Stability and Seakeeping

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Norman L. Skene's(in SKENE'S ELEMENTS OF YACHT DESIGN) gives 2 methods of judging the sea-keeping and stability of a boat, methods based on statistical stability diagram of several boats.

• Firs method is called Wind pressure Coefficient Method [page 292]
• Second method is called The Dellenbaugh Angle Method [page 296]
• At page 299 there you can find a the flowing table which allows you to judge a boat's stability by analyzing the transverse metacenter GM.
  • Note 1: If G is below M the vessel is stable and if G is above M than the vessel is unstable
  • Note 2: A vessel with a large GM comes to the upright position very suddenly, whereas a vessel with a small one comes to the upright position more slowly and is more comfortable in a seaway

Table of Trans. GM for different Types of Vessels
Harbor vessels, tugs       | GM=0.35-0.45 m
Small power cruisers       | GM=0.60-0.76 m
Shallow-draft river boats  | GM=     3.65 m
Merchant streamers         | GM=0.30-0.91 m
Sailing Yachts             | GM=0.91-1.37 m