Twin Merc V8 and different fuel usage

[alldodge]

2023 Merc 250 V8 Verado twin install on Chap 280 OSX
Props are 19P Rev4

Does not have Axius but does have adaptive trim


Idle shows fuel is same
As power is increased the fuel burn on starboard increases and at cruise is mostly 1 Gal /hr more then port. Pretty much stays that way from 1000 rpm and up to WOT

Trim tabs do next to nothing on the boa unless on slow cruise. That said the tabs are fairly small for a 26 foot hull


Could be the adaptive cruise is taking care of keeping boat level.


It's probably nothing but just reaching out to see what others may have come across

 

[dingbat]

2023 Merc 250 V8 Verado twin install on Chap 280 OSX
Props are 19P Rev4

Does not have Axius but does have adaptive trim


Idle shows fuel is same
As power is increased the fuel burn on starboard increases and at cruise is mostly 1 Gal /hr more then port. Pretty much stays that way from 1000 rpm and up to WOT

Trim tabs do next to nothing on the boa unless on slow cruise. That said the tabs are fairly small for a 26 foot hull


Could be the adaptive cruise is taking care of keeping boat level.


It's probably nothing but just reaching out to see what others may have come across

Counter rotators?

Swap props to see if burn figure stays with prop

 

[alldodge]

Counter rotators?

Swap props to see if burn figure stays with prop

Errr what ?

Starboard CW, Port CCW
Swap props so I run in reverse at cruise ?

 

[Chris1956]

Sometimes one engine has different stuff than the other. i.e. one engine has the power steering pump and system, so It will use more fuel.

Do you have an engine synchronizer?

 

[alldodge]

Motors have Digital controls, speed and RPM stay within a few RPM but the PCM. Both motors use electric power steering. Only thing that is different is port motor has a isolator installed to change house Bat

 

[dingbat]

Errr what ?

Starboard CW, Port CCW
Swap props so I run in reverse at cruise ?

Then you have counters......can't swap props.

Have never run counters (150,200 and 300 hp) that did have different burn rates. Typically in the 1-2 gph difference as you noted

 

[alldodge]

Thanks
It probably is normal but the counter (port) burns less then the standard

 

[Chris1956]

Do both motors charge the battery that runs the electric power steering?

 

[alldodge]

Don't know but probably not. Something worth looking into

 

[flyingscott]

How are you getting that info? Could be as simple as a slight calibration difference

 

[alldodge]

Smart craft via can buss

 

[QBhoy]

Hi. It’s a very common trait, with certain twin outboard rigged boats. One engine will always use more than the other. Many boring reasons and hydrodynamic reasons and variables to explain it, perhaps too late and too many beers had, for me to put in writing at this time of night where I am…but basically and fundamentally, the way most rigs are set up with twins (especially on a transom and hull that can do single or twin as an option…with offset positioning), will always result in a less efficient or harder working engine than the other. Closely related reasons to a degree, also mean that twin engines on most rigs similar will also always mean a less efficient condition, compared to a same hp single engine set up. So two 100hp outboards splayed across such a transom (especially when not closely synchronised), will always be considerably less efficient and lacking in performance, compared to a single and well set up 200hp.
Could bore you with my geeky thinking more..but the above basic reasons as well as a mechanically adapted (in terms of certain models that suffer from drivetrain power loss, through the required additional gearing to do so) one of the pair, having to work harder being responsible…somewhere closely related lies the answer. Not to mention that all engines are not absolutely identical to another. Occasionally, neither are props too perhaps..all be it likely only making up for a tiny variance.

 

[tpenfield]

As a percent . . . how far off are the engines? RPM the same?

Isn't the fuel usage a calculated amount (based on injector pulse and RPM)?

 

[alldodge]

Watched it a bit close yesterday and Idle shows fuel is same
As power is increased the fuel burn on starboard starts increasing, 1000 .1 more 2000 .6, 3000 1 gal and pretty much stays that way up to WOT

Other things like temp are not the same but close. Think its just just differences in parts and ECM

 

[nola mike]

Watched it a bit close yesterday and Idle shows fuel is same
As power is increased the fuel burn on starboard starts increasing, 1000 .1 more 2000 .6, 3000 1 gal and pretty much stays that way up to WOT

Other things like temp are not the same but close. Think its just just differences in parts and ECM

One or 2 tanks? Since that value is calculated, might be able to figure out actual burn between the motors by keeping track of miles traveled/gallons required to fill tank. Every car that I've owned has had an optimistic MPG display that doesn't correlate with actual mpg.

 

[alldodge]

one tank

 

[nola mike]

one tank

How hard to run each motor on a separate Jerry can? This would give you the most accurate info. How far off are they as a %?

 

[alldodge]

Not going to do that without actually knowing there is a problem that needs to be solved.

 

[tpenfield]

If the % difference is low, then it may be the accuracy of the calculations, etc. Maybe not worth any concern.