Sir, explain me please, on below mentioned example... - We dont have any draft and other limitations. - Loading & discharging ports are in Summer Load line zone - Loading port density is 1.018 - Discharging port density is 1,005 - dont take in account any consumptions (FO,FW,DO etc) I understand that our draft will be increasing. So question is: How we must calculate the cargo, that can be loaded? (Using summer max displasement on 1,025 according to Hydrostatic tables, but in such way our load line summer draft will be sinked in both ports)??? We wouldnt brake any rules in such situation because our summer zone load line is sinked or not? Or we must take our summer displacement multiply it on 1,005, than devide on 1,025 and according to received (LOWER) density load our vessel, because in such way we wouldnt sink our summer zone load line?
To calculate the cargo to load: Take the ship's summer displacement from the hydrostatic table as the ship's entire voyage is within the summer zone. Since that displacement is in salt water, apply density correction to determine the equivalent displacement in the loading port with S.G. 1.018 using the formula: Displacement at loadport = summer displ. x S.G. loadport (1.018) / 1.025. Once the displacement in loadport is determined, calculate the max. cargo that can be loaded using this formula: Corrected Displacement - Lightweight = Deadweight - Deductibles/ROB/Non-cargoes = Cargo & Constant - Constant (K) = Max. Cargo that can be loaded in the loading port. When the ship leaves the loading port (S.G. 1.018) and reaches saltwater (S.G. 1.025), the draft will decrease, allowing the ship to float at her summer load draft. Upon arriving at the discharging port (S.G. 1.005), a slight increase in draft will occur due to the lower density. However, since the vessel was floating at her summer draft in saltwater (S.G. 1.025), this increase in draft at the discharging port does not violate load line regulations. Always remember that regardless of an increase in draft in the loading and discharging port due to water with lower densities, ensure that the ship floats at her assigned load line draft upon reaching saltwater. In your scenario, in which the voyage remains in the summer zone, make sure the vessel meets her summer draft requirements when she arrives in saltwater.
Hi, at the last example, ive notice that you calculate as if the ship is going from higher R.density to Lower R.density. But as the example ship is depart from 1.007 to 1.018. Draft should rise then right? It should be decrease in draft. Kindly clarify. By the way great animation and lessons. Thank you🙂
Hi! Thank you for your comment. In my last example, in the final step, I subtracted the dock water allowance from the departure draft to find the arrival draft, since the ship sails from a lower R. density (1.007) to a higher R. density (1.018). The effect on the ship upon reaching higher density, she will rise, and as a result, there will be a decrease in the ship’s draft. That is why DWA should be subtracted from the dep. draft to find the arrival draft as shown in my final step which is also stated in your comment, a decrease in the arrival draft. Maybe you are confused when I take the difference of the departure and arrival relative density because, in my solutions, I have shown (1.018 - 1.007) which is the arrival R.D 1.018 minus the dep. R.D 1.007. What I did is subtract the lesser from the greater R.D. so that I would have a positive DWA, but this procedure does not affect the ship’s draft yet. As you mentioned in your comment the ship will rise in this problem, and there should be a decrease in the ship’s draft “You are right”. That is why in my final step, I have subtracted the DWA from the dep. draft to determine the arrival draft because the effect is a decrease in draft. Now you can also follow this format (1.007 - 1.018) which is departure R.D 1.007 minus arrival R.D 1.018, you will have a negative DWA. A negative DWA should be subtracted from the departure draft, and the result will be a decrease in the arrival draft as shown in my final step. Thank you very much👨
thank you very much for your detailed answer sir, your channel is very helpful and insightful. plus the animation is superb. make it more easy to understand. have a great day.
When a ship moves from water of higher density to lower density, or vice versa, a phenomenon known as "sinkage" or "rise" affects the ship's draft. This is often called "density effect" or "density correction." The change in water density influences the ship's buoyancy, causing the entire vessel to "sink or rise" by a few centimeters in the water. This will cause a change in the ship's draft both forward and aft including the mean draft. Thank you for the comment.
Thank you. In the comment section, it's hard to explain how this formula was derived and why 4 became a constant. I will try to make a separate video about the derivation of the formula of freshwater allowance. Usually, onboard we can extract the value of the freshwater allowance in the stability manual provided by the shipbuilder. But try his one, Derivation of the FWA formula: Consider a ship floating in SW at load Summer draft at waterline WL. Let the volume of SW displaced at this draft be ‘V’. Now let W1L1 be the waterline for the ship when displacing the same mass of fresh water. Let ‘v’ be the extra volume of water displaced in FW. The total volume of freshwater displaced will be V + v. Mass = Volume x density Mass of SW displaced = 1025V Mass of freshwater displaced = 1000 (V + v) But the mass of FW displaced = Mass of SW displaced. 1000(V + v) = 1025V v = V/40 Assume that ‘w’ is the mass of SW in volume v and ‘W’ in volume V, Then, replacing the factor as obtained above we get: w = W/40 But w is a factor that is a product of the FWA and the TPC Now since the FWA is in mm and the TPC is in cm, they both have to be converted to metres Thus: W = (((FWA mm x 100) cm X TPC cm) / 100) metres Simplifying we have: w = (FWA x 100 x TPC) / 100 = W / 40 Or (FWA x TPC) = W / 40 But w = TPC x (FWA/10) Hence W/40 = TPC (FWA/10) or FWA = W/(4 x TPC). Where ‘W’ = Loaded SW displacement in tonnes.
FWA is the number of millimeters by which the mean draft changes when a ship passes from saltwater to freshwater, or vice versa, while floating at the loaded draft. This is typically measured when a ship is moving from seawater to freshwater, such as when entering a river or a lake. Dock Water Allowance (DWA): DWA is the number of millimeters by which the mean draft changes when a ship passes from saltwater to dock water, or vice versa, when the ship is loaded to the Summer displacement. Dock water is a type of water with a density between that of seawater and freshwater. DWA is typically measured when a ship is moving from seawater to dock water, or vice versa, while in a dock or a shipyard. FWA is the change in draft when a ship sails from seawater to freshwater or vice versa, while DWA is the change in draft when a ship sails from seawater to dock water or vice versa or from dock water to another dock water with different water densities. The key difference is the type of water involved, with FWA involving a transition between seawater and freshwater or vice versa, and DWA involving a transition between seawater and dock water or vice versa.
@@nauticalacademy001 so we can calculate the change of draft by FWA value and TPC value with the given formula DWA= change in draft= displacement * change in density/ 0,025
Alas!I discovered your videos v late...❤❤❤
Thanks.
Thank you very detailed and informative
You are welcome!
Sir, explain me please, on below mentioned example...
- We dont have any draft and other limitations.
- Loading & discharging ports are in Summer Load line zone
- Loading port density is 1.018
- Discharging port density is 1,005
- dont take in account any consumptions (FO,FW,DO etc)
I understand that our draft will be increasing.
So question is:
How we must calculate the cargo, that can be loaded?
(Using summer max displasement on 1,025 according to Hydrostatic tables, but in such way our load line summer draft will be sinked in both ports)??? We wouldnt brake any rules in such situation because our summer zone load line is sinked or not?
Or we must take our summer displacement multiply it on 1,005, than devide on 1,025 and according to received (LOWER) density load our vessel, because in such way we wouldnt sink our summer zone load line?
To calculate the cargo to load:
Take the ship's summer displacement from the hydrostatic table as the ship's entire voyage is within the summer zone. Since that displacement is in salt water, apply density correction to determine the equivalent displacement in the loading port with S.G. 1.018 using the formula: Displacement at loadport = summer displ. x S.G. loadport (1.018) / 1.025.
Once the displacement in loadport is determined, calculate the max. cargo that can be loaded using this formula: Corrected Displacement - Lightweight = Deadweight - Deductibles/ROB/Non-cargoes = Cargo & Constant - Constant (K) = Max. Cargo that can be loaded in the loading port.
When the ship leaves the loading port (S.G. 1.018) and reaches saltwater (S.G. 1.025), the draft will decrease, allowing the ship to float at her summer load draft. Upon arriving at the discharging port (S.G. 1.005), a slight increase in draft will occur due to the lower density. However, since the vessel was floating at her summer draft in saltwater (S.G. 1.025), this increase in draft at the discharging port does not violate load line regulations.
Always remember that regardless of an increase in draft in the loading and discharging port due to water with lower densities, ensure that the ship floats at her assigned load line draft upon reaching saltwater. In your scenario, in which the voyage remains in the summer zone, make sure the vessel meets her summer draft requirements when she arrives in saltwater.
Many thanks for your explanation., 🤝
Hi, at the last example, ive notice that you calculate as if the ship is going from higher R.density to Lower R.density. But as the example ship is depart from 1.007 to 1.018. Draft should rise then right? It should be decrease in draft. Kindly clarify. By the way great animation and lessons. Thank you🙂
Hi! Thank you for your comment. In my last example, in the final step, I subtracted the dock water allowance from the departure draft to find the arrival draft, since the ship sails from a lower R. density (1.007) to a higher R. density (1.018). The effect on the ship upon reaching higher density, she will rise, and as a result, there will be a decrease in the ship’s draft. That is why DWA should be subtracted from the dep. draft to find the arrival draft as shown in my final step which is also stated in your comment, a decrease in the arrival draft.
Maybe you are confused when I take the difference of the departure and arrival relative density because, in my solutions, I have shown (1.018 - 1.007) which is the arrival R.D 1.018 minus the dep. R.D 1.007. What I did is subtract the lesser from the greater R.D. so that I would have a positive DWA, but this procedure does not affect the ship’s draft yet. As you mentioned in your comment the ship will rise in this problem, and there should be a decrease in the ship’s draft “You are right”. That is why in my final step, I have subtracted the DWA from the dep. draft to determine the arrival draft because the effect is a decrease in draft.
Now you can also follow this format (1.007 - 1.018) which is departure R.D 1.007 minus arrival R.D 1.018, you will have a negative DWA. A negative DWA should be subtracted from the departure draft, and the result will be a decrease in the arrival draft as shown in my final step. Thank you very much👨
thank you very much for your detailed answer sir, your channel is very helpful and insightful. plus the animation is superb. make it more easy to understand. have a great day.
Welcome.
Which draft will be change, if there's correction? F, M or aft?
When a ship moves from water of higher density to lower density, or vice versa, a phenomenon known as "sinkage" or "rise" affects the ship's draft. This is often called "density effect" or "density correction." The change in water density influences the ship's buoyancy, causing the entire vessel to "sink or rise" by a few centimeters in the water. This will cause a change in the ship's draft both forward and aft including the mean draft. Thank you for the comment.
Why TPC is multiplied by 4?
Thank you. In the comment section, it's hard to explain how this formula was derived and why 4 became a constant. I will try to make a separate video about the derivation of the formula of freshwater allowance. Usually, onboard we can extract the value of the freshwater allowance in the stability manual provided by the shipbuilder.
But try his one, Derivation of the FWA formula:
Consider a ship floating in SW at load Summer draft at waterline WL.
Let the volume of SW displaced at this draft be ‘V’.
Now let W1L1 be the waterline for the ship when displacing the same mass of fresh water.
Let ‘v’ be the extra volume of water displaced in FW.
The total volume of freshwater displaced will be V + v.
Mass = Volume x density
Mass of SW displaced = 1025V
Mass of freshwater displaced = 1000 (V + v)
But the mass of FW displaced = Mass of SW displaced.
1000(V + v) = 1025V
v = V/40
Assume that ‘w’ is the mass of SW in volume v and ‘W’ in volume V,
Then, replacing the factor as obtained above we get:
w = W/40
But w is a factor that is a product of the FWA and the TPC
Now since the FWA is in mm and the TPC is in cm, they both have to be converted to metres
Thus: W = (((FWA mm x 100) cm X TPC cm) / 100) metres
Simplifying we have: w = (FWA x 100 x TPC) / 100 = W / 40
Or (FWA x TPC) = W / 40
But w = TPC x (FWA/10)
Hence W/40 = TPC (FWA/10) or FWA = W/(4 x TPC).
Where ‘W’ = Loaded SW displacement in tonnes.
@@nauticalacademy001 thank you for answer
what is the difference between FWA and DWA?
FWA is the number of millimeters by which the mean draft changes when a ship passes from saltwater to freshwater, or vice versa, while floating at the loaded draft. This is typically measured when a ship is moving from seawater to freshwater, such as when entering a river or a lake.
Dock Water Allowance (DWA): DWA is the number of millimeters by which the mean draft changes when a ship passes from saltwater to dock water, or vice versa, when the ship is loaded to the Summer displacement. Dock water is a type of water with a density between that of seawater and freshwater. DWA is typically measured when a ship is moving from seawater to dock water, or vice versa, while in a dock or a shipyard.
FWA is the change in draft when a ship sails from seawater to freshwater or vice versa, while DWA is the change in draft when a ship sails from seawater to dock water or vice versa or from dock water to another dock water with different water densities. The key difference is the type of water involved, with FWA involving a transition between seawater and freshwater or vice versa, and DWA involving a transition between seawater and dock water or vice versa.
@@nauticalacademy001 so we can calculate the change of draft by FWA value and TPC value with the given formula DWA= change in draft= displacement * change in density/ 0,025