Speed may, in fact, be an important factor. In some cases it may be more cost-effective to proceed more slowly and to economise on bunkers. Particularly might this be so where bunkers are expensive and freight rates are low, or in coastal estimating, where voyages are frequently dependent on tidal depths. There may be little point in steaming full speed, only to have to await a suitable tide for some hours following arrival off port. On the other hand, if an early arrival off a port means the master can tender notice of readiness that much sooner, it may still be more cost advantageous to proceed at full speed. Canal transit duration must also be calculated. Although usually without incident, occasionally the transit of vessels through canals is seriously disrupted, and although there is usually little notice of such events, sometimes it is common knowledge that delays can be anticipated and their effect should be taken into account. Multiple ports, where a vessel has to call at, say several loading and/or discharging ports, calls for extra time to be allowed for delays in entering and leaving each port. Bunkering calls can on occasion be lengthy, but generally it is appropriate to allow half an extra day (plus idle port consumption of bunkers) in an estimate. Bad weather does not normally affect the drafting of a voyage estimate unless it is certain from the nature of the trade that delays will be experienced, either at sea or in port. When all distances and times are calculated, it should be possible to calculate estimated bunker consumption both at sea and in port, and to conclude this stage of the estimate, although allowance must also be made for a vessel’s bunker consumption through the confined waters of a canal, as this may bear little resemblance to normal consumption whilst steaming in un-obstructed waters at sea.