What is wrong with this chart

[boscoe99]

It has been slow around here lately. Let's put our brains to work.

I discovered what I believe to be an error in an Evinrude Performance Bulletin. Anyone care to see if they can find it?

Hint - Has to do with range.

Is it an error by mistake or an error by intent?

Not picking on Evinrude. I see this in other PB's as well.

[pstephens46]

Are you thinking the GPH burn would be higher with a full tank of gas? Your GPH would improve as the boat became lighter. How do you factor that concept? Sounds like math to me. Most of these tests are performed with a less than full tank. I always assumed it was to improve the data including top speed.

That boat is missing an engine...

[pstephens46]

Reminds me of a 747 that takes off from LAX on the way to India. Full load of fuel, 50000+ gallons of kerosene. Fuel weight of over 350000lbs. Very powerful aircraft... The higher the plane flies, the better the economy. But he is too heavy to get to that altitude for awhile. Has to burn some of that fuel. Computer figures out the details.

[99yam40]

My guess is that they tested at 250 gallons and not with the 377 gallons it would take to get 580 miles.

And like was said, could a single 300 push a boat like that?
Only 1/4 of the rated HP for the boat

[pstephens46]

Boscoe be lying in wait....

[boscoe99]

Boscoe be lying in wait....

Do you work for, or have you worked for, Gulfstream?

[pstephens46]

Nope. Coca-Cola

[boscoe99]

Reminds me of a 747 that takes off from LAX on the way to India. Full load of fuel, 50000+ gallons of kerosene. Fuel weight of over 350000lbs. Very powerful aircraft... The higher the plane flies, the better the economy. But he is too heavy to get to that altitude for awhile. Has to burn some of that fuel. Computer figures out the details.

Yes, very powerful.

Now tell us dear sir, what climbs faster? A B747 with four motors or a B777 with two motors. And explain your answer please.

[pstephens46]

Don't know. Tell me. Lying in wait....

777 has tremendous engines....they strapped one on a 747 at one point in testing. Can't remember if it was able to maintain altitude by itself? Maybe..

[fairdeal]

they tested at 250 gallons and not with the 377 gallons it would take to get 580 miles.

True...

But while surely one would get "worse" fuel economy whilst burning that first 127 gallons over 250 -

as one continued to run down the level, below 250, the mpg would increase;

getting "better and better" as the tank came closer to empty.

Seems it would require "The Calculus" to get an answer.

Or an actual ~580 mile test....

In any case, my guess is it was an "innocent assumption"

not a deliberate intent to deceive

[Jason2tpa]

They definitely tweaked the chart. But there is a little more happening here than just the range.

Fuel Data Range (miles) based on 90% Fuel Capacity states 1.54mpg=580mi range. However, the results of this performance test was conducted using 60% Fuel Capacity.

250 gallons of fuel (fuel load during test) represents 60% of the boat's total fuel capacity of 419 gallons. 90% fuel capacity of a 419 gallon fuel tank is 377 gallons.

I'm sure a mathematical equation was used to translate the results of the actual tested 60% fuel capacity mpg/mph/range, to a hypothetical 90% fuel capacity mpg/mph/range. The "x" factor, the variable, is the 762lb difference of fuel weight between 60% and 90% fuel capacity. The results of this equation is the data listed under "Performance Data" and "Performance Results".

Therefore, my guess is the the "Performance Data" and "Performance Results" (90% Fuel Capacity) are not exact, but are to be considered mathmatically relative to the actual "Test Conditions" (60% Fuel Capacity).

Considering all of the above, to answer boscoe's question, when the average consumer looks at the "Performance Summary" they see this:
*Fill up with 250 gallons, 2 people in the boat, windy & choppy conditions, run the boat at 36mph, get a fuel consumption of 1.54mpg, be able to run for 580miles*
The problem is they will run out of fuel before reaching the 580 mile mark. Oops.

[pstephens46]

I read twins. It needs three....

[cpostis]

To answer Boscoe's question, I can't find a significant error.

Per Yellowfin's website:

This mid-sized Yellowfin gives you unsurpassed flexibility in terms of fishing features.
It’s a live-bait fisherman’s dream, with a 55 gallon transom live well and the options of an additional 55 gallon floor well, for maximum bait-keeping capability. You can power the 34 with twins or triples and it easily cruises 40MPH while burning only 24GPH with twins, or 27 GPH with triples. Length: 34'8"
Beam: 10'
Weight: 8,800 lbs.
Fuel Capacity: 419 Gallons
Power: Twin or Triple Outboard (1,250 HP Max)

So, the range data based on the test conditions used is about correct.

At 4,000 RPM, 36 MPH, 23.4 GPH, 1.54 MPG, 377GLS fuel (90% capacity of 419) will be 580 Mile Range. Granted the boat at the test conditions was very lightly loaded.

I looked up used 34 Yellowfins, most all are powered w/twin 300's.

Under powered with twins? I think not, looking at the performance data and summary in the bulletin. Seems to pretty good to me! Sure you could put trips on it, if you wanted better performance.

Here's 33 Dusky performance bulletin data for a "Loose Comparison":

[IMG]Dusky 33 by Charles Postis, on Flickr[/IMG]

Wish I could afford the 34 Yellowfin, if I could, I'd go for the twins over trips!

[99yam40]

I guess the 1250 rating means it could handle twin 557s or 3 350 or 4 300s without a problem

[pstephens46]

But alas, we'll never know..

Boscoe is AWOL...

Boscoe may be dodging tornados..