Container and bulk freight rates move far more sharply than the volume of goods being shipped. The gap between the two is a property of how shipping capacity is built and financed.
Capacity cannot adjust quickly
A large vessel takes years to design, order and deliver. Once it exists, it is expensive to idle and effectively impossible to shrink, so the supply of shipping capacity is close to fixed in the short run.
Demand for that capacity changes with the seasons, with inventory decisions and with disruptions on particular routes. A fixed supply meeting a variable demand produces violent price movement.
The same physics applies to ports, containers and inland haulage. A bottleneck anywhere on the chain removes effective capacity even when ships are available.
Why rates spike before volumes appear in accounts
Goods are booked and shipped well before they are sold and recorded as revenue. Freight prices therefore respond to orders placed for a season that has not yet arrived.
A retailer restocking for a peak period bids for space months ahead. The rate paid reflects expectations about consumer demand rather than any sales that have happened.
When those expectations prove wrong, the correction appears in freight before it appears anywhere else. Bookings are cancelled while the goods already shipped are still crossing the ocean.
How the cost flows into corporate margins
Freight is capitalised into inventory rather than expensed immediately in many accounting frameworks. The cost appears in the income statement only when the goods are sold.
That lag means a rate spike shows up in gross margin one or two quarters later. Companies buying at the peak carry the cost into a period when rates may already have normalised.
The reverse creates a flattering comparison. Margins improve on cheap freight long after the rate itself fell, which can be mistaken for improved pricing power.
Why the signal is noisy
Published spot rates cover a small share of actual cargo. Large shippers negotiate annual contracts, so their real cost moves later and less dramatically than the headline index.
Route matters as much as level. A disruption on one corridor can push a global average up while most trade lanes are unaffected.
Direction matters too, because containers must be repositioned after unloading. A lane can be expensive outbound and nearly free on the return leg, which averages badly into a single index.
Reading rates alongside inventory
Freight strength paired with rising inventories suggests goods are being pulled forward rather than sold. Strength paired with falling inventories suggests genuine restocking demand.
The two series together describe the position of the cycle more reliably than either alone. Neither is a forecast, and both are revised as customs and port data settle.
Order backlogs at shipyards complete the picture over a longer horizon. Heavy ordering during a rate spike delivers capacity years later, usually into a weaker market, which is why the cycle repeats.