| Author |
Message |
    
Cameron searle
Member
Username: my_heap
Post Number: 65
Registered: 12-2006
| | Posted on Sunday, May 11, 2008 - 07:03 pm: | 
|
anyone know what rate of fuel consumption is at 2,200 RPM's and again at 3,000 RPM's?
I have this engine installed in a Bayliner explorer 27' foot.
What should my cruising RPM's be for this motor.
Has 270 outdrive |
El Pescador
Senior Member
Username: el_pescador
Post Number: 3130
Registered: 02-2006
| | Posted on Sunday, May 11, 2008 - 09:39 pm: |
|
Few people would run that type of engine below 3500-3700 RPM for the simple reason that few boats will plane below those RPM, and most of those engines are installed on planing hulls.
On a planing hull, a reasonable cruising speed for your type of engine would be anywhere from 4300 to 5000 RPM. |
Lawrence Darmanin
Member
Username: dansera
Post Number: 36
Registered: 08-2007
| | Posted on Monday, May 12, 2008 - 03:30 pm: |
|
Hi El,
my 18 foot Coronet stays on the plane at between 2500 and 3000 rpm. The engine is a VP AQ151C with a 290 outdrive and 15 x 17 aluminium prop. Do you think my tach may need calibration and if so how do you go about doing this? |
El Pescador
Senior Member
Username: el_pescador
Post Number: 3136
Registered: 02-2006
| | Posted on Monday, May 12, 2008 - 10:47 pm: |
|
Don't know about your particular case, I only can tell you what I have seen in some fiberglass boats. Maybe other forum members with similar boats/engines will post at what RPM do their boats plane. |
Mike
Advanced Member
Username: mike77cj
Post Number: 140
Registered: 06-2007
| | Posted on Tuesday, May 13, 2008 - 05:02 pm: |
|
I have a 23' Formula. I begin to plane around 2600 rpm. I religiously run the boat at 3000-3200 rpm, planing nicely. I turn 4700 @ WOT. The VP owner's service manual states that the max. permitted cruising speed should not exceed 500 rpm below WOT. I've always found running an engine around 80% WOT prolongs it's life. |
El Pescador
Senior Member
Username: el_pescador
Post Number: 3145
Registered: 02-2006
| | Posted on Tuesday, May 13, 2008 - 05:58 pm: |
|
Mike, I think you are comparing apples and oranges. My current 22.5 foot boat weighs over 6000 lbs and planes at the same RPM as yours, but both of us have 350 V-8 engines (around 300 HP), and the gear ratio in our outdrives is 1.61:1. Lawrence's boat has a 4 cylinder engine 140-145 HP, and a gear ratio in the outdrive of 2.15:1. 2600 RPM on your V8 engine would produce approximately the same propeller shaft RPM as 3500 RPM on a 4 cylinder engine.
I agree that 80% of WOT will prolong engine life, but that is not necessarily the best setting for your fuel bill. I have observed on several boats the size of yours and mine with 350 Chevs that the fuel consumption per mile is pretty steady between 3300 and 3900 RPM, but skyrockets at 4000 RPM and above (or below 3200 RPM). My engine currently burns 1.9-2 liters of gasoline per nautical mile in the above RPM range. For comparison purposes, I would be interested in finding what is your engine fuel consumption per nautical mile (mine is a pre-Vortec, though). |
Thomas Coulter
Member
Username: tjwc1
Post Number: 32
Registered: 09-2007
| | Posted on Tuesday, May 13, 2008 - 08:28 pm: |
|
I have a 20' AquaStar with AQ151C and 290. I run around 2800 rpm on plane @ 28mph. seems the best speed and rpm for my fuel consumption. Last summer I did a 2 hour run at this RPM and only cost me 48 bucks in fuel at a $1.25 per liter. Have since done some tune-ups so hopeing it will gett a little more economical. |
El Pescador
Senior Member
Username: el_pescador
Post Number: 3147
Registered: 02-2006
| | Posted on Wednesday, May 14, 2008 - 02:24 pm: |
|
Thomas, according to my math:
$48 divided by $1.25 equals 38.4 liters.
38.4 liters in 2 hours equals 19.2 liters per hour.
28mph equals 24.33 knots (or nautical miles per hour).
So, based on the data you posted:
1) Your engine consumes 0.789 liters of gasoline per nautical mile as installed in your boat (19.2 liters per hour at 24.33 knots).
2) To achieve 24.33 knots at 2800 RPM with a 290 drive that has a 2.15:1 gear ratio you would need at least a 23" pitch propeller and zero slip at all times.
If I ever found a boat capable of performing like yours, not only I would never sell it, but I would make sure I would mass-produce it. It would be such a best-seller with today's high fuel prices that I wouldn't be surprised if I would force all the competition out of business while I would become an overnight billionaire. 
Now seriously, I think you need to review your figures a little. |
Thomas Coulter
Member
Username: tjwc1
Post Number: 33
Registered: 09-2007
| | Posted on Wednesday, May 14, 2008 - 08:47 pm: |
|
El ,
Thanks for doing all the math. You are correct, I will check my log this weekend when I am at the boat, I have been very very happy with the amount of fuel it comsumes. But you do have a very valid point in the figures. I just yestureday was sandblasting my prop and the spare to repaint them, the one I took off I cannot find a # on it at all. The spare which is much smaller in size and looks of the pitch has 15x17 stamped in it, in two places. With the larger prop I can only get 4000-4200 RPM. I was planning on trying the spare to see what it does.
Thanks again for your input
TJ |
