Choosing a Scientific Marine Scale for a Research Vessel
Start from the samples: list each weighing task with its mass range and required resolution, then choose capacity, readability and platform per station. Check motion compensation under realistic conditions, stabilisation time, wind protection, corrosion resistance and cleaning, and make sure weights flow directly into survey software with a stability flag, timestamp and scale identifier.
Start with the samples, not the scale
The right scientific marine scale follows from the samples: list every weighing task, the lightest and heaviest item in each, and the resolution the data need, then choose capacities and platforms that cover those ranges with some margin. Most survey vessels end up with several scales rather than one.
- List weighing tasks per station. Typical stations are the sorting area (baskets and categories), the measuring station (individual fish) and the wet laboratory (organs and stomach contents). The workflow is described in Biological Sampling on Research Vessels.
- Define mass ranges. Note the lightest and heaviest item per task, for instance 2–300 g for small fish or 5–60 kg for baskets.
- Set the resolution. A practical rule is a readability of no more than 1 % of the lightest item you will record; see Precision Weighing of Small Samples at Sea.
- Check the data format. Confirm the units and fields your database expects. ICES DATRAS, for example, stores catch, subsample and individual weights in grams (DATRAS units).
- Then compare scales against the checklist below.
Requirements checklist
A scientific marine scale has to satisfy metrological, environmental and data requirements at the same time. This checklist summarises the questions that most often decide whether a scale performs well on a survey.
| Requirement | Why it matters | What to check |
|---|---|---|
| Capacity and readability | Determines the lightest and heaviest sample that can be recorded with useful resolution | Capacity/readability combinations per platform; whether readability changes with load or mode |
| Motion compensation | Vessel accelerations change the force on the load cell | Behaviour in realistic sea states; ask for a demonstration or trial on board |
| Stabilisation time | Throughput at the measuring station, often hundreds of fish per haul | Time to a stable reading for typical samples; adjustable filtering |
| Platform size | Long fish overhanging a small platform cause eccentric loading and handling problems | Platform dimensions against the longest fish; use of trays |
| Wind protection | Air movement disturbs light samples | Availability of a wind cover for small platforms |
| Materials and sealing | Salt water, fish slime and daily washdown | Stainless steel grade, waterproof construction, smooth cleanable surfaces |
| Power | Mains quality varies; some tasks are portable | Supply voltage range, battery option and battery endurance |
| Data interfaces | Direct capture avoids transcription errors | RS232, USB, Ethernet, Bluetooth LE or Wi-Fi; documented protocol |
| Data content | A weight without context is hard to validate | Stability flag, timestamp, unit and scale identifier in the output |
| Calibration and service | Credibility of the data and uptime at sea | Calibration procedure, check-weight routine, diagnostic and backup tools |
| Operator interface | Wet gloves, poor light, time pressure | Display readability, keys usable with gloves, clear stability indication |
Capacity and readability: matching ranges to tasks
Capacity ranges should overlap the tasks with some margin, and the readability of each range should suit its lightest sample. The table shows how the ranges of WPL's scientific and bench scales map onto common survey tasks; the same logic applies to any comparison.
| Range (readability) | Platform | Suits, for example |
|---|---|---|
| 300 g (0.1–0.2 g) | 120 × 120 mm | Gonads, livers and stomach contents from about 10–20 g; small fish such as sprat |
| 600 g (0.2–0.5 g) | 120 × 120 mm | Small pelagic fish, juvenile gadoids, larger organs |
| 1,500 g (0.5–1 g) | 120 × 120 or 270 × 270 mm | Herring, mackerel, whiting; large gonads |
| 3,000 g (1–2 g) | 120 × 120 or 270 × 270 mm | Medium roundfish and flatfish |
| 6,000 g (2–5 g) | 120 × 120 or 270 × 270 mm | Larger individual fish up to a few kilograms |
| 15 kg to 60 kg (2–20 g) | 400 × 300 to 600 × 400 mm bench scale | Baskets, catch categories and subsamples; very large individual fish |
Note that a 270 × 270 mm platform is more practical for fish longer than about 30 cm, while a small platform with a wind cover is more stable for light samples.
Data capture: from scale to survey database
Connecting the scale directly to survey software removes transcription errors and links each weight to the right station, species and fish. Survey data capture systems have done this for decades: the Cefas research vessel data capture system records catch element weights either from manual input or directly from marine scales, and collects individual fish weights from linked scales during length sampling (Silva et al., 2013).
Interfaces
- RS232 serial is simple and robust, and widely supported by existing survey software, but needs cabling and adapters on modern computers.
- USB suits a scale connected to a single workstation.
- Ethernet allows several scales on the vessel network to report to one system.
- Bluetooth LE and Wi-Fi reduce cabling, but reliability should be tested in the steel environment of a wet laboratory.
Integration steps
- Define a data dictionary. Fix units (for instance grams), decimal places, and the fields that accompany each weight: stability flag, timestamp, scale ID.
- Decide the trigger. Either the operator confirms a stable weight on the scale, or the survey software requests the current stable value.
- Test in port. Run a mock station with the actual software, cables and operators before sailing.
- Handle failures. Define a fallback for manual entry and flag manually entered values.
- Back up. Keep a local log on the scale or system as a second record, exportable after each haul or day.
Broader integration patterns, from serial strings to APIs, are covered in the Data Integration hub.
Calibration, verification and quality assurance
For scientific use, what matters most is traceable calibration before the survey and documented checks during it. Calibration of non-automatic weighing instruments, including eccentricity, repeatability and uncertainty, is described in EURAMET Calibration Guide No. 18, and the metrological requirements for such instruments are set out in OIML R 76-1.
The EU directive on non-automatic weighing instruments, Directive 2014/31/EU, distinguishes uses such as commercial transactions and the application of laws from "all other applications". Survey science normally falls in the latter group, but where research or observer data serve control or trade, check which rules apply; see the Legal Metrology hub.
- Carry test weights matching each range and check them every watch.
- Log check results with date, time, scale ID and sea conditions.
- Recalibrate after repairs, relocation or a failed check.
Installation on board
Where a scale is installed affects its performance as much as its specification. Mount scales on rigid benches or bulkheads close to midships and low in the vessel where the layout allows, away from vibration sources, doors and ventilation outlets. Route cables clear of washdown water and hose areas, provide a stable power supply, and keep the display at eye level for operators wearing protective clothing.
How WPL approaches this
WPL's M3 Series Scientific Marine Scale is motion-compensated, built in 316L stainless steel and waterproof, with ranges from 300 g to 6,000 g on 120 × 120 mm or 270 × 270 mm platforms, and options including a wind cover, battery, USB, Bluetooth LE and the WeightControl IOT module. WeightControl runs directly on the R10 scale without a separate PC, logs every weighing, exports CSV and provides a JSON API with current weight, stability status and commands such as Zero and Tare, while the R10 Configuration Panel supports calibration, diagnostics and backup. For an overview of the whole research weighing topic, see the Research Vessels hub.
Frequently asked questions
Is one high-capacity scale with fine readability enough for a survey?
Rarely. At sea the usable resolution is limited by residual motion noise, and a large platform is awkward for small samples. Most vessels use separate scales for baskets, individual fish and small samples, which also allows several stations to work in parallel during busy hauls.
Can our existing survey software read a new scale?
Usually, if the scale offers an interface and data format the software already supports, such as a documented serial output or a network API. Ask for the protocol documentation early, test with the actual software in port, and plan for small adaptations in the software's device configuration.
How often should scales be checked during a survey?
A common practice is a check with a test weight at the start of each watch, after moving or cleaning a scale and whenever readings look suspicious. Recording each check with time, scale ID and conditions provides the evidence needed to defend the data afterwards.
Does a research scale need an accuracy class?
Accuracy classes belong to legal metrology and are required where the law applies, such as trade. For survey science the key requirement is usually a traceable calibration with known uncertainty. If data will also serve control or trade purposes, check the applicable rules first.
Sources
- ICES Data Centre. DATRAS 3.0 – Units in DATRAS
- Silva, J.F., Ellis, J.R. & Ayers, R.A. (2013). Length-weight relationships of marine fish collected from around the British Isles. Cefas Science Series Technical Report 150
- EURAMET Calibration Guide No. 18 – Guidelines on the Calibration of Non-Automatic Weighing Instruments
- OIML R 76-1 Non-automatic weighing instruments. Part 1: Metrological and technical requirements
- Directive 2014/31/EU on non-automatic weighing instruments (EUR-Lex)
Written and reviewed by WPL Industries weighing engineers. Technical and regulatory content is checked against the cited sources. Editorial policy