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rickmcd53

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Reply with quote  #1 
I don't have the boat at the shop yet to give specific information so need to start with a general question.
I have a customer that bought a used catamaran with twin 06 90hp Etecs.
He is reporting that the port engine burned 22 gallons while the starboard engine burned 17 gallons.
Is a fuel burn difference normal on a catamaran?

The boat will be coming in sometime soon for me to fix the I-Command gauges and see if I can figure out why both engines run the same rpm but burn different amounts of fuel. I'll have to go through basic tests first the check throttle percent and load on each engine.
PhilH12

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Reply with quote  #2 
Hi Rick,

Due to underwhelming response, I'll take a shot from under the shade tree.  [wink]

I think you're absolutely correct on the things you'll be checking, and "Load" comes to mind.  Both motors turning the same direction, or one Counter?  Could be prop turbulence from one side to the other, or maybe even Trim Tab settings?  Just sounds to me like port has to work harder to overcome "something" - thus the Load thought.

That's all "assuming" that they are both the same compression-wise, etc.  And, are they both the same LU's and prop's? Not sure what may be available, but if anything is different there, it could be something to take a peek at.

Good luck!

Phil 

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20' Weeres fishing pontoon
90 HP E-Tec E90DPLSUM  05184332
Lake Tawakoni, TX - Catfish Capital of Texas
olypopper

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Reply with quote  #3 
Burn rates will be the same if the engines are same models and all other basics are good.  I've got a customer that reported wild fuel burn differences between engines and he had a bad injector.  There will be a problem with one or the other!
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steelhead

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Reply with quote  #4 
Almost "normal" on any twin app, outboards, inboards, Odrives, diesels, gas motors, unbalanced fuel burn.

Run on the water, one motor at a time.  WOT and his normal cruise rpm with normal trim levels.
Record fuel burn rate each, load %, tps, engine temperature each.

The build component and firmware +- tolerances in a mass production motor is a major cause of difference, 1 90 may dyno at 81hp, other 90 may dyno at 99hp.  Luck of the draw and randomness off the assembly line.

Throw in mass produced prop differences and we have a pot of beans randomness.

The EMM "fuel burn" algorithm can not be perfectly exact.  Based on sensor readings, the sensors are mass produced.

Try digital load% syncing instead of rpms or by ear syncing, see what the fuel burns are then.
rickmcd53

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Reply with quote  #5 
Oly and Steelhead, Thanks for the advice, I'll check some things when he brings it in. After I verify that both engines are running equally on all cylinders then we will have to see if he's willing to pay for water testing hours. Most of our customers opt to let us do what we can at the shop and water test it themselves.
Huey

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Reply with quote  #6 
Hi Rick, that is a big difference and the I-3 in my experience tend to use about 30L/hr at WOT so if one used around 20L more per hour, if that is the case or perhaps over a day's boating I would give the injectors a good clean and replace the VST return filters at a minimum.
rickmcd53

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Reply with quote  #7 
Thanks Huey
Woul it make a difference if both engines we're standard rotation?
This is just one of many customers that don't want to miss any fishing time and think we should be able to give them an appointment to bring it in and have it fixed within a few days. We are doing that for a lot of customers that have "first of the season" water in fuel or won't pump water problems but can't schedule any quick turn around on problems that take some diagnostic time.
Huey

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Reply with quote  #8 
Not that sort of difference mate
PhilH12

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Reply with quote  #9 
++ to the guys, and Olypopper!  Almost 1/3 more (17 vs 22) on the port says there's something "fishy" going on there.  A bit more than "tolerances" or "turbulence", I think.  [wink]

Phil

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Always check the Easy Stuff First!
20' Weeres fishing pontoon
90 HP E-Tec E90DPLSUM  05184332
Lake Tawakoni, TX - Catfish Capital of Texas
steelhead

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Reply with quote  #10 
Question for the boat owner, fuel burn from the ICommand gauges and motor EMM calculations or from twin tanks fill?  Boat tank fill measuring via dip stick or fuel hose shut off and retail sale pump gauge is often uneven due to boat angle, etc.

Only accurate measurement is to look at fuel burn per hour on each motor ICommand.

'06 motors on an old recent purchase boat and there is actual large difference in fuel burn rate, I'd also check for fuel restrictions to the motors and do a complete boat fuel system test.

'06 vintage, may be the old turbine Flowscans in the fuel lines.  Notoriously inaccurate and motor killers when they plug up which happens far too often.  Pull and throw away
nauticat

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Reply with quote  #11 
I have a 27' cat twin g2 300s port burns more fuel  counter rotation prop. I filled both tanks 70 gal each I refuled tanks port 30 gal star 24 not a big difference. I converted from 4.3 v6 Volvo with jack shafts and duo props same port always burned more. I can say that the g2 300s vs 4.3 190hp burns 35-40%% less the engines only have 121 hrs also I have a shudder between 950-1100 rpm both engines checked with each engine in neutral. I am going to have the props computer checked the engines are 2018.
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Huey

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Reply with quote  #12 
This gentleman Rick asked about will not have a C/R engine but yes a C/R engine are not as efficient and while single engine have RH rotating props standard. Hard to comment on the shudder without feeling said shudder but yes getting the props checked would be a good move.
wejohns

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Reply with quote  #13 
At one time Glacier Bay's recommendation was to rig the C/R on the starboard.  They said it would help with the handling and engine efficiency.  As for unequal fuel burn on what should be the same engine,  I think steelhead is spot on in his post.  I have a Dodge 2500 5.7 diesel.  A very good friend of mine has the exact same model as mine, down to the paint color and trim packages.  Same gear ratio, same size tires, everything identical.  He will get 22mpg on the hwy while I am doing good to 19.  We have even switched trucks on the same trips to see if it was driver habits and styles.  No difference.  Dealer basically said he got lucky and I did not.
Huey

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Reply with quote  #14 
Yes, over the many many years doing this there have been some hulls that work better with a C/R engine on the starboard side.
PhilH12

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Reply with quote  #15 
I'm still seeing near 30% difference in fuel consumption in this case.  The two trucks described were about 15% - could be "tolerances" there (or ungreased wheel bearings, low tire pressure in one, etc, etc), but 30% on 'identical' engines on a single boat?

Hmmm, I'm still with Olypopper - something else there... although it could well be "How Measured".

Phil

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Always check the Easy Stuff First!
20' Weeres fishing pontoon
90 HP E-Tec E90DPLSUM  05184332
Lake Tawakoni, TX - Catfish Capital of Texas
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