Stability of Boats and Ships

Roger Long

Stability is one of my favorite subjects. In addition to spending nearly four decades trying (successfully) to insure that the boats I design don't fall over, I have been involved in the investigation or analysis of some well know stability failures. In the mid 1980's, I was the researcher for a joint industry / Coast Guard task force establishing new stability regulations for sail training vessels and formulated the basic method that distinguishes the rules for sail training vessels from those applied to passenger sailing ships. This led to my being retained as an expert witness and consultant for the British government in the wreck inquiry following the capsizing of a sail training vessel with heavy loss of life. I have many times over the years lectured on the subject to sail training students (once in the forecastle of a huge Russian square rigger going through the tail end of a hurricane) and professional mariners groups. This will be an expanded paper version of those lectures which attempted, successfully from all I was ever told, to provide a visceral understanding of the subject with minimal math and calculations. This is a work in progress and I don't know how long it will take to finish so check back frequently.

If you would like to read about some of my adventures in stability, I recommend:

Tall Ships Down by Dan Parrott Read Excerpt Here

Pride of the Sea by Tom Waldron

It's not stability but, for another of my adventures in accident analysis and the story of my trip down to see the Titanic, read:

Titanic's Last Secrets by Brad Matsen

Table of Contents

Why Buoyancy is Imaginary

The Gravity of Centers

The Imaginary Center of the Imaginary

What's Upsetting?


Righting Arms

The Mythical Metacenter

The Balance of Forces

Heeling Arm Curves

Why the Stability of Large Sailing Vessels can be Treacherous

Coast Guard Foolishness