Re: Tide calculations at Palo Alto

From: Ken Poulton (poulton@zonker.hpl.hp.com-DeleteThis)
Date: Tue Aug 19 1997 - 02:48:11 PDT


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Date: Tue, 19 Aug 1997 02:48:11 -0700 (PDT)
From: Ken Poulton <poulton@zonker.hpl.hp.com-DeleteThis>
Message-Id: <199708190948.CAA28618@zonker.hpl.hp.com-DeleteThis>
To: wind_talk@opus.hpl.hp.com-DeleteThis
Subject: Re:  Tide calculations at Palo Alto
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A couple of years ago, I had great ambitions to verify the tidal
calculations for Palo Alto. I'm not sure, but the coefficients I have
may be for the old harbor (now filled with silt) and I don't know how
accurate they are for the harbor mouth where we launch. I made a tidal
gauge on one of the dock's posts and started taking readings... but
then I stopped sailing very much at Palo Alto.

My goal for "safe" is to have 2.5 feet of water. This is only safe if
you're planing - slogging with a 16" fin (or any size fin with a
sinker board) is still likely to drag.

I'm open to suggestions on
    1 the most useful definition of "safe"
    2 some other description than "safe"
    3 data on what absolute level hazards are at
    4 data on whether the tidal calculations are right

#3 is most easily obtained by noting when specific hazards are covered
up as the tide comes in. Try this some morning with a 0-ft low tide
at your favorite site and mail me the results. The next two days are
good candidates.

#4 requires a lot of data points. We could re-mark the tidal gauge
and take height+time data points.

>From my windspeed.info file:
    
    The program also calculates "safe" times for 3rd and Palo Alto.
    These are chosen at pretty conservative levels: +2.5 for 3rd and
    +4.0 for Palo Alto. At these heights, I sail with no worries. At
    both sites I sail in as much as a foot less after reminding myself
    where the bars are. (One foot typically corresponds to 40-60
    minutes time difference.)

    For sailing at Palo Alto, we used to need a tide level of at least 4
    feet. With the new dock, 2.5 feet seems to be okay if you stay in
    the little harbor channel until you pass the downwind point. The
    "deep"-water channel runs right next to the white poles; everything
    else near the shore is mud flats at +1 to +2 feet. Hazards: there
    seems to be something hard at about +6.0 near the downwind point
    several hundred yards out.

Finally, note the disclaimer:

    Disclaimers: The calculated tide levels may be wrong, or the
    measured "safe" levels may be wrong. Sandbars shift, people leave
    anchors or other trash in shallow water. You might be sailing with
    a fin deeper than mine. A near-miss by an asteroid might produce an
    extra low tide. Lawyers may be lurking just below the water surface
    at any time, any place. Shit happens. So use your own judgement at
    all times and don't blame me if you hit something.

Ken Poulton
poulton@opus.hpl.hp.com-DeleteThis

"Insisting on perfect safety is for people who don't have the balls to
live in the real world." -- Mary Shafer, NASA Ames Dryden



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