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Old 06-09-2012, 01:39 AM
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Interesting thread. I have a few thoughts and questions.

In the 80s, I was at a Honda power equipment presentation. They told us that the usual rebuild time was 2000 hours. I think that I have also heard that figure elsewhere.

Doing some fuzzy math: Consider a car: 50 mph times 2000 hours equals 100,000 miles. How does that sound?

I also wonder about hour meters. I had a 1965 Chris Craft cabin cruiser with a 283 Chevy inboard. It had a mechanical tachometer and hour meter. The manual said that one hour equaled a certain number or revolutions, and it was not based on time. I think it was 3000 RPM, but I am not sure. So one hour at 3000 RPM was one hour on the meter.

As I understand it, engine hour meters are just clocks. I have an old stewart warner engine hour gauge that I took apart. It has a clock mechanism in it. Pretty cool.

I guess for our engines, run at the same RPM for long hours, an hour is an hour. The RPM, whether 1400 or 2400 probably is not significant.

So, how about that 4700 hour engine? Say the boat runs at 6 knots.
6 nautical miles/hour times 4700 hours equals: 28,000 nautical miles
Now that is more then the circumference of the earth!!

2000 hours at 6 knots equals: 12000 nautical miles. How does that compare with 100,000 automotive miles?

I ran down the ICW from Annapolis to Florida, about 1000 nautical miles.

1000 nautical miles equals 6 knots times 167 hours. Does that mean that I ran the engine for 167 hours? If I ran for 8 hours a day, which sounds right, it comes out to 21 days. That is what my log book says too.

Then the question is how many miles would 167 hours be on a car. Since the engine is running at almost full power, compare to a car going at 100 MPH.
167 hours times 100 mph equals: 16,100 miles. That sounds right to me.

Getting back to the 4700 hour engine. How many car miles would that be?
4700 hours times 100 miles per hour equals : 470,000 miles.
Earth circumference is 24,901 miles, according to wiki.
That means that at 4700 hours, a car would have gone, at 100 MPH, 18.9 times around the earth.

So it is 130 am and I am sitting here in front of my computer, at home, and not snuggling my wife, in the Vee berth, swinging on the hook....

Then again; if a sailboat leave the dock heading north at 4.5 knots, with a 12 knot sw wind........
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