Platform Type Comparison: Mobile Ship vs Stationary Platform

Draft High Research 1,431 words Created Mar 3, 2026

Platform Type Comparison — Mobile Ship vs Stationary Platform

The original assumption was a stationary FPSO moored in the GPGP. But as the research deepened, a mobile processing vessel emerged as the stronger Phase 1 architecture. This document compares the two approaches and explains why.

1. The Two Architectures

Option A: Stationary Platform (FPSO / Semi-Sub)

A converted VLCC or semi-submersible moored permanently in the GPGP. Plastic is delivered by passive boom collection, drone fleet, and/or dedicated towed collection vessels.

This was the original concept. It mirrors how offshore oil works — the platform stays put, the resource comes to it.

Option B: Mobile Processing Vessel

A converted vessel that moves through the GPGP under its own power, collecting and processing plastic as it goes. Self-powered by syngas from the plastic it processes. Returns to port periodically for crew rotation and maintenance.

This is the emerging concept. It mirrors how factory fishing ships work — the vessel goes where the resource is.

2. Head-to-Head Comparison

Factor	Stationary Platform	Mobile Ship	Winner
Mooring cost	$220–440M (world-record 4,500m depth)	$0	Ship
Can chase density hotspots	No — fixed position	Yes — follow the plastic	Ship
Storm avoidance	Must ride it out	Can steam away	Ship
Port access for maintenance	Requires 1,000 nm tow or at-sea repair	Self-propelled to nearest port	Ship
Crew rotation	28/28, crew change vessel from Honolulu	28/28, or port-based crew change	Ship
Supply logistics	PSV from Honolulu, $175–450K/trip	Resupply in port during crew rotation	Ship
Classification	Novel — no existing class for "floating waste processor"	Ship conversion — well-established path	Ship
Collection capability	Passive booms + drones (depends on currents)	Active collection while moving + booms	Ship
Processing uptime	Higher (always on station)	Lower (transit time to/from port)	Platform
Stability for processing	Excellent (large hull, moored)	Good (but ship motion in sea states)	Platform
Energy self-sufficiency	Must generate ALL power on-board	Same — but can refuel in port if needed	Tie
Phase 1 CAPEX	$480–750M (incl. mooring)	$150–350M (no mooring)	Ship
Scalability	Add processing barges alongside	Add more ships	Tie

Score: Ship wins 9 of 13 categories.

3. The Mooring Elephant

The single biggest factor is mooring. At 4,500m depth, a permanent mooring system would be the deepest ever installed — a world record by 65% over the current deepest (2,728m). It costs $220–440M and is the same price regardless of platform type.

A mobile ship eliminates this entirely. No mooring, no anchoring, no world-record engineering challenge. The ship holds station with its own engines when processing, and moves when it needs to.

This alone saves enough money to build a second ship.

4. The Collection Advantage

A stationary platform at the GPGP faces a fundamental physics problem: the core of the gyre has the densest plastic but the weakest currents (0.01–0.05 m/s). Passive boom collection depends on current pushing plastic into the booms. At dead centre, almost nothing moves.

A mobile ship solves this by creating its own relative water flow:

Collection Method	Stationary Platform	Mobile Ship
Passive booms	Depends on current (near-zero at core)	Ship motion creates flow past booms
Towed net/barrier	Not possible (platform doesn't move)	Can tow collection barrier like System 03
Drone fleet	Yes — drones sortie from platform	Yes — drones sortie from ship
Effective sweep rate	Limited by current × boom width	Ship speed × boom width (much higher)

At even 1 knot (0.51 m/s), a ship with 200m boom coverage sweeps ~102 m²/s — roughly 10× the flow rate of a stationary platform relying on 0.05 m/s currents.

The Ocean Cleanup's System 03 collects at 75–100 kg/hr while towing at 1.5 knots. A processing ship with similar collection geometry could match or exceed this — while processing the catch in real-time instead of storing it for weeks.

5. The Uptime Tradeoff

The one area where a stationary platform wins: processing uptime. A moored platform processes 24/7/365 (minus maintenance). A mobile ship loses time to:

Transit to/from port for crew rotation: ~7 days round trip to Honolulu
Major maintenance periods: 2–4 weeks/year in port
Storm avoidance transits: occasional

Estimated uptime comparison:

Scenario	Stationary Platform	Mobile Ship
Days on station per year	~340	~280–300
Processing uptime (75%)	~255 days	~210–225 days
Annual throughput at 5 TPD	~1,275 tonnes	~1,050–1,125 tonnes

The ship loses ~15–20% uptime vs. a stationary platform. But it gains ~$220–440M in saved mooring costs and dramatically better collection rates. The math overwhelmingly favours the ship.

6. Operating Model

The Processing Cruise

The ship operates on a repeating cycle:

1. DEPART PORT (Honolulu or Long Beach) - Fresh crew aboard (28-day rotation) - Supplies, spare parts, consumables loaded - Transit to GPGP: ~3–4 days at 12–15 knots 2. OPERATE IN GPGP (~21–24 days) - Deploy collection booms/barriers - Slow cruise through high-density zones (1–2 knots) - Collect plastic continuously via booms + drone fleet - Process catch in real-time via PRRS plasma system - Syngas powers ship — no fuel consumed - Vitrified slag stored on-board - Track density hotspots via satellite/sensor data

3. RETURN TO PORT (~3–4 days) - Offload slag (construction aggregate) - Crew rotation - Maintenance, resupply - Hydrogen offload (Phase 2+) - Document plastic credits earned

Cycle time: ~28–30 days Processing days per cycle: ~21–24 days Cycles per year: ~12 Annual processing days: ~250–290

Self-Sustaining Energy Loop

During GPGP operations, the ship runs entirely on syngas from processed plastic:

Consumer	Power Draw
Plasma torch(es)	300–500 kW
Shredder + pre-processing	100–200 kW
Ship hotel load (lighting, HVAC, galley, comms)	200–400 kW
Collection systems (booms, winches, drones)	100–200 kW
Slow-speed propulsion (1–2 knots)	200–500 kW
Total	~900–1,800 kW

At 5 TPD, syngas generation produces ~575 kW continuous — tight. At 10 TPD, ~1,150 kW — comfortable. The ship should target 10 TPD processing to ensure energy self-sufficiency during operations.

For transit (12–15 knots), diesel propulsion is needed. Transit fuel cost: ~$50,000–100,000 per round trip. Funded by credit revenue.

7. Hull Selection

The ship conversion uses the same hull candidates as the stationary FPSO concept, but with different priorities:

Hull Type	Deck Area	Propulsion	Speed	Cost	Verdict
Aframax tanker	5,500–8,000 m²	Yes (existing)	14–16 kts	$20–50M	Best for Phase 1 — adequate space, self-propelled
Suezmax tanker	8,000–12,000 m²	Yes (existing)	14–16 kts	$30–60M	Good — more room for growth
VLCC	12,000–18,000 m²	Yes (existing)	14–16 kts	$30–75M	Overkill for Phase 1; best for Phase 2+
Barge	3,000–5,000 m²	No (must be towed)	4–6 kts tow	$10–25M	Eliminated — not self-propelled

Phase 1 recommendation: Aframax tanker conversion. It's the cheapest hull with self-propulsion and enough deck space for 5–10 TPD processing. An Aframax already has engine room, navigation bridge, crew quarters, and ballast systems — reducing conversion scope.

Phase 2+: Suezmax or VLCC if processing capacity needs to scale beyond what an Aframax can accommodate.

8. Cost Comparison — Phase 1

Cost Item	Stationary FPSO	Mobile Ship
Hull acquisition	$30–75M (VLCC)	$20–50M (Aframax)
Hull conversion	$30–80M	$20–40M
Processing equipment (5–10 TPD PRRS)	$30–80M	$30–80M
Syngas power generation	$10–30M	$10–30M
Collection systems	$20–50M	$20–50M
Crew quarters upgrade	$10–30M	$5–15M
Mooring (4,500m)	$220–440M	$0
Engineering + classification	$30–80M	$20–50M
Total Phase 1	$380–865M	$125–315M
With 30% contingency	$494–1,125M	$163–410M

The mobile ship costs 60–70% less — primarily because mooring is eliminated.

9. Scaling Strategy

Phase	Ship(s)	Processing	Annual Throughput	Cumulative CAPEX
Phase 1	1× Aframax	5–10 TPD	~1,000–2,000 tonnes	$163–410M
Phase 2	1× Aframax + 1× Suezmax	15–25 TPD	~3,000–5,000 tonnes	$400–800M
Phase 3	Fleet of 3–5 vessels	50–100 TPD total	~10,000–20,000 tonnes	$700M–1.5B
Full scale	10+ vessel fleet	200+ TPD total	~40,000+ tonnes	$2–4B

Each additional ship is an independent unit — no shared mooring, no barge-to-platform connections, no single point of failure. If one ship breaks down, the others keep operating.

This is fundamentally more resilient than a single stationary platform, where a mooring failure or major equipment breakdown shuts down the entire operation.

10. Risk Comparison

Risk	Stationary Platform	Mobile Ship
Mooring failure (4,500m)	Catastrophic — platform adrift	N/A
Major equipment failure	Repair at sea (1,000 nm from port)	Steam to port for repair
Storm damage	Must survive in place	Avoid storm entirely
Collection shortfall	Stuck in one position	Move to denser area
Regulatory challenge	Novel "floating waste processor" class	Ship conversion — established path
Insurance	First-of-kind premium (2–5× standard)	Lower — converted cargo vessel
Crew emergency	Helicopter can't reach (1,000 nm)	Steam toward helicopter range or port
Technology failure	Stranded with non-working reactor	Return to port, fix, go back

11. The Recommendation

The Claw should be a mobile processing vessel, not a stationary platform.

The mobile ship architecture:

Eliminates the $220–440M mooring problem
Reduces Phase 1 CAPEX by 60–70%
Enables active collection (10× the sweep rate of passive booms)
Provides storm avoidance, port access, and operational flexibility
Uses established ship conversion classification (not novel floating processor)
Scales by adding ships, not connecting barges
Is self-sustaining: syngas from plastic powers the ship

The stationary platform concept may become relevant at full scale (Phase 3+) as a permanent processing hub that receives plastic from a fleet of collection vessels. But for Phase 1 — proving the technology, validating the energy loop, establishing credit revenue — a mobile ship is the clear winner.

Phase 1 spec:

Parameter	Value
Hull	Aframax tanker conversion (15–20 years old)
Length	230–260m
Beam	32–44m
Processing	1× marinized PRRS (5–10 TPD)
Power	Syngas gas engine (1–2 MW) + diesel for transit
Collection	Towed boom/barrier + 5–10 collection drones
Crew	20–30 on-board (40–60 total with rotation)
Operating cycle	28-day cruises from Honolulu
Hull cost	$20–50M
Total Phase 1 CAPEX	$163–410M
Annual throughput	~1,000–2,000 tonnes
Revenue	Plastic credits + carbon credits (~$3–10M/year)

Analysis compiled March 2026. Based on FPSO conversion market data, PyroGenesis PAWDS/PRRS specifications, Ocean Cleanup System 03 collection performance, GPGP density distribution research, and offshore platform engineering analysis from The Claw knowledge base.