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Orca3D provides a lot flexibility when running hydrostatics and stability analyses. Analyses can be run assuming that you know the displacement (weight), or assuming that you know the waterplane. The flotation condition can be specified with any one of the following combinations:

 Weight, LCG, TCG  Weight, LCG, Heel  Weight, Trim, TCG  Weight, Trim, Heel

 Model Sinkage, Trim, Heel

Definition of Terms

Following are the required inputs for an analysis, which define the flotation plane. More than one flotation condition can be specified, by listing values in each input field.

Note that these values define the equilibrium flotation plane, and in the case of entering a heel or trim, are used to determine the center of gravity. If a range of heel angles is also

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entered, the 0 degree condition is taken as the original model orientation, not the equilibrium flotation plane. If a non-zero TCG or a non-zero Model Heel are entered, there will be a non- zero righting arm at 0 degrees of heel. Zero righting arm will correspond to the heel angle at the equilibrium flotation plane.

Weight: the overall weight of the vessel, in the units shown

If you have chosen the Weight option (rather than Model Sinkage), you may also click on the "Weight/Cost" icon, and the total weight and center of gravity will be computed from the objects in the model that have weight properties, and the values filled in to the Weight, LCG, TCG, and VCG fields (this option requires that you have Orca3D Level 2, which includes the Weight/Cost Tracking module). Note that these values represent only what is explicitly modeled (it does not double the weight when you check Mirror About Centerplane, for example), and only the objects that have Weight properties assigned to them. If you have only modeled half of the hull, you should double the Weight value, and (presumably) move the TCG to 0. Note: this is not a permanent link. You must click the icon each time you wish the values to be updated. You can manually compute the overall weight and CG of a number of items using the Calculator icon. For example, if you know the weight and CG of the lightship, crew & effects, and fuel, you can enter each of them individually, and the sum will be entered into the appropriate fields in the Hydrostatics dialog.

LCG: the longitudinal center of gravity of the vessel, in the current length units, from the world origin

TCG: the transverse center of gravity of the vessel, in the current length units, from the world origin

VCG: the vertical center of gravity of the vessel, in the current length units, from the world origin (this is required in order to run a stability analysis at one or more heel angles) Model Sinkage: the depth of the world origin below the resultant flotation plane,

perpendicular to the resultant flotation plane. Positive sinkage is defined as the origin being below the flotation plane. This is sometimes referred to as "origin depth."

Trim: the trim angle of the vessel, in degrees from the horizontal plane in the world coordinates. A right-hand coordinate system is used, so that if positive Y to starboard, a positive trim angle is bow up

Heel: the heel angle of the vessel, in degrees from the horizontal plane in the world coordinates. A right-hand coordinate system is used, so that if positive X is aft, a positive heel angle is to port

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Notes on Entering Multiple Conditions In all of the fields in the Hydrostatics & Stability dialog (except "Override Initial Plane Height"), you may enter a list of values, separated by commas or ellipses (...). For example, a list of Model Sinkages might be

1,2,3,4,5

As a shorthand, you may also enter the following to get the same list:

1,2,...,5

The spacing implied by the two numbers before the ellipses will be used until the number after the ellipses is reached or exceeded (note the commas before and

after the ellipses). Multiple spacings may be

entered, as in the following example for heel angles:

0,5,...,30,40,...,90,120,...,180 This is equivalent to entering:

0,5,10,15,20,25,30,40,50,60,70,80,90,120, 150,180.

The matrix of flotation conditions that will be computed is created from all of the

combinations of the various entries. For example, if you enter:

Model Sinkage: 1, 2, 3 Model Trim: 1.5, 2.5 Model Heel: 5, 10

12 flotation conditions will result.

Optional Inputs

Description: This field will be included in the output for the analysis

Override Initial Plane Height for Free Float Iteration: When a Weight is specified (a Free Float condition), Orca3D must make an initial calculation at some waterplane to use as a starting point. Once the displacement and center of buoyancy have been determined at this initial guess, the program iterates sinkage, trim, and heel to converge to an equilbrium condition (weight=displacement, centers of gravity and buoyancy are aligned). The Initial Plane Height defaults to the vertical midpoint of the model in its current orientation. This usually works well, but in some models this will be a poor guess; for example, if a sailboat model has a deep keel, so that the initial guess is somewhere in the keel, it will be more difficult (and time consuming) for Orca3D to converge properly. In these cases, you can

check this box, and enter a height that is closer to the equilibrium waterplane height. Mirror About Centerplane: checking this box assumes that you have modeled half of a symmetric hull, and wish the program to assume the mirror image. Note that hulls that are not centered at Y=0 will give incorrect results; therefore a symmetric catamaran hull model, where only one side of each hull has been modeled, should be moved to the centerplane before analyzing it.

Add Plane(s) Representing Water Surface: checking this option will insert a planar surface to represent each equilibrium flotation condition, and will include markers

representing the centers of buoyancy and flotation. It will also include a plot of the sectional area curve, if stations have been defined. The scale and color of this curve may be set in Orca3D Document Properties, in the Hydrostatics tab

Transform Model to Resultant Condition: This option will cause the model to be moved (only that portion of the Rhino model that was selected for the hydrostatics calculation). The model is first heeled about the world longitudinal axis, then trimmed about the world

transverse axis, then sunk along the world vertical axis. Note that output results (such as

VCB) are reported in the coordinate system of the original model orientation.

Compute Righting Arm at these Heel Angles: When selected, you may enter a list of heel angles to be analyzed, separated by commas. A list of evenly spaced values may be

entered in the format a, b, ...,c where a is the first angle, c is the final angle, and intermediate angles will be included at a spacing of (b-a).

Note that the 0 degree condition is taken as the original model orientation, not the

equilibrium flotation plane. If a non-zero TCG or a non-zero Model Heel are entered, there will be a non-zero righting arm at 0 degrees of heel. Zero righting arm will correspond to the heel angle at the equilibrium flotation plane.

The calculation of the righting arm allows the model to trim as it heels to maintain a true hydrostatic balance (this is true even if a Model Trim was entered to define the equilibrium flotation plane; the Model Trim is used to determine the center of gravity, which is then used as the model is heeled).

The value of the heel angles must be between -180 to 180 degrees.. For example: 0,10,...,180 will compute every 10 degrees from 0 to 180

or

0,-20,...,-60 will compute every 20 degrees from 0 to -60 or

-150,-140,...,0,5,...,60 will compute every 10 degrees from -150 to 0, then every 5 degrees from 0 to 60

Print Full Output for Heeled Conditions: By default, the output does not include a

complete table of hydrostatic data at each heeled condition. Checking this box will cause the complete hydrostatic data to be included in the report for each heel angle.

Also Write Output to CSV File: If you also want output written to a comma-separated-value (CSV) format (suitable for import into Excel, or parsing with another program), check "Also Write Output to CSV File," and enter the path and filename. The format of this file is self- documenting.

Use Custom Conditions: Defining multiple conditions at once is easy in Orca3D, by simply

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entering a list of values in the various fields. For example, if you specify Sinkage values of 1.0, 1.1, and 1.2, Trim values of 0 and 1, and Heel values of 2 and 4, Orca3D will run the 12 combinations of these values (3 Sinkages x 2 Trims x 2 Heels). However, you may only wish to run a few of these combinations, and at the same time include a few conditions that are defined by Weight, LCG, and TCG. In this case, check the "Use Custom Conditions" check box, and the following table will be shown in the Hydrostatics & Stability dialog. The table will be initially populated with all of the various combinations of the values in the selected input fields (e.g., Weight, Model Sinkage, etc.). By default, the conditions are sorted in the output according to Displacement, but you may specify that the results are sorted by draft, trim, or heel.

Here, you can turn a condition off by unchecking its box in the Run column, and change its name by double-clicking its entry in the Name column (this name will be displayed in the report). New entries may be added at the bottom of the list.

There are two Types available; "Fixed Plane" (Sinkage, Trim, and Heel), and "Free

Float" (Weight, LCG or Trim, TCG or Heel). By clicking on the Type for a condition, you can select the type:

Once this is selected and you have moved the cursor to one of the fields, the fields that will not be used are shown in gray. In the example above, Condition 2 has been changed to a Free Float condition, so Sinkage is now gray (even though a value is entered in the field, it will not be used). At this point, you can enter the Weight. Next, enter either the LCG or Trim. The same is true for TCG and Heel. Finally, enter the VCG. If you enter both, a warning will be given when you move to a different row in the table or try to Calculate, and the fields in question will be highlighted in yellow, and you will need to clear one field or the other. In the example below, Condition 2 has been changed to a Free Float. A Weight has been entered (the Sinkage value is now ignored), and a TCG has been entered. However, there is still a Heel value entered, and you must choose between one or the other by clearing the entry of one of them.

If you uncheck the "Use Custom Conditions" check box, and then re-check it, the following prompt will appear:

If you answer Yes, the form will be repopulated using the values in the fields of the Hydrostatics & Stability dialog (any custom conditions will be lost). If you answer No, the form will be shown with your previous data.

Pre-Float: Clicking this button will execute an analysis to look for commonly encountered errors. While it doesn't guarantee to discover all potential sources of error, it can find things such as CG locations outside of the bounds of the hull, negative displacement due to

incorrect outward normals , and section definitions that are not consistent with the selected surfaces.

After clicking Run, the status of each check will be shown. If any of the checks fail, the status will be shown as "See Details." Click the Details button to get further information on how to rectify the situation.

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 LCG, TCG, VCG Bounds: check to be sure that the center of gravity is within the bounds of the selected surfaces

 Positive Displacement: Check for any surfaces with negative displacement.There are occasions when this is correct; for example a surface that is modeling a bow thruster tunnel. If any surfaces with negative displacement are found, the status will be shown as "See Details," and the surface(s) in question will be selected. You can click on the Details button for more

information, or click the Flip button to flip the normal direction .

 Section Consistency: If the surfaces that are selected for hydrostatics are not the same surfaces that were selected when the sections were defined, this check will fail and the status will be "See

Details." The section-based values (sectional area curve, Cp (prismatic coefficient), and the Cx (maximum sectional area coefficient)) will be

based on the surfaces that were selected for the hydrostatics.

Add Objects: Clicking this button allows the addition of other surfaces or meshes to the selected set for analysis

Orca3D Units: To change any units except for the length unit (which is a Rhino unit and must be changed in the Rhino Properties dialog), click on the Orca3D Units button. The Orca3D Properties dialog is shown, with units information at the bottom. See Properties and Units for more details.

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