I think the conclusion here was that because you have a functioning 30 amp breaker system in the boat, the risk of a problem from using a 30 amp extension cord plugged into a 50 amp service is at least reduced.
I waded through the IEEE article on AFCI and thought that this was very interesting - here is the link again
http://combinationafci.com/resources/doc_ieee_combination_afci.pdf
Lots of interesting stuff but I start with a couple snips. There is a section in there on how shorts in the AC wiring should have blown a fuse but didnt
"The conditions when the two conductors of a cord come in contact, as the result of cord overheating or insulation damage, are significantly different. In this case the wires, once they make contact, can move apart by normal magnetic forces. The typical fault current and voltage for such an event, shown in Fig. 3 " Results were that the current pulsing creates a lot of heat but not enough RMS current to blow the fuse or that it takes too long to blow the fuse.
Another really interesting thing in there is the Glowing contact section
"The test is disturbingly simple to perform, thus adding support to the claim that glowing contacts are a serious home wiring hazard. A length of AWG 14 solid copper wire is looped around a wire-binding screw of an electrical receptacle. The screw was not tightened, so the loop was loose. A 15A resistive load was plugged into the receptacle. The loop was then manipulated so that loop-screw connection could be jiggled to create a make/break arcing action. The arcing was not continuous, but rather more a series of sparks. After typically a minute of jiggling, the loop will adhere to the screw, at which time the jiggling is terminated. In about 30 seconds the connection will begin to glow the color of a toaster’s coil; thus the name"
The section on Glowing contacts in VIII - really interesting regarding a mechanism that can start a fire and not blow a fuse and it just involves a loose or corroded connection. Scary for in a home but a home doesnt experience the vibration and constant movement that a boat does that could tend to aid loose connections. And of course the more corrosive environment around salt water.
Makes me wonder about AFCI and boats.. GFCI is great for human safety but makes me wonder how effective the old standard fusing and earth ground system is for AC boat fires. I had never even heard about AFCI until this thread..
Google found this so I dont know how accurate but its some stats on what caused boat fires. Link
https://mija.com/blog/140-boat-fire-causes/ Some quotes from this link
DC Electrical – 35% of fires are caused by problems with the 12 volt DC electrical system
Off Boat Sources – 25% of boat fires start from fires that are not even on the boat. (like a boat next to you burning up and catching your boat on fire)
AC Electrical – 17% of fires are caused by AC electrical problems.
