|
ContinuousWave Whaler Moderated Discussion Areas ContinuousWave: Whaler Performance 305 CONQUEST with Twin VERADO 250-HP
|
Author | Topic: 305 CONQUEST with Twin VERADO 250-HP |
jac1257 |
posted 08-10-2009 08:31 PM ET (US)
[Editor's note. This article has been extensively re-written--jimh.] I have a Boston Whaler 305 Conquest with twin VERADO 250-HP. I fish in the Texas Gulf coast. I would like to improve the boat's fuel ecomony. I always go out with a full tank of fuel and about five people. My fuel economy is 0.9 MPG. The propellers are 15-inch pitch. I would like to get about 1.3-MPG. Is there a way to increase fuel economy by propeller selection? Do others have a 305 CONQUEST with the same problem? |
jimh |
posted 08-11-2009 09:23 AM ET (US)
I assume your boat has the standard MIRAGE 15-3/4 x 15 propellers supplied from Boston Whaler. There is a performance report from Boston Whaler giving data on this configuration at http://www.whaler.com/site_media/Performance_Data/305CQ_EnginePerf.pdf The report shows the fuel economy at optimum cruise speed of 26.4-MPH to be 1.35-MPG. This is at an engine speed of 4,000-RPM. The data was collected with the fuel tank level at 150-gallons and with only 355-lbs of crew weight. In your configuration the boat has 150-gallons of additional fuel, or about 940-lbs more fuel. Your crew of five probably weights 1,000-lbs, or about 645-lbs more than Boston Whaler's test crew. At a minimum we can figure the boat is probably 1,600-lbs heavier than when tested by Boston Whaler. In addition, if you are heading out to fish, I suspect you have additional equipment aboard. Let's say your boat weight is 2,000-lbs greater. How can we assess the influence of this weight on the performance? To assess influence of weight on performance, we turn to Crouch's Calculator. First we look at the performance in the test report. We see: LBS = 12312 Using the calculator we predict the horsepower to be 265-HP. We compare this with the fuel flow data, 19.6-GPH. This gives us a Brake Specific Fuel Consumption figure for the engine at optimum cruise of 19.6-gallon/1-hour x 6.25-lbs/1-gallon x 1-hour/265-HP =0.46-lbs/HP-hour That is a reasonable figure for a four-cycle fuel-injected engine operating at optimum. Now we increase the weight on the boat to 14,312-lbs and see how much horsepower we need to get back to 26.4-MPH: the calculator says 308-HP. If we assume the BSFC is the same, we will be burning 308-HP x 0.46-lbs/HP-hour x 1-gallon/6.25-lbs = 22.7-GPH This fuel flow will reduce our fuel economy to 26.4-miles/1-hour x 1-hour/22.7-gallons = 1.16-MPG We find that the additional weight being carried has reduced the fuel economy to 1.16-MPG from the test data's 1.35, a decline of about 15-percent in fuel economy. This demonstrates that fuel economy is inversely proportional to weight, and there is quite a sensitivity. You can further expect that the fuel economy reported in the test data was likely produced in optimum sea conditions. Also note that the report has an explicit disclaimer about other boats being able to reproduce this same performance. Now we turn to your request. You report an average fuel economy of only 0.9-MPG, but you have not given us any data about the boat speeds being used when this fuel economy is obtained. You wish to improve the fuel economy to 1.3-MPG, an increase of 0.4-MPG. This is an improvement of 44-percent. Can we obtain a 44-percent improvement in fuel economy simply by altering the propeller selection? There is a reasonably consistent trend with four-blade propellers that mid-range fuel economy is typically better than with a three-blade propeller. That is a very general statement, and subject to many arguments. Based on this general trend, you might try four-blade propellers such as the Mercury REVOLUTION4. This propeller is now being made in low pitches like a 15-inch pitch. However, I would be surprised if the fuel economy improvement was as dramatic as the 44-percent boost you are seeking. The only way you can really get back to a fuel economy figure close to the test data's 1.3-MPG is by reducing weight in the boat and operating it at the optimum speed for fuel economy. |
jimh |
posted 08-11-2009 11:27 AM ET (US)
Fuel economy with the VERADO, and particularly with the GEN ONE version of the motor--which I believe you can identify because the plastic logotypes on the cowling are not as thick as on the GEN TWO version--is quite dependent on where the throttle is set. In the Boston Whaler data we see that at wide open throttle the Verado motors are making 500-HP and using 57.8-gallons/hour, which is a rather astonishingly high BSFC of 0.72-lbs/HP-hour, a value that makes a carburetor two-cycle look like an economy motor. The influence of this is simple, if you are on the throttle of these VERADO motors their BSFC declines rapidly. This could also be an influence in the variance between your fuel economy and that obtained in the test data. |
Tom W Clark |
posted 08-11-2009 11:35 AM ET (US)
The Mercury Revolution 4 in a 15" pitch would be a good propeller for the Conquest 305, unfortunately, Mercury does not make a counter rotating version of the 15" pitch Rev 4. |
glen e |
posted 08-16-2009 12:06 PM ET (US)
Whaler is running enertia 17s on the 305 now for 09's ...reports are good |
towboater |
posted 08-16-2009 12:41 PM ET (US)
My 26 ft Stamas, 30 ft Skagit and 40 ft Tugboat were/are SLUGS with a full load of fuel. |
Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.