On 10/12/2017 9:51 AM, Keyser Soze wrote:
wrote:
On Thu, 12 Oct 2017 00:33:16 -0400, wrote:

Diesels 'usually' last longer than a gas job and are much more
economical on fuel. But what you save in fuel costs probably don't
over ride the massive up front expense of the whole unit. Bad trade off IMO.


===

Increased range because of greater fuel economy is the most common
reason for justifying the higher cost. Diesels use almost 50% less
fuel for the same power output, and have higher low end torque.


Which also allows bigger, more efficient props running at lower RPM.


I was reading an article somewhere else that said the economy might
not make the difference in less than 10,000 hours. They also assume
higher maintenance cost, particularly with a belt drive. I am curious
how the belt is working out on the 7 Marine.

===

Here's a real world example of the diesel vs gas engine trade off. Our
old Bertram 33 had a 320 gallon fuel tank which seems like a lot but
it had 454 gas engines which burned 35 gallons per hour. Cruising
speed barely reached 18 knots on a good day. Doing the math, you come
up with a safe fuel range of less than 140 miles, not enough for
offshore canyon fishing in the NY area. Converting to diesel engines,
the burn rate drops to about 20 gallons per hour, and cruising speed
climbs to 23 knots or so, for a fuel range of around 300 miles. That's
a big difference in the capability of the boat and has nothing to do
with the price of fuel or reliability.

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About $75,000 to $100,000 for removal of gas engines, engineering,
plumbing, new pair of 250 to 300 HP diesels. If gasoline is three bucks a
gallon, the conversion would cover 25,000 gallons of gasoline. Ouch. 😀


THere's something about gas engines running for hours at 3,600 to 4,000
RPM that disturbs me, even though I realize they have cams, etc., that
are designed for it. Seem to remember the general rule was 1,000 to
1,500 hours before a rebuild.

I have the same problem with land yachts. Had a large Pace Arrow
motorhome with a big ass gas engine that I thought would explode
climbing the hills out on Rt. 84, heading for Florida. At a certain
size/weight diesel is the only way to fly.