General HydroStatics Tutorials

The Real Lessons We’ve Learned From the Field

Laramie Test 8

About Our Tutorials

General HydroStatics (GHS) is a powerful tool, but like any advanced software, it comes with a learning curve. At DMS, we use GHS every day to tackle real-world stability challenges, and we’ve learned a few things along the way.

These tutorials are designed to help engineers, naval architects, and maritime professionals understand the software faster and get more out of its capabilities. Whether you’re running your first stability analysis or troubleshooting a tricky load case, we’re here to walk you through it.

Our Tutorials

010 Introduction to GHS

210 GHS Modeling Tools

220 GHS Model Organization

230 GHS Part Types

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Focuses on creating hull type parts in Rhino. Attaching the proper structure. And how to create negative displacement hull parts in Rhino.

Edit 1: Negative displacement parts are very temperamental in Rhino. Rhino accomplishes this by changing the permeability or effectiveness. Sometimes GHS will not allow this. Try it in Rhino, but if GHS gives trouble, it is better to just define the part using GHS Part Maker (see tutorial 240).

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Expands on homework 231. Now adds tank parts to the Rhino GHS model. Includes adding nested parts. And how to use the same shape objects to create symmetrical tank parts.

Edit 1: For the most consistent use of Rhino, no centerline geometry parts should be modeled across the vessel centerline. This applies to all center tanks. The best way to model these in Rhino: Define the tank as a centerline part, and then manually edit the Rhino limits for that shape so that the transverse limits stop at centerline (Y=0).

Edit 2: For any parts that cross centerline, but are not symmetric about centerline: Do not name these parts with the .C extension. GHS will try to mirror them and get confused. Instead, simply name them with the dominant part side (.P or .S).

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Expands on homework 232. Focuses on adjusting permeabilities and tank contents, using Rhino. Also covers how to define sounding tubes in Rhino.

Edit 1: For the most consistent use of Rhino, no centerline geometry parts should be modeled across the vessel centerline. This applies to all center tanks. The best way to model these in Rhino: Define the tank as a centerline part, and then manually edit the Rhino limits for that shape so that the transverse limits stop at centerline (Y=0).

Edit 2: For any parts that cross centerline, but are not symmetric about centerline: Do not name these parts with the .C extension. GHS will try to mirror them and get confused. Instead, simply name them with the dominant part side (.P or .S).

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Completes the set of Rhino modeling skills for GHS. Now adds sail type parts to the GHS model built in Rhino. Also shows how to create non-displacement skegs in Rhino.

Edit 1: Non-displacement skegs are not really useful. Unfortunately, reducing the effectiveness of the part also reduces its effective wind area. The easier way to model a free-flooding skeg is to model the skeg as buoyant and then add in the weight of the skeg water as a fixed weight item.

240 GHS Part Maker

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Simple exercise to just open Part Maker and save a new file.

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Create a simple canoe hull, using only LOCUS commands.

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Full exercise to create the entire barge model using part maker only.

  • Engine room has contents of AIR (Spgr = 0.0001).
  • LNG Tanks have contents of LNG (Spgr = 0.544).
  • Stern notch is modeled with a negative displacement.
  • Include permeability for all tanks, contents of all tanks
  • Engine room tunnel defined as a component of the main engine room. NOT a separate part.
  • LO and HO tanks deducted from the engine room part.
  • Extra credit: Include the sounding tubes for each tank as well.

250 GHS Geometry Properties

310 GHS Report Generation

320 GHS Report Formatting

330 Viewing GHS Reports

340 Condition Graphics

410 GHS Draft and Trim

430 GHS Status Command

440 GHS Hydrostatics

510 GHS Limits

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Homework 511 covers how to develop limit statements. The homework includes several arbitrary limit statements that are created. These don’t represent any specific regulatory criteria; they only serve to demonstrate the capabilities of GHS limit statements. Homework and solution files included in download.

Edit 1: If you apply the stability limits directly as the homework requires, GHS will throw an error. The area limits require a minimum area of 0.573 ft-deg. Please adjust your limit requirements accordingly.

530 GHS Heeling Moments

540 IMO Severe Wind and Roll Criteria

550 GHS Max VCG Command

610 GHS Damaging Compartments

620 GHS Deterministic Damage Stability

630 GHS Probabilistic Damage Stability

640 GHS Floodable Lengths

710 GHS Longitudinal Strength

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Homework 711 covers basic longitudinal strength. The main focus of this homework is to understand the correct way to add weight items as distributed loads. The light ship weight gets added as a distributed weight. And there is a deadweight item also added as deadweight. Tank weights are also included. Finally, the homework covers how to define frame locations for a longitudinal strength analysis. Download includes homework files and solution.

Edit 1: The light ship weight distribution needed to modified, otherwise GHS was not happy. Please use the following light ship weight distribution.

Location, Weight rate
0.0 m, 5.0 MT/m
10.0 m, 40.0 MT/m
90.0 m, 50.0 MT/m
100.0 m, 10.0 MT/m

TCG = 0.0 m
VCG = 3.0 m

720 GHS Advanced Longitudinal Strength

730 GHS Adding Waves

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This homework covers how to define waves in GHS. Homework files and solution are included in the download.

Edit 1: The wave amplitudes were specifically chosen to be obviously visible in condition graphics. But they were actually too visible. Please use the following wave configurations instead.

Sinusoidal Wave 180 deg phase 100 m length 3.0 m amplitude (6.0 m wave height)

Stokes Wave (In Place of Trochoidal Wave) 0 deg phase 30 m length 1.5 m amplitude (3.0 m wave height

830 GHS Flow Control

840 GHS Keyboard Shortcuts

910 GHS Grounding

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Homework 911 covers how to use ground points to perform a docking analysis.  You define four simple ground locations.  And then change the depth of water to slowly drop the water level until the vessel is supported almost entirely on the blocks.

Edit 1:  The ground points defined in the video will cause trouble with the barge hull form.  (When you see them plotted in condition graphics, you will understand.)  Instead, use the following ground points.

Block 1
X = 10.0 m
Y = 0.0 m
Z = Minimum point

Block 2
X = 50.0 m
Y = 8.0 m stbd
Z = Minimum point

Block 3
X = 50.0 m
Y = 8.0 m port
Z = Minimum point

Block 4
X = 89.0 m
Y = 0.0 m
Z = Minimum Point

Edit 2:  Simply changing the drafts will not work in this case.  Draft will only change the waterplane, but not the location of the grounding blocks.  Instead, you must use the Depth command.  This is one of the few times where it is appropriate to use the depth command.  You will also need to reset the depth of the vessel between runs.  Use Solve Depth.  If any doubts, refer to the GHS manual.  There is also a good tutorial example on GHS port.com.

Download includes homework files and solution.

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