1998 2 cycle 150 Johnson Oceanrunner RPM's

[eddy2419]

I have recently bought a 1998 Wellcraft 21 ' CC with a 150 Johnson Oceanrunner. I have used it a couple of times and am struggling with the opitum RPM's. The prop seems well matched. What is max RPM's and what would be the most efficient cruise RPM's? It seems 3500 sounds good. This is full load, 4 people, 28 gal bait tank, 78 gals fuel and "drinks" and ice.

 

[angus63]

Re: 1998 2 cycle 150 Johnson Oceanrunner RPM's

Welcome to the forum!!!!!

Appx 5800 rpm wide open with average load is your goal for setup.
Cruise at just enough throttle for maintaing an even plane for best efficiency.
My 175 oceanpro pushes my 21 Trophy walkaround nicely at 3600 rpm (25-30 mph and 7-9 gallon/hr).
Good luck

 

[ob]

Re: 1998 2 cycle 150 Johnson Oceanrunner RPM's

One important detail pertaining to finding your rigs best cruising speed is to run it at or near wide open throttle initially and then throttle back until you determine a sweet spot.It will likely be between 3600-4000.Each rig with respect to hull design,horsepower to boat length ratio,and even water conditions will have its own ideal rpm cruising speed for best fuel economy.I agree as aboved mentioined to first insure that your rig is propped and set up properly to be capable of achieving in the upper limits of its recommended wide open throttle operating range with an average load aboard.

 

[eddy2419]

Re: 1998 2 cycle 150 Johnson Oceanrunner RPM's

I just got back from 5 days of fishing in the Gulf. With below average load I was only able to get about 4900 RPM's WOT in calm water. Average load for me is actually a full load, 78 gallons of gas, 28 gallons of baitwell water, and 1,000 #'s of gear and people.

With full load and moderate waves, it would run about 20 MPH @ 3000 and go up 1 MPH per 100 RPM's to 30MPH @ 4000 RPM's. There is no cavitation with a full throttle start, or at any other time. The prop is a 15x17. Do you think I need to try a 16 pitch? I do not have a spare so I need another prop anyway since we sometimes go 25 miles out from port.

 

[wilde1j]

Re: 1998 2 cycle 150 Johnson Oceanrunner RPM's

You need to go to 15x15, one inch of pitch will only up RPM 150 or so, and even that will be too low. Where is cav plate relative to bottom of hull? If it's lower than or even, you can probably move the motor one or two holes higher, which will increase rpm and speed. Then look at changing props.

 

[eddy2419]

Re: 1998 2 cycle 150 Johnson Oceanrunner RPM's

It's slightly higher so I will get a 15 and try it. Thanks for the help. I was probably off topic after I realized there was a prop forum.