A seaweed farm cost model that looks good in a spreadsheet and falls apart in the second season is not a cost model. It is a funding document. The difference between the two is usually a handful of specific inputs that producers either do not know about or choose to be optimistic about. This article covers the inputs that matter most.

Start with wet-to-dry conversion

Sugar kelp is approximately 85 to 90 percent water by weight at harvest. That means one tonne of wet biomass produces roughly 100 to 150 kilograms of dried product, depending on your drying method and the blade condition at harvest. If your cost model is built around wet weight and your buyer is quoting a price per kilo of dried product, you need to convert carefully. Many first-season producers discover this gap when they receive their first payment and it is a fraction of what the spreadsheet projected.

Post-harvest loss beyond drying

After drying shrinkage, there is sorting loss (blades that do not meet specification), transport damage, and the percentage of each batch that fails quality testing. In a well-run operation, total post-harvest loss from wet biomass to saleable dried product runs between 85 and 92 percent. In a first-season operation, it is often higher. Build in a post-harvest loss assumption of at least 88 percent and revisit it after your first harvest.

Labour: spikes, not steady state

Seaweed farming has three labour-intensive periods: seeding (October to November in the North Atlantic), line maintenance (January to March), and harvest (March to May). Outside these periods, labour requirements drop significantly. A cost model that spreads annual labour costs evenly across twelve months will understate your cash flow pressure in the peak months and overstate your costs in the quiet months. Model labour by month, not by year.

Buyer payment terms and working capital

Food ingredient buyers typically pay on 60 to 90-day terms. Some cosmetic raw material buyers pay on 120-day terms. If your cost model assumes payment within 30 days of delivery, your working capital requirement is understated. For a small producer selling 10 tonnes of dried product at EUR 3,000 per tonne, a 90-day payment delay means EUR 30,000 of revenue that is earned but not yet received. That gap needs to be funded somehow.

Equipment replacement and maintenance

Ropes, buoys, anchors, and longline hardware degrade in seawater. A realistic cost model includes an annual equipment replacement budget of 15 to 20 percent of initial capital expenditure. This is often omitted from first-season models because the equipment is new. By season three, it becomes a significant cost line.

The cost model template in the resources we publish is built around these inputs. It is a working document, not a pitch document. If you are preparing numbers for an investor conversation, it is worth running your assumptions through a model that has been stress-tested against real farm data before you sit down in that meeting.