The STCW requirement "May" be a requirement of paticular jurisdictions outside of the US for vessels under 200 tons. For example, I believe the Moorings in BVI require their paid captains be STCW certified. I'm not clear if that's a company policy or a BVI policy.
I think if it's your goal to captain
vessel in the caribbean
you should check with the employer or the governing authority as to their individual requirements...
In addition, I believe the BVI has requirements for the Vessel..Like a stability test..
So I think the answer is that there's no one size fits all rule
in the small vessel charter business..