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Old 13 April 2017, 03:44   #1
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Measuring speed without a gps

Is there an easy way to measure speed in a rib without the use of a GPS? Is to allow for estimation of position on a chart
Tsm
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Old 13 April 2017, 04:06   #2
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Measuring speed without a gps

Quote:
Originally Posted by two stroke mick View Post
Is there an easy way to measure speed in a rib without the use of a GPS? Is to allow for estimation of position on a chart

Tsm


You can time yourself over a known distance, e.g between 2 buoys. You can compensate for tide if you have tide data to hand, it depends how accurate you want to be. After a while, you get to know your boat. I know that at 4000rpm with my usual load on calm sea I'm doing around 25kn
You could also use a pitot or paddle wheel speedo, but these can very inaccurate.
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Old 13 April 2017, 04:24   #3
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In calmish water, running at a "standard" load, you may find that a given rev will equate to a reasonably accurate speed. e.g. - I "know" that 3000rpm will give me 29-30kts.
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Old 13 April 2017, 04:26   #4
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.....e.g. - I "know" that 3000rpm will give me 29-30kts.


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Old 13 April 2017, 04:27   #5
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Why not use your phone or borrow a car gps.
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Old 13 April 2017, 04:31   #6
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Or for a Real world number....just go out with another Boat which Has!...and test at revs
If it's a real concern (I used a Zodiac SIB for years without one) you can pick up an older used unit,or hand held extremely cheaply.
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Old 13 April 2017, 04:47   #7
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Quote:
Originally Posted by jonp View Post
Why not use your phone or borrow a car gps.
Quote:
Originally Posted by Maximus View Post
Or for a Real world number....just go out with another Boat which Has!...and test at revs
If it's a real concern (I used a Zodiac SIB for years without one) you can pick up an older used unit,or hand held extremely cheaply.
I suspect that TSM isn't short of a GPS - but rather planning a bit of chartwork for educational purposes.

You know, Distance x Time = Fuel Burn or Position...
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Old 13 April 2017, 04:49   #8
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Soz - missed your post above - you must have thought there was an echo
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Old 13 April 2017, 05:22   #9
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Easy if you know the length of your boat, throw something that floats in the water and time how long it takes to get to the stern. You just have to be very good with a stopwatch...
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Old 13 April 2017, 06:14   #10
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Easy if you know the length of your boat, throw something that floats in the water and time how long it takes to get to the stern. You just have to be very good with a stopwatch...


I usually throw the logs straight over the stern, saves getting streaks on the hull
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