I have seen far too many instances of "inaccurate" figures (inaccurate to the point of being fraudulent, not just "close but wrong", but "not anywhere within the hemisphere wrong") to just take as valid ANY figures being used by an agency with an agenda, especially when the simple math fails to even get close to the ballpark.

I could do more math, but since the "average" car drives 18K a year (every one of those 250.8 million cars), with an "average" fuel consumption of arround probably 20 mpg, road-vehicles are going to turn out, over the entire 12 month year, to burn about 98% of the gasoline used, while 6.8% (boats), used (on average, 5 months of the year, and most, only on weekends, so 20 weekends a year (typical) or 40 days, are going tu burn MAYBE 3 or 4% of the fuel used, compared to what that other 93% of the vehicles, driving 300+ days emit.

The numbers don't add up just off the cuff, not even close, let alone if you dig into them to get exacting at it.

The environment nuts who want us back to the pre-fire-usage stone age are among the worst of the liars when it comes to the figures they claim. (burning wood in a fire is bad, CO2 emissions you know)

Man Made Global Warming (a whole pile of falsified info there)
The bald-faced lies of DDT "toxicity" from the 70's
Apparently engine emissions now,
Many, many more.

Well, next year we should start seeing the folks with the cat'd exhaust systems, and the next 5 years will be a telling time.

What's the typical life span of you folk's exhaust manifolds before leak-driven replacement tends to occur?
My logs went almost 25 years BUT, Lowrider sat quite a few years unused by dad before she became mine, so that helped, but it makes any comparison less valid.
I see typical replacement non-cat manifolds like so many of you folks run pricing arround $1000 to $2500, depending on what you want.
That's parts only, you install.

I will also virtually guarantee that since the CAT systems were developed by Mercruiser and Volvo, theirs will be OEM parts only, and you KNOW what that does to the price, plus dealer tech instalation @ $100/hr (or zero waranty).
I forsee a 3-5grand price tag range to replace, with ZERO aftermarket alternatives.

Anyone seen the price of Platinum and Paladium lately (used in CAT Converters).
NOT cheap, and getting less cheap all the time.

BTW, one more part for metal thieves (tweakers (meth-heads)) to steal (been a rash of cat converter thefts here, cut right from cars and trucks), sold to scrap dealers for drug $$$$.

D-Rod, a few points.

Do we think the EPA is cooking the books with their statistics? Heck yes. The EPA has a long history of making the numbers reflect what they want them to. Yes our government lies to us, especially the bureaucrats that want to ensure job security.

Are the new engines going to be more maintenance or less? A little of both. The more devices that are attached to an engine, the more likely of failure. And a boat is a lot harsher environment than a car is. The first few years will be a pain in the wallet for new boat owners. And they will be so complicated that the average boater will not be able to work on them. And you will find a severe shortage of trained capable mechanics. The lack of people willing to work on boats may actually force the industry to rethink the typical drive system. The difficulties in working on engines may force Mercury and Volvo to design a new way of installing motors that will allow them to be more easily accessed, or something.

We are also not afraid of technology, but have experienced how difficult it can be in the early production units. Anyone that can remember when they first came out with electronic ignitions, or EFI and testify to the failure rates. Look at the first models of the Optimax and OMC's equivalent. Look at any manufacturers experience with direct injection diesel engines. I can remember the first time I saw a smog rated GM straight 6. I could not get to anything because of all the hoses going everywhere. And my 83 F150 with the smog rated 300-6 was often a headache due to the carb that I could not tune or do anything with.

We will pay a lot more for engines in the future, both in initial cost and maintenance costs. And the fuel improvements and environmental improvements will not be worth it to most of us. But we can always hope that it will lead to better things that can make a real improvement on our boating experience. For example, the high cost of boating motors may lead someone to finally build a hydrogen engine that works. Theoretically, a boater could use wind generation to extract hydrogen from water and store it in tanks on a boat. Pontoons could be ideal for that function. A person could justify the cost of the motor by the almost free fuel. It could actually make it viable to work past all the myriad of issues with hydrogen.