Below is a table showing the mileage I received during the trip. I can't find the old data, so I don't know if this is better or worse. My sense is that the prop repitch worked, and that these stats are at least 10% ahead of what I had.
Ken W
| Port | Stbd | Port | Stbd | Total | Indicated | TRUE | NM/ | Range | ||||
| rpm | Eng Load | Eng Load | GPH | GPH | GPH | Speed | Speed | Gallon | 20% reserve | |||
| 1150 | 30 | 30 | 4.10 | 3.50 | 7.60 | 8.40 | 7.50 | 0.99 | 2,368 | |||
| 1285 | 40 | 38 | 5.80 | 4.90 | 10.70 | 9.40 | 8.50 | 0.79 | 1,907 | |||
| 1375 | 47 | 46 | 7.40 | 6.10 | 13.50 | 9.80 | 8.90 | 0.66 | 1,582 | |||
| 1540 | 60 | 60 | 10.20 | 9.20 | 19.40 | 10.60 | 9.70 | 0.50 | 1,200 | |||
| 1675 | 74 | 65 | 13.00 | 12.00 | 25.00 | 11.30 | 10.40 | 0.42 | 998 | |||
| 1775 | 90 | 80 | 14.80 | 13.60 | 28.40 | 11.35 | 10.45 | 0.37 | 883 | |||
| 1850 | 100 | 89 | 16.70 | 16.30 | 33.00 | 11.40 | 10.50 | 0.32 | 764 | |||
| 1900 | 100 | 100 | 16.70 | 17.50 | 34.20 | 11.50 | 10.60 | 0.31 | 744 | |||
| Notes | ||||||||||||
| – The difference between indicated speed and True speed is Current. I was being pushed by a .9 knot current | ||||||||||||
| – Range is computed by assuming fuel capacity of 3,000 gallons, with a 20% reserve (2,400 gallons useable) | ||||||||||||
I just discovered some old stats, from a year ago. Below is a chart, comparing my NMPG (nautical miles per gallon) before repitching the props, to after repitching the props.
Neither set of data was captured perfectly, so I'm trying to control enthusiasm, but the indication is certainly that I've picked up approximately 20% in range at the RPMs I usually cruise at (around 1375 rpm).
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6 Responses
Ken,
On the subject of one of the twin engines running a slightly higher load than the other. In addition to the obvious pumps etc running off one engine, there is a built factor constantly causing one engine to work a little harder due to rotating its propeller counter to the other. Why? I have been told the simple answer is; extra and/or modified gears added to one of the transmissions to make things run in reverse. It makes sense because I have owned three twin engine boats where there was always one engine working a little harder.
Dean
Chuck:
The column that says “True speed” is my best guess as to the “speed over ground”.
I’m not 100% certain what the current was, but feel pretty good about how I guesstimated it at .9 knots.
Here’s what I did:
1) Nobletec claimed that the current was .9 knots (it shows a current arrow on the chart)
2) At 100% throttle I was moving 11.5 knots. My hull speed is 10.6 knots. I’m fairly certain I wasn’t doing more than hull speed, thus I must have been being “helped” by a current. I picked .9 knots as the current, because of Nobletec, and because 11.5 – .9 = my hull speed (10.6 knots).
-Ken W
Ken: You comment about a current of .9. Did you not do fuel consumption numbers going with the current also so that you could average the results?
Ken: So which of the two speeds is “SOG”?
Adam:
I have no idea.
It seems strange that the load percentages are the same at low rpms, but then the port engine shows significantly higher load as the rpms increase.
My theory:
Each of the engines has the option to power a hydraulic pump (which powers the stabilizers). Normally I run with only a single pump going. From the fuel consumption we can see that the port engine was powering the hydraulics. Thus, it makes sense that this engine would be under a greater load. As we sped up, the load on the stabilizers increased dramatically, as shown in the data.
I’ll try to do some testing Monday in Lake Washington, where current isn’t a factor, and the seas should be calm enough to run without the stabilizers.
-Ken W
Ken, I’m surprised to see such a big delta between port and starboard engine loads (at some speeds). I recall Grace of Tide’s numbers being very close together in David’s post about his repitching. Curious as to your thoughts.
/adam