Chapter 37: Weather Routing
Weather routing selects the track that best satisfies safety, schedule and fuel objectives given forecast conditions — dynamically, as the forecast changes.
Climatological and dynamic routing
Climatological routing uses Pilot Charts and long-term statistics of wind, current, ice and wave height to pick a seasonally sensible track; it is planning-stage guidance. Dynamic routing uses current forecast fields and the vessel's own speed-loss curves in the prevailing sea state to compute an optimum track, updated as new forecasts arrive. The US Navy's Optimum Track Ship Routing (OTSR) and commercial shoreside services provide recommendations, but the master always retains the decision.
- Climatology for planning, dynamic forecasts for execution
- Least-time, least-fuel and least-damage routes are different routes
- The master decides; the routing service advises
Ship response and storm avoidance
Routing depends on the vessel's response: speed loss in head seas, slamming and deck wetness thresholds, parametric roll risk in following and quartering seas, and cargo-specific limits such as container lashing loads. Storm avoidance applies the tropical cyclone semicircle rules plus a forecast-uncertainty margin, and for extratropical lows uses the developing centre's track to stay in the weaker sector. Aim to cross ahead of a system only when the margin is unambiguous; otherwise slow down and let it pass.
Key takeaways
- • Climatological routing plans; dynamic routing executes.
- • Routing must use the specific ship's speed-loss and motion limits, not a generic ship.
- • When the margin is doubtful, slowing to let a system pass is usually the better decision.
Knowledge check
Immediate feedback with rationales. Answer each question to see the explanation.
Chapter 37 quiz
0 of 3 answered
1.Climatological routing differs from dynamic routing in that it uses:
2.A least-time route and a least-fuel route:
3.Responsibility for accepting or rejecting a shore routing recommendation rests with: