Let me offer a 'fundamental' difference between the FUNCTIONAL structural needs of blue water and coastal designs.
First, a blue water boat should be designed and built so that the boat can withstand long term survivability of extreme weather, and afford reasonable protection of the crew and no matter the 'experience' of the crew' ... A boat that is purposely built to REPEATEDELY and often withstand the MAXIMUM that 'mother nature' can provide and do so for long (materials 'fatigue' considerations).
A 'coastal' cruising boat should be able to the withstand a brief or relatively short period of maximum weather and sea state ... because it 'can' easily run for safe harbor and to avoid the average 'maximum' conditions.
The structural differences are the blue water boat is usually designed at 3 to 4 times the calculated strength for 'normal' maximum conditions expected. The Coastal boat is normally designed at 2 to 2.5 times the calculated strength for 'normal' mqximum conditions expected. That is a BIG difference!!!!!!!!
Yes, a lightweight flimsy Clorox Bottle or even a Magregor 26X 'can' do a circumnavigation .... but, and a VERY important BUT is, that the lightweight Clorox Bottle has a higher 'probability' by its 'design strength' of becoming 'broken' in comparison to a 'blue water' boat .... by a factor or 3:2. (or 4:2 for when comparing to the 'top quality' Blue Water boats). And this is a far different consideration than the boats being compared 'LOOK the same' or have experienced or non-experienced crews, etc. Also, you have to ask why these 'customary' safety factors have evolved to establish the 'scantlings' that yield 'coastal' or 'offshore .... that answer is those that didnt have sufficient scantlings numbers simply had a higher failure rate for the service intended.
Just because a coastal design LOOKS LIKE a purpose-built blue water boat doesnt make it a blue water boat. The FUNDAMENTAL considerations / differences of a blue water designed boat is its purposely built 'stronger' than a coastal designed boat and thus has a much greater probability of surviving long term in the 'open ocean'.
Its the structural NUMBERS that makes the difference, not what you 'think' or assume.