Logo
FULL SITE MENU

Improved Fuel Efficiency

J

JJDebeers

Regular Contributor
I'd like people to weigh in with their opinions here...

I bought the boat last summer: 31 foot Silverton Sedan with twin 318s.

I ran it from the point of purchase, to my home port at 15 knots for about 4 hours. I consumed about 3/8 tank of fuel, which equals about 21 gallons per hour.

This summer, I've gone through both engines quite extensively. Full tune-ups, installed new Mallory distributors (the timing was off on both engines when purchased), replaced ancient gunked up carbs with newly rebuilt Carter AFBs, all new filters, etc....

Yesterday I ran the boat for 2 hours at 17 knots, and consumed about 1/8 of a tank, which equals about 14 gallons per hour.

I know there's some inherent error in the fuel gauge, and in the calculations, etc... But there's no denying that I saw a huge improvement in fuel consumption. I'm burning way less fuel at a faster speed.

Is 14 gallons per hour possible with this boat or is there something wrong here?

-JJ
 
Perhaps the hull is riding better up on the step, and at 15 knots maybe she is out of trim, and plowing water. Plus the improved performance from the work done, maybe 17 knots is her sweet spot.
 
My single 318 burns 11 gph at 3,000 rpm. What rpms are you cruising at? 21 gph sounds about right for a twin installation at 3,000 rpm. 14 gph seems extremely low.
 
Dog House said:
My single 318 burns 11 gph at 3,000 rpm. What rpms are you cruising at? 21 gph sounds about right for a twin installation at 3,000 rpm. 14 gph seems extremely low.
Click to expand...

Are you saying it sounds extremely low compared to your fuel consumption? Has your motor been tuned recently, and is your TA timing correct? I'm wondering if you could get better fuel efficiency.

-JJ
 
It's possible I could get better fuel efficiency. On the other hand, my previous boat had a brand new Chevy 350 MPI (fuel injection) and burned 7 gph at 3,000 rpm. I can't say for sure, but I think it is unlikely that a carburated engine with a distributer would get the same efficiency as a fuel injected engine with electronic ignition. It may be possible, but I would be surprised if it was.
 
Dog House said:
It's possible I could get better fuel efficiency. On the other hand, my previous boat had a brand new Chevy 350 MPI (fuel injection) and burned 7 gph at 3,000 rpm. I can't say for sure, but I think it is unlikely that a carburated engine with a distributer would get the same efficiency as a fuel injected engine with electronic ignition. It may be possible, but I would be surprised if it was.
Click to expand...

Well, what was the size of the boat that 350 was pushing? I don't think we can make that comparisson unless we're talking about the same power to weight ratios.

Grease, I've only gone as fast as 21-22 knots at about 3,300-3,400 rpm.

-JJ
 
The boat with the Chevy 350 MPI was a 24' cuddy (~4500 lbs.) and the boat with the Chrysler 318 is a 26' cabin (~6000 lbs.). I don't think the boat will affect fuel consumption (gph) though. Fuel consumption should only be affected by engine rpm.
 
Dog House said:
The boat with the Chevy 350 MPI was a 24' cuddy (~4500 lbs.) and the boat with the Chrysler 318 is a 26' cabin (~6000 lbs.). I don't think the boat will affect fuel consumption (gph) though. Fuel consumption should only be affected by engine rpm.
Click to expand...
Of course the boat affects fuel consumption. Weight, drag, and sea conditions will have a substantial affect.

-JJ
 
JJ,

Repeat the experiment, and see if you get the same results, under the same conditions, with the same measurable fuel loading aboard as you had over the weekend.
 
Best I ever had mine was 22 knots @ 2800 with about 50 to 100 gallons fuel couple people,just cleaned the bottom.V drive 2.05-1,18x19 4 blade,31C,12k lbs

sagging rear mounts on the star., old carters,neede a tune im sure,

Just like to compare with another silverton thats similar
 
kimcrwbr1 said:
Have you mapped the advance curve it would be good to know for future diagnostics and maybe someone here could benefit from that info also.
Click to expand...

I think i'm the only one here who's mapped advance curves for a 318. See my previous threads.

Don't get me wrong, i'm not complaining about the better mpg. I just thought 14 was unthinkable. Lets say its really 16 with all the error factored in, thats still a huge improvement. Im psyched.

-JJ
 
JJDebeers said:
I think i'm the only one here who's mapped advance curves for a 318. See my previous threads.

Don't get me wrong, i'm not complaining about the better mpg. I just thought 14 was unthinkable. Lets say its really 16 with all the error factored in, thats still a huge improvement. Im psyched.

-JJ
Click to expand...

There is no majic, older gas engines burn 10% of their hp per hour so if you were burning 14gph you were putting out 140 hp. Use any of the free marine calculators and enter your boat weight and speed, this will tell you if you are in the ball park with 140 hp.

Dan
 
JJDebeers said:
I'd like people to weigh in with their opinions here...

I bought the boat last summer: 31 foot Silverton Sedan with twin 318s.

I ran it from the point of purchase, to my home port at 15 knots for about 4 hours. I consumed about 3/8 tank of fuel, which equals about 21 gallons per hour.

This summer, I've gone through both engines quite extensively. Full tune-ups, installed new Mallory distributors (the timing was off on both engines when purchased), replaced ancient gunked up carbs with newly rebuilt Carter AFBs, all new filters, etc....

Yesterday I ran the boat for 2 hours at 17 knots, and consumed about 1/8 of a tank, which equals about 14 gallons per hour.

I know there's some inherent error in the fuel gauge, and in the calculations, etc... But there's no denying that I saw a huge improvement in fuel consumption. I'm burning way less fuel at a faster speed.

Is 14 gallons per hour possible with this boat or is there something wrong here?

-JJ
Click to expand...


JJ you said you went through the motors, tune ups,new distibutors and replaced carbs. Maybe btw the extra 2 knots and all the work you did. This really made a difference !?
 
Back
Top