As a personal conclusion to this discussion. I ended up buying both an Evinrude G2 300 and an Axopar 28 AC - so not technically relevant to this forum I appreciate. That said, a number of rib owners are switching to cabined Axopar's because they are all weather and all year boats that can have a heater and so still provide fun in the winter as well as summer. So maybe a bit relevant here.
But I thought i would post now that i have done 1,700 nautical miles and over 100 hours. I also didn't find anywhere in one place the mix of facts that I will now write.
The G2 300 engine has performed well and without fault so far - the only difficult issue has been the four blade propeller which propels her forward very well - but does not thrust in reverse very well at all - but that i understand is an issue with most four blade propellers. Much of the steering mechanism is within the engine - so you have to add other brands engine weight to the weight of their steering mechanisms to get the true set up weight.
I found it very difficult to get good data on the various engines to make a good comparison. I was put off Yamaha's 300+ engines by some issues on corrosion and flywheels which is well documented elsewhere. I was put off by the weight of the Suzuki products at this Hp. There are few if any really bad outboards now - every brand produces good products and so you have to decide what is important to you in making your choice.
My focus was fuel efficiency, emissions and weight.
The following analysis was the most helpful thing i found online
Mercury VERADO 350 v. Evinrude E-TEC G2 300 - Moderated Discussion Areas
My experience is the following fuel burns at different rpms and speeds
5,150 revs - 32 knots - 63 LPH
5,350 revs - 36 knots - 75 LPH
5,800 revs - 41 knots - 95 LPH
on a boat that weighs 2.8 tonnes
A friend said an old style 300 Verado, flat out would use 120 litres per hour.
Overall i have been happy with the engine.
I think the new V8 Mercury engines have better fuel economy (10%) than the old engines and I think they would also be easier and cheaper to service without superchargers in them.
With a partner who has just completed a Phd in environmental economics - a power boat of any sort was unpopular. What does seem clear is that the fuel injection system of the Evinrudes (Direct injection) is superior to that of all the current four strokes, which use a less precise method of fuel injection which is not direct in to the cylinders. It's more precise capability to put exactly the fuel that is needed in to the cylinders for the revs that have been chosen on the throttle and so use less fuel at many RPMs. This is particularly impressive at low revs. They also produce significantly less emissions (I am talking 4 times less) than an equivalent 4 stroke. (this is G2 technology not G1 tech - though G1 was still a good tech)
I don't know why emissions data is not available like it would be for cars. It is overall terrible in comparison to car engines because no car engine would be run regularly and for long periods at 4,500 to 6,000 revs.... But i would still like to see it
What this means for me is that if i put the boat just in gear, I use 1.3 litres an hour of fuel. I can't find any other 300 hp engine that can close to that. There are some lakes in the USA that only allow Evinrude DI technology because the emissions are so much better than their 4 stroke equivalent.
Flat out i use perhaps 10-20% less fuel than an equivalent four stroke. However between 4,500 and 5,500 the gap is not that large - so while emissions are lower, the fuel economy is equivalent or at least not so big a gap at cruising speeds.
The four stroke engine makers can catch up by incorporating just the same tech in to their engines, but for now they have not. I think the reason BRP have done the work is because their tech goes in to aircraft, ski doos, quad bikes etc...
So overall I got a G2 300 because
1. Emissions and fuel economy appeared factually better than the competition. I think you can always argue a bit on economy - but emissions are certainly hugely better.
2. I have a full ten year parts and labour warranty on the engine
3. The engine with steering is lighter in weight than the competition and the steering is a super neat install on the transom
4. I get two stroke torque and response
5. Servicing is only every three years or 500 hours
6. You can winterise and wake up the boat yourself without help.
1. At idle the engine is noisier than a four stroke. I think overall the evinrudes are nosier at almost every rev range than a four stroke. It is just more noticeable at lower rev ranges.
2. Buying two stroke engine oil and filling up the engine with a litre for every 100 litres of fuel is a real cost at £45 per 3.75litre canister.
1,700 miles at about 2 litres a nautical mile is an embarrassing amount of fuel to have used in a few months. But that would be the same with any equivalent boat.