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Chapter 4

Final Stage of Loading Work

§§§§ Procedure for the final stage of loading work

Implement the final stage of loading work according to the procedure given below.

1. Deciding the target ullage (P.4-2 to P.4-3)

During the loading work of a VLCC, the final API is acquired generally after the loading is completedor during the Early Departure Procedure (EDP) after the ship sails, and the official loaded quantity isdecided. For this reason, the estimated API is used to decide the target ullage.

2. Rate reduction (P.4-4)

After deciding the target ullage, decide the timing for reducing the loading rate. The timing for reducing the rate should be decided after considering the target ullage, the number oftanks loaded and the permissible flow rate in the piping.

3. Topping off work (P.4-5 to P.4-7)

During the topping off work, the items given below should be considered. a) Top off tanks with small ullage first and then top off tanks with large ullage. b) Take tanks that are unaffected by trim as the tanks to be topped off. c) Use a rate that is equal to or less than the rate at which one tank can be loaded. d) As far as possible, plan to top off two tanks. e) Adopt measures to prevent pressure surges.

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1. Deciding the target ullage

1.1 Estimated API and Final API

The difference between estimated API and final API before and during loading work is generally about0.1 to 0.3. Sometimes a difference as large as 1.0 may also be observed. If the difference between estimated API and final API is large, check the points given below.

1) When the final API is less than the estimated API (specific weight is large) The draft or the tolerance may be exceeded. 2) When the final API is greater than the estimated API (specific weight is small) Deadfreight may occur and range of tolerance may not be satisfied.

Example: Assume the loading order volume as 500,000 NET BBLS, and the ship-estimated API as 30.0. Assumethat the target ullage is decided taking the loading temperature as 100°F.

500,000 ÷ 0.9821 (TABLE 6A ) 509,113 G.BBLS500,000 × 0.13899 ( TABLE 13) =69,495 MT

(1) FINAL API 29.0 (when less than the estimated API)509,113 × 0.9823 ( TABLE 6A) = 500,102 N.BBLS500,102 500,000 102 N.BBLS increase in NET capacity500,102 × 0.13985 ( TABLE 13) = 69,939 MT69,939 69,495=444 MT (increase in weight)

(2) FINAL API 31.0 (when greater than the estimated API)509,113 × 0.9819 ( TABLE 6A) = 499,898 N.BBLS499.898 500,000 102 N.BBLS (decrease in NET capacity)499,898 × 0.13813 ( TABLE 13) = 69,051 MT69,051 69,495= 444 MT (decrease in weight)

The TPC of a 280,000-ton VLCC is about 170 MT. In the example (1) above, the draft increases byabout 2.6 cm. As can be seen in the example above, a change in the API does not have any appreciableeffect on the weight.

1.2 Considerations when deciding ullage

Click here to view video – 067.mp4

After loading starts, even if the API measurements and approximate oil temperature are identified onthe ship, accurate calculations are not possible unless the API is decided. In such cases, various patternscan be simulated at the planning stage of loading using the Loading Calculator (SHIPCAL).The items mentioned below should be considered when deciding the final ullage.

1) The safe range of ullage should be established and the corresponding quantities estimated afterconsidering the tolerance of the contractual volume (Bbls), cargo weight and draft.

2) The API and oil temperature assumed during the preparation of the loading plan are generallydifferent from the actual values, and fine adjustments are always necessary. If the volume is to lie

within the tolerance of the contractual volume for a ship under time charter contract, andfurthermore, if the contractual weight (weight of cargo oil) is to be cleared for a ship under voyagecharter contract, then draft restrictions at the discharging port are to be considered, making theconditions very severe. However, in principle, the tanks should be selected without changing all thetanks scheduled to be loaded so that there is no adverse effect on the trim, hog and sag.

3) Simulation should be carried out using the API measured on the ship and the API obtained from theterminal.

4) The main points of the simulation are to confirm the loadable quantity, the draft and the trim, tostudy the differences in API when it is based on the final discharging port or upon arrival of theship at the discharging port, and to make the selection depending on the conditions at that time.

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5) If the API is varied in steps of 0.1 and the oil temperature in steps of 1°F, then the effect on theloadable cargo weight and net capacity can be studied, which facilitates deciding the target ullage.

6) If the study is carried out based on the final discharging port or based on the arrival at thedischarging port, the safe range of loadable quantities can be determined. Thus, the risk ofexceeding the draft can be mitigated.

7) If the situations given below are anticipated or if they do occur, the operator should be notifiedimmediately, and further instructions from the operator should be awaited.

a) If the contractual weight cannot be loaded b) If deadfreight occurs c) If the tolerance of contractual volume is not satisfied.

As mentioned earlier, in tankers under voyage charter contract, cargo should be loaded within the tolerance ofthe contractual volume (Bbls) and greater than the contractual weight (weight of cargo oil). The differencebetween maximum loading capacity and the contractual weight is extremely small, and is in the range of a fewhundred tons (less than 1,000 tons). In such tankers, comprehensive investigations on overdraft, contractualwei ht and draft restrictions are necessar .

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2. Rate reduction

2.1 Deciding the timing for rate reduction


If the timing for rate reduction is delayed, that is, if the period of full rate is prolonged, the loading timecan be shortened but the risk increases. Accordingly, the timing for reducing the rate should be decided

after considering the target ullage, the number of tanks to be loaded and the permissible flow rate in thepiping. The timing for rate reduction also depends to a large extent on the competence of the crewmembers. If the number of tanks for receiving the cargo is large, the rate should be reducedsequentially in several steps. The reduction in rate should be such that the topping off work can beperformed safely. Particularly in tanks loaded to 98% of the capacity where the ullage is very small, the

rate should be reduced sequentially taking care to prevent overflow.

2.2 Calculating the time of rate reduction

Before reducing the rate the terminal should be notified at intervals, that is 10 minutes before, 15minutes before rate reduction, and so on. These periods should be considered when deciding the time ofrate reduction. For instance, when loading 500,000 Bbls of cargo at a specified loading rate, the time 10 minutesbefore the reduction and the time of completion of loading can be easily calculated using SHIPCAL.

2.3 Example of calculating the time of rate reduction

Scheduled loading quantity: 500,000 BBLS Current rate: 60,000 BBLS / hr.Loading rate: 20,000 BBLS / hr. Loading time: 1 hour Notification required 10 minutes before reducing the rate

1) Deduct the loading rate of 20,000 BBLS from the loadable quantity at target ullage of 500,000BBLS. 500,000 BBLS 20,000 BBLS = 480,000 BBLS

2) Quantity that can be loaded for 10 minutes at the existing rate (60,000 BBLS/h) 60,000 X ( 10 / 60 ) = 10,000 BBLS

3) Quantity loaded until 10 minutes before the notification for reducing the rate is issued 480,000 10,000 = 470,000 BBLS

4) Notify the terminal (10 minutes before rate reduction) when 470,000 BBLS of cargo has beenloaded.

5) By entering the ullage reading in the Loading Calculator, the quantity currently loaded can becalculated. From this quantity, the time at which the loading pump should be stopped can be easilycalculated.

6) The request for stopping the pump should be made after considering the pump stoppagenotification given beforehand and the "quantity of oil that can be loaded from the time the requestfor stopping the loading pump is made to the actual stoppage of the loading work," which has beenconfirmed during the pre-loading meeting.

2.4 Confirming the rate reduction

After a request for rate reduction is made, always confirm from the terminal that the requested ratereduction has actually been implemented. Although the rate reduction can be confirmed from thechange in the tank pressure on the ship, yet the implementation of rate reduction by the terminal

Generally, the time from the start of rate reduction (topping off rate) to the completion of loading is about one hour,but this value also depends on the number of tanks to be loaded. However, care is necessary to avoid delay on theship's side without valid reasons after the issue of the final order to reduce the rate, since claims may arise from theshore terminal.

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according to the ship's request should be confirmed.3. Topping off work

3.1 Precautions


Take the precautions mentioned below during the topping-off work.

1) Target ullageTop off tanks of relatively small ullage first, and finally top off tanks with relatively large ullage. Thismeasure is to prevent the overflow of oil. It ensures that if by chance the loading pump does not stopas desired, some amount of cargo oil can be received by tanks with large ullage thus preventingoverflow of oil. 2) Trim As far as possible, take a tank that has no effect or very little effect on the trim as the final tank to beloaded , so that the ship just goes down bodily preferably amidships tanks . It is preferable tomaintain the ship on even keel and in the upright condition by ballast adjustments since calculation ofloading volumes becomes easier in this condition. 3) Loading rate The minimum loading rate should generally be the rate at which one tank can be loaded. This rate isconfirmed at the pre-loading meeting. The permissible flow rate in the piping should be decided afterconsidering the target ullage and the trim. During the loading of the final tank, measure the change inullage over a one-minute interval using a stop watch and confirm that the rate of cargo flowing intothe tank is the minimum loading rate requested by the ship. 4) Number of tanks to be loaded Formulate plans to receive cargo in two tanks whenever possible, in addition to one-tank loading. If the desired rate reduction has been confirmed after issue of the request, one-tank loading may beperformed without any problems. However, bear in mind that loading may sometimes be performedwithout reducing the rate to the desired level even though the request to reduce the rate has been made.

Accordingly, such rough operations (ignoring the request to reduce the rate) should be anticipated atthe planning stage and measures should be framed beforehand to ensure safety.

5) Method of preventing pressure surges and completion of loading If many tanks are to be loaded and if the maximum loadable rate is appreciably larger than the actualloading rate, the loading may be completed sometimes without reducing the loading rate. If this tank is tentatively considered an end tank (1P/C/S, SP/SS, 5C), and if the valve is fully closedall at once, the oil that is flowing into the end tank has no place to go and a pressure surge occurs.

Major problems may occur simultaneously with the pressure surge, such as tripping of the shore pumpdue to excessive pressure or damage to shipside line, dresser, flange or valve. Since the problems arenot limited to the end tank alone, it is essential that the valve be operated with extreme care.

3.2 Method of operating the valve so as to prevent pressure surge


1) Gradually throttle and adjust the valve carefully so that the flow of oil is not changed abruptly.Flow rate adjustments of butterfly valves can be performed easily. However, when the flow ratechanges abruptly in valves that have been opened by 50%, adequate care should be taken to operate

During loading operations in the Persian Gulf at special religious periods of the year, there have been instanceswhen the ship was forced to make adjustments so that the loading work could be completed during the shifthour because of an overlap of the shift hour of the workers and the estimated time of completion of loading .Although the ship's request to reduce the loading rate was acknowledged orally, the rate was never changed inpractice. Fortunately, the wing tanks (two tanks) were being loaded at that time and the loading could becompleted without problems. However, there have been instances when loading was performed under severe

conditions, such as loading at the one-tank loading rate.It is important to formulate plans that account for unanticipated events during loading work after studyingsafety measures at the planning stage so as to avoid being restricted to one-tank loading operation.

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the valve gradually. 2) Change the oil flow rate by throttling the valve further from 50% to 30%. 3) At the valve opening of about 30%, the oil flows in slowly. At about 20%, the flow of oil is so slow

that it appears to have stopped. Accordingly, it is important to keep the valve open to about 30%before the target ullage is reached.

4) In the vicinity of target ullage, open the valve to about 20% and allow the oil to settle. 5) Confirm that oil flows into other tanks correctly and then fully close the valve.

If the other tank valve is adequately open and flow rate is less than the permissible flow rate in thepiping, no problems will occur even if you quickly close the valve all at once from an opening of 20%or less. 6) The valve in the final tank to be loaded should be kept fully open until the Loading Master's

permission to close the valve is obtained, the loading pump stops and the flow in the pipeline stopscompletely.

* Preventing problems

Water hammer, cavitation and pressure surge are important terms that should be understood properly sothat problems due to their occurrence can be prevented. These phenomena cannot be actually observed,therefore it is not only important to study the theory and occurrence of the mechanisms but also toimagine their occurrence.

3.3 Time of completion of final loading

Perform the work from the loading of the final tank to the stoppage of the loading pump bearing inmind the points mentioned below.

1) Inflow rate from the time of request to stop the loading pump The inflow rate from the time the request is made to stop the loading pump to the actual stoppage offlow of oil is confirmed at the pre-loading meeting. The tank level at this time can be calculated fromthe capacity of the tank to be loaded. Accordingly, the request to stop the loading pump should bemade when this level is reached. 2) Change in ullage In addition to calculations using the Loading Calculator (SHIPCAL), the change in ullage can bemeasured at fixed intervals and the time for reaching the target ullage can be calculated approximately.This method is often used because the monitoring of ullage becomes more important at the final stageof loading. For instance, if 30 cm remains until the target ullage, and if the change in ullage perminute is 3 cm at the loading rate at that time, then the target ullage will be reached about 10 minuteslater. If the rise in level appears to be faster than the required loading rate, the Loading Master shouldbe notified immediately and the rate reduced to a safe loading rate. 3) Target ullage and frequency of tallying the readings The readings obtained using MMC during the loading are to be taken as positive. As far as possible, adeck rating should be stationed at the tank before the target ullage reaches 1 m. Even if there is nochange in the target ullage, the ullage values should be reported from time to time and the operator atthe CCR and the deck watch should tally these values with each other. The readings should be talliedfor every 10 cm of loading before the 50-cm level and every 1 cm of loading before the 10-cm level isreached. If the change in ullage is large, the frequency of tallying the readings should be changed. 4) Loading during ship motion If the ship is berthed at a terminal facing the open seas or at a port that is subjected to swells, then

loading has to be performed when the ship is in motion. At such terminals, the loading may have to beperformed using float gauges. Before loading, the readings should be tallied with the MMC readings and the error, if any, should benoted. When time permits and there is a reserve margin in the ullage and loading rate, close (or throttle) thevalve of the tank to be measured, allow the oil level to settle and tally the readings a few times. Readthe indicated values of the ullage a few times, and take the average of the upper and lower limits ofullage as the target ullage. 5) Timing for stopping the pump Give the specified notification before stopping the pump and issue the S/B request just before (2 to 3

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minutes before) issuing the notification to stop the pump. The request to stop the loading pump shouldbe given at an ullage volume that includes the volume of oil that flows in after the request to stop thepump is made.6) Confirming the stoppage of the pump Confirm from the ullage and manifold on the ship that the inflow of cargo oil has stopped. If there isno reserve margin in the target ullage, check the availability of empty tanks or tanks with reservecapacity anticipating overflow, and keep the valves of these tanks open so as to prevent overflow.

3.4 Operation of valves on the ship after stopping the pump

After the loading pump stops, confirm at the manifold, tank side (MMC) and at the CCR that theinflow of oil has fully stopped. Operate the valves on the ship as described below after the pump hasstopped.

1) Maintain the status of the final loading lines and valves on the ship in the same condition as whenthe pump was stopped.

(When two tanks have been loaded simultaneously, if a level difference exists in the two tanks andthere is a possibility of shift of oil, the valve in one tank may be fully opened and the valve in theother tank may be kept fully closed. This measure is to ensure that one loading line is available untilthe end and to prevent pressure surge.)2) Fully close the gate valve with the approval of the Loading Master. 3) Confirm that the gate valve has been fully closed, then fully close the tank valve.

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