250 new ship calls can turn into 2,000 tug jobs surprisingly fast
The ship-call number is the easy part. The fleet decision comes from arrival plus departure, how many tugs have to work at the same time, how long they are tied up, and whether those movements arrive neatly spaced or all land in the same weather window.
Additional annual vessel calls.
Approximate additional arrival and departure movements.
Extra vessel calls per week on average.
Tug engagements if each movement requires two to four tugs.
Then add maintenance, weather, schedule recovery and peak-demand margin. That is the useful fleet number.
250 calls under three operating profiles
Two tugs per movement, 1.5-hour job window and 20% planning reserve.
Three tugs per movement, 2-hour job window and 25% planning reserve.
Three working tugs plus one committed standby, 2.5-hour movement window and 25% planning reserve.
*Tug-year examples use an illustrative 2,500 usable service hours per tug per year. This is a planning assumption, not an industry standard.
The mistake is sizing only from annual hours
A three-tug movement needs three compatible tugs at once. Annual utilization may look low while peak coverage is already exhausted.
A terminal adding 250 feeder calls is a very different problem from adding 250 large tankers, LNG carriers or 300-metre container ships.
Tug time includes transit to the ship, hookup, escort or channel work, berthing, release and return, not just the final push alongside.
Weather openings, tidal windows, berth schedules and vessel delays can place several movements into the same few hours.
A fleet sized to exactly meet the daily schedule fails as soon as a tug enters planned maintenance or develops a machinery problem.
Public benchmarks worth watching
| Benchmark | Published operating picture | Capacity lesson |
|---|---|---|
| Brunswick | 733 vessel calls, 24/7 docking operations and three local Moran tugs identified in the public fleet update. | Roughly 250 incremental calls are material compared with a real three-tug U.S. port workload. It is a useful scale check, not a fleet-sizing formula. |
| Singapore | Current terminal guidelines commonly range from two tugs to four tugs depending on vessel length, berth and operating conditions. | Ship mix can change tug demand more than the headline number of calls. |
| Rotterdam | Minimum-tug planning and cross-chartering were introduced to improve nautical capacity and response during demand peaks. | Flexible capacity can delay a newbuild if neighboring fleets can reliably cover peaks. |
| Terminal towage | Svitzer describes terminal contracts as making a predetermined number of tugboats available, commonly against a fixed day rate rather than volume alone. | The commercial question is availability, not simply cost per ship call. |
| Woodside model | Svitzer’s published terminal case study uses five tugs, 34 crew and 24/7 operations. | High-consequence terminals carry resilience and crew capacity beyond the average hourly workload. |
If 250 extra calls are spread evenly and the existing fleet has real spare capacity, one additional tug may be enough for ordinary two-tug harbor work. If each movement needs three tugs and today’s fleet is already tight, two additional units becomes a much more realistic screen. If the terminal requires three working tugs plus dedicated standby, peak coverage can push the physical requirement higher even when annual utilization looks modest.
250-call tug capacity model
Change the movement assumptions and see when annual workload or peak availability forces another tug into the fleet.
