Doc #143 — Powered Vessel Propulsion

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RECOMMENDED ACTIONS

Phase 2–3 (Years 1–7)

1. Preserve marine diesel engines — mothball and protect engines from NZ’s fishing fleet, recreational vessels, and commercial shipping.¹ These are irreplaceable until NZ can manufacture marine engines.
2. Trial biodiesel in marine diesel engines — test cold-weather performance, salt-air effects, and fuel system compatibility (Doc #138).
3. Experiment with wood gas for harbour craft — test gasifiers (Doc #56) on harbour tugs or pilot boats.
4. Design hybrid sail-power coastal traders with removable auxiliary engine modules integrated into Doc #138 vessel designs.

Phase 3–4 (Years 3–15)

5. Commission 5–10 hybrid sail-biodiesel coastal traders.
6. Begin low-pressure hydrogen production at coastal sites near hydro or geothermal power.
7. Test hydrogen-fuelled harbour craft as a learning exercise.

Phase 5–6 (Years 15–60)

8. Expand hybrid fleet to Tasman traders as biodiesel production scales.
9. Develop hydrogen vessel storage if pressure vessel metallurgy or metal hydride alloys become available.
10. Assess ammonia and Fischer-Tropsch feasibility as industrial chemistry matures.

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ECONOMIC JUSTIFICATION

The economic case is not about replacing sail — it is about reducing the cost of unreliable schedules and expanding the sailing fleet’s operational envelope.

A sail-dependent Tasman crossing takes 1–4 weeks depending on weather.² An auxiliary engine capable of 5 knots in calms could increase annual round trips from 3–4 to 5–6 per vessel — a 40–70% increase in cargo throughput. For a vessel carrying 50 tonnes per trip, this adds 100–150 tonnes of trade goods annually. Across 10 Tasman traders, hybrid propulsion adds roughly 1,000–1,500 tonnes of annual trade capacity — meaningful for NZ’s import needs (copper, alumina, rubber, specialist tools). An auxiliary engine also eliminates the need for harbour tugs and provides a critical safety margin on a lee shore.

Labour investment. Total for a 10-vessel hybrid fleet: approximately 5,000–10,000 person-hours of vessel modification (500–1,000 per vessel for engine bed, fuel system, and exhaust), plus 2–3 FTE per major port for engine maintenance. Biodiesel production infrastructure is already justified for land transport (Doc #57). This is modest relative to the cargo throughput gains.

Fully powered ocean voyaging is not economically justified. A powered Tasman crossing consumes 2,000–5,000 litres of fuel.³ Hybrid sail-power — motoring only in calms — uses 500–1,500 litres per crossing. Fully powered operation should be reserved for emergencies.

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1. FUEL OPTIONS: COMPARATIVE ASSESSMENT

1.1 Overview

Each candidate fuel must be assessed on five dimensions: NZ producibility, energy density (critical for maritime range), engine and storage requirements, safety characteristics, and realistic timeline. The following table summarises; detailed analysis follows in subsequent sections.

Fuel	NZ Producible?	Energy Density (MJ/litre)	Engine Type	Storage Complexity	Safety Hazard	Earliest Maritime Use	Feasibility
Biodiesel (tallow)	Yes, Phase 2–3	33–34	Existing diesel	Simple (tanks)	Low (high flash point)	Phase 3–4	[B]
Wood gas	Yes, Phase 1–2	~0.005 (gas)	Spark-ignition, converted	Gasifier on board	CO poisoning, fire	Phase 3–4	[B]
Hydrogen (low-pressure)	Yes, Phase 3–4	0.5 at 10 bar	Spark-ignition, converted	Pressure vessels	Flammable, embrittlement	Phase 5	[C]
Hydrogen (compressed)	Uncertain	4.5 at 700 bar	Fuel cell or spark-ignition	High-pressure vessels	Flammable, embrittlement	Phase 6+	[C/D]
Ammonia	Phase 6+ at earliest	12.7 (liquid at -33C)	Modified diesel or fuel cell	Refrigerated or pressurised	Toxic, corrosive	Phase 6–7	[D]
Synthetic diesel (F-T)	Phase 6+ at earliest	34–36	Existing diesel	Simple (tanks)	Low	Phase 6–7	[D]
Ethanol	Yes, Phase 2	21.2	Spark-ignition	Simple (tanks)	Flammable	Phase 3–4	[B]

Key observation: The fuels that NZ can produce soonest — biodiesel, wood gas, ethanol — are the ones most suitable for early hybrid sail-power vessels. The fuels with the best long-term potential — hydrogen, ammonia, synthetic diesel — require industrial infrastructure that takes decades to develop. Planning should follow this sequence, not leapfrog to fuels whose precursor industries do not yet exist.

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2. BIODIESEL: THE FIRST PRACTICAL MARINE FUEL

2.1 Why biodiesel is first

Biodiesel from NZ tallow (Doc #57) is the most accessible powered-propulsion option for maritime use because:

• NZ already has the feedstock (tallow from meat processing)
• The transesterification chemistry is well-understood and production can begin Phase 2–3, though it requires methanol (from wood distillation or syngas — Doc #57, Section 2.1) and a catalyst (NaOH or KOH from NZ-producible inputs)
• Existing marine diesel engines can burn biodiesel with minor or no modification⁴
• Liquid fuel storage on vessels is proven — no new containment technology required
• Energy density is close to but below petroleum diesel (33–34 MJ/litre vs. 36–38 MJ/litre — an 8–13% reduction in range per litre, plus a further power penalty from tallow biodiesel’s higher viscosity at low temperatures)

2.2 Marine-specific considerations

Cold weather performance. Tallow biodiesel’s cloud point of 12–16C (Doc #57, Section 1.3) is a serious constraint for maritime use. The Tasman Sea surface temperature ranges from approximately 12C (winter, southern) to 22C (summer, northern).⁵ A vessel operating in winter in the southern Tasman or around the South Island coast will encounter ambient temperatures below the cloud point. Fuel waxing in lines and filters causes engine failure.

Mitigations: blending with petroleum diesel (while stocks last); winterisation of the biodiesel (filtering high-melting fractions, at the cost of yield); heated fuel lines and tanks (using engine waste heat or a dedicated heating loop); and seasonal/route planning that reserves neat tallow biodiesel for warmer waters and seasons.

Corrosion. Biodiesel is more hygroscopic than petroleum diesel — it absorbs water from the atmosphere. In a marine environment with high humidity and salt air, water contamination of biodiesel fuel stores is a significant concern. Sealed fuel tanks with breather desiccants, and regular water draining from tank bottoms, are necessary.⁶

Storage life. Biodiesel degrades within 6–12 months (Doc #136, Section 5.3). For a trading vessel making multi-week passages, this is acceptable — fuel is consumed within weeks of bunkering. For shore-side fuel depots at remote ports, storage life limits the ability to pre-position fuel. Biodiesel bunkering should be available at ports with tallow supply (major NZ ports near meat processing), not pre-positioned in small quantities at remote locations.

2.3 Practical implementation

Engine selection. NZ’s existing marine diesel fleet includes engines from small fishing boats (20–100 kW) to coastal freighters (500–2,000 kW). For hybrid sail-power vessels, a modest auxiliary engine of 50–200 kW is appropriate — enough for 4–6 knots in calms on a 15–25 metre vessel. Smaller engines are easier to maintain and consume less of NZ’s limited biodiesel supply.

Fuel consumption estimate. A 20-metre hybrid sailing trader with a 100 kW auxiliary engine at cruising power (~60% load) consumes approximately 15–20 litres of biodiesel per hour, or 360–480 litres per day of continuous motoring.⁷ A Tasman crossing of 2,000 km at 5 knots under engine alone would take approximately 8 days and consume 3,000–4,000 litres. Under hybrid operation — motoring only in calms, using sail whenever possible — fuel consumption per crossing might be 500–1,500 litres. This is a meaningful but manageable demand on NZ’s biodiesel production.

Supply chain. Biodiesel production at coastal rendering plants (Napier, Timaru, Bluff — all near major meat processing) aligns well with port locations. Coastal distribution is circular: biodiesel-fuelled vessels can transport biodiesel to ports that lack local production, though this consumes some of the fuel being carried.

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3. WOOD GAS: COASTAL AND HARBOUR APPLICATIONS

Wood gasification (Doc #56) is proven on land but maritime adaptation faces three constraints. First, bulk: a marine engine consumes approximately 0.8–1.2 tonnes of dry wood per day of operation (depending on engine size and load), requiring significant deck storage that displaces cargo.⁸ Second, reliability: tar fouling (Doc #56, Section 3.4) is more dangerous at sea where engine failure is life-threatening. Third, carbon monoxide: the CO risk is heightened in enclosed vessel spaces.

These constraints limit wood gas to short-range applications: harbour tugs and pilot boats (refuelling frequently at port); river and estuary barges on the Waikato, Whanganui, and similar navigable waterways; and sheltered coastal routes of 50–100 km (Hauraki Gulf, Marlborough Sounds) with 1–2 tonnes of wood aboard.

A sailing vessel with a small wood gas auxiliary for calms and harbour manoeuvring is worth considering. Fuel consumption of 500–1,000 kg of wood per coastal passage is achievable — wood is available at every NZ port — and avoids consuming any liquid fuel. The engineering challenge is integrating a gasifier into a working sailing vessel’s deck layout without compromising safety or sailing performance.

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4. ETHANOL: A SUPPLEMENTARY MARINE FUEL

Ethanol (Doc #51, Part 2) can power spark-ignition marine engines. NZ’s fermentation capability makes it available earlier than hydrogen or ammonia, but it has significant maritime disadvantages: lower energy density (21.2 MJ/litre vs. 33–34 MJ/litre for biodiesel — approximately 60% more fuel by volume for equivalent range)⁹; cold starting difficulty below approximately 10–13C (ethanol’s higher heat of vaporisation and lower vapour pressure compared to petrol make cold starting unreliable at the sea-surface temperatures common around the South Island and southern Tasman, typically requiring a petrol or diethyl ether starting aid)¹⁰; and competition with higher-priority medical uses (antiseptic, diethyl ether feedstock).

Best application: small harbour launches and tenders with spark-ignition engines already fitted. For ocean-going or coastal trade vessels, biodiesel in diesel engines is superior on every practical dimension.

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5. HYDROGEN: THE INTERMEDIATE-TERM POSSIBILITY

5.1 NZ’s hydrogen advantage

NZ has a genuine advantage for hydrogen production: abundant renewable electricity. Alkaline electrolysis — splitting water into hydrogen and oxygen using electric current — is well-established 19th-century technology. No exotic materials are required for basic electrolysis. NZ’s hydroelectric and geothermal generation (Doc #65, Doc #66) can provide the electricity without consuming scarce fuel.¹¹

The dependency chain for basic hydrogen production is shorter than for most industrial chemistry, though not trivial:

• Water (abundant in NZ)
• Electricity (NZ grid — 85%+ renewable, expected to continue)
• Electrolyser: steel or nickel electrodes (NZ Steel can supply mild steel; nickel must be imported or salvaged from existing alloy stock); potassium hydroxide (KOH) electrolyte (requires potash from wood ash and lime from NZ limestone — both NZ-producible but the KOH concentration and purity needed for efficient electrolysis requires careful preparation)¹²; steel pressure vessel for the electrolyser body (NZ Steel capability)

This makes hydrogen production one of the more accessible industrial chemistry achievements in the Recovery Library, though the KOH supply chain and electrode durability are constraints that limit the rate of scale-up. Doc #63 covers stationary hydrogen applications; this section addresses the additional challenges of using hydrogen for vessel propulsion.

5.2 The storage problem

Hydrogen’s fundamental disadvantage for mobile applications is its extremely low volumetric energy density. At atmospheric pressure, hydrogen contains approximately 0.01 MJ/litre — roughly 3,000 times less energy per litre than diesel.¹³ Even compressed to 350 bar (a common industrial storage pressure), hydrogen contains approximately 3 MJ/litre — still about 10 times less than diesel. At 700 bar (the current standard for hydrogen fuel cell vehicles), it reaches approximately 4.5 MJ/litre — still 7–8 times less energy per litre than diesel.

What this means for a vessel: To carry the energy equivalent of 3,000 litres of diesel (enough for a Tasman crossing under engine), a hydrogen vessel would need approximately 34 m3 of compressed gas at 350 bar, or 19 m3 at 700 bar — both requiring storage volumes and pressure vessel metallurgy far beyond NZ’s foreseeable capability (Doc #64). Even liquid hydrogen (-253C, approximately 3,500–4,500 litres depending on engine efficiency assumptions) requires cryogenic technology NZ cannot produce.

Realistic assessment: Low-pressure hydrogen (10–50 bar) is storable in vessels fabricated from NZ steel, but the volume required limits hydrogen-powered vessels to very short range — harbour operations, estuary crossings, and perhaps coastal hops of 20–50 km.¹⁴

5.3 Metal hydride storage and engines

Metal hydride storage — hydrogen absorbed into alloys (lanthanum-nickel, iron-titanium) and released by heating — offers better volumetric density (~1–2 MJ/litre) at near-atmospheric pressure.¹⁵ However, the alloys require metals NZ does not mine (likely imported from Australia), the beds are heavy, and alloy degradation limits cycle life. This is a Phase 5–6 technology dependent on trade.

Hydrogen burns in spark-ignition engines with modifications within NZ workshop capability — enlarged fuel supply, retarded ignition timing, compatible valve seats.¹⁶ Internal combustion hydrogen engines achieve approximately 20–25% thermal efficiency (comparable to petrol engines but significantly below the 35–45% thermal efficiency of marine diesel engines). Combined with hydrogen’s severe volumetric energy density disadvantage, this means a hydrogen-fuelled vessel needs roughly 15–25 times the fuel storage volume of a diesel vessel for equivalent range — a performance gap that confines hydrogen to short-range maritime applications for the foreseeable future. Fuel cells achieve 40–60% efficiency but require proton exchange membranes and platinum-group catalysts NZ cannot produce. NZ’s binding constraint is hydrogen storage, not production or combustion.

5.4 Realistic maritime hydrogen scenario

Phase 5 (years 15–30): One or more harbour vessels in major NZ ports (Auckland, Wellington, Lyttelton) operating on low-pressure hydrogen produced by dockside electrolysers. Range: 20–50 km per fill. Application: harbour tugs, pilot boats, inter-harbour ferries (e.g., across Auckland’s Waitemata Harbour or Wellington Harbour).

Phase 6 (years 30–60): If metal hydride storage becomes available through trade or domestic alloy production, hydrogen range extends to 100–200 km, enabling Cook Strait crossings and short coastal passages. Still unsuitable for Tasman or Pacific voyaging.

Hydrogen is not a realistic primary fuel for NZ’s ocean-going trade fleet within the timeframe covered by this document. It is a harbour and short-coastal fuel, supplementing biodiesel for longer passages and sail for ocean voyaging.

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6. AMMONIA: THE DISTANT PROSPECT

Ammonia (NH3) has reasonable volumetric energy density when liquefied (12.7 MJ/litre at -33C or ~10 bar) and was attracting significant pre-event interest as a marine fuel.¹⁷ However, the dependency chain for production is formidable.

Ammonia synthesis via the Haber-Bosch process requires: hydrogen from electrolysis (achievable Phase 3–4); nitrogen from air separation; a reactor operating at 150–350 bar and 400–500C in specialised alloy steel¹⁸; an iron-based catalyst with specific preparation¹⁹; and compression equipment far beyond basic NZ fabrication capability. Doc #114 covers this as a multi-decade roadmap. NZ is unlikely to achieve domestic ammonia synthesis before Phase 6 (year 30+). Australia is more likely to develop the capability first.

Even with ammonia available, maritime use poses additional challenges: acute toxicity (IDLH 300 ppm — a fuel leak in an engine room can be rapidly fatal)²⁰; corrosion of copper, brass, and zinc fittings common on vessels; and difficult combustion requiring pilot fuel injection, since no commercial marine ammonia engines existed as of 2025.²¹

Realistic assessment: Ammonia-fuelled NZ vessels are a Phase 6–7 (30–100 year) prospect. The production dependency chain and the combustion and safety engineering challenges make this the most difficult fuel option covered in this document.

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7. SYNTHETIC HYDROCARBONS: FISCHER-TROPSCH

Fischer-Tropsch (F-T) synthesis converts syngas (CO + H2) into liquid hydrocarbons — synthetic diesel, kerosene, or petrol — that can be used in existing engines without modification.²² This is the ideal marine fuel: drop-in compatible, high energy density, proven technology. It is also the most industrially demanding to produce.

F-T synthesis requires everything that methanol synthesis requires (Doc #111, Section 2.2), plus different catalysts (iron from NZ ironsand is accessible but less selective; cobalt is more selective but must be imported)²³, pressure vessel capability for 200–350C at 20–40 bar, and downstream fractionation — essentially a small refinery. The economics favour scale that NZ may not achieve for decades.

Realistic assessment: F-T capability is Phase 6–7 (30–60+ years). Biodiesel serves NZ’s marine fuel needs in the interim. F-T becomes relevant when — and if — NZ’s industrial chemistry matures to syngas-to-liquids conversion at useful scale, or a trading partner develops the capability first.

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8. HYBRID SAIL-POWER VESSEL DESIGN

8.1 Design philosophy

The hybrid sail-power vessel is the practical bridge between the pure sailing fleet of Phases 2–4 and hypothetical fully powered vessels of Phase 7+. The design philosophy is:

• Sail is the primary propulsion for all ocean passages
• The engine is auxiliary — used for calms, harbour manoeuvring, schedule management, and emergencies
• Fuel consumption must be minimised because all NZ-produced fuels are scarce
• The vessel must be capable of operating entirely under sail if fuel is unavailable
• Engine and fuel systems must be maintainable with NZ materials and skills

8.2 Integration with sailing vessel designs

Building on Doc #138’s vessel types:

Hybrid coastal trader (12–20 metres):

• Rig: gaff ketch or junk rig (Doc #140, Section 3.2)
• Auxiliary: 30–75 kW diesel engine running biodiesel, or spark-ignition engine running ethanol/wood gas
• Fuel capacity: 200–500 litres (biodiesel) or 1–2 tonnes dry wood (wood gas)
• Auxiliary range under power alone: 150–400 km (biodiesel) or 50–100 km (wood gas)
• Engine hours per passage: estimated 10–30% of passage time (calms, harbour approaches, Cook Strait tidal windows)

Hybrid Tasman trader (20–30 metres):

• Rig: gaff ketch or schooner
• Auxiliary: 75–200 kW marine diesel running biodiesel
• Fuel capacity: 1,000–3,000 litres biodiesel
• Auxiliary range under power alone: 500–1,500 km (roughly one-quarter to three-quarters of a Tasman crossing)
• Primary function of engine: reducing worst-case passage times, not replacing sail. A vessel that can motor through 500 km of calms in the mid-Tasman turns a potentially 3–4 week frustrating passage into a reliable 10–14 day transit.

8.3 Engine preservation and maintenance

NZ’s stock of marine diesel engines is finite and irreplaceable. Preservation requires: oil fogging and sealed storage for mothballed engines (fogging oil sprayed through the intake while the engine runs coats internal surfaces and prevents corrosion for 1–3 years in dry storage; longer-term preservation requires periodic re-fogging or inert-atmosphere storage)²⁴; salvage and central allocation of injectors, turbochargers, gaskets, and seals from decommissioned vessels; and marine diesel maintenance as a dedicated trade skill (Doc #157). NZ machine shops (Doc #91) can rebore cylinders, regrind crankshafts, and fabricate many replacement parts. What they cannot replace: fuel injection pumps and electronic engine management systems. Priority should go to mechanically governed engines over electronically controlled ones.

8.4 Propeller and drive train

Sailing vessels with auxiliary engines need propeller arrangements that minimise drag under sail:

• Folding or feathering propellers: Reduce drag when sailing by folding the blades. Existing NZ stock of these is limited; fabrication from bronze is possible but requires precision casting (Doc #93).
• Shaft clutch: Allows the propeller shaft to freewheel under sail, reducing drag. Standard marine hardware.
• Shaft seal: Prevents water ingress where the propeller shaft penetrates the hull. A critical maintenance item — traditional stuffing box seals using greased flax packing (which NZ can produce from harakeke fiber, Doc #100) are a proven solution that predates modern lip seals.²⁵

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9. SMALL-PORT OPERATIONS AND FISHING FLEET COORDINATION

Mothballing and preserving the commercial fishing fleet’s engines (Recommended Action 1) should be coordinated with iwi fisheries authorities, who have institutional knowledge of which vessels and engines are most valuable and the workforce to assist with preservation. NZ’s commercial fishing fleet is a significant fraction Māori-owned or crewed, and iwi fisheries organisations are the most efficient coordination point for this task.

Many of NZ’s most strategically important small ports — Ōpōtiki, Tokomaru Bay, Karamea, Ōkiwi Bay — are in predominantly Māori communities. Local knowledge of bar crossings, weather windows, and mooring conditions at these ports is an operational requirement for vessels calling safely. This knowledge should be captured during the port assessment phase (Recommended Action 2, Doc #140) through direct engagement with local communities.

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10. TIMELINE SYNTHESIS

The following timeline represents the most likely development sequence, not a plan that can be executed on schedule. Each step depends on precursor developments that may proceed faster or slower than estimated.

Phase	Years	Maritime Propulsion Capability	Fuel Source	Dependency
2–3	1–7	Experimental wood gas harbour craft	Wood (Doc #56)	Gasifier fabrication
3–4	3–15	First hybrid sail-biodiesel coastal traders	Tallow biodiesel (Doc #57)	Biodiesel production, methanol supply
4–5	7–30	Hybrid sail-biodiesel Tasman traders	Tallow biodiesel	Scale-up of biodiesel production
5	15–30	Hydrogen harbour vessels	Low-pressure H2 from electrolysis	Electrolyser fabrication, pressure vessel metallurgy
5–6	15–60	Extended hydrogen range (if metal hydrides available)	H2 with metal hydride storage	Metal alloy trade (Australia) or domestic production
6–7	30–100	Ammonia coastal vessels (if synthesis achieved)	NH3 from Haber-Bosch	Ammonia synthesis (Doc #114), pressure vessels, catalyst
6–7	30–100	Synthetic diesel (if F-T achieved)	F-T hydrocarbons from syngas	Catalyst, pressure vessels, refining

Sail remains the backbone of ocean transport through Phase 6 and possibly beyond. Powered propulsion is a supplement that improves over decades, not a replacement arriving on a predictable schedule.

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11. CRITICAL UNCERTAINTIES

Uncertainty	Impact	Mitigation
Biodiesel production volume for marine allocation	Fleet size is fuel-limited	Scale production (Doc #8); prioritise trade vessels
Marine diesel engine stock and condition	Determines maximum hybrid fleet	Census (Doc #8); mothball engines; maintain rebuild capacity
Pressure vessel metallurgy	Gates hydrogen and ammonia storage	NZ Steel research; Australian trade in speciality steels
Biodiesel cold-weather operability	Limits southern NZ and winter use	Blending trials; heated fuel systems; seasonal planning
Industrial chemistry trajectory	Determines all advanced fuel options	Sustained investment in chemical engineering (Doc #57)
Trade partner fuel development	Australia may produce fuels NZ cannot	Monitor Tasman trade opportunities

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12. CROSS-REFERENCES

• Doc #8 — National Asset and Skills Census (marine engine inventory)
• Doc #56 — Wood Gasification (producer gas for marine engines)
• Doc #57 — Biodiesel from NZ Tallow and Alcohol Production (primary marine fuel pathway)
• Doc #63 — Hydrogen: Stationary Applications (electrolyser design)
• Doc #64 — Hydrogen for Mobile Use (storage and pressure vessel challenges)
• Doc #65 — Hydroelectric Maintenance (electricity for electrolysis)
• Doc #89 — NZ Steel Glenbrook: Continuity (steel for pressure vessels, gasifier fabrication)
• Doc #91 — Machine Shop Operations (engine rebuilding, equipment fabrication)
• Doc #93 — Foundry Work (bronze propeller and fitting casting)
• Doc #100 — Harakeke Fiber Processing (cordage for vessel lashing and rigging)
• Doc #114 — Ammonia Synthesis (production roadmap and dependency chain)
• Doc #138 — Sailing Vessel Design (hull and rig designs for hybrid vessels)
• Doc #141 — Boatbuilding Techniques (construction methods)
• Doc #142 — Trans-Tasman and Pacific Trade Routes (operational context)
• Doc #151 — NZ-Australia Relations (trade in metals, alloys, fuel)
• Doc #157 — Trade Training (marine diesel maintenance as trade skill)
• Doc #160 — Heritage Skills Preservation (traditional maritime knowledge)
• Doc #162 — University and Research Reorientation (chemical engineering research)

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FOOTNOTES

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1. NZ marine engine stock: approximately 1,200–1,500 commercial fishing vessels (most diesel-powered), 200,000+ recreational vessel registrations, and several dozen commercial coastal vessels. Source: Maritime NZ vessel registration data.↩︎

2. Tasman crossing duration under sail varies from 8 days (favourable conditions) to 4+ weeks (calms, headwinds). Planning estimate: 10–18 days. Sources: NZ/Australian sailing accounts; Hiscocks, E., “Cruising Under Sail,” Oxford University Press.↩︎

3. Marine diesel consumption at 70% load: approximately 200–220 g/kWh. A 150 kW engine consumes ~26–28 litres/hr. Source: standard marine engineering references; MAN Energy Solutions data.↩︎

4. B20 biodiesel blends are generally accepted for marine diesel engines without modification. Source: CIMAC position papers on biofuels; Lloyd’s Register alternative fuels guidance.↩︎

5. Tasman Sea surface temperatures: ~12–15C winter (southern), 18–22C summer (northern). Source: NIWA sea surface temperature data. https://www.niwa.co.nz/↩︎

6. Biodiesel absorbs approximately 15 times more water from ambient humidity than petroleum diesel. Source: He, B.B. et al., “Biodiesel Fuel Stability,” Applied Engineering in Agriculture, 2007.↩︎

7. Fuel consumption of 15–20 litres/hr based on 75–100 kW marine diesel at 60–70% load. Source: Calder, N., “Marine Diesel Engines,” 3rd ed., International Marine, 2006.↩︎

8. Wood gas fuel consumption: a gasifier-powered engine producing 30–50 kW at the shaft consumes approximately 1.0–1.5 kg of dry wood per kWh of shaft output, yielding approximately 0.8–1.2 tonnes of wood per day at continuous operation. Source: FAO, “Wood Gas as Engine Fuel,” FAO Forestry Paper 72, 1986; Reed, T.B. and Das, A., “Handbook of Biomass Downdraft Gasifier Engine Systems,” SERI, 1988.↩︎

9. Ethanol: 21.2 MJ/litre vs. diesel 36–38 MJ/litre. Well-established thermodynamic data.↩︎

10. Ethanol cold-start threshold: pure ethanol (E100) requires intake air temperatures above approximately 10–13C for reliable unassisted starting due to its high latent heat of vaporisation (840 kJ/kg vs. 350 kJ/kg for petrol) and low Reid vapour pressure. E85 blends improve cold starting but still require auxiliary heating or starting fluid below ~0C. Source: Bergstrom, K. et al., “ABC — Alcohol Based Combustion Engines,” SAE Technical Paper 2007-01-3993; also consistent with Volvo and Scania E85 engine operating data.↩︎

11. NZ generates 82–85% renewable electricity (hydro ~57%, geothermal ~18%, wind ~7%). Source: MBIE NZ Energy Statistics.↩︎

12. KOH for electrolysis: typical alkaline electrolysers use 25–30% KOH solution. KOH is produced by reacting potash (K2CO3, obtainable from wood ash leaching) with slaked lime (Ca(OH)2, from NZ limestone). The reaction is straightforward but producing KOH of sufficient purity and concentration for efficient electrolysis requires careful washing and evaporation steps. Source: Zeng, K. and Zhang, D., “Recent progress in alkaline water electrolysis for hydrogen production and applications,” Progress in Energy and Combustion Science, 2010.↩︎

13. Hydrogen volumetric energy density: 0.01 MJ/litre at 1 bar; ~3 MJ/litre at 350 bar; ~4.5 MJ/litre at 700 bar; ~8.5 MJ/litre as liquid (-253C). Compare diesel at 36–38 MJ/litre. Source: Zuttel, A., “Hydrogen storage methods,” Naturwissenschaften, 2004.↩︎

14. Carbon steel pressure vessels can contain hydrogen at 10–50 bar, with hydrogen embrittlement as a limiting factor. Higher pressures require alloy steels NZ does not produce. Source: API Standard 941; ASME BPVC Section VIII.↩︎

15. Metal hydride storage (e.g., LaNi5) achieves ~90 kg H2/m3 at near-ambient pressure. Source: Sakintuna, B. et al., “Metal hydride materials for solid hydrogen storage,” International Journal of Hydrogen Energy, 2007.↩︎

16. Hydrogen ICE conversion requires enlarged fuel supply, retarded ignition timing, and compatible valve seats. Within NZ workshop capability. Source: Verhelst, S. and Wallner, T., “Hydrogen-fueled internal combustion engines,” Progress in Energy and Combustion Science, 2009.↩︎

17. Ammonia energy density: 12.7 MJ/litre liquefied (-33C or ~10 bar). Source: Valera-Medina, A. et al., “Ammonia for power,” Progress in Energy and Combustion Science, 2018.↩︎

18. Haber-Bosch: 150–350 bar, 400–500C, promoted iron catalyst. Source: Smil, V., “Enriching the Earth,” MIT Press, 2001.↩︎

19. Classic Haber-Bosch catalyst: fused Fe3O4 promoted with K2O, CaO, Al2O3. Iron available from NZ ironsand. Source: Schloegl, R., “Catalytic Synthesis of Ammonia,” Angewandte Chemie International Edition, 2003.↩︎

20. Ammonia IDLH: 300 ppm. Detectable by smell at 5–50 ppm. Source: NIOSH Pocket Guide to Chemical Hazards; DNV GL, “Ammonia as a Marine Fuel,” 2020.↩︎

21. No commercial marine ammonia engines existed as of 2025. Ammonia flame speed is approximately one-fifth that of methane. Source: Dimitriou, P. and Javaid, R., International Journal of Hydrogen Energy, 2020.↩︎

22. Fischer-Tropsch synthesis: developed 1920s Germany; used at scale by Germany (WWII) and South Africa (Sasol). Source: Dry, M.E., “The Fischer-Tropsch process: 1950–2000,” Catalysis Today, 2002.↩︎

23. Iron F-T catalysts are accessible from NZ ironsand but less selective. Cobalt catalysts are more selective but cobalt must be imported. Source: Khodakov, A.Y. et al., Chemical Reviews, 2007.↩︎

24. Engine preservation by oil fogging: standard marine mothballing practice. Fogging oil (or any clean lubricating oil atomised through the intake) coats cylinder walls, valve seats, and internal passages, preventing corrosion for 1–3 years in dry covered storage. Source: Calder, N., “Marine Diesel Engines,” 3rd ed., International Marine, 2006; also consistent with Caterpillar and Cummins engine storage recommendations.↩︎

25. Stuffing box shaft seals using flax or cotton packing greased with tallow: standard marine practice from the 18th century through the mid-20th century, still in use on many vessels. Harakeke (Phormium tenax) fibre has comparable water-resistance and compressive properties to European flax for packing applications. Source: Calder, N., “Marine Diesel Engines,” 3rd ed., International Marine, 2006; harakeke fibre properties per Doc #100.↩︎