60/0.81=74.07 gallons
60/0.90=66.66 gallons

60/25=2.4 hours
60/29=2.06 hours

Just come up to Canada. Your boat will get 17% better fuel economy instantly.

We're also considering going to Metric time.
100 seconds/minute, 100 minutes/hour, 100 hours/day.
25 MPH will equal about 87.4326 decimetres/nanosecond squared.

 

Mpg is almost a meaningless concept for a boat. Take this simple illustration. A boat heading up river fighting a 5mph current is going 10mph slower than the same boat, at the same rpm and gph, that is going downriver. If both travel the same distance in their respective directions the downriver boat will cover the distance in a shorter amount of time. The downriver boat will burn less fuel over the same distance and generate a higher mpg number than the boat going upstream. But they are the same and the power plants are performing identically. This can get more complicated by the addition of a crosswind.

Gph on the other hand is a characteristic of the boat, but mostly the engine. So if you know your gph for a given rpm, know your net speed, or SOG, and distance to destination it's easy to determine if you have enough fuel. Distance divided by speed gives you time to destination. Time to destination times gph then gives you fuel needed. As long as fuel needed is less than the amount of fuel in tank, all is good.

Henry

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The same rules , water, wind conditions, apply to gph as well.

 

I think he was just trying to do a simple comparison, he gave the test parameters, and he got the 'mpg is worthless' lecture.:smt043

 

That may be possible, but it doesn't change the fact that mpg is flawed as a metric for measuring a boat's performance.

I also find it amusing my explanation is "a lecture", yet other longer posts solely involving calculations escape without comment from you.

Henry


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Go fast burn gas Go faster burn more gas
Go slow burn less gas

 

Does this make sense then? I know weather conditions, tides ect..play parts too

3 blade prop.....#1 boat cruises at 25 mph and does .81 mpg at 3500 rpm going on a 60 mile trip

4 blade prop.....#2 boat cruises at 29 mph and does .90 mpg at 3500 rpm going on a 60 mile trip

#1---60/0.81=74.07 gallons
#2---60/0.90=66.66 gallons

#1----60/25=2.4 hours
#2----60/29=2.06 hours


74.07 - 66.66 = 7.41 gallons at $3.75 gal = $27.78 fuel savings for 2.06 hrs of cruise time.


(75 hr season) = 36.44 x 2.06 = 75.06 hrs.


$27.78 x 36.44 hrs = $1,012.30 in fuel savings for the season...

 

The only thing I'd question is this....25 vs 29mph and .81 vs .90mpg. Those are 16% and 12% increases....that's big, are they realistic expectations?:huh:

 

How about this....just go slow and enjoy the ride, as the boat ride is why we own them. Or go really fast


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Thanks for the advice..that helps.... Just wondering though,,what speed to you is go slow and enjoy the ride and go really fast?

 

99, I cruise at 900rpm. My burn rate is 3-4gph per engine and speed is 9kts. Takes forever to go places but I love the view and calmness of it all. Work is always a rush/hurry. Or I just run at 70% of load about 1750rpm and burn 21-23gph per side and go as fast as I can without hurting engines. I wish I could go 40-50, that would be better


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