [6], and [7].

Recommended YouTube Search Terms

• "flash steam" hydroplane model boat
• monotube boiler model steam boat 1000 psi
• uniflow steam engine model running
• steam model boat outrigger hydroplane
• flash steam boiler coil winding stainless
• Arduino RC steam boat control
• model steam engine poppet valve cam
• high pressure model steam engine

Books

Online Communities

• Model Boat Mayhem Forum — modelboatmayhem.co.uk
• Model Engineer Magazine — model-engineer.co.uk
• Home Model Engine Machinist Forum — homemodelenginemachinist.com
• RCGroups — rcgroups.com

Wikipedia Articles

• Uniflow Steam Engine
• Monotube Steam Generator
• Flash Boiler
• Poppet Valve
• Coleman Fuel
• Hydroplane (boat)

9. Design Decisions

Resolved

Remaining

1. Propeller diameter — with 5"+ pitch, diameter TBD by testing (1.5–2.5" typical)
2. Bolt size & bolt circle — measure from existing engine body. M5 or M6 recommended.
3. Cylinder head seal — copper gasket, O-ring groove, or lapped face
4. Fittings — all stainless, Swagelok or equivalent, rated 800+ psi

Research compiled March 2026 — update as design decisions are made and testing proceeds.