Workboats for Seaweed Farms: What the Crew Actually Uses

Every seaweed farm has a second farm nobody puts in the business plan: the boat. Kelp grows submerged, out of sight, and everything that matters about it — deploying seeded line, tensioning headers, checking storm damage, hauling four wet tonnes against a falling tide — happens from a deck. Choose and rig that deck well and the farm feels effortless; choose it badly and every visit becomes a small emergency. This article is a working guide to the vessels and gear real kelp crews use, what actually matters when choosing, and the mistakes that quietly cost whole seasons.

If you are costing a first farm, our equipment and budget rundown covers the shore side; here we stay on the water.

What the boat actually has to do

Before brands and hull shapes, write down the jobs. A farm workboat must:

• Transit reliably in lumpy water — farm sites are exposed by design, chosen for the currents and nutrients that kelp loves, as our site selection guide explains. You will motor out in weather a sensible person stays home in.
• Hold station alongside a line — hours of slow, precise manoeuvring along headers, often in wind and swell, without snagging the very gear you're tending.
• Lift and pull — tensioning headers at deployment, hauling anchors occasionally, and pulling seed-sleeved or blade-loaded grow-line aboard at harvest.
• Carry bulk, wet weight — harvested kelp is 85–90% water and dense; a tonne of it fills space fast and sits heavy.
• Run every week, alone, cold — most visits are short solo trips in winter light.

Rate any vessel against this list, in this order, and most mistakes never happen.

The three vessel tiers most farms use

Tier 1: The open skiff (5–7 m)

The backbone of small and medium farms. A centre-console or open work skiff in aluminium or reinforced polyethylene with a 40–90 hp outboard does 90% of the job at a fraction of bigger-boat cost: fast to trailer, cheap to run, easy to shove off a beach.

Rig it for the work, not the showroom. What matters most: a flat, uncluttered working deck aft; a small davit or a line-hauler for grow-line; gunwales low enough to work the water comfortably; and seating that doesn't eat deck space. Non-slip deck coatings and a simple splash rail are worth more than electronics beyond a chartplotter and VHF.

Tier 2: The working cat or landing craft (7–10 m)

When the farm passes a few hectares — or the site sits far offshore — you step up. Catamaran workboats and bow-landing-craft designs dominate here because both deliver what kelp work actually wants: a wide, stable, flat working platform and serious deck load. Cats hold station beautifully alongside lines; landing craft kneel their bow to a beach or ramp so forklifts and bulker bags roll straight off.

Typical rig at this tier: a small hydraulic crane (0.5–2 tonne lift), a capstan or line-hauler, twin outboards or inboard diesels, and deck space for four to six bulker bags. Many of these vessels earn their keep beyond the farm — subcontracting to other growers, mussel farms or marine contractors — which is how most small operations justify owning one.

Tier 3: Contracted heavy lift (gourmet problem, common solution)

Almost nobody should own a crane barge. But almost every farm needs one workboat-with-crane day a season: setting anchors at deployment and lifting moorings at breakdown. The standard industry answer is hiring a local aquaculture contractor or fishing vessel with a crane, by the day. Contracted well, this is vastly cheaper and safer than wrestling 500 kg anchors off a skiff with a davit and hope.

Our half-hectare farm walkthrough describes the rhythm: skiff for everything weekly, contract vessel twice a year.

Propulsion: what the water chooses

• Outboard petrol dominates under ~10 m. Reliable, simple, trailered home. Two strokes are vanishing; modern four-strokes are the default.
• Inboard diesel dominates working cats and landing craft. Torque for station-holding and lifting, fuel economy under load, and the machinery doubles as crane hydraulics.
• Twin engines are worth it on exposed sites — the swim home after a single failure in farm chop is a story nobody wants.
• Electric outboards are arriving and genuinely fit some farms: short-hop, sheltered sites with shore power. Range and saltproofing still limit them; watch this space rather than lead it unless your site truly fits.

Whatever the engine, guard the prop. Kelp farms are rope forests, and a line around the shaft is the most common mechanical failure in the industry. A line-cutter on the shaft, a spare shear pin kit, and practised neutral-and-reverse work near gear will save you a season-ending tangle.

Deck layout: the farm's real workshop

The difference between a boat and a workboat is its deck. The layout that works, whatever the size:

• A clear working zone, aft or forward, at least 2 × 2 m. No cleats, lockers or trip hazards in the area where line and kelp come aboard.
• The hauler at deck edge, not centre. Line should come aboard over the gunwale, across the hauler, and into a bag or onto a rack in one motion.
• Load low and centred. Wet kelp bags stacked high transform stability from arithmetic into prayer. Keep the load low, strapped and amidships; know your vessel's limits cold.
• Rinse and stowage. Salt water destroys gear systems; a deck-wash pump and dry stowage for knives, gloves and spare shackles extend every kit item's life.
• One seat you can rest in. Harvest days run eight hours. The crew who can sit for ten minutes between lines works the last line as well as the first.

Safety and survival gear is farm gear

Farms kill through drowning, cold and propellers, and the prevention is unglamorous: personal flotation worn (not stowed), an immersion plan for your latitude's water temperature, VHF plus a charged phone in a waterproof case, a knife on your person rigged to cut you free of line in one motion, and a kill cord used every single time the engine runs. Tell someone shore-side your plan and return time, every trip. Kelp is patient; crews are not always.

The mistakes that cost seasons

After years of watching farms fit out their first vessel, the recurring errors are consistent:

1. Buying speed instead of stability. A fast planing hull feels great empty and terrifying loaded beside a line in swell. Stability, deck space and load capacity beat knots.
2. Underestimating wetted length. Boats that are fine for recreation in your bay may be undersized for the exposed fetch where good kelp grows.
3. Dealer layouts. Showroom boats are arranged for fishing or comfort, not line work. Plan to strip and re-rig, and budget for it.
4. No line-hauler. Hand-hauling seed line in autumn is a test of character; hand-hauling a tonne of wet grow-line in spring is an injury with a schedule. Even a small hauler transforms the work.
5. Skipping the contracted crane day. Stretching a small davit past its rating to save one contractor invoice has ended more than one farm's season in a morning.

Key takeaways

• Rate any vessel against the jobs: exposed-water transit, station-holding, lifting, bulk wet load, and solo reliability.
• Most farms run a two-vessel model: an owned open skiff (5–7 m) for 90% of the work, plus contracted crane capacity a few days a season.
• Work cats and landing craft earn their keep above a few hectares, and best when they also subcontract off-farm.
• Guard the prop, rig a line-hauler, lay out a clean working deck — these three choices decide daily quality of life more than the hull does.
• Stability and deck load always beat speed. Flotation worn, kill cord clipped, plan filed: unglamorous, non-negotiable.

FAQ

What size boat do I need for a half-hectare farm?

A 5–7 m open skiff with a 40–90 hp outboard handles essentially all routine work at that scale, including harvest, provided it has a clean working deck and a small line-hauler. Contract a crane vessel for the two days a season you need to set or lift moorings.

Catamaran or monohull?

For active farm work, cats win: a wide, stable working platform, minimal roll at rest alongside lines, and huge deck area for kelp bags. Good monohull landing craft are the close alternative, especially where beach launching matters. Fast monohulls are the poor choice — speed that a working farm does not need, stability it cannot offer.

Should my first boat be new or used?

Used, inspected and simple. Kelp farming is brutally hard on boats — salt, load, beaching, knocks against gear — and a working vessel will wear the marks within a season. A sound used hull with a serviced engine, re-rigged for line work, leaves budget for the hauler, crane days and safety kit that actually change outcomes.

Do I need a crane on the boat?

On the boat you own, usually no. On the boat you contract for deployment and breakdown, yes. A small 0.5–2 tonne hydraulic crane becomes worth owning only at several hectares or when you subcontract to other farms — many workboat owners cover their vessel costs exactly this way.

What's the single most common boat mistake?

Working a rope forest without protecting the propulsion. A grow-line around the shaft is the industry's signature failure: it kills propulsion at the worst moment, threatens to pull gear across the farm, and is miserably hard to clear in swell. Fit a line cutter, practise drifting through gear in neutral, and never reverse hard without knowing what's behind you.