Collection System Design — How a Mobile Ship Collects Plastic

Draft Medium Research 1,381 words Created Mar 4, 2026

Collection System Design — How a Mobile Ship Collects Plastic

The mobile ship architecture fundamentally changes the collection equation. Instead of waiting for currents to deliver plastic (stationary platform problem), the ship creates its own relative flow by moving through the debris field. This mirrors the Ocean Cleanup's System 03 approach — but with on-board processing instead of hauling waste to shore.

1. The Mobile Collection Advantage

Stationary vs Mobile — The Physics

Factor	Stationary Platform	Mobile Ship
Relative water speed	0.05–0.15 m/s (ambient current)	0.5–1.0 m/s (ship speed)
Sweep rate (200m boom)	~10–30 m²/s	~100–200 m²/s
Daily area swept	~0.9–2.6 km²	~8.6–17.3 km²
Collection multiplier	1× (baseline)	~6–10×

At even 1 knot (0.51 m/s), a ship sweeps 6–10× more ocean area than a stationary platform relying on ambient currents. At the GPGP's mean concentration of 50 kg/km², that translates directly to 6–10× more plastic collected per day.

Real-World Benchmark: Ocean Cleanup System 03

Metric	System 03	The Claw (projected)
Barrier length	2,200m	200–600m (smaller, ship-mounted)
Tow speed	1.5 knots (0.77 m/s)	1–2 knots (0.5–1.0 m/s)
Collection rate	75–100 kg/hr	30–80 kg/hr (shorter barrier)
Extraction cycle	Every 3–4 days (haul to ship)	Continuous (on-board processing)
Record haul	158,757 kg (single lift)	N/A — no accumulation needed
Annual collection	~200–300 tonnes (6-month season)	~500–1,500 tonnes (year-round)

The Claw's advantage: no extraction downtime. System 03 collects for 3–4 days, then stops to haul and empty. The Claw processes continuously — plastic flows from boom to shredder to reactor without interruption.

2. Collection Architecture

Primary: Ship-Towed Boom/Barrier

The main collection system is a boom array towed or deployed from the ship's stern or sides:

Spec	Value	Notes
Configuration	V-shape or U-shape boom pair	Funnels plastic toward central intake
Boom length	200–600m total (2 arms × 100–300m)	Shorter than System 03 — ship is smaller
Boom draft	1–3m	Captures ~90% of floating mass
Boom material	HDPE pipe flotation + HDPE mesh screen	Same technology as System 03
Deployment	Hydraulic winch + davit cranes from stern	Retractable for transit and storms
Collection point	Stern intake ramp or midship side channels	Conveyor feeds pre-processing
Retraction time	2–4 hours	For storm avoidance or transit

Secondary: Collection Drones

A fleet of semi-autonomous surface drones operates ahead and alongside the ship, sweeping adjacent areas:

Spec	Value
Fleet size	5–10 units
Type	5–8m catamaran, electric + solar
Payload	500–1,000 kg per sortie
Endurance	24–48 hours
Range	10–30 km from mother ship
Return cycle	Docks at ship stern, offloads via crane, recharges
Navigation	GPS + computer vision + AIS
Cost per unit	$500K–2M

Drones extend the effective sweep width beyond the boom coverage, particularly useful for targeting visible debris clusters detected by satellite or on-board sensors.

Tertiary: Opportunistic Net Recovery

Ghost fishing nets (up to 46% of GPGP mass by some estimates) can be spotted and recovered individually:

Method	How	Feasibility
Lookout + manual grapple	Crew spots large nets, crane hooks them	Simple, proven on fishing vessels
Drone-assisted spotting	Aerial drone identifies nets from altitude	Extends visual range
Dedicated net-retrieval skiff	Small boat with winch approaches tangled nets	For nets too heavy for crane

3. On-Board Plastic Flow

From collection to reactor — the processing chain on the ship:

OCEAN → Boom barrier (filters plastic from water)
     → Collection point (stern ramp / side channel)
     → RECEIVING DECK — initial sort, remove large non-plastic debris
     → Freshwater rinse (remove worst salt, loose biofouling)
     → SHREDDER (PAWDS-type: handles mixed waste, no sorting needed)
     → Dewatering centrifuge (reduce moisture to <5%)
     → Conveyor to PRRS reactor
     → PLASMA GASIFICATION (5,000°C destruction)
     → Outputs: syngas → gas engine → ELECTRICITY
                 vitrified slag → storage hold

Key Design Considerations

Issue	Solution
Water ingress with plastic	Boom lip above waterline; conveyor drainage; receiving deck sloped to drain
Salt contamination	Quick freshwater rinse on receiving deck (desalinated seawater)
Biofouling on plastic	Doesn't matter — plasma gasifies everything organic
Tangled nets	Pre-shredder cutting station with hydraulic shears
Non-plastic debris	Manual sort on receiving deck — metal, wood, glass removed
Varying feed rate	Buffer hopper between collection and shredder (2–4 hour capacity)

4. Collection Rate Estimates — Mobile Ship

Daily Collection at Various Speeds and Densities

Assumptions: 400m effective boom width, 2m draft, 75% capture efficiency.

Ship Speed	GPGP Zone	Concentration	Daily Sweep Area	Daily Collection
1 knot	Outer	10 kg/km²	~17 km²	~130 kg
1 knot	Inner	50 kg/km²	~17 km²	~640 kg
1 knot	Core hotspot	200 kg/km²	~17 km²	~2,550 kg
1.5 knots	Inner	50 kg/km²	~26 km²	~960 kg
1.5 knots	Core hotspot	200 kg/km²	~26 km²	~3,830 kg
2 knots	Inner	50 kg/km²	~34 km²	~1,280 kg
2 knots	Core hotspot	200 kg/km²	~34 km²	~5,100 kg

Annual Throughput Estimates

Scenario	Operating Zone	Speed	Days at Sea	Annual Collection
Conservative	Inner ring, 1 knot	1 kt	250	~160 tonnes
Moderate	Inner ring, 1.5 knots	1.5 kt	250	~240 tonnes
Optimistic	Inner + core hotspots	1.5 kt	250	~960 tonnes
With drone fleet	Mixed + 10 drones	1.5 kt	250	~1,200–1,500 tonnes

Reality Check: Matching Collection to Processing

Processing Capacity	Collection Needed	Achievable?
5 TPD	1,250 t/yr (at 250 days)	Yes — moderate scenario + drones
10 TPD	2,500 t/yr	Challenging — requires core hotspot operation + drones
25 TPD	6,250 t/yr	Requires multiple ships or dedicated collection vessels

At 5 TPD processing, the collection matches. This validates the Phase 1 target. At 10 TPD, the ship would need to consistently operate in high-density zones and deploy a full drone fleet. Scaling beyond 10 TPD on a single ship likely requires additional collection assets (dedicated collection vessels feeding The Claw, similar to the complementary model described in the Scale & Dimensions analysis).

5. Route Planning & Density Tracking

How the Ship Navigates the GPGP

The Claw doesn't just drive in a straight line. It follows the plastic:

Data Source	What It Shows	Availability
Satellite imagery (Sentinel-2, Planet)	Large debris fields, ghost net clusters	Daily updates, 10m resolution
NOAA ocean current models	Where plastic is likely accumulating	Real-time forecasts
Historical density maps	Lebreton et al. concentration data	Static baseline
On-board forward-looking sonar/camera	Real-time debris detection ahead	Continuous
Drone aerial reconnaissance	Scout ahead for density patches	On-demand

Operating pattern: "Lawn-mower" sweeps through high-density zones, with real-time density feedback adjusting speed and heading. When density drops below a threshold (~20 kg/km²), relocate to a denser zone using satellite/current data.

6. Bycatch Mitigation

A moving ship introduces higher bycatch risk than a stationary platform (faster relative speed). Mitigations:

Measure	Implementation
Slow speed	1–2 knots — most marine megafauna can outswim
Escape gaps	Boom draft limited to 2–3m; animals dive under
Turtle excluder devices	Adapted from shrimp trawl TEDs on boom intake
Camera monitoring	AI vision on boom and receiving deck; auto-alert crew
Nighttime protocol	Reduced speed or boom retraction in sensitive areas
Marine mammal observers	Standard offshore industry practice
Acoustic deterrents	Pingers on boom (similar to gillnet bycatch reduction)

The Ocean Cleanup reports minimal bycatch with System 03 at 1.5 knots — The Claw at 1–2 knots would have comparable or better performance.

7. Weather and Seasonal Operations

Season	Conditions	Collection Status
Apr–Oct	Calm (Hs 1–2m, winds 10–15 kts)	Full operations
Nov–Dec	Transitional (Hs 2–3m, occasional storms)	Reduced — boom retracted in storms
Jan–Mar	Winter swells (Hs 3–5m, storms)	Limited — may return to port for maintenance

Unlike System 03 (which returns to Victoria, BC for the winter), a mobile processing ship can:

Continue operating in calmer zones during winter
Retreat toward Hawaii for shelter during worst storms
Use winter port calls for maintenance and crew rotation

Estimated annual operating days: 250–290 (vs System 03's ~120 towing days)

8. Collection System Cost

Component	Low	High	Notes
Boom/barrier system (400m)	$3M	$10M	Custom HDPE, hydraulic deployment
Receiving deck + conveyor	$2M	$5M	Stern ramp or side intake
Pre-processing (rinse, sort)	$1M	$3M	Freshwater, sorting station
Collection drones (5–10 units)	$2.5M	$15M	Purpose-built catamarans
Drone handling system	$0.5M	$2M	Cradle, crane, charging
Sensors + planning software	$0.5M	$1.5M	Satellite integration, AI density tracking
Total	$9.5M	$36.5M

9. Key Findings

1. Mobile collection generates 6–10× more throughput than stationary passive collection — the ship creates its own flow.

2. At 5 TPD processing, collection matches in the moderate scenario with drones. The bottleneck shifts from "not enough plastic" to "can the reactor keep up."

3. Continuous processing eliminates extraction downtime. System 03 stops for 1–2 days every 3–4 days to extract. The Claw never stops.

4. Ghost nets can be recovered opportunistically on top of boom collection — potentially adding significant mass.

5. Route planning using satellite data lets the ship chase density hotspots rather than sweeping empty ocean.

6. Year-round operations possible (with reduced winter capacity) — doubling System 03's effective season.

Analysis compiled March 2026. Based on Ocean Cleanup System 03 data, GPGP concentration maps (Lebreton et al.), collection drone technology survey, and stationary collection system research from The Claw knowledge base.