tcm
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The log that measures how far you have travelled I mean. in ragboating these are relied upon as though they are 100% accurate: "...and the log now read 8.2 so having travelled in z direction and allowing for the tide of x knots in y direction and the leeway means your estimated position is here" say the rya exams.
But in a powerboat most mechancial means of finding the speed are miles out. I don't think I've ever been on a powerboat where the thing was within 10%. One or two read "error" and some said "88.8". I think mine occassionaly read 00.0 and then woke up to say 15ish knot regardless of how fast your went. These days, i just use a stack of gps's. And i have a better idea of the speed from engine revs: the clever people who do timed log rallies also rely on engine revcounters, not paddlewheel speed instruments.
Presumably if the speed reading is wrong then the log is junk too - it must use the same wheel thingy to add up how long you have been travelling at what speeds.
Ergo, do the nav before setting off on paper. Then verify calculated SOG with GPS. Verify actually location with GPS too. have a spare gps and another if you must. Keep a note of speed from engine revs. To be non-gps-dependent, build up a good record of what engine revs under what conditions mean what speeds - much more relaible than paddlewheel.
Shouldn't we ignore the stupid mechanical speed devices. Indeed, should we question any fool who insists upon using such dangerous devices which require that you have a walloping great 2inch hole drilled into the bottom of the boat which is plugged by a dodgy bit of plastic and an o-ring or two?
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But in a powerboat most mechancial means of finding the speed are miles out. I don't think I've ever been on a powerboat where the thing was within 10%. One or two read "error" and some said "88.8". I think mine occassionaly read 00.0 and then woke up to say 15ish knot regardless of how fast your went. These days, i just use a stack of gps's. And i have a better idea of the speed from engine revs: the clever people who do timed log rallies also rely on engine revcounters, not paddlewheel speed instruments.
Presumably if the speed reading is wrong then the log is junk too - it must use the same wheel thingy to add up how long you have been travelling at what speeds.
Ergo, do the nav before setting off on paper. Then verify calculated SOG with GPS. Verify actually location with GPS too. have a spare gps and another if you must. Keep a note of speed from engine revs. To be non-gps-dependent, build up a good record of what engine revs under what conditions mean what speeds - much more relaible than paddlewheel.
Shouldn't we ignore the stupid mechanical speed devices. Indeed, should we question any fool who insists upon using such dangerous devices which require that you have a walloping great 2inch hole drilled into the bottom of the boat which is plugged by a dodgy bit of plastic and an o-ring or two?
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