Just Security has an examination of the various authorities at work in the application of blockades as used in conjunction with the conflict with Iran.
Since boardings are Coast Guard’s bread and butter, you may find it interesting.
They also have a look at the Coast Guard’s peacetime authorities here, “Maritime Law Enforcement on the High Seas: Authority, Jurisdiction, and the Seizure of The Skipper.“
Chuck Hill's CG Blog 
Lack of understanding of U.S. Navy international maritime responsibilities has been driven mostly by politics. Key capabilities like sufficient Carrier Strike Groups, ESCORTS, Amphibious force assets, and elimination of the Navy’s ability to operate & maintain itself . . . has been depleted to the point of irresponsibility. Shrinking the carrier force, not maintaining the Cruisers, and parking (withdrawing from service) our EXCORTS, and elimination of Expeditionary Logistics and Maintenance Activity simply must be reconstituted. This illicit activity has really taken a toll, and we are not done yet. If one cannot maintain one’s self then operations when peer-to-peer combat begins . . . will be brief.