SB Engine Uses 26 gal More Fuel

[RT Firefly]

Greetings,
Mr. s. My only comment would be regarding the tach's. IF you're trying to synchronize the engines by using the tach's you're chasing your tail IMO. Learn to synchronize by ear (match harmonic vibrations.)

 

[DavidM]

Frankly you have more unknowns than knowns right now. Is it worth it to get to the bottom of this issue as it will take a lot of work, and expense (prop scans) to figure it all out.


If you cruise at slow, displacement speeds most of the time, I wouldn't bother. If you cruise fast most of the time then one engine is possibly overloaded thereby reducing its life, so it probably is worth it.


David

 

[sammy999]

Thanks to all for the information. I have learned a lot and realize I have a lot more to learn. I hope to talk to a boat yard today and will let you know.

 

[BandB]

Thanks to all for the information. I have learned a lot and realize I have a lot more to learn. I hope to talk to a boat yard today and will let you know.

I have a question. Why so much interest in fuel burn by engine? Or by engine and by generator? What will having that information do for you, if you're ever able to get it accurately? Just seems to me you are running yourself ragged chasing a target and I'm not sure why. I would see things such as RPM at WOT and temperatures and load measurement being more useful. Also, understanding how your tanks work together, if fuel is balanced, how it is returned. If ultimately you were able to prove one engine used more fuel than the other, so what? Outside of a Floscan or similar system, your numbers are general estimates at the best. They are "I use this much fuel based on an average of this RPM or speed over a long trip" which is more than adequate for most purposes, but then figuring out how much the starboard engine used or the port engine used, is even less precise and of less value because of it's lack of precision. Once you try to get more precise than you used this many gallons over this run, I don't see that you've got much.

I'm just asking this as often we focus on trying to find precise answers we aren't equipped to find and we don't need. Meanwhile, we're not looking at more important things.

 

[DavidM]

BandB:


Your comment is exactly the point I was trying to make above. Why bother?


The only real reason might be to find out if one engine is overloaded which can affect life. But there are easier ways to do this:


Get a phototach. Calibrate your dash tach at the dock against the phototach at 2,800 rpm (use hearing protection). Then check to see if both engines can rev to about 3,100 rpm in neutral- the so called high idle speed.


Then go out for a sea trial. Run both engines at wot and measure rpms (phototach adjusted). Both should hit 2,800 or greater at wot. If one engine or both is below 2,800 then it needs to have its prop pitch adjusted.


I think you will be better served by focusing on what is important- getting the props set right so you don't overload the engine than worrying about differential fuel consumption.


David

 

[smitty477]

Sammy999 wrote this....


"Thanks to all for the information. I have learned a lot and realize I have a lot more to learn. I hope to talk to a boat yard today and will let you know."


"You all have given me some things to check out, especially the tachs, engine temp, and fuel line returns. Thanks again and any more input is much appreciated!!"


"We bought this boat 16 months ago in Ft Myers, FL and ran it up to Pickwick Lake in MS; about 800 miles. We didn't go far in that time at Pickwick but now we are headed to the Florida Keys and I'm trying to get some good fuel consumption rates going different speeds."

 

[BandB]

Sammy999 wrote this....


"Thanks to all for the information. I have learned a lot and realize I have a lot more to learn. I hope to talk to a boat yard today and will let you know."


"You all have given me some things to check out, especially the tachs, engine temp, and fuel line returns. Thanks again and any more input is much appreciated!!"


"We bought this boat 16 months ago in Ft Myers, FL and ran it up to Pickwick Lake in MS; about 800 miles. We didn't go far in that time at Pickwick but now we are headed to the Florida Keys and I'm trying to get some good fuel consumption rates going different speeds."

I wasn't questioning any of that, just why having the consumption rates broken down by engine was important to him. That's what he opened this thread on. That's just not something you often hear of people concentrating on. Most people here have no way to get that data.

 

[Lobstah]

Our MT34, Whistful, drove me nuts for a few years.
I'd fill tanks in the fall, and then next year, after several trips, the boat would have a noticeable list to starboard. I had twin tanks. I'd use the fuel valve to balance the tanks back out.
After awhile I realized the return only went to the starboard tank, and there was no line between the two tanks so they never equalized.

 

[sammy999]

I agree with a lot of the posts that this is not a big deal as far as fuel consumption goes. I was more concerned that maybe something was wrong. We will be in the Keys for 3 months this winter and will give me more time to investigate. I will follow the plan in post 33 and see what happens. We are scheduled to leave next week and the boat yard here is really busy so not sure how much I have time for here; however, they should be able to show me where all the return lines go. I don't want to overload an engine and shorten its life so hopefully I can find tune things regarding tachs and propeller pitch this winter. Thanks again to all!

 

[sammy999]

Sorry, meant to say will follow plan in post 35