A Better Cruising Speed

Flytrade

Flytrade

Active Member
Feb 20, 2018
302
Bradenton, FL
Boat Info
2006 320 Sundancer
Engines
Twin 6.2L Mercruiser
I have had my 32 Sundancer for a few weeks now, and I have been experimenting with different cruising options.
I have the outdrives set at a +2 on the gauges, and at 3400 rpm I cruse at 25 mph. However, I just noticed that if I increase to 3600 rpm I then cruise at 30 mph.
That would seem to tell me that at the higher speed the boat is higher on plane, reducing the drag of the water. However, I have not been on any extended trips at this speed to evaluate my gas mileage. I was getting about 1 mile to the gallon, and I would be interested to see if this higher speed has any beneficial effects on my gas mileage.

Your experience and thoughts would be appreciated.
 
Gather some data and you can figure out what the best cruising speed is.
Make a chart listing engine speed every 100 rpm. Once up on plane, record the total gph and speed at each 100 rpm increment.
A second set of hands helps.

You’ll be able to calculate miles per gallon from this data and find your most efficient cruising speed.

I’m sure some 320 owners will provide some info as well.
 
Not sure of the motors you have. I run 496’s with Bravo 3 out drives.
I find that I can not trim the drives up much as they will cavitate. I don’t rely much on the trim gauges.
Typically, I throttle up to get on plane, back both motors down to 3200 rpm. Trim the outdrives just to the point where the cavitation starts. You will hear the engine rev slightly and feel a bit of vibration. I lower the drive just a bit and leave it. Then reset throttles to 3200 rpm. GPS speed is 30 mph. I believe my fuel burn per the vessel view is 23-24 gph. The boat just seems to be happy there. I can drop the rpm to 3 grand and she will stay on plane, but again, she just feels better at 31-32 hundred rpm. This is only my second year with this boat so I am still getting use to her, or vise versa! I find that the faster I go, the boat “feels” like it rises out of the water more. As I approach 50 mph, she feels very light in the water. My son has taken videos of our boat on plane, at various speeds and the attitude of the boat is very horizontal. Not much bow rise. I don’t use the tabs other than leveling the boat side to side if need be.
 
Last edited:
Mike sandor said:
Not sure of the motors you have. I run 496’s with Bravo 3 out drives.
I find that I can not trim the drives up much as they will cavitate. I don’t rely much on the trim gauges.
Typically, I throttle up to get on plane, back both motors down to 3200 rpm. Trim the outdrives just to the point where the cavitation starts. You will hear the engine rev slightly and feel a bit of vibration. I lower the drive just a bit and leave it. Then reset throttles to 3200 rpm. GPS speed is 30 mph. I believe my fuel burn per the vessel view is 23-24 gph. The boat just seems to be happy there. I can drop the rpm to 3000 grand and she will stay on plane, but again, she just feels better at 31-32 hundred rpm. This is only my second year with this boat so I am still getting use to her, or vise versa! I find that the faster I go, the boat “feels” like it rises out of the water more. As I approach 50 mph, she feels very light in the water. My son has taken videos of our boat on plane, at various speeds and the attitude of the boat is very horizontal. Not much bow rise. I don’t use the tabs other than leveling the boat side to side if need be.
Click to expand...
Um.......got any video of those big blocks singing near 50 mph??

That would be some really cool boat porn!!
 
will see what I can do this week end!!
 
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