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Old 21-11-2013, 14:46   #31
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Re: Water Height and Bridge Clearence

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Originally Posted by a64pilot View Post
Yes, but you have to know the exact distance to the bridge, all you need is a plumb bob, a cheap protractor and a piece of wood and an assistant, to read the degrees on the protractor.
Used this as a kid to determine how high the model rockets I built went.
We did that in Boy Scouts, nut tied to a string for plumb bob... same theory timber surveyors use to get the height of trees. Might be tough to stretch a tape measure across water , but GPS should tell how far the boat is from the bridge.
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Old 21-11-2013, 14:48   #32
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Re: Water Height and Bridge Clearence

> how do you know what MHW is at any particular place

Check the relevant chart. I've just taken a look at two AUS charts:

AUs 621 says: "overhead clearance heights are above Highest Astronomical Tide, all other height are above Mean High Water Springs"

Aus 379 (which does not have any clearance heights marked) just says the latter.

Both maps include a panel which shows " Heights Above Datum" for MHHW, MLHW,MSL, MHLW, MLLW at the local Tide Stations.
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Old 21-11-2013, 15:05   #33
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but GPS should tell how far the boat is from the bridge.
I was thinking laser range finder, but better not bring up anything gun related I've discovered.
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