This is from Daniel Dennett here
Maritime law is notoriously complicated, strewn with hidden traps and escape clauses that only an expert, a sea lawyer , can keep track of, so sea-lawyering is using technicalities to evade responsibility or assign blame to others.
That part about evade responsibility or assign blame seems reasonable but not quite right. I don’t think it has to do with how complex maritime law is.
I always thought it was like seagoing teenage kids, i.e. someone who will spend an hour explaining in the most convoluted way possible why they don’t have to do a job that would have taken them half an hour 
From Duck Duck Go:
A querulous or captious sailor, disposed to criticize orders rather than to obey them; one who is always arguing about his work, and making trouble.
Said to have first appeared around 1805 - 1829, Merriam-Webster puts the origin as 1829.
My experience dating back to the 1970s and onward was a seaman who was frequently citing instances where the union contract was not being properly followed.
“Captious” is good word for it:
Captious comes from Latin captio , which refers to a deception or verbal quibble. Arguments labeled captious are likely to “capture” a person; they often entrap through subtly deceptive reasoning or trifling points. A captious individual is one who might also be dubbed “hypercritical,” the sort of carping, censorious critic only too ready to point out minor faults and raise objections on trivial grounds.
I’ve always thought of a sea lawyer as a sailor who dispenses legal advice to shipmates freely but without a formal law education to validate his advice.
Yes. Like a “jailhouse lawyer”. Several good answers here. Also like many posters here on gCaptain
Term comes from the Royal Navy during the Napoleonic Wars. Following the mutinies at the Nore, a greater emphasis was placed on seaman’s rights and regulations preventing their abuse and some fellows got rather good at nitpicking regulations.
I have printed and laminated sheets explaining the most commonly raised ones today and rather than spend time arguing I just hand them to the litigious individual and tell them to hit their rack or go to work.
Wikipedia: * Sea Lawyer: (1) A sailor or his buddy, making eloquent but completely spurious arguments at Captain’s Mast, or in response to some disciplinary action. (2) An argumentative, cantankerous or know-it-all sailor. A sea lawyer is adept at using technicalities, half truths, and administrative crap to get out of doing work or anything else he doesn’t want to do, and/or to justify his laziness.
The army equivalent is the barracks lawyer.
I’ve heard the term most often to refer to the crew members who like to take deep dives into the union contract, or now also the SMS rules.
Change a few words and that could describe a lot of politicians. 
That’s a common iteration, I’ve seen that one as probably anyone who has been Chief Mate/Master or 1st AE/Chief. But they don’t just dwell at sea. I have seen more than a few opining on USCG policy on this site.