Vessel Ownership Days: Shipping Fleet Size Over Time

Vessel ownership days are the aggregate number of days during a reporting period that a shipping company owns the vessels in its fleet.

They are a time-weighted measure of fleet size.

Basic calculation

For a single vessel owned for an entire 365-day year:

1Ownership Days = 365

If a company owns 10 vessels for the full year, it records roughly 3,650 ownership days. A vessel acquired halfway through the year contributes only about half a year's ownership days.

Why ownership days matter

Ownership days help investors distinguish fleet growth from rate growth.

Shipping revenue can rise because:

• the company owns more vessels;
• vessels are owned for more of the reporting period;
• utilization improves; or
• daily charter economics improve.

Ownership days isolate the fleet-size/time component better than period-end vessel count alone.

Ownership days versus average vessel count

A rough relationship is:

1Average Owned Vessels ≈ Ownership Days ÷ Calendar Days in Period

If a 365-day year contains 3,650 ownership days, the fleet averaged about 10 owned vessels.

This is more informative than simply comparing year-end fleet counts when acquisitions or disposals occur during the period.

Ownership days versus available days

Vessel Available Days are normally lower than ownership days because scheduled maintenance, drydockings, upgrades, special surveys, and related positioning can remove vessel time from revenue availability.

The difference can be expressed as:

1Ownership Days - Available Days = Defined Scheduled/Planned Off-Hire Days

The exact exclusions vary by issuer.

Ownership days and cost analysis

Ownership days are commonly used as a denominator for Daily Vessel Operating Expense.

That makes ownership-day changes important when separating:

• fleet expansion;
• per-vessel cost inflation; and
• one-time maintenance effects.

A rise in total vessel operating expense does not necessarily mean per-day costs deteriorated if the fleet simply became larger.

Ownership days are not operating days

Ownership does not mean a vessel was available or earning revenue.

A ship can be owned while undergoing drydock, scheduled repair, upgrade, or other off-hire activity.

Vessel Operating Days therefore answer a different question: how much available time was actually operating under the issuer's methodology.

Worked example

Suppose a company begins the year with eight vessels and buys two more exactly halfway through the year.

Approximate ownership days are:

18 × 365 = 2,920
22 × 182.5 = 365
3Total ≈ 3,285 ownership days

The year-end fleet is 10 vessels, but the time-weighted average fleet is only about nine vessels.

Filing examples

Safe Bulkers defines ownership days as the aggregate days each vessel is owned and notes that they indicate fleet size over a period. Globe International Carriers similarly describes ownership days as affecting both revenues and expenses.

Sources:

• Safe Bulkers 2025 Form 20-F
• Globe International Carriers 2025 Form 20-F

Bottom line

Vessel ownership days are a time-weighted fleet-size measure. They help investors separate changes caused by fleet expansion or contraction from changes in vessel availability, utilization, charter rates, and per-day operating costs.

Explore more topics in the Financial Research Encyclopedia.