rgano
Guru
- Joined
- Oct 8, 2007
- Messages
- 4,995
- Location
- USA
- Vessel Name
- FROLIC
- Vessel Make
- Mainship 30 Pilot II since 2015. GB-42 1986-2015. Former Unlimited Tonnage Master
I just installed a Floscan in my Mainship 30 Pilot II which is powered by a Yanmar LPA-STD (315 HP), and today I went out and completed a data run to compare the GPH, MPH, and MPG versus RPM. Being a data dinker in my previous life as an acoustic trial director for US Navy destroyer and cruisers, I plotted all this data and compared the plots I got with the Floscan to the same plots I made from a Yanmar table provided for this boat and engine combination. It should be noted that I recently reduced prop pitch from 24 to 22 inches on my five-bladed 22 inch diameter prop to correct a lower than expected WOT RPM.
I have attached the Excel plot, and I think the various data series agree quite well, especially in the MPG plots at mid to high range RPM.
I notice a kind of a sweet spot in the 1500-1600 RPM range where if I could stand to run at that slow speed (7-8 MPH with hull speed for this boat being about 7.2 MPH) I would realize a nice fuel economy of as much as 5.5 MPG.
There is a slight hump in the speed between 2100 and 2800 RPM where I gain five MPH as the boat gets over the hump and the bow comes down without trim tab assist after which no matter what RPM is run, the MPG curve goes vertical at about 2 MPG and that´s all she wrote.
Clearly, the turbo is whining and doing its thing over 2100 RPM, but what is going on with engine/turbo health at the slower and more economical 7-8 MPH RUNNING 1500-1600 RPM? Engine heat seems to be good at a steady 175F at 1600. Is this one of those ranges where you can run all day at but need a good half hour at say 2800-3000 RPM to blow out all the carbon?
I have attached the Excel plot, and I think the various data series agree quite well, especially in the MPG plots at mid to high range RPM.
I notice a kind of a sweet spot in the 1500-1600 RPM range where if I could stand to run at that slow speed (7-8 MPH with hull speed for this boat being about 7.2 MPH) I would realize a nice fuel economy of as much as 5.5 MPG.
There is a slight hump in the speed between 2100 and 2800 RPM where I gain five MPH as the boat gets over the hump and the bow comes down without trim tab assist after which no matter what RPM is run, the MPG curve goes vertical at about 2 MPG and that´s all she wrote.
Clearly, the turbo is whining and doing its thing over 2100 RPM, but what is going on with engine/turbo health at the slower and more economical 7-8 MPH RUNNING 1500-1600 RPM? Engine heat seems to be good at a steady 175F at 1600. Is this one of those ranges where you can run all day at but need a good half hour at say 2800-3000 RPM to blow out all the carbon?