Ship Stability

Electric power entices us with its flexibility and adaptability. And that extends to our charging sources. We gain the ability to recharge our batteries from nearly any source, assuming everything works together. Discover the critical issues to combine multiple charging sources for electric propulsion.

Which battery to choose? The batteries form one of the most expensive components in electric propulsion. Today, review the basic battery chemistries out there, allowing you to quickly identify the best battery strategy.

Going electric requires you to design a whole custom electric system for your ship. The challenge with electric systems is the interaction. The requirements for one minor component may determine key settings for the whole system. Today I cover some key settings for the electric system. After deciding these points, the complexity of shopping should simplify into a few simple paths.

Designing an electric system requires more than just spinning a propeller. Much of an electric boat focuses around safety and emergency planning. This article covers several key decisions to design an electric system that delivers far more than propulsion. Instead, our electric system ensures reliable safety.

Electric power and electric propulsion are still growing industries for yachts and small ships. In this field, a few marketers may stretch the truth a little to make sale. This led to many myths and misunderstand about electric propulsion. Today I debunk five common myths.

How to design a ship? How to go from a blank sheet of paper to a sensible design for a ship, when you have nothing to start with? So here are my secrets revealed.

A critical review of my previous analysis with an eye towards statistics and the importance of context in numbers.

Why would you pay more for engineering than for the ship? The value of engineering comes from the lives protected, not the design of the yacht. How much is that protection worth? This risk analysis has an answer to the value of safety.

Commercial ships are a world apart from recreational yachts. They contend with tougher requirements, and they need far more safety features. But what are those differences? How is the commercial ship safer?

No doubt, the math of propulsion devices is complicated. But it is all the same physics. By dividing each of these devices into their essential tasks, we find new opportunities. New methods of propulsion from different combinations of old tricks. Insight into this continuum allows us to better classify marine propulsion and dissect past successes to search for new combinations.

How to maneuver a massive freighter into port? CAREFULLY. We design freighters around the scenario of open ocean passage at full speed. But each freighter needs to enter port, pass through canals, and a host of other precision maneuvers executed at a fraction of their design speed. How do massive commercial ships manage precision maneuvers every day?

Like everyone else, I watched the story of the Ever Given and formed my own theories about what happened. Except I was wrong. As the events unfolded, new information came out and I learned the increasing complexity of the accident. Each time, I developed a new theory, which failed with new information. Over a year later, what is the answer? Let’s review what we know and still do not know about the Ever Given incident.

For small vessels, the major problem with stability letters is explaining it to the captains. Today I will review a stability letter and give plain English interpretation of all the boring mumbo-jumbo.

Three neat things you didn’t know about marine cranes! Every now and then, it’s fun to step back and appreciate the innovation that allowed us to adapt industrial cranes to the marine environment.

In the marine world, we see cranes daily; they are very useful pieces of equipment. Despite their common appearance, we need to remember their potential for disaster. Cranes on ships generate new, subtle risks for lifting operations. Unless you know what to look for, the risks can go undetected. This article reviews the major dangers of cranes on ships.

No foundation is perfect. Each design reveals new insight and opportunities for further improvement. The art of foundation design finds an efficient arrangement to redistribute concentrated loads into the general ship structure. I review basic strategies for foundation design.

Class societies are not perfect, but they are absolutely necessary. We need organizations to provide quality assurance on ships, whose primary motivation lies solely in the quality of the ship, and not with national interests. Despite this necessity, a class society works best when we remember that they are not perfect. Everyone has their bias, and when we balance these biases, we create a fine seaworthy ship.

No matter what, building your own yacht will always require more than you anticipated. Before making the commitment to build your own boat, take time to seriously consider all the hidden costs and extra effort required. The best yacht for you is the one you can finish.

Without proper management, the shifting liquid in a ship’s tanks can create a lethal scenario. Free surface moment (FSM) is one of the most frequently misunderstood elements in ship operation. The deck officer that values their life wants to understand free surface moment. The physics behind it, and how it applies to ship operating limits.

Theoretically, composites promise strength several thousand times greater than steel. So why don’t we have composite materials everywhere? The practical design of composites severly limits their capabilities. Once you understand the practical limits, it provides a useful design guide for how to apply composites and maximize their advantages.

Every naval architect learns the theory of how to perform a stability test. But a well executed stability test employs very little theory, and a great deal of practical experience. This guide imparts some of that hard earned experience to make your next stability test go well.

What science could possibly link moving a few weights on deck with calculating the light ship weight? Armed with knowledge, we carefully exploit physics to achieve high quality science without the fancy equipment. Today I explain some of the theory behind the stability test.

A stability test requires extensive work to prepare the vessel. Where do you go to find that work list? This guide should give you some advanced warning of what to expect. It covers all the practical matters for a Chief Engineer to prepare for their next stability test.

Smooth stability tests require planning, and practicality. As the vessel Master, you want to prepare for this thing that completely disrupts vessel operations. But you are a busy person, and engineers are very long winded. Instead, this guide provides a brief overview, focusing on the major elements that concern you with a stability test.

What are the practical steps necessary to execute a stability test? How to avoid the pitfalls? Who do you call to arrange everything? This guide gives advice to the vessel owner on how to prepare for a stability test, from start to finish. Instead of theory, we focus on the logistics and coordination.

Certain as the sea, ships will require stability tests at some point in their life. Or maybe not. This article discusses the different types of stability tests and when regulations require them.

Stability tests do not arrive instantly after you order one. It takes time and planning, and you should expect extensive coordination with several different organizations. But the ultimate benefit justifies the expense: a ship with reliable stability performance. This article unravels some of the mystery behind a stability test and why you want one.

Weight control is not sexy, but the consequences of ignoring it can be very scary. If we ignore weight control, we risk a potentially unusable ship. That is why proper weight control starts with the right attitude: understanding the risks and the necessity of a weight estimate.

Naval architects work daily as systems integrators, but it’s difficult to point to any one system and show where this adds value. So today I want to review some T-AO UNREP equipment, and show how none of this is possible without systems integration.

Ships evolved to require a combination of expertise from highly specialized disciplines. If you want a modern vessel, expect a modern team of experts. So let’s meet all the different roles and learn who it takes to create a modern ship.

The physics of model scaling make it impossible to perfectly convert between model scale and ship scale. Learn how to get around the scaling correlation problem and convert from model scale to ship scale measurements.

Time for an upgrade! Far beyond the single purpose testing facility, the modern towing tank expanded into a Swiss Army knife of experiments. Armed with new gadgets and advanced capabilities. Time to see what new tricks the tank holds for us!

It may look like a swimming pool, but towing tanks exist for a different purpose. Dragging models down the tank propelled the science of ship design forward across the years. These pools deliver critical measurements for ship hydrodynamics. Discover why we pay such a high price for a fundamental tool of ship design.

In computational fluid dynamics (CFD), we often need to model scenarios that involve more than one fluid. Volume of fluid modeling (VOF) expands the capabilities of CFD to allow limitless combinations of different fluids. The world of VOF encompasses everything from droplets of diesel spraying in cylinder all the way up to tsunami waves crashing against the city of Tokyo. How does VOF achieve this, and what are the implications for CFD modeling?

Mesh deformation is incredibly frustrating, complicated, unstable . . . and unavoidable if you want to incorporate body motions into CFD. Modeling body motion demands mesh deformation, changing the mesh on the fly, while using it to solve transport equations. As you might expect, that brings a host of new challenges. This reviews several new strategies that the CFD engineers needs to consider.

When we add the time domain, simulations change from modeling steady scenarios to unsteady, where boundary conditions change over time. Beyond the physics, modeling unsteady flow requires a few changes to the CFD solver. Inner iterations, timestep, Courant Number, and data management all enter into the strategy for the CFD engineer. Today we discuss each of these.

Computational Fluid Dynamics (CFD) can model multiple fluids with the volume of fluid method. (VOF) The volume of fluid method opens new horizons for advanced modeling, which requires additional planning from the CFD engineer. Dive into the boundary conditions, meshing strategy, stability concerns, and more. Discover the world of VOF modeling.

Turbulence demands modeling just like any other equation in computational fluid dynamics (CFD). As the CFD engineer, you need to describe boundary conditions for your turbulence equations. This article describes how to define boundary conditions for turbulence and provides typical values for normal simulations.

Turbulence does tricky things near walls. Boundary layers and laminar sublayers compact interesting flow patterns into a very small space. Small it may be, but experience proved we cannot ignore it. The boundary layer forms on the body, which is our object of interest, arguably the most critical region. Turbulence is most critical near the wall, and we need to consider near wall effects.

How we address turbulence is the defining feature of modern computational fluid dynamics (CFD). No modern computer has the power to directly compute the full details of turbulence (as of 2019). Instead, we make approximations and develop empirical models. What type of approximation, and which models should you select?

The heart of any CFD program is an extremely efficient linear algebra solver. But CFD equations are non-linear. How do we stretch the limits of linear algebra to accommodate non-linear CFD equations? How do we take the mathematics from one cell and apply them to millions of cells?

What makes a waterjet work? What is the difference between a good and bad waterjet? Waterjets may appear to be brutes of power, but they rely on delicately balanced design equations. Learn the common elements that go into all waterjets and discover the best practices that you should expect from any decent waterjet design.

CFD convergence is not an exact science. The CFD engineer relies on three tools to judge when a simulation finishes: monitors, flow patterns, and residuals. But none of these tools work 100% of the time. The well-trained engineer understands how to use these tools and how to combine them into a cohesive picture and reliably judge a converged CFD simulation.

The core of all calculus problems require us to consider something infinitely small. Ask a computer to ponder the concept of infinity and watch its circuits fry. If we want to solve the equations of computational fluid dynamics (CFD), we need a way to fake calculus. This impacts the stability, the mesh quality, and the ultimate simulation quality. Enter interpolation equations.

What is the utility of a transport equation? What do they achieve? Transport equations form the fundamental language of computational fluid dynamics (CFD). CFD engineers use them to communicate ideas, program CFD software, and diagnose problems with their simulations. But they only work if you understand the language. Today we explain transport equations and the significance of their terms.

Navier Stokes Equation. Shrouded in mystery and intimidation. Navier Stokes is essential to CFD, and to all fluid mechanics. This equation defines the basic properties of fluid motion. But there is more to gain from understanding the meaning of the equation rather than memorizing its derivation. Today we review Navier Stokes Equation with a focus on the meaning behind the math.

Just fresh out of college, and the boss assigned your first project for computational fluid dynamics (CFD). You are excited. You can’t wait to begin the challenge. You sit down at your computer, start up the CFD software . . . and freeze like a deer in headlights. How to begin? What to do first? Today we discuss the general workflow for a CFD project and highlight some general modeling advice.

What happens behind the curtain when the CFD engineer goes to work? What goes into making a CFD simulation? As a project manager, you need to understand the workflow of a CFD project; this helps you plan the project and track budget expenses. When we understand the workflow, we know the right questions and can anticipate project delays.

Is there anything that CFD can’t do? Practically speaking, we can achieve the result, but you may regret paying for the answer. Several CFD projects involve combinations of different CFD methodologies. Combined together, they evolve into a major project risk. Gain some insight about the risk factors for your next CFD project. Plan a strategy to minimize project risks so that you don’t get caught by combining unknown cost increases.

What is CFD? It uses the computer and adds to our capabilities for fluid mechanics analysis. If used improperly, it can become an incredible waste of time and money. With the right engineer, CFD can be cost effective, incredibly informative, and offer unparalleled flexibility. But what is this wonder of modern science? Learn more about this expansive tool.

Why are ship structures so labor intensive to design? Engineers need to anticipate multiple methods of failure, which makes a lot of work. The trick of efficient structural analysis focuses on recognizing which methods of failure are likely in each scenario. This article reveals six major methods of structural failure, with examples of common applications. Because it will be the failure mode you didn’t consider that ultimately leads to catastrophe.

Waterjets are fun. They give you great maneuvering control and promise much higher efficiency at high speeds. But that flexibility comes with the price of more subtle limits on performance. Used incorrectly, waterjets perform worse than propellers. This article focuses on the merits of waterjets, with focus on the most important factor: efficiency.

We all want to feel good about paying for engineering analysis. Sometimes the best answer drives us to maximize value, rather than minimize cost. In those cases, you do better to go beyond basic safety and search for enhancements. Today we discuss four engineering tasks where you can maximize your value. Extract every last drop of knowledge from your engineering project.

No discussion of hydrofoils is complete without addressing their application to the 2013 America’s Cup yachts. Catamarans screamed across the ocean. But with all that excitement, we sometimes forget how the crew jeopardized their lives in every race. This article presents an engineering perspective on the America’s Cup hydrofoils of 2013, with options for improvement.

Why would an airplane company design a ship? When considering hydrofoil ships, aircraft share many of the same requirements. More specifically, every hydrofoil vessel needs a method of motion control, even sailing hydrofoils. This article discusses the problem of hydrofoil control and several solutions.

Meet the Intercon AT/B connector system. A beautiful piece of engineering used to connect tugs and barges for inland and coastal trade.

Stability and seakeeping are frequently misunderstood. To understand the limits of these sciences, we must unveil the motivation behind their development. How to guarantee ship safety on an uncertain ocean?

A refined hull shape epitomizes the link between tradition and science. When we link the science of ship design with the experience of past ships, we identify the successes and isolate previous failures. This article glimpses into the background of hydrodynamics by exploring the link between the science of Bernoulli’s equation and the shape of ship hulls.

Monohull, catamaran, trimaran . . . so many choices. Which hullform to pick? Can we draw upon any science to guide our choices, or we beg Lady Luck to guide us? This article provides a rational and design map for selecting hullforms applicable to any type of mission. This organized approach allows us to see past the limitations of historic examples and consider new alternatives.

How man tons in a pound? When ships weigh thousands of tons, you really need to know which type of ton. So take five minutes and get clarity on the esoteric measurements of ship design.

An experienced engineer doesn’t have some magic button to deliver great FEA. Masters of FEA trade-craft hoard many little tricks and nuggets of wisdom to deliver better FEA. These tricks yield better ways to detect human errors and ensure model reliability. Or methods to deliver faster results. Today we share six nuggets of wisdom for better FEA.

Axe bow, X-bow; slim size, […]

Monohull, catamaran, trimaran . . […]

ZOOM!!!  No better way to […]

Welcome to luxury cruising.  Glide […]

Three hulls are better than […]

What distinguishes a yacht designer […]

Hull speed is bogus, but […]

Tips to Improve Your FEA […]

Why FEA Singularities Are Acceptable […]

FEA Errors from Mesh Size […]

Get The Most From Your […]

  Many heard about the […]

I confess.  I get excited […]

An Overview of FEA Work […]

How to Contract an FEA […]

I love to learn how […]

How Propeller Dimensions Affect You […]

Hey you!  I have this […]

The widespread availability of FEA […]

Efficiency Limitations of Propellers Propellers […]

Today, we pause for a […]

I love data and science.  […]

Snap, crackle, pop . . […]

Skynet is ready to perform […]

Propellers are dull, unimaginative, and […]

Avoid the hassle and frustration […]

1.0 The Limitations of Mechanical […]

GHS is nothing without macros. […]

EVER WASTE MONEY ON SPECIALISTS!  Here are a few simple-do-it-yourself tests to check for ship list and angle of loll.

1.0 Introduction How do you […]

PANIC! That should be your reaction if your ship developed a permanent list. Angle of loll shines like a bright red warning sign, indicating serious stability problems. Today we discuss an angle of loll (AOL): what it is, how to find it, and what to do about it.

Did you know that GHS can also do structural analysis?  Often, we only require a simple longitudinal strength analysis.  GHS provides all the tools for this.  

Why is Ship List Bad? If ignored, it continues grow and place your ship at risk.  Be proactive and stop the list once you first suspect it.  Your crew

How many different ways can […]

Steel is cheap.  No one cares about reducing the structure weight just to save on some steel costs, right?  WRONG!  And when you see the next bunkering bill, you will care too.

How to perform a stability analysis in GHS? These tutorials explain the process.

Imagine a technology that delivers cheap and reliable vessel communications with land.  Bandwidth high enough for every sailor to enjoy daily video conferencing with their loved ones.

1.0 Introduction Behold the lowly […]

I found this wonderful article that gives a great overview of bulk carriers.  A great reference to quickly understand the essential design aspects of a bulk carrier.

Consider the use of catamarans as massive industrial equipment.

General Hydrostatics (GHS):  The de facto standard software for hydrostatics and stability in the USA. Watch these tutorials to learn GHS.

Bulbous bows are not miracle devices. They only work under specific circumstances. Understand the limits of bulbous bows.

We all know that a drillship goes out and drills wells, but can you name all the steps required to drill that well?  Here are a series of fun videos that give an overview about how a drillship works.

This video provides a quick introduction to bulbous bows.

Your beautiful new ship is […]

Advice for unconventional places to find a job for naval architects. Useful when the the economy is slow.

Ship stability is not about operations in normal weather. See a few examples of how stability protects you from extreme emergencies.

Did you know that a perfectly stable vessel can become unstable and useless?  Understand how stability decay affects your vessel life.

Many ship designs require a resistance and powering study. This provides an overview of the resistance study.

An overview of what you get with project management services.

An overview of the services provided for a global FEA analysis.

An overview of the services provided for FEA of structural foundations.

An overview of what you get with services for structural design of foundations.

An overview of what to expect from engineering services for a stability test.

An overview of engineering services to provide structural scantling calculations.

What to expect from a damage stability analysis.

What to expect from your engineer when ordering a stability book.

Intact stability analysis is part of the process to determine your vessel’s operating limits and satisfy regulatory authorities.

Floodable lengths are one factor that determines the load line.  This is a measure of reserve buoyancy in the vessel.  Other fac

Every vessel and owner must […]

Watch a big strong ship bend like a reed in the wind.

This video from NAFEMS covers […]

A brilliant example of naval architecture at its finest. The stern landing craft!