Weighing and Grading on Factory Vessels
Factory vessels weigh raw material at intake, product after each processing step for yield, pieces for grading and batching, glaze before and after application, and finished packs for labels. Controlling yield, giveaway and glaze requires motion-compensated scales at work stations, a grader for batching, platform scales for pallets and one data system.
What weighing does on a factory vessel
On a factory vessel, weighing controls the economics of the whole operation: it measures raw material coming in, yield through processing, grading and batching into packs, glaze and pack weights, and the labels that carry weight and lot information into the supply chain. In some fisheries, at-sea scales are also part of official catch accounting.
Because the vessel is at sea for weeks and product is frozen on board, errors cannot be corrected ashore. A carton that leaves the plate freezer overweight has given product away, and one that is underweight may be rejected or break labelling rules.
Weighing points along the processing line
A typical line has six to eight weighing points, each answering a different question.
| Weighing point | Question it answers | Typical equipment type |
|---|---|---|
| Raw material intake | How much catch entered processing? | Hopper, belt or platform scale |
| After heading and gutting | What is the yield of the first processing step? | Bench scale with tub or hopper |
| Filleting and trimming | What is the fillet yield per batch or operator? | Bench scales at work stations |
| Grading | Which size class does each piece belong to? | Weight grader |
| Batching into packs or blocks | Does each pack reach its nominal weight with minimal overfill? | Batching grader, hopper scale |
| Glazing | How much glaze was applied? | Bench scale before and after glazing |
| Finished pack | Is the pack within limits, and what goes on the label? | Checkweigher or bench scale with label printer |
| Palletising and hold | How much product is stored? | Platform scale |
Yield, giveaway and glaze
Three ratios decide whether processing at sea pays: yield, giveaway and glaze.
- Yield is output weight divided by input weight for a processing step, for example fillet weight divided by headed and gutted weight. Weighing both sides of a step, per batch or per shift, shows where product is lost.
- Giveaway is the product packed above the nominal weight. If 20 kg cartons average 150 g over nominal, 0.75 % of the product is given away: 150 kg for every 1,000 cartons.
- Glaze is the protective ice layer on frozen fish. The FAO technical paper on freezing and refrigerated storage in fisheries describes glazing after freezing by spraying, brushing or dipping in chilled water. For food sold in the EU, the declared net weight of glazed food must exclude the glaze (Regulation (EU) No 1169/2011, Annex IX).
To measure glaze, weigh the same product on the same scale before and after glazing and express the difference as a percentage of the glazed weight, stating which definition you use, since customers and methods differ.
Automatic weighing and at-sea monitoring rules
Where weights are used for trade or official purposes, automatic weighing equipment falls under specific metrology rules. In the EU, automatic catchweighers, including grading and weight-labelling instruments, are covered by Annex MI-006 of the Measuring Instruments Directive 2014/32/EU, and the international recommendation for such instruments is OIML R 51.
Some fisheries set their own at-sea scale requirements. In Alaska, at-sea scales account for most of the catch of catcher-processors and motherships (NOAA Fisheries). Federal rules require approved scales to be inspected annually and tested daily; belt and automatic hopper scales must pass a daily material test within ±3 %, and platform and hanging scales used in testing have a maximum permissible error of ±0.5 % (50 CFR 679.28). See the Legal Metrology hub for the European framework.
Recommended WPL set-up
A factory vessel usually combines bench scales at work stations, label systems for cartons, platform scales for pallets and a central data system; grading and batching machinery is specified as a separate part of the line.
| Position | Suggested equipment | Notes |
|---|---|---|
| Intake, gutting and trimming stations | M2-M or M2-L with 15 kg (2–5 g) or 30 kg (5–10 g), with hopper or tub platform | Motion-compensated; USB, RS232 and Ethernet |
| Cartons, blocks and labels | M2 with label printer, or R50 Catch Label System | R50 supports registration, sorting, filling, packing and freezing workflows |
| Pallets and frozen stock | M5 or M6, 600–3,000 kg | M5 platform flips up for cleaning and deck space |
| Yield statistics and labels | WeightControl and R10 Configuration Panel | Statistics per preset and period, CSV and JSON export; ZPL label design with preview |
Where a weight grader or batching line is added, check its piece weight range and throughput against the product, its hygienic design and IP rating, and whether its data can be exported to the same system as the bench and platform scales. A grader used on board must also cope with the vessel's motion, and where pack weights are used for trade it must meet the automatic weighing rules described above. See weight grading of fish and reducing giveaway with batching for what to look for.
Related knowledge
- Onboard Processing hub – grading, batching and traceability in depth
- Hygiene and Materials – stainless steel grades and IP ratings
- Weighing Solutions for Trawlers
- Data Integration hub
Frequently asked questions
How much does giveaway cost on a factory vessel?
It scales directly with volume. An average overfill of 150 g on 20 kg cartons is 0.75 % of product, or 150 kg per 1,000 cartons. Batching pieces to target weights and monitoring average pack weight per shift are the usual ways to reduce it without risking underweight packs.
Does the label weight of glazed fish include the glaze?
Not for food sold in the EU: Annex IX of Regulation (EU) No 1169/2011 requires the declared net weight of glazed food to exclude the glaze. Measuring glaze on board, by weighing before and after glazing, helps ensure the declared net weight is correct.
Are processing scales on board subject to legal metrology?
It depends on how the weights are used and where. Weights used only for internal yield control are generally not regulated, while weights used for trade, prepackages or official catch accounting can require approved and verified instruments. Check the rules of the flag state, market and fishery.
Sources
- Johnston, W.A. et al. (1994). Freezing and refrigerated storage in fisheries. FAO Fisheries Technical Paper 340
- Regulation (EU) No 1169/2011 on food information to consumers, Annex IX (net quantity; glazed food)
- Directive 2014/32/EU on measuring instruments, Annex MI-006 automatic weighing instruments (EUR-Lex)
- OIML R 51-1 Automatic catchweighing instruments. Part 1: Metrological and technical requirements
- NOAA Fisheries – Catch Weighing and Monitoring in Alaska
- 50 CFR § 679.28 – Equipment and operational requirements (scales)
Written and reviewed by WPL Industries weighing engineers. Technical and regulatory content is checked against the cited sources. Editorial policy
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