There are some tried and true definitions used by boat designers and marine insurance underwriters that generally categorizes boats as to their usage - namely 'scantlings rules' or what broke or fell apart and then sunk under what conditions and most importantly what was the underlying 'strength' of the boats that survived in such conditions vs. those that didnt. Scantling rules have been effect since Mr. Lloyd (London) was a pup, such is the foundations and constant evolution of marine design and the marine insurance industry. The historical record of scantling rules is long and detailed; many of the 'smiley faces' you see on nautical charts locates a fix on those that ... 'didnt stand up' to the scantling rules.
Offshore boats.
The nominal definition of an 'offshore or open ocean boat' is one that is built to 3 to 4 times the strength needed to 'survive' the strongest storm normally encountered. The historical scantlings of such boats has proven itself over hundreds of years of accumulated data says that an open ocean boat should be to this level if it has a good chance to survive the 'usual' unexpected. This discounts entirely the skill of the captain or crew, the fancy gizmos, the 'modern construction', etc. as all of these aspects are subject to capricious actions of crew, materials, craftsmanship, etc.
Being 3 - 4 times stronger than needed also insures that the rigging and other metallic components -usually stainless steel- does not become 'embrittled' and fatigued leading to sudden catastrophic failure - ie. without warning. Stainless steel, the metallic material of much of the modern boat construction, as rigging, etc., easily 'fatigues' due to the constant load cycling encountered in the open ocean. Typically 300 series stainless will be VERY prone to failure if the material is repetitively stressed beyond 30% of its ultimate (breaking) tensile strength - usually 1 million load cycles at above 30% usually results in FAILURE; keep that maximum stress below that 30% value and you 'may' have a rig that lasts 'forever'. Fiberglass acts in the same way; the US Navy has 100s of documents highlighting the stress values and the fatigue characteristics of fiberglass.
The caution here is: dont think NEW will keep you secure. What will keep you secure on the open ocean where the impact stresses are constant and additive is: Scantlings History of the design - your designer built it that way on purpose, and your insurance underwriter insisted on it or they wouldnt insure you.
Coastal designs.
Coastal designs are built to a scantling rule of approx. 2 times the maximum strength needed. 2 is less than 3. Above 3 three, youre statistically safe from the boat falling apart due to constant repetitive / cyclical stress. Less than 3 your chances of 'not making it' are higher.
Repeat - most 'costal designs' (aka - most 'production' boats) are built to a scantling rule that is not up to par for the long term stresses encountered on the open ocean for long periods of time. Not that you cant sail around the world in a 'coastal' design, not that you cant do long distance sailing or island hopping; but, statistically speaking and from historical scantlings perspective, youre going to have a much higher chance of NOT 'making it' than if you were in a boat built to offshore scantlings ... at an overall inbuilt factor of safety of 3 or 4. Coastal designs are usually at near a design safety factor of only 2.
Inshore design.
Factor of Safety is ~ 1.5. 1.5 is 'half' of 3. 'Nuff said.
"Modern Design" and "new"
Just take a good look at the boats that are in 'charter service' after only 1 year. Just because a boat is 'new' does not mean strong or 'proven', ... remembering the keels that were falling off of expensive Bavarias and the many spade rudders falling of the Jeanneaus and other french boats, etc.
'Proven' is a word that means the 'scantling history' as accumulated over time is OK or that most successfully completed long distance passages were without incident or failure of materials, design, etc. Fatigue and its subsequent catastrophic failure of materials is what mostly sinks and breaks apart boats, especially in boats that werent designed for the service intended.
'Proven' is far vastly better than 'new', or 'modern'. "Proven" means well defined and successfully scantling history. When in doubt about a boat, any serious boat, ...... contract with a reknown marine designer/architect.
;-)
