For what it's worth, I was poking around my propane locker last weekend and took some pics of the gas shutoff solenoid. I have attached a picture of the Burkert part number 125301 solenoid label below. The solenoid on my SM (Hull #440) is definitely a 24 Volt solenoid and is powered from the main 24V breaker panel. It would seem very odd to me that Amel would have ever used a 12V solenoid for the gas shut off solenoid at any point in the building of SMs as I think they were built as 24V boats from the very beginning. Someone with more knowledge/experience can correct me if I am wrong in that.
Regardless of whether it is 12v or 24V solenoid, Amel would have been required to put in some kind of switch in the galley in proximity to the stove to control the gas shutoff solenoid. Does your main 24V panel have a breaker for the gas solenoid? If so, that is where it gets it's power from and it would appear that someone replaced the 24V solenoid with a 12V solenoid. That would obviously be bad as it would likely draw significantly more current than a 24V solenoid would assuming a similar coil resistance.
SM #440 Cara
Deale, MD USA