If I had a choice from the jump....I choose the Yanmar. Let's face it....something to be said about not worrying about fumes blowing us up
In reality, the chances of blowing up because you have a gasoline engine onboard is probably less than blowing up because you have a propane stove onboard. Keep in mind that 99 percent of all the recreational boats in the US are gasoline powered, and most of the explosions take place as the result of doing something stupid while refueling, such as leaving the engine running, or not turning on the bilge blower before restarting the engine. According to the last boat US report I read about marina fires, they were the result of an electrical problem, or someone placing a heater onboard in a bad location.
Now, I was watching Deadliest Catch on the Discover channel a few months ago and one of the boats experienced a cracked fuel injector line, which triggered the explosive gas alarm. The diesel fumes were so thick that the mechanic had to wear a respirator and hazmat suit in order to get to the shut off valve and facilitate the repairs. They also had to use a special, sparkless fan to evacuate the fumes from the engine room. Fires aboard diesel-powered commercial fishing boats are not at all uncommon, and there have been many resultant explosions.
Another source of boat explosions is the result of shorted batteries that are on chargers or being charged while underway with the alternator. I experienced this first hand while fishing at the Marquesses Keys many years ago. At the time, I owned an 18-foot Starcraft Mariner, center console fishing boat powered with a 75 HP Johnson outboard. The battery was housed in a compartment beneath the transom well and accessed via a sliding door. That was also where all the electrical connections were made on an open terminal block and the relay for the power tilt and trim was housed. Apparently, the battery developed a shorted cell, thus causing the alternator to overcharge the remaining cells and produce a large quantity of explosive gasses. The explosion occurred when I activated the power trim as I entered the flats near Boca Grande Key. The blast blew the sliding door completely off the transom, sounded like a grenade going off and scared the hell out of the other two anglers in the boat as well as myself. Fortunately, we were in the company of another boat that had a spare battery that allowed up to clean the boat up and get back to Key West.
For many years, I've written about and advocated an automatic bilge blower than must be activated for at least three minutes before the ignition switch can become operable - just makes sense. I have also been a big proponent of constant ventilation in the battery compartment when the batteries are under charge, either at the dock or while underway.