Re: Tankless Water Heater, CNG?
Oh, as far as being "compliant, last I checked ABYC is a voluntary standard that is mainly forced onto boat owners through problems with surveys, and subsequently insurance companies that will not insure your boat. I'm not saying we should not have some standards, but from my 35 years of boating experience, it is a rare builder that builds boats that meet all ABYC standards. Then there are problems with the standards differing from those in Europe, something else to be aware of.
Surveyors do sometimes misinterpret rules, and this has resulted in people, myself included, in having to modify boats to get insurance. Meanwhile they miss things all over the place. I was just aboard a boat that had the fuel tank vented in the bilges (diesel), and batteries installed in the bilge on their side, and not well fastened down. The survey did not even mention these things.
As far as gas water heating, if done right, I think it is very safe. With systems that have vents, I don't see a problem; I do like power venting ones best, as they assure proper draft. I would not use an unvented heater, but I think some unvented ones can be modified to have vents. I know some boater have done so.
The few instances of problems, and some were quite serious and involved deaths, were the result of people not following installation instructions or common sense. One happened near where I live. The person involved had installed the flash water heater in the head shower without a vent. This was a live aboard situation, and the person used it in the winter, with the hatches close up, with disastrous consequences. You can hardly fault the equipment for the result.
I don't like to see these heaters mounted in living spaces. A cockpit locker would be a better choice. If you have the room and are really concerned, I think you could make any one of these heaters ABYC complaint by building a gas tight locker to put it in. Supply outside air and a flue and you have it. Maybe this is more than most people are capable of, but it's not impossible. The Precision Temp would be ideal for this, as it is power vented. If done this way, you are not taking combustion air from inside the boat. I think the Precision Temp is plenty safe even if using inside air for combustion.
I would also argue that a flash water heater is an attended appliance. It is not left on when no one is on board. Even if power was left on to it, it should not cycle on. I don't see any reason for it to be on except when one is right there using it. In this regard it is no different than a galley stove.
You ought to have a smoke and carbon dioxide detector on your boat too. Common sense, but I don't think this is required by ABYC.
All-in-all, even with all the modern convinces being added to boats, boating has never been safer. Very few people are injured or die from this activity. The number of deaths has fallen over the years. Remarkable when you think of things like Jet Skis showing up on the water with hundreds of horsepower. Your chances of becoming a statistic are much greater in a boat with no motor and less than 16 feet. More people die falling on their front steps than boating. I'm growing tired of all the "safety police" trying to tell me how to conduct my business. No activity is without risk, but people will jump in a car and think nothing of it, while people are flying past them driving with less thought than they use brushing their teeth!
Anyway, I say these units can be installed in a safe and effective way. The risk can be mitigated. They are no worse than the galley stove. When gas stoves fist started showing up on boat, many people said they were unsafe. It turned out insurance company clams fell, as compare to older technologies like fuel oil or alcohol stoves. Suddenly they were no problem.
Does it take some thought and careful planning, sure, but I think they are a great idea for increased comfort. I used one everyday for over eight years living aboard without a problem of any sort. Make up your own mind; I'm just a guy with an engineering background, and a licensed 100T CG captain with thousands of hours on the water. What do I know?