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Old 10-29-2016, 10:06 PM   #1
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30 Pilot II initial Floscan data Yanmar 315 HP

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?
Attached Files
File Type: pdf Fuel usage plot.pdf (175.4 KB, 85 views)
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Old 10-30-2016, 05:32 AM   #2
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Very interesting data. Good to know your data tracks the Mainship/Yanmar data well. That suggests the published data for other model/engine combinations they produced may be more than just marketing puff.
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Old 10-30-2016, 09:23 AM   #3
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That's what we data dinkers LIVE for - data compatibility.
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Old 10-30-2016, 09:40 AM   #4
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It would probably be a good idea to run it up into the boost range if you were to run "hours on end" at 1600rpm.
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Old 10-30-2016, 10:48 AM   #5
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Interestingly, at one point ,2200 RPM, your data follows the 2.7 exponent prop fuel curve.
((22/36)^2.7)*13.5=3.57

You can check the other points.

22 is 2200 RPM
36 is WOT RPM
13.5 is max fuel

3.57 is fuel predicted at 2200
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Old 10-30-2016, 11:31 AM   #6
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Yep, right in the transition zone.
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Old 10-30-2016, 11:47 AM   #7
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Rich in your PIX the bow is pretty high. Was that full on plane?
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Old 10-30-2016, 11:51 AM   #8
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Quote:
Originally Posted by bayview View Post
Rich in your PIX the bow is pretty high. Was that full on plane?
These boats run bow high. I know many have installed extensions onto their trim tabs to get the nose down. Mainship went to a tunnel on the Pilot 2 which puts the thrust vector more parallel to the boat's longitudinal axis. A convention set up would provide the needed downward force. It was lost with the tunnel.....that is my theory anyway.
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Old 10-30-2016, 12:10 PM   #9
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I was initially unsatisfied with how high the bow rose on this boat - I couldn't see where I was going! I detailed here in earlier posts about how through a pair of small fixed tabs and the Bennett drop-fin modification to my smallish Bennett tabs I was able to resolve the issue to my satisfaction. Nowadays, in smooth water, I get the boat to somewhere around 3000 RPM with the hydraulic tabs retracted 100%. At this point the bow has fallen through the transition and is a little high but not unduly so. Once settled out at this RPM, I touch the tabs down a tad at a time until I see the GPS speed fall off a tenth or two and then back off on the tabs to regain the highest speed - it is not a dramatic shift, and I might be nearly just as well off not doing anything with the variable tabs. As the photo shows, the bow is up on this probably 3000-RPM run, and I think reducing the wetted surface by getting the bow out of the water versus getting the bow down for best forward visibility and best speed is balanced well in the trim you see there.
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