How to Choose a Marine Scale: A Buyer's Guide

Choosing a marine scale means answering a handful of questions in the right order: what you weigh, how heavy and how light it gets, what it sits in, how rough the conditions are, what the weight will be used for, and where the data has to go. This buyer's guide walks through those decisions step by step, summarises the key numbers and links to detailed articles for each topic. It ends with a request-for-quotation checklist you can send to any supplier.

Step 1: Define the weighing job

Start with the job, not the scale. Two vessels with the same catch can need very different scales depending on whether they grade, pack, sample or simply record box weights. Write down the answers to these questions before comparing products:

Question	Why it matters	Example answer
What is weighed?	Determines platform, hopper or grader	Whole fish in 40 kg boxes; biological samples
Heaviest gross load?	Sets capacity, including container and ice	45 kg per box
Lightest regular load?	Sets the readability needed	50 g samples
Container footprint?	Sets platform size	800 × 450 mm boxes
How many weighings per hour?	Speed, ergonomics, automation	200 boxes per hour at peak
What is the weight used for?	Trade, labelling, catch records, science	Box labels and catch records
Where does the data go?	Connectivity and software	Label printer and a spreadsheet
Where will it be installed?	Mounting, space, motion, drainage	Processing deck, wall-mounted

If several very different jobs appear in the list, such as heavy boxes and gram-level samples, plan for more than one scale. One scale for everything almost always compromises both jobs.

Step 2: Choose capacity and readability

Capacity must cover the heaviest gross load with a margin; readability must be fine enough for the lightest regular load. The two are linked, because a larger capacity normally comes with a coarser step.

• Capacity. Add product, container, ice and water, then allow for dynamic peaks: on a deck accelerating upwards at 1.5 m/s², a load presses on the load cells about 15% harder than at rest.
• Minimum load. OIML R 76-1 sets the minimum capacity of a class III instrument at 20 verification scale intervals. As a rule of thumb, keep regular loads above 20 divisions and preferably above 200, where one division is 0.5% of the load.
• Readability versus accuracy. A finer display step does not make a scale more accurate. At sea, a steady reading in 5 g steps is more useful than a restless one in 1 g steps.

The full explanation, including a table of every WPL weighing range with its illustrative minimum load, is in Capacity vs Readability: Choosing the Right Weighing Range.

Step 3: Choose platform size and form

The platform must carry the full base of your largest regular container without anything else touching it. Typical European fish boxes fall into three footprint families: 600 × 400 mm for 10 to 15 kg fillet boxes, 800 × 400 to 800 × 450 mm for 20 to 40 kg boxes, and up to about 885 × 555 mm for 50 kg boxes, based on published dimensions from packaging manufacturers such as Craemer. Measure your own boxes at the base, because the rim of a nestable box is larger.

Also decide on the form of the scale:

Form	Choose when
Bench scale on wall or column mount	Boxes, crates and baskets are lifted on and off by hand
Bench scale with hopper	Loose product is batched into a container
Small precision platform	Individual fish, organs and other samples are weighed in grams
Floor platform scale	Pallets, tubs, bags or equipment are moved by trolley or crane
Fold-up platform	Deck space is scarce or the area underneath must be cleaned daily
Grader	Individual fish must be sorted or batched by weight at high throughput

Footprint tables and a container-to-platform matching guide are in Choosing the Platform Size for Fish Boxes, Baskets and Samples.

Step 4: Check motion, tilt and gravity compensation

Motion compensation is what separates a marine scale from a waterproof land scale, so ask what it achieves and how it has been tested. An uncompensated scale shows the deck's acceleration as weight: a vertical acceleration of 1 m/s² changes the reading by about 10%. The physics is explained in the Weighing at Sea guide.

Questions that reveal real performance:

1. Test conditions. At which accelerations, tilt angles and frequencies was the scale tested? The ship section of WELMEC Guide 2 describes dynamic tests up to ±3 m/s² at no more than 0.3 Hz and tilt tests up to 15°.
2. Results. How far did readings deviate from the true load during those tests, and how long did a stable reading take?
3. Tilt. Is tilt corrected, or only detected? Uncorrected tilt makes a scale read low, by about 0.4% at 5°.
4. Gravity. Gravity is about 0.5% stronger at the poles than at the equator. Is gravity compensated, or must the scale be re-adjusted when the fishing area changes?
5. Settings. Can stability and display-speed settings be adjusted to suit fast packing or fine sampling?

Detailed background: Motion Compensation in Marine Scales: What It Does and How to Judge It and Gravity, Latitude and Why Marine Scales Need Gravity Compensation.

Step 5: Clarify legal and regulatory requirements

Whether a scale must be legally verified depends on what the weight is used for and where. Weighing for trade, for prepackages that carry a nominal quantity, or for official catch records can fall under legal metrology rules; internal process control and scientific use often do not. Clarify this before choosing, because it can rule out models or configurations.

• Accuracy classes. OIML R 76-1 classifies non-automatic weighing instruments into classes I (special), II (high), III (medium) and IIII (ordinary), each with rules for verification scale interval, number of intervals and minimum capacity.
• Ships. WELMEC Guide 2 includes specific guidance for weighing instruments installed in ships, including gravity compensation, tilt and dynamic acceleration tests.
• Fisheries control. The European Commission notes that the revised Control Regulation (EU) 2023/2842, in force since 9 January 2024, requires electronic recording of all catches, with implementing rules on weighing of fishery products.
• Prepackages. If you pack to a nominal weight, average-quantity rules apply, which directly affects giveaway.

Ask the supplier which certificates apply to the specific model and configuration offered, not to the product family in general. The framework is explained in the legal metrology hub.

Step 6: Assess materials, hygiene and durability

A scale on a fishing vessel is washed down daily, exposed to salt spray and handled roughly, so construction decides its service life. Look for:

• Stainless steel grade. AISI 316 or 316L for parts exposed to seawater and cleaning agents.
• Hygienic design. Smooth, rounded surfaces without crevices where fish residue collects; surfaces that drain.
• Sealing. Load cells, indicator and connectors protected against water ingress under daily washdown.
• Cleanability. Removable or fold-up platforms, and access underneath.
• Compatible mounting hardware. Galvanic corrosion attacks less noble metals such as aluminium or galvanised steel where they touch stainless steel in the presence of seawater, as Euro Inox explains.

See the hygiene and materials hub for more.

Step 7: Plan connectivity and data

A weight that is written on paper is a weight that has to be typed again later. Decide early where the data goes, because it determines interfaces and software.

Destination	Typical interface or function
Label printer	USB or serial connection; label templates per product
Spreadsheet or reporting	CSV export of logged weighings
Catch-management or processing software	Ethernet, RS232 or an API delivering weights in a structured format
Multiple scales on board	Central software that manages presets and logs for all scales
Shore office during the trip	Network or data transfer from the vessel

Automatic logging also removes transcription errors: in controlled data-entry studies, single manual entry produced errors in about 1% of records. The data integration hub covers the options.

Step 8: Plan installation and service

Installation determines how much of the scale's potential accuracy you actually get. Plan the position close to amidships and the centreline, a rigid mount fixed to structure, protected cable routes, a suitable power supply and free drainage. Also plan how the scale will be checked and serviced: test weights on board, a logged daily check, and a way to back up and restore settings after repairs.

A step-by-step guide is in Installing a Marine Scale on Deck or in the Fish Hold, and the day-to-day practice at sea is in Getting Accurate Weights in Rough Seas.

Step 9: Compare on total cost of ownership

Compare offers on what the scale costs over its life, not on purchase price. The recurring costs are giveaway from overfilling on unsteady readings, downtime at sea, recalibration, corrosion damage and manual data handling. In a hypothetical example, reducing average overfill by 45 g on 2,000 packs of 5 kg a day over 150 days saves 13.5 tonnes of product a year. The method and more examples are in Total Cost of Ownership of a Marine Scale.

WPL range overview

The table maps WPL products to the jobs described above. Full specifications are on each product page.

Product	Job	Key specifications
M2 Series Marine Scale	Boxes, crates, baskets, packing and labelling	6 to 400 kg; platforms 300 × 250 to 800 × 600 mm; motion compensated; AISI 316; USB, RS232, Ethernet; platforms and hoppers
M3 Series Scientific Marine Scale	Biological and scientific samples at sea	300 g to 6,000 g; readability from 0.1 g; platforms 120 × 120 and 270 × 270 mm; 316L; motion compensated
M5 Series Marine Platform Scale	Heavy loads where deck space is scarce	600 to 3,000 kg, higher on request; 1000 × 1000 to 1500 × 1500 mm; fold-up platform; compensates motion, tilt and gravity change; 4 load cells
M6 Series Marine Platform Scale	Heavy loads, economical platform option	600 to 3,000 kg; same platform sizes as M5; fully sealed; optional access ramp; compensates motion and tilt
R50 Catch Label System	Catch registration and labelling	Records catch area, fishing method, weights and lengths; optional GPS and NFC
WeightControl	Logging, statistics, export and integration	Runs on the scale; browser access; CSV export; JSON API

Request-for-quotation checklist

Send the following information and questions with every enquiry, so that offers can be compared on equal terms.

1. Products and containers weighed, with base dimensions of the containers.
2. Heaviest gross load and lightest regular load.
3. Required readability and whether legal verification is needed, and in which country.
4. Weighings per hour at peak, and whether labelling or grading is involved.
5. Vessel type and length, operating areas and their latitude range.
6. Proposed installation position, available space and mounting surface.
7. Power available, and whether battery operation is needed.
8. Required interfaces and software destinations for the data.
9. Question: does the scale compensate for motion, tilt and gravity, and what were the results under which test conditions?
10. Question: which certificates apply to the exact model and configuration offered?
11. Question: how are calibration, service and spare parts handled for vessels at sea?

How WPL approaches this

WPL Industries designs and builds motion-compensated weighing systems for fishing, offshore and research at sea, and has delivered them to fishing and research fleets across Europe, the Americas and beyond. WPL holds NMi certificates EK-5417 and CE-284. Settings such as capacity, rounding, stability count, display speed and marine filtering are configured with the R10 Configuration Panel. To discuss your application with the checklist above, use the quote request.