Chapter 33: Ice Navigation
Ice changes every rule: radar becomes unreliable, charts are sparse, and the margin between routine passage and structural damage is thin.
Types and terminology
Sea ice forms from frozen seawater: frazil and grease ice, then nilas, pancake ice, young ice, first-year ice and multi-year ice, which is harder, less saline and far more dangerous to a hull. Pack ice is described by concentration in tenths — open water, very open, open, close, very close, compact. Glacial ice gives icebergs, bergy bits and growlers; growlers are the acute hazard because they are small, nearly awash, dark-toned and poor radar targets, yet massive enough to hole a ship.
- Multi-year ice is harder and stronger than first-year ice
- Concentration is reported in tenths of sea surface covered
- Growlers are the classic radar-invisible killer
Operating in ice and the Polar Code
Practical rules: reduce speed early, meet ice at right angles, avoid glancing blows and never allow ice to strike the propeller or rudder, keep way on to maintain steering, and use leads and ice-blink/water-sky observation to route. In convoy or under escort, maintain the icebreaker's ordered distance and be ready to stop. The IMO Polar Code (SOLAS Chapter XIV) requires a Polar Ship Certificate, a Polar Water Operational Manual, ice-strengthened categories A, B and C, enhanced equipment and survival provision, and appropriate ice navigator training under STCW.
Key takeaways
- • Growlers and bergy bits are poor radar targets — post extra look-outs and reduce speed.
- • Meet ice with the bow, slowly, and protect the propeller and rudder.
- • The Polar Code requires a certificate, a Polar Water Operational Manual and trained personnel.
Knowledge check
Immediate feedback with rationales. Answer each question to see the explanation.
Chapter 33 quiz
0 of 3 answered
1.The most dangerous ice hazard to detect by radar is:
2.Pack ice concentration is expressed in:
3.Under the IMO Polar Code, a vessel operating in polar waters requires: