Cruising rpms question

[jmarines]

Im thinking about purchasing a 2001 Larson 230SEI, 5.7L Volvo Penta I/O with around 500 hours on the clock. Its a one owner and always docked on a lift when not in use. Im not familiar with the 5.7 and wanted to see if anyone here has any input on this boat. Im not sure about what kind of prop and I wont be able to see it until 3 weeks due to the owner going on vacation. My main question is whats the cruising rpms on this type of set up and if possible.. what would be the top speed I should expect.

 

[jerryjerry05]

Most boats have a "sweet spot" that gives good speed and fair fuel economy.
​Depending on the boat/motor combo??
Some run at 3400 and their speed is again contingent on the boat/ motor combo.
My 32 with twin 260hp I ran at 3800 rpm's just before the 4 bbls. kicked in. The speed ??
My 21 with twin outboards I again run about 38-4200 rpm's and get about 27-28 mph.
Running at 5500 it gets 32-33mph. But uses a bunch more fuel for the speed I get.
I also never usually run wide open.

The Larson co. can give you performance specs if you send them the hull #
They should tell you the prop specs too.

Basically you'll need to run it and see how it runs.

New boats usually come with the best/ optimal propeller for all around use.
You can change the prop to do different things like tubing or for speed.

 

[evantful]

As Jerry said, running it will be your best gauge of where to cruise it. Props, hull, weight can make for a lot of variation between boats

I have a Cobalt 206, about 3600 pounds with fuel, gear and me and I find its sweet spot fuel economy wise is right at 3000-3100rpm with gets me 30-34mph.

This is with a Volvo Penta 5.0Gi and a DP-SM Outdrive (1.95 ratio) running F-6 Props

 

[Scott Danforth]

My 24' boat with a 5.7 liter and duo prop drive would cruise at 30mph at about 3300 rpm. At 5000 RPM, I would be just shy of 50mph.

 

[Thalasso]

My best fuel economy on twin 5.0's is 3200 burning 8.1 gal an hour per engine at 30mph. (flow meter #'s)
11000lb boat

 

[SkiDad]

My theory is back off 1000 rpm from full throttle. Maybe a tad more.