Conversion Candidate · Burial & Repair Conversion

ST321

SW Duke — Skipsteknisk ST-321 · Turnkey Conversion to Plough-Capable Cable Burial & Repair Vessel

Design Skipsteknisk ST-321 Built 2010 · Factorías Juliana, Spain

A towing platform, converted by Dimension as a turnkey project through partner shipyards, with leading vendor support across the plough and cable-handling spread. 145 t continuous bollard pull — comfortably over the MD3-XT requirement — with bow, stern and azimuth thrusters already fitted and 20 kn transit speed for rapid-response work. Configured around ploughing rather than cable volume.

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Vessel NameSW Duke

Previous NamesPolar Duke (to 2020) · Blue Arrow (to 2011)

Keel Laid2007

ClassificationDNV ✠1A1 COMF(V-2) E0 HELDK(S, H) NAUT(AW) RP TMON

Teal-flagged items in the specification below denote new or modified equipment within the conversion scope.

Capabilities & Scope

Class Leading Ploughing Capability

It's ploughing, not post-lay burial, that decides the bollard pull requirement. With 145 t on the hook — and power in hand to support a high-power trencher — the ST-321 suits a plough-burial and repair role, or works alongside a lay vessel, rather than a high-volume carrying mission.

Built to tow — 145 t continuous bollard pull, 1.8× the MD3-XT 80 te tow load, with bow, stern and azimuth thrusters already fitted at 4,225 kW total.
Built for fast response — 20 kn maximum, 17 kn transit, 11,000 nm range; 60 berths retained for crew change on station.
One power plant, two duties — four MAN engines at 15,000 kW with shaft generators comfortably cover thrusters, hotel and cable spread on DP.

The Conversion

Retained & New

Dimension delivers this as a turnkey conversion — engineered in-house and executed through partner shipyards, with leading vendor support across the plough and handling spread. The existing equipment comes out, releasing around 900 t of lightweight, and the main hold becomes a Ø13 m below-deck cable tank with the compressor room reworked as the cable machinery space. The back deck is rebuilt around the plough: MD3-XT, tow winch and A-frame, with the cable spread sized to suit burial rather than high-volume carrying.

RRetained — Hull, four main engines and their shaft generators, full thruster set, accommodation, anti-roll tank.
NNew (≈1,260 t) — Cable tank and spread, MD3-XT plough, tow winch, A-frame, ROV and LARS, DP2.
TTimeline — 12–14 months, subject to equipment lead times.

Technical Details

Principal Particulars

Principal Particulars
Design	Skipsteknisk ST-321
Built	2010 · Factorías Juliana, Spain
Length overall	107 m
Beam, waterline / max	19.2 / 22.0 m
Max draught	6.5 m
Gross tonnage	7,130
Deadweight	To be confirmed
Water ballast	1,230 m³
Roll reduction	Passive anti-roll tank
Cable Capacity — Converted
Cable tank, below deck	≈1,250 t · Ø13 m
FOC per load-out	≈1,700 – 2,100 route-km
Stowage form	Below-deck cable tank
Power & Propulsion
Main engines	2 × 4,500 + 2 × 3,000 kW MAN
Total installed power	15,000 kW
Propulsion	2 × 7,100 kW geared, twin CPP
Shaft generators	4 × 2,200 ekW on PTO
Electrical capacity	8,800 kW, shared with shafts
Bow / stern thruster	1,200 / 925 kW
Retractable azimuth	2,100 kW
Total thruster power	4,225 kW
Performance, Accommodation & Class
Max / transit speed	20 / 17 kn
Range at transit	11,000 nm
Endurance	34 days at sea
Fuel / fresh water	1,820 / 173 m³
Continuous bollard pull	145 t
Dynamic positioning	DP2 — retrofit
Persons on board	60

All-New FO Cable Handling Spread

Burial ROV · DOHB · Stern Sheaves · Plough · Work-Class ROV

Cable Handling & Deck — All New
Lay & burial ROV	SMD QT600
Burial depth	3.0 m · 2,500 msw · 450 kW
Drum cable engine	SMD, Ø4.0 m, 40 t
DOHB	4 wheel-pair, 4 t
Stern sheaves	2 × Ø3.0 m
Plough	SMD MD3-XT
Plough trench depth	3.3 m · 23.5 t in air
Plough max tow load	80 te
Plough LARS	A-frame 60 – 100 t SWL
Tow winch	80 t · 3,500 m
Work-class ROV	2,000 m rated, with LARS
Grapnel & A&R winch	60 t

ST321

Class Leading Ploughing Capability

Principal Particulars

Burial ROV · DOHB · Stern Sheaves · Plough · Work-Class ROV

Other Hulls Under Review

Interested in the ST321 conversion?

ST321

Class Leading Ploughing Capability

Principal Particulars

Burial ROV · DOHB · Stern Sheaves · Plough · Work-Class ROV

Other Hulls Under Review

SX124

SX134

ST327

Interested in the ST321 conversion?