Charter Party Clause in Focus: Speed Through Water vs. Speed Over Ground – Who Controls the Throttle?

 ⚓Charter Party Clause in Focus: Speed Through Water vs. Speed Over Ground – Who Controls the Throttle?

🤔 Think Before You Sail — 3 Questions to Consider:

1. Can you be held accountable for underperformance if RPMs are changed at charterer’s request?
2. Is Speed Through Water (STW) a fair benchmark in rough weather?
3. Are frequent RPM changes harming your vessel's engine efficiency and your case in arbitration?

 

🔍 Clause Breakdown: What’s Going On?

In the evolving world of vessel performance monitoring, the clash between Speed Through Water (STW) and Speed Over Ground (SOG) is becoming a hot topic. In this particular case, the charterers (via Routing Company) are frequently instructing speed adjustments (e.g., from 12.5 to 12.7 knots STW), often at short intervals — even during poor weather conditions or days of non-performance.

Key Terms:

• STW (Speed Through Water): Speed relative to the water the ship moves through.
• SOG (Speed Over Ground): Speed relative to a fixed point on the seabed — what GPS shows.
• RPM (Revolutions Per Minute): The engine speed, which directly affects fuel consumption and wear-and-tear.

 

⚠️ Implications for Vessel Operators and Owners

1. Performance Claims Risk

If the vessel is run at higher RPM based on third-party (e.g., ZeroNorth) data suggesting higher STW, but the actual SOG is lower due to adverse currents or weather, you may be accused of underperformance despite following instructions.

2. Fuel Supply Mismatch

Higher RPM = Higher fuel consumption. When bunker requests are based on ECO-speed assumptions, increased speed requirements lead to under-supply of fuel, risking delays, detentions, or commercial disputes.

3. Engine Health and Wear

Frequent RPM changes for marginal STW gains are not advisable from an engineering standpoint. Over time, this causes increased maintenance, possible faults, and reduced machinery life.

4. Legal & Commercial Ambiguity

Unless the Charter Party (CP) clearly states how speed is to be measured and who has overriding authority for adjustments, you're entering gray areas that can result in disputes, especially if performance warranty is pegged to weather or sea conditions.

 

📚 Real-World Insight & Commentary

Case Law Example:
In The Didymi [1987], performance warranties were evaluated in good weather only — making it crucial to clearly define terms like “good weather” and how speed/consumption is measured.

BIMCO Guidance:
BIMCO advises clearly defining STW vs SOG in CPs and limiting frequent changes that don’t take sea conditions into account.

 

✅ Practical Steps for Operators, Owners & Managers

1. Refer to the CP:
   Confirm if performance is judged based on STW or SOG, and under what weather conditions.
2. Ask for Written Instructions:
   Always get RPM/speed requests from charterers in writing, especially when they deviate from CP-agreed ECO speed.
3. Track & Record Weather:
   Log wind, wave, and current data. It’s your defense against underperformance claims based on unrealistic STW expectations.
4. Communicate Fuel Impact:
   Immediately notify charterers when higher RPMs will result in fuel shortfalls — as was done in your message.
5. Log RPM Adjustments:
   Maintain clear records showing engineer objections to frequent changes and the reason why RPM was changed (charterer's instruction).
6. Push for CP Clarity:
   In future charters, clearly define speed and consumption basis (ECO/Full), and set a buffer to avoid disputes.

 

📢 Final Thoughts & Call to Action

STW might be a useful metric in calm seas, but when weather acts up, it becomes an unreliable compass for performance evaluation. Unless your CP accounts for this, you may be setting yourself up for avoidable disputes and losses.

💬 Let us know: Have you faced similar instructions from third-party monitoring systems like ZeroNorth? How did you manage it?

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⚠️ Disclaimer:

This post is for informational purposes only and does not constitute legal advice. All vessel names, company names, and identifying details have been omitted or altered to ensure confidentiality.