Answer
The term "sub-charting" usually refers to Sub-Chartering (the commercial practice of a charterer re-leasing a vessel to another party).
1. Sub-Chartering (Commercial/Legal Context)
Sub-chartering occurs when the original charterer (the "Disponent Owner") of a vessel leases it to a third party (the sub-charterer). This is a common practice in the shipping industry for several strategic reasons:
Market Arbitrage: A charterer might have secured a vessel on a long-term Time Charter at a low rate. If market freight rates rise, they can sub-charter the vessel to a third party at the current higher rate, pocketing the "spread" as profit without owning the asset.
Logistical Flexibility: A large shipping company may charter a vessel to cover a specific contract of affreightment (COA). If their own cargo volume drops or schedules change, they sub-charter the ship to avoid paying "dead freight" or having the vessel sit idle while still paying the head-owner.
Operational Optimization: An operator might sub-charter a vessel to a subsidiary or a partner to fulfill a specific regional trade requirement where the sub-charterer has better local infrastructure or cargo access.
Risk Mitigation: It allows companies to manage their fleet capacity dynamically. If a company has over-tonnaged its fleet, sub-chartering acts as a hedge against fixed chartering costs.
Legal Note (MS Act, 2025 & Charter Parties): Under standard clauses (like NYPE or Shelltime), the charterer typically has the right to "sub-let" the vessel, provided the original terms of the head-charter are respected. The head-owner still holds the original charterer liable for performance and safety.