Predicts when wind and tidal stream set the same way, so the tailing tug can be stood down. Advisory only: the pilot on the berth decides.
Heading is where the bow points while she lies to the SBM. With the draft entered it comes from the hawser model; without it, it is estimated from wind and stream. Not to scale.
Wind barbs point to where the wind comes from: each long feather 10 kn, short feather 5 kn, pennant 50 kn, circle calm; F = Beaufort force, then knots. Current arrows point the way the stream sets. Current speed is estimated from the tide range; set your berth's peak stream under Rules and limits.
With the tailing tug stopped the tanker lies to the SBM on her bow hawser and swings until wind and stream balance. The planner finds that heading, adds up the wind and current forces on the hull, and reports their resultant as the expected hawser load.
These are steady loads from simplified, typical tanker wind and current coefficients (of the kind published by OCIMF for VLCCs). Surge, yaw, fishtailing and waves add dynamic load on top, often several times the steady value. It is a planning aid, not a mooring analysis.
| Time | Verdict | Tide | Current sets (est.) | Wind (from) | Angle | Expected hawser load if tug stopped | Tug pull needed to hold her |
|---|
| Date / time | From | kn | Gust |
|---|
| Date / time | Tide | Height m |
|---|
The tug may be stopped when the wind blows within the angle limit of the way the current sets, the wind is above the light-air limit, and it is not slack water. In light airs, a stop is possible when the estimated current is above the set speed. Current speed is estimated from the tide: zero at HW and LW, strongest mid-tide, scaled by the tide range against the peak stream you set for the berth. Directions are degrees true.
At an SBM the tanker swings to wind and stream on the hawser. The planner works out the heading she settles on, the steady hawser load and the hawser angle off the bow, and keeps the tug if the angle or the load is over its limit, or if the hawser would go slack (ship riding up on the buoy). Loads are steady values from typical tanker wind and current coefficients; surge and yaw can add a lot to them.