Lessons
Which advance for tonight's wheel-over?
The booklet gives the advance only for ballast and loaded, so interpolate it by tonight's displacement — and make sure it is the advance column, not the transfer.
The rule
- Advance is the distance gained along the original course during the turn; transfer is the distance gained at right angles to it.
- Find where tonight's displacement sits between ballast and loaded, as a fraction.
- Apply the same fraction to the advance column.
- It is a planning figure — the sea trials were run in deep, open water without current; once the turn is under way, watch the parallel index, not the number.
- The booklet advance is for a 90° turn hard over: a smaller alteration needs a shorter wheel-over distance, while a turn on less rudder has its own figure — longer than hard over for the same alteration, because the turning circle is wider. Don't reuse the hard-over advance for every turn.
Worked example
| Displacement in the present condition | 120080 t |
| Displacement in the ballast condition the booklet was measured in | 68000 t |
| Displacement in the loaded condition the booklet was measured in | 152000 t |
| Advance with hard rudder, ballast condition | 668 m |
| Advance with hard rudder, loaded condition | 902 m |
| Transfer with hard rudder, ballast condition | 336 m |
| Transfer with hard rudder, loaded condition | 468 m |
- Fraction = (120080 − 68000) ÷ (152000 − 68000) = 52080 ÷ 84000 = 0.62
- Advance spread = 902 − 668 = 234 m
- Advance tonight = 668 + 0.62 × 234 = 813.08 ≈ 813 m
Common mistake
Interpolating the transfer column instead of the advance.
The two columns look alike, but transfer measures the shift across the old course, not the run along it — here it gives 418 m where the advance is 813 m, so a wheel-over laid off with it puts the turn far too late.