search.noResults

search.searching

dataCollection.invalidEmail
note.createNoteMessage

search.noResults

search.searching

orderForm.title

orderForm.productCode
orderForm.description
orderForm.quantity
orderForm.itemPrice
orderForm.price
orderForm.totalPrice
orderForm.deliveryDetails.billingAddress
orderForm.deliveryDetails.deliveryAddress
orderForm.noItems
be obtained when the doubler plate at the bottom of the sounding pipe is corroded and worn, increasing the sounding and hence the apparent weight of water in the tank. Often, particularly on older vessels, sounding rods and brass bobs may remain in the sounding pipe, giving readings less than true, as will be the case if the sounding pipe has become blocked with rust scale or other debris, such as rags left in the tank during maintenance or dry-docking. The presence of sediment in the tank covering sounding rods and tapes can also lead to erroneous readings. The figures for the ballast extracted from the sounding book may be in error due to inaccuracies in interpolation or not allowing for the trim or list of the vessel, further, the figures may be calculated assuming an incorrect ballast water density, and it is recommended that ballast tanks are overflowed for a length of time such that a truly representative ballast water sample can be obtained for density determination.


UNFACTORED WEIGHTS


Often weights are not deducted or allowed for when determining the cargo quantity, the commonly forgotten weights are:


• Bilge water present in the cargo holds, machinery spaces, duct keel, void spaces and the chain lockers.


• Swimming pool water.


• Anchor and anchor cable on the seabed, either when at anchor or alongside and an anchor has been deployed as part of the mooring arrangement.


• Silt and mud can accumulate in the double bottom tanks of vessels regularly ballasting in rivers or estuaries. The extra weight can give rise to an apparent increase in the cargo loaded.


As an example:


If we assume a single ballast tank with a 500m3


capacity.


On arrival prior to loading the tank is overflowed and full of seawater.


Therefore the assumed weight of water = 500m3


x 1.025 t/m3


However, there is 40m3 the tank.


= 512.5t. of mud in


Therefore the true picture of the tank’s contents is as follows: Water: 460m3


x 1.025 t/m3 Mud: 40m3 x 1.9 t/m3 = 76t


Total weight of tank contents = 471.5t + 76t = 547.5t


As 512.5t is assumed to be the weight of ballast in the tank, the remaining 35t will appear in the constant.


On completion of loading it is assumed the tank is empty. However, 76t of mud remains, only 35t of which is in the constant, the remaining 41t will appear to be cargo loaded.


SQUAT


As most mariners know, squat is the bodily sinkage and trimming of a vessel making way with limited underkeel clearance. However, a vessel alongside a river berth may also be susceptible to squat, leading to inaccurate draught readings.


Squat will occur when there is limited space for the water to flow between the vessel and the river bed. In order for the river water to pass between the flat bottom and the river bed there will be an increase in velocity of the water flowing past the hull, and consequently a decrease in the water pressure. The decrease in pressure leads to the ship bodily sinking and also a change of trim.


The Report • September 2018 • Issue 85 | 41


= 471.5t


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80