Sachs you are right. The total emissions are lower on a 2 stroke then 4 stroke.
That includes ETEC & Orbitals system. I dont have the figues for Yamaha's HPDI but would guess they are about the same.
Ford you are right as well. Good lad.
One thing that has happened with the change to 4 strokes is the amount of people how are getting CO poisoning.
If you could amagine a cabin boat with canopy's covering the deck , what happens when travelling is the " station wagon" effect.
The engine fumes are sucked back into the boat.With 4 strokes having high CO emissions people are getting sleepy while trolling.
I know of 1 guy who fell asleep but luckerly he woke up before hitting anything.
CO is the silent killer.
When I was selling 4 strokes I used to advise customers to make sure they opened the forward hatch to get air flow through the boat.
The whole emission thing has brain washed so many people into thinking 2 strokes are bad that i still have people look at me sideways when i say ETEC's have lower emissions. Evinrude did not make up the emission outputs, They are published by the government.