# Difference between “Latereal Area” location mark and “Displacement” location mark

DELFTship forum Hydrostatics and stability Difference between “Latereal Area” location mark and “Displacement” location mark

• Author
Posts
• #38640
John
Participant

The hydrostatic marks show several locations. One shows the center of displacement, and yet another shows the center of Lateral Area. Do either of these correspond to the center of Gravity? Do either correspond to the center of Buoyancy? Would be important to know in order to place the bulb keel ballast so that its center lines up with the hull center so the boat sits on its water line.

• #38642
Robert Holme
Participant

Use the design Hydrostatics page

HTH
Maryak

• #38643
Icare
Participant

Just as their names mean it:
– “Lateral Area” refers to an area (2D).
– “Displacement” refers to a volume (3D).
– The center of gravity refers to the mass and density variations inside the ship.

Imagine an arrow: its lateral area is displaced backwards by the stabilizators meanwhile its volume is not really displaced by the stabilizators’ volume and the weight of its head move the center of gravity forwards.

Does this image make it easier to understand the difference of meanning?

• #38644
John
Participant

I’m quite aware of the meanings of the terms … my question related to what the marks corresponded to, turns out that none of the marks on the plans corresonds to the location of the centre of buoyancy given in the hydro report, which is the value I needed to calculate where to put the ballast.

• #38646
Robert Holme
Participant

turns out that none of the marks on the plans corresonds to the location of the centre of buoyancy given in the hydro report

If you take the provided figures in the design hydrostatics report, the position of displacement in the plans equals the centre of bouyancy and is located directly below the position of KM.

HTH
Maryak

• #38647
John
Participant

I found that they did not line up but then discovered the reason; I had ‘added’ a bit aft (a minus 100mm value on x) and then tried to measure the hydro figure from the aft section on my dxf transfer …
On another note, there is a figure of long centre of effort … in a sail boat the centre of effort is normally associated with the sail area, and you position it relative to the centre of buoyancy, bt DS knows nothing about my sails, so what does the mark for LCE refer to?

• #38649
Robert Holme
Participant

The LCE in the DH report is the position of the centre of effort of the volume of the hull derived from the Lateral Area at the draft.

Without sails this only only relevant to the hull in its designed condition.

Sorry but I know nothing about yachts other than as an operator. My profession was a Marine Engineer before retirement some 10 years ago.

Regards
Maryak

• #38650
John
Participant

mmm, it’s just that the LCE figure given in the DH report for my boat is “5.022” which looks about the same as the position in the drawing view for the Lateral Area location icon. But there is another location icon on the drawing view saying LCE=4252! I would have thought that LCE mark on the plans would be the longitudinal Centre of Effort mentioned in the DH, rather than the Lateral Area icon postion….
cheers, John.

• #38652
Robert Holme
Participant

Hi John,

I have no idea where your 2nd location came from!

The attachment in my previous post was done handraulically before I’d even heard of Delftship. There were no plans of the vessel so I had to start from scratch and 1st principles.

Attached is the fbm file of the same vessel using Delftship. I was very pleased that the two are almost identical.

The original was done to enable the vessel to be placed on dry land as she was in grave danger of floundering due to old age and insufficient funds to keep her in the water. Nelcebee was 116 years old when we beached her and she still sits on the wharf in Port Adelaide South Australia.

Regards
Maryak