1989 Sea Ray 300 Sundancer, RPM for best fuel economy

R

Rodie

New Member
Jun 29, 2015
10
Michigan
Boat Info
1989 Sea Ray 300, Sundancer
Engines
2x 5.7
I got a 89 Sea Ray 300 Sundancer with 2x 5.7 350. Can anyone tell me the best RPMs for good fuel economy at hull speed and on plane? I read that anything under 1000 rpm is good for slow speed and anything between 2700 and 3000 is best while on plane for this size boat. I am thinking on purchasing a fuel flow meter,LMF-200 by Lowrance at some point get this figured out. I am assuming that 1.5 MPG is the best I may get.

Thanks
 
All of this depends on you and your boat, its weight and the state of the waters your running it in.

i run with a half tank of water, full tanks of fuel. My low end is 1000 to 1500 with a no wake at 900

im up on plane at 3300 then I settle at 28/2900. I'm burning 13/14 gallons per hour
 
Depends on the load on the boat, number of persons, sea state, bottom condition etc. That said, keep the secondaries on the four barrels closed and you will get better economy. For my boat, I find they open around 3200+/- so I try to cruise at about 3200 and I burn about 10-12 gph per engine.
 
Running the engines at about 700 rpm while going DOWNSTREAM with a 4 to 6 knot current seems to be the best for my boat. Even better with them switched OFF!

I'm with those above, stay out of the secondaries, get it up on plane and level it as best as possible. I usually set the rpm around 2800 to 3000 and then without touching the throttles, manipulate the trim, trim tabs and watch the GPS. It can vary 2 - 3 miles per hour based on how you have it trimmed!
 
dwna1a said:
All of this depends on you and your boat, its weight and the state of the waters your running it in.

i run with a half tank of water, full tanks of fuel. My low end is 1000 to 1500 with a no wake at 900

im up on plane at 3300 then I settle at 28/2900. I'm burning 13/14 gallons per hour
Click to expand...

Is that per engine or overall?
 
Haha ok. That makes more sense.
 
As others have said; it depends on the individual boat including load, props, etc., and sea conditions.
In it's current configuration, under normal circumstances, and with my wife and two teenage kids along with me, my boat likes to cruise on plane in the 3100-3200 RPM range. Things change in chop, or if the water is extremely calm.
The best way to judge fuel economy is with fuel flow gauges.
I have them hooked in to my NMEA 2000 network, and displaying on my Garmin GPS/Chartplotter. It also calculates amount of fuel on board, range, and MPG at current speed. I've found it to be fairly accurate.
You'd be amazed at how much difference in fuel burn a little movement one way or the other on the throttles will make.
 
Thanks JVM225. I just got a Lowrance fuel flow gauge kit and I am concerned about cutting the fuel line for the installation of the sensor since both lines are made with factory crimped threated end. I am not sue if I should cut the line or just add another fitting and then add the fuel sensor in between. Also, I was going to place the sensor after the fuel filter but before the water separator since that's the only soft line I have then its all steel lines to the carbs. Any advice would be appreciated.
 
I cut mine just before the fuel switches. It has not been a problem, I installed the sensors about 5 years ago.

Sent from my SM-G900W8 using Tapatalk
 
Thanks for the info. Ill be cutting the lines this weekend.
 
I hate to tell you this but a gallon a mile each engine is what I average. If on a long trip I can get 1.5 doing hull speed. I do have a generator so that adds weight, put a dingy and 600 lbs of food and cloths and you really have to keep an eye on the fuel flow, water and the holding tank. Our longest trip was 7 weeks on the boat and only a few nights at a marina.

We will be doing the North Channel again next summer.

Ken

Sent from my GT-P5210 using Tapatalk
 
Rodie said:
Thanks JVM225. I just got a Lowrance fuel flow gauge kit and I am concerned about cutting the fuel line for the installation of the sensor since both lines are made with factory crimped threated end. I am not sue if I should cut the line or just add another fitting and then add the fuel sensor in between. Also, I was going to place the sensor after the fuel filter but before the water separator since that's the only soft line I have then its all steel lines to the carbs. Any advice would be appreciated.
Click to expand...

For the port motor I cut in to the soft fuel line behind the motor, and after I double clamped it, I used zip ties around it to keep it up there nice and tight. It's been on there a few years, and never had a problem with it because of the installation.
For the starboard motor, I cut in to the soft line where it runs along the side of the fuel tank. No problems with installation there either.
Both are easy to see to inspect when I'm looking in the bilge, neither has ever leaked, and either one is easy to get to if I ever have to replace them.
Both are after the sperator/filter mounted back by the tanks, but before the ones mounted on the motors themsleves, so no worries there.
Mine are made by Garmin. The want a 30 micron filter used with theirs, and include a plastic inline filter in the box. The Fram canisters that are mounted on the tanks on my boat use a cartridge that gets replaced every year. I called Fram, and the CS rep had to check it out, but got back to me a day or so later to let me know that the cartridge (1110PL?) is a 10 micron filter. That means no need for the 30 micron that Garmin wanted me to use.
 
Thanks again for the great info, Ill let you know how it goes when I get it done.
 
Well, I got it installed. I ended up cutting the fuel line just passed the fuel filter as recommended. The hardest part was running the cable through the side cavity into the helm area. So, per my first sea trial I found the following: on a calm day at 2800 RPMs at approximately 29 MPH I am getting 8.5 GPH per engine. Thanks again for all the input and help. Thank you

 
Rodie said:
Well, I got it installed. I ended up cutting the fuel line just passed the fuel filter as recommended. The hardest part was running the cable through the side cavity into the helm area. So, per my first sea trial I found the following: on a calm day at 2800 RPMs at approximately 29 MPH I am getting 8.5 GPH per engine. Thanks again for all the input and help. Thank you

Click to expand...

Glad it worked out for you. That sounds like pretty good fuel numbers at that speed. What kind of props are you running?
Yes, it was a bit of a pain to get everything forward along the starboard side from the bilge, but not impossible.
 
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