T&T: rules that apply to vessels over 20m (65 feet)

[Steve Hazlerig]

There seem to be a number of rules (such as the Bridge to Bridge Radio
Telephone Act referred to by Kevin) that apply only to vessels over 20m (which
is actually 65' 7.4").

Does anyone know how this is measured?  Is it LOA?  LOD?  Official length as
listed on the Certificate of Document?  I've found nothing in my searches to
clarify this.

Thanks,
Steve Hazlerig