>The West Marine catalog has another kind of handheld knotmeter, and I'm
>wondering if anyone has had any experience with it. The photo in the
>catalog shows a hand holding a clear plastic tube with some numbers
>along the length of it. The end of the tube has a line coming out of it
>which trails off the stern of the boat. I don't know if there is some
>object on the end of the line, but it appears that the line pulls a
>spring in the tube, and an indicator on the spring aligns with the
>numbers on the tube depending on your speed through the water.
Yea.....I have one of the above units.
It has three full scale ranges.... 0 - 3 knots, 0 - 6 knots and 0 - 9
knots. The range scale is determined by which of three small plastic
disks of three respective diameters [ all about an inch or less in diameter
] that are attached to the end of a long [ and elastic ] line that you
toss over the side and drag through the water. The smallest disk gives
the largest full scale reading...the smallest...the most sensitive smaller
full scale reading. The elastic line damps out much of the dithering of
the reading on the spring inside the tube that gives you the reading. The
readout on the handheld plastic tube is very legible with 1/2 knot
graduations.
The unit gives " true " speed _ through the water _ not being effected by
following and / or foul current....ie....Knotstick reading plus current [
+/- ] is speed over the ground. The unit canm't plug up...but if the disk
grabs some seaweed or something [ like a fish ] you will not get a good
reading.;-D
It seems to work quite well although I have no way to calibrate it against
some " trustworthy " standard. I have tried to compare it with my
handheld GPS [ which I use only to mess around with ]...but the GPS speed
reading is not too reliable IMHO.
My only worry is that in my was-a- Bay- Hen sail boat [_now a motor launch_
][ a long story ] ...I worry a bit not to have the long line get into the
prop. Since the unit is actually designed for sailboats...what can I say
? Actually...I'd like to find out more about that " pitot tube " approach
!
Bill Zeitler
Ex- P-15 " # 2060 Just Wight "
Wilmington, Delaware
Now in a converted Bay Hen "motor launch " (!)[ another story for another
time ! ]