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Author Topic: fuel consumption difference between twin rig 300s  (Read 1116 times)
longknife
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« on: March 12, 2018, 08:13:18 pm »

2014 300v23ld twin rigged verados

I have twin 300s rigged with power steering on my stb engine and port engine the slave via a tie bar. Both engines same hours, 1550. Stb engine is right hand rotation port side letfthand (obviously).
There is a large difference in fuel consumption between the 2 engines with stb side using up to 15-20L per hr more than port side at cruising revs (3900-4100rpm). If opened right up there is well over 20l per hr difference. At idle the difference is negligible an nothing to be concerned with but as a commercial operator that sort of difference really hurts. With 4 clients myself and crew, 700L of fuel and fully rigged for gamefishing I can have one side using 60L per hr and the other using 40L! We fish about 240 days per year so this really adds up.  Both engines are religiously maintained and serviced by myself (Im a qualified marine engineer) and a very capable outboard tech when its over my head or specialty tools are needed. Being a commercial vessel and operating in the remote Kimberly region of Western Australia we have no support so we  are very big on maintenance and looking after our engines.
I have done all the trouble shooting I can think of and cant come up with any explanation other than maybe powering the power steering is sapping power from the stb engine.

If anyone else has had this issue or could shine some light on my problem I would greatly appreciate it.

Thank you your time.

     
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31Jupiter
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« Reply #1 on: March 15, 2018, 05:06:09 pm »

I have the same issue with a pair of 2006 250's.  No insight?
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Jfritz.fish
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« Reply #2 on: March 25, 2018, 04:07:04 pm »

I don't know the answer - but I wonder - which engine is the problem one? Could the engine which uses less fuel be making less power? Can you plane this boat on one engine and if so is there a speed difference?Could it be that the supercharger on the more economical engine is making less boost and thus less power/fuel usage? So if each engine is making 300 hp at full throttle operating range then fuel consumption per hour should be about 95 liters each (0.5 lbs/hp/hr * 300 hp /6.1 lbs/gal * 3.8 l/gal)   Other engine parameters the same (oil temp, water temp/pressure). Does the boat ride level (one engine isn't buried when it is running?) Gear cases both good? Both props in similar condition? Are your guages accurately reflecting fuel consumption? Fuel filters?
Thats about all I can think of.

Good luck
« Last Edit: March 25, 2018, 04:56:33 pm by Jfritz.fish » Logged
longknife
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« Reply #3 on: March 27, 2018, 10:10:44 pm »

Hi Jfritz, and thanks for your reply.

I had also wondered about which is the motor with the problem. I hadnt tried planing on one screw to see but I will, should be interesting to see although, both motors "feel" extremely torquey when I give them a stab. The vessel lists ever so slightly to stb <which is the problem side> but it is negligible and I have trimmed engines separately to trouble shoot that. All engine parameters are all equal more or less and all fuel filters are changed every 100hrs as being a remote operation better to be safe than sorry. Propellers are in pretty much exact condition and the gear cases are both reasonable.

On a strange note, I did a trip yesterday with just myself onboard. On the way out the fuel discrepancy was there <the sea was nearly a glass off with no wind or swell> and on the way home the weather totally glassed off to oil calm seas and the fuel burn almost matched up? Only 3L/p hr difference. It ran that way the whole 32mile trip home. I then took her out quickly this morning and had the 15-20L per hr difference back again?
Now Im really confused. Will keep trying to sort it out and will post any results or outcomes for others.
Thanks again   
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massbay
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« Reply #4 on: March 28, 2018, 10:51:27 am »

2 motors and trying to plane on just one you are overpropped approx 6" pitch.
Lot of load on that motor, use the other motor @ 2000 rpm to help it along.
You'll still see what your looking for without taking out a powerhead.
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thunderstruck
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« Reply #5 on: March 28, 2018, 10:55:36 am »

To tell if a motor is not making the same power as the others stab the throttles from low cruise speed (not sync controlled) and see if one motor rpm increase lags the other(s).  Trim both motors all the way down.  The motor that lags the other cannot be making the same power.    

If you had a trip where the motors matched fuel burn I would look at trim.  Try to look at the motors with the same trim setting.  Maybe the trim indicators are different.

If both motors are making the same power (tach increase test) then look at trim differences, prop differences, trim tab position differences anything on the hull in front of the lowers that would cause ventilation.


If you are auto synching the motors, the motor that is (possibly) not making the same power will burn more fuel.

 
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longknife
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« Reply #6 on: April 02, 2018, 05:56:36 am »

Thanks for some very educated replies guys. Will try trouble shooting some more and let people know if I find the answer.

All the best
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