Great Debate: 4 stroke vs. 2 stroke - MPG

[77SceptreOB]

I know this is a much talked about subject, but I wanted some opinions and FACTS of the subject.

I have a bunch of friends who are DYING TO SPEND MY MONEY, or lack of it as I explain to them. Many believe that the gain in effeciency of a 4 stroke will more than pay for itself in better fuel mileage vs. the monthly cost of buying a NEW engine. I for one don't believe this wishfull thinking logic, BUT, am open minded enough to hear some facts from the crowd. So here goes:

I have a OLD 2 stroke Yamaha (1988 Yamaha Excel - 225hp) It burns about 11 gallons/hr cruising at 4200 RPMs and pushes my 1977 23' Sceptre right at 31 mph. That nets out at
an effecient 2.81 miles per gallon. The attached picture, taken today (with a light load) shows a little better at 2.91 miles per gallon.

My well heeled and intended friends SAY a four stroke would burn 40% less fuel at cruising speed. If true, which I DONT believe, that would mean a F225 would burn around 6.5 gallons per hour. Again, unbelievable and unachievable fuel burn rate...IMHO. I believe MAYBE, and I mean Maybe, a F225 might burn as little as 9 GPH. That would be a 18% gain in effeciency.

I use my boat for about 5 months of the year, accumulating approximately 80 hours/year (Shown on my hours gauge) Of the 80 hours, I would estimate 55 hours are at cruising speed. So it works out this way:

55 hours x 11 gallons/hour = 605 gallons of fuel annually

605 gallons x $4.50/gallon = $2,722 of fuel consumed annually (At Cruise)

Got to add the oil too. At 50:1 mix (Which is probably high consumption) So that is 12 gallons of YamahaLube @ $25/gallons = $300.

So add the fuel and oil and I spend about $3,000/year on fuel (At cruise)

So lets assume that a 4 stroke can and will make a 20% gain in effeciency. That is 8.5 - 9 GPH at cruise.

55 hours (cruising) x 8.8 GPH = 484 gallons used annually x $4.50/gallon = $2178/year

So there is a savings of about $845 annually using a 4 stroke vs. 2 stroke

A Yamaha F225 is approx $19,000 rigged and ready to go...

So $19,000/845 = 22.5 years to break even given all other things equal.....

Ok, before all the 4 strokers start throwing tomates, rotten bananas, and empty 2 stroke oil containers at me; I agree a NEW 4 stroke offers a lot of intangibles such as:

Better reliability & Safety if offshore
Better for the environment
Quieter
Etc, Etc.

BUT..... it takes A LOT of use to justify a NEW 4 stroke.....

Your thoughts?????