Low Tide

Yacht Designer Tad Roberts' Web Log

Safety and Stability


I just finished my first quick read-through of the Leviathan accident report from TSB. Initially I’m totally disappointed. Usually I’m impressed by these reports but I know there is at least one lawsuit underway and this report leaves out (In my mind) some critical information. While the report states that an inclining was done and[.....]


Stability information presented to the public is usually simplified to the point of being useless. When I see a published stability curve like that above, my reaction is “That’s nice and it looks good, but it tells me almost nothing.” It’s a nice graphic but key information is missing, mainly data on the conditions under[.....]


This article was originally published in Western Mariner November 2015.


This article originally appeared in Western Mariner September 2014.

Change in Stability with Dinghy Aboard

I’m often asked about the advisability of adding a heavy dinghy stored on the roof, people wonder how much difference this will make to stability. The answer always involves a lot of questioning about the particulars of the boat and load condition. So today I made a study of a typical 1985 “trawler” yacht, the[.....]

CCG Hero Class and Safety Concerns

It should not come as any surprise that large, expensive, incredibly complex machines raise issues of competing interest. Union of Canadian Transportation Employees members are alleging un-addressed safety concerns on the CCG newest ships. Chronicle Herald Story here From the story it sounds like TC has been issuing operation certificates with promises by CG that[.....]

Stability of Canadian OFSV

CBC has just published a story CoastGuard Ship Redesign, outlining the discovery of apparent instability in the initial design of our new OFSV’s (Offshore Fisheries Science Vessel), three of which Seapan has under contract and the first under construction. This story seems like pot stirring coupled with the usual misinformation. These are large and immensely[.....]

Capsize of Refugee Boats in the Mediterranean

Mass drownings in the Mediterranean Sea day after day. A horrible situation that’s entirely preventable, or would be if someone (UN?) could enforce some simple loading guidelines. Of course I realize the problems are not anything close to simple, and the only real cure is to eliminate the need of people fleeing their homelands in[.....]

Stability and the Leviathan II

Leviathan II has been recovered and is floating upright. This is good and it will allow investigators to gather facts on the precise condition of the ship at the time of the accident. Unfortunately, damage is so extensive that any “real stability at time of capsize” will be impossible to establish. This is the reality[.....]

Small Boat Stability

Before we start looking at specific stability issues and possible regulatory problems, it’s important to get the basics understood. Above is a basic diagram showing three stability cases. The “Stable Condition” where G is below M and there is a positive GZ. Gravity is pushing down through G, the Buoyancy force is pushing up through[.....]