How to build the Bonjean Scale with the program Orca3D

Discussion in 'Stability' started by Rabah, Feb 19, 2017.

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RabahSenior Member

How to build the Bonjean Scale with the program Orca3D
The outcomes of the Hydrostatics, received with the program Orca3D, enable firms developing the design of the vessel to build the so-called Bonjean Scale which represents an aggregate of curves of the immersed areas of the station lines depending on the draft. It is the obligatory operational document, given to the client and the ship master.
Let's trace how this document is created taking for example the same model of the Harbor tug 34м from my former publications:
1. In dialog box Orca3D it is noted
Sinkage 0,0.1, …, 5.6 /see fig.1/
2. From the received outcomes a table is compiled for the immersed areas depending on the draft /through 0,5м/ for each stations line /see fig.2/. Data for Zmin we take from the Table of offsets.
3. Using the data from the table of fig.2 with program AutoCAD we do the drawing the Bonjean Scale /see fig.3/:
3.1 In the beginning it is necessary to create the grid for 21 station lines /0-20/ through ΔL=Lbp/20=34/20=1,7m and through ΔT=0,5m. At first we do the grid in equal scale on a length and on height /1м^1м/.
3.2 We trace buttock-line CL based on the data from the Table of offsets or it is taken as a ready schedule from the 3dm file of model.
3.3 We trace splines of curves of the stations immersed areas at fit tolerance 0 /that is splines should be passed through the specified points/.
The scale of the areas is accepted: 1м/1000мм/ ^ 10m2
3.4 For greater clarity only the scale on height /draft/ is multiplied twice:
2м ^ 1м
4. We test the Bonjean Scale for accuracy of data on a concrete water-line with trim, without heel. Certainly we can take any declined water-line but it will be better if we choose a case of loads which is really possible at operation of the vessel.
4.1 We use outcomes of account of a damaged stability with the program Sea Hydro /more detail about this program see on the site www.seatech.ru / for the following emergency case:
The vessel with total displacement receives a breached in the shell plating next to after peak bulkhead /on 1,46m from the transom/ and thus water has penetrated simultaneously in a stern ballast tank and in steering compartment. Both will be filled by water up to definite levels until then while the vessel will reach equilibrium state /i.e. when LCB and LCG will be on one vertical / .
The vessel receives a trim by the stern = -1,672deg. at draft Тf=3,65m and Тa=4,643m
Displacement in a damage state: Ddamage=939,908t; LCB=16,366m; VCB=2,607m;
hо=1,754m; h=1,521m-with allowance for effect of free surfaces of all liquid loads.
For a stern ballast tank it is received:
Mass of seawater got in tank=14,095t; X=0,857m from AP; Y=0m; Z=3,969m from BL.
For steering compartment:
Mass of seawater got in compartment=42,793t; X=3,362m from AP; Y=0m; Z=3,782m from BL.
4.2 We execute account of hydrostatics with program Orca3D selecting Orca3D Weight Calculator and adding to data for the vessel with total displacement new data on the stern ballast tank and steering compartment /see fig.4/.
At displacement 939,908t; LCG=16,41m from AP; TCG=0m /at accident deluging of the compartments is symmetric/ and VCG=3,939m from BL it is received the following final results about the water-line of balance with program Orca3D:
Trim by the stern = -1,659deg; Sinkage = 4,651m; LCB=16,372m; VCB=2,62m; h=1,97m disregarding effect of free surfaces of liquid loads.
To know Тf and Тa it is necessary to mark before account of hydrostatics the following critical points for Main deck-CL:
In stern X =0 from AP; Y=0; Z=5,6m from BL
In bow X =34,436m from AP; Y=0; Z=6,827m from BL
We receive the draft in the fore: 6,827-3,171 = 3,656m. This draft is in the bow apart from AP LOA=34,436m.
Graphically or account we receive the draft at the forward perpendicular /Lbp=34m/ Тf=3,668m
Draft on AP: Тa=5,6-0,947=4,653m Тa=4,653m
4.3 On the received data for Тf and Тa we mark in yellow color the damage waterline on the Bonjean Scale /see fig.3/.
4.4 We take data about the immersed areas on the marked trimmed water-line. On station lines 5, 10 and 15 it is shown as it is done.
4.5 Data from the Bonjean Scale it is noted in the table /see fig.5/. For comparison near to them it is noted also those, received with program Orca3D from last account.
At once it is possible to note major accuracy of graphic construction that means that at damage of the computer on the vessel or for want of it, the captain or his assistant can define without problems displacement and his centre at any cases of loads of the intact and damaged vessel.
Arises and the following output: The outcomes of hydrostatics with two programs Orca3D and Sea Hydro are very similar and the variance inappreciable.
Has developed: NA Razmik Baharyan

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• Tug 34m-Stations immersed areas by trimmed WL-Fig 5.doc
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Last edited: Feb 21, 2017
2. Joined: Sep 2011
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TANSLSenior Member

Thanks Rabah for this interesting work that many nostalgics will like to read. Fortunately for many years the calculation of Bonjean values is no longer necessary. Current calculation programs, using 3D virtual models, directly calculate the hydrostatic values for any trim and heel, without having to go through those intermediate calculations. As a result, calculations are faster and more accurate than using Bonjean values.
I do not think many young designers today know what that is, how it is calculated and what it is for, but it is always exciting to read the history of naval architecture.
By the way, I had always seen that for every frame there were at least 5 Bonjean values. Why in the attached figure only the area is represented ?. It would be useful to know also, by means of a graph or a table, the position of its c. of g.

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