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Why don't engine makers tell what fuel usage is

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Why don't engine makers tell what fuel usage is

Old 09-23-2020, 08:39 AM
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Default Why don't engine makers tell what fuel usage is

I have a 24 foot maxium and my engine needs replacement. After having the boat 8 years I'm the second owner. I have noticed I don't need the 4 lt Merc that I have. I plan to replace the engine with something smaller which will allow access for service. I noticed while looking every brand says they are so efficient but none show fuel consumption rates I wonder why? Everyone the boats weight, hull design and length will affect speed but fuel consumption is based on mainly rpm. So why not tell how much fuel they burn.
Old 09-23-2020, 08:45 AM
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ahhhhh , could depend on how you use the motor ... just guessing off course.
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Old 09-23-2020, 08:46 AM
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Originally Posted by Randyask757 View Post
I have a 24 foot maxium and my engine needs replacement. After having the boat 8 years I'm the second owner. I have noticed I don't need the 4 lt Merc that I have. I plan to replace the engine with something smaller which will allow access for service. I noticed while looking every brand says they are so efficient but none show fuel consumption rates I wonder why? Everyone the boats weight, hull design and length will affect speed but fuel consumption is based on mainly rpm. So why not tell how much fuel they burn.
every engine/boat combination is different, different propeller on the same boat will give different performance and fuel results, there is no way for them to know how it will react in your installation.
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Old 09-23-2020, 08:50 AM
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Too many variables.
Old 09-23-2020, 08:57 AM
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If propped correctly when did fuel burn reported as Gph have variables?
Old 09-23-2020, 09:00 AM
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Originally Posted by gotboostedvr6 View Post
Gph has little variables
Hmmm, .... I put the same engine on a light little skiff or a big heavy barge and run it at the same RPM and GPH certainly will be different.
Old 09-23-2020, 09:01 AM
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There are so many variations. You would be better off going to boat test.com and finding the engine you want on a similar size hull and weight and seeing what their test numbers are.
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Old 09-23-2020, 09:03 AM
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Originally Posted by gotboostedvr6 View Post
If propped correctly when did fuel burn reported as Gph have variables?
Ahhh, that is pretty correct. However how many prop variations are there, and how many guys are going to go through a dozen or more props to get exactly the right one in order to hit that GPH number?
Old 09-23-2020, 09:04 AM
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Originally Posted by Randyask757 View Post
I have a 24 foot maxium and my engine needs replacement. After having the boat 8 years I'm the second owner. I have noticed I don't need the 4 lt Merc that I have. I plan to replace the engine with something smaller which will allow access for service. I noticed while looking every brand says they are so efficient but none show fuel consumption rates I wonder why? Everyone the boats weight, hull design and length will affect speed but fuel consumption is based on mainly rpm. So why not tell how much fuel they burn.

Every company publishes performance bulletins using different boats and engine models that include fuel consumption in gallons per hour which you can use for comparison
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Old 09-23-2020, 09:07 AM
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Call them up and ask them for the brake specific fuel consumption Then you can look at that and be confused but it could tell you what you want.
Old 09-23-2020, 09:37 AM
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You will get 0.75-1.5 mpg.

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Old 09-23-2020, 09:39 AM
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You plan to go smaller than 4L in a 24' boat? For the record....that's a horrible idea. Efficiency is the last thing you will gain. 4L all on its own sounds under powered. You can likely increase efficiency by going up in motor. Seriously.
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Old 09-23-2020, 09:43 AM
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https://www.boat-fuel-economy.com/me...ion-us-gallons
Old 09-23-2020, 09:55 AM
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Originally Posted by gotboostedvr6 View Post
If propped correctly when did fuel burn reported as Gph have variables?
Originally Posted by NedLloyd View Post
Hmmm, .... I put the same engine on a light little skiff or a big heavy barge and run it at the same RPM and GPH certainly will be different.
Reread my post and try harder.
Old 09-23-2020, 10:06 AM
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Originally Posted by gotboostedvr6 View Post
If propped correctly when did fuel burn reported as Gph have variables?
Changes in load or sea state. Would like to be able to say that we could get the same GPH on the way out loaded with fuel on deck as we do coming in with 1/4 tank. But not how the world works. Same for sea state calms seas make for great GPH, large following seas makes for horrible GPH at the same RPMs.

For manufactures it would be impossible to tell you fuel burn of a motor that is true for all hull designs, weights, gearing, usage, etc...

Simple example anyone should be able to understand is a Ford 5.0motor in a mustang compared to the same 5.0 motor in a F150 truck. Same exact motor, very different fuel burns.
Old 09-23-2020, 10:09 AM
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Old 09-23-2020, 10:11 AM
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Originally Posted by gotboostedvr6 View Post
Reread my post and try harder.
Define “propped correctly”.

I have three different props that achieve three different things - top speed, hole shot and mid-range efficiency. Each had different GPH at the same RPM.

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Old 09-23-2020, 10:11 AM
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An engine will burn the same amount of fuel at same rpms with the same load. In lab testing the same load is easy. In practice the load on the engine will depend on the hull, the prop, the sea state, what's on the boat (fuel, people, cargo), how recently was the bottom cleaned, etc.
Old 09-23-2020, 10:14 AM
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I found this to be pretty close to my engine once I got it propped very close to the max WOT recommended
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Old 09-23-2020, 10:45 AM
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Going smaller isn't unheard of. Depends on what your intended use is. This 28' Bayliner had a 7.4/B2 swapped out for twin 9.9HT Zukes.
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https://www.kijiji.ca/v-powerboat-mo...7930?undefined

Last edited by fishbum69; 09-23-2020 at 10:51 AM.

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