Dirty Product Duration: Separate Sea and Port Exposure

Overview

A single voyage-day figure hides those trade-offs. A buyer may spend effort comparing small differences in sea time while a larger uncertainty sits in the discharge estimate. Breaking the programme into components helps the desk decide which input to verify and which commercial alternative is worth pursuing.

Key takeaways

• Define the start and finish of the period being estimated.
• Use an effective cargo-transfer assumption for the stated proposal, not an unexplained equipment figure.
• Model waiting separately from the duration of the transfer itself.
• Compare sensitivities in time units before translating them into cost.
• Keep the physical planning estimate separate from contractual time accounting.

Set the boundary of the model

State whether the estimate begins at departure from loading, arrival at loading or another defined event. State whether it ends at arrival, completion of the receiving call or a later commercial milestone.

The boundary determines which components belong in the total. An estimate beginning after loading should not quietly include loading time, while a port-completion estimate needs more than the sea passage alone.

For the proposed dirty-product cargo, ask the responsible vessel and terminal sources for the relevant programme inputs and their conditions. The coordinator should not derive technical performance from a product nickname or prescribe the operating method needed to achieve a target.

Record the cargo pack and receiving proposition behind the estimate. A revised cargo requirement or shore arrangement may change the planning basis even when the nominal voyage route remains the same.

Use effective transfer time deliberately

A commercial transfer-duration estimate can be expressed as cargo quantity divided by an assumed effective rate, provided the responsible source confirms what the rate represents. The analyst should know whether the supplied figure already reflects the intended planning scope or whether separate allowances are required.

An equipment capability, an instantaneous observation and an effective whole-parcel planning rate are different inputs. Do not substitute one for another simply because each uses a quantity-per-hour unit.

Ask what is included in the effective estimate and what is excluded. If a source's total already includes specified non-transfer periods, adding them again would double count time.

Work through a port-duration comparison

The following inputs are invented for a commercial planning example. The rates are assumptions for the arithmetic, not operational instructions, terminal capabilities or expected performance for any dirty-product cargo.

ILLUSTRATIVE: Consider a period beginning at departure from loading and ending after the receiving call. Assume 25,000 tonnes of cargo, 192 hours of sea time, 12 hours of waiting and 12 hours of other port time.

At an assumed effective transfer rate of 1,000 tonnes per hour, transfer duration is 25,000 ÷ 1,000 = 25 hours. Total modelled duration is 192 + 12 + 25 + 12 = 241 hours, or 10 days and 1 hour.

A second scenario uses 750 tonnes per hour and 28 hours of waiting, with other inputs unchanged. Transfer duration becomes 33 hours and 20 minutes. Total duration becomes 265 hours and 20 minutes, or 11 days, 1 hour and 20 minutes.

In this example, the waiting change contributes more time than the transfer-rate change. The commercial team should therefore avoid focusing exclusively on the cargo-transfer assumption while ignoring the receiving-call uncertainty.

The result does not establish which scenario is likely. It shows where the model is sensitive and helps the desk decide what evidence would be most valuable next.

Translate time into decisions before cost

First ask which commercial milestone the additional time affects. It may change a receiving commitment, the availability of a subsequent employment option or the buyer's inventory planning assumption.

Then identify the relevant cost model if management needs a monetary comparison. Do not automatically multiply every additional hour by a demurrage rate or daily hire figure. The applicable agreement and employment structure determine the commercial treatment, and those questions require authorised review of the current text.

A planning delay can still matter even where no immediate additional invoice follows. It may consume flexibility or alter another commitment. Describe that consequence rather than forcing every effect into an unsupported cash charge.

Conversely, a shorter modelled duration does not prove a saving unless the business can identify which cost or obligation actually changes. Keep the time result and cost interpretation separate enough to review.

Compare an alternative receiving arrangement

If the business considers another receiver, obtain a complete set of relevant assumptions rather than replacing only the sea-time line. The alternative may have a different waiting scenario, effective transfer estimate or other port allowance.

Compare the complete periods on the same start-and-finish boundary. A shorter sea passage can be offset by a longer receiving-call estimate; a longer passage can still support an earlier completion under a different set of assumptions.

The recommendation should identify which inputs are confirmed, indicative or internal stresses. A precise total should not conceal the fact that one alternative has much weaker evidence.

Fictional case: the shortest passage is not the earliest finish

A fictional dirty-products buyer compares two receiving options and initially prefers the one with the shorter sea estimate. Its spreadsheet uses the same port duration for both because the cargo quantity is unchanged.

The analyst asks the responsible sources for scoped receiving estimates. The alternatives have different waiting and effective transfer assumptions. Rebuilding the model shows that the shorter passage does not necessarily produce the earlier completion in the scenarios under review.

The buyer now compares the complete receiving propositions and seeks better evidence on the input that drives the difference. It does not instruct either terminal or vessel to achieve the modelled rate. The calculation supports the commercial choice while leaving execution with the responsible parties.

Common mistakes

Using an unexplained equipment rate as the whole-parcel planning rate can understate or misrepresent the intended transfer-duration basis.

Another mistake is to include the same non-transfer period in both an effective estimate and a separate allowance.

Finally, avoid converting every planning hour into a contractual charge automatically. Physical duration and contractual time accounting answer different questions.

Where Zeaclub fits

Zeaclub offers digitalised procedures across the voyage workflow.

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