Re: Low Tech (knotmeters in particular)

Bill Zeitler (WZeitler@compuserve.com)
Wed, 25 Nov 1998 08:04:12 -0500


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West Wight Potter Website at URL
http://www.lesbois.com/wwpotter/
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>> 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,

>Since you've already got so much invested in the Bay Hen, you might want
to
>really consider a Speedmate knotmeter. It uses a little impeller that
>attaches to the bottom of the hull with a transponder attached to the
inside
>of the hull. There is no through hull drilling or attachments. The
Speedmate
>is accurate to 1/1000 Knot or Mile per hour, will give you total distance
>traveled, max speed and average speed. For those who do a lot of
beaching, as
>I do, they have the same knotmeter available with a trailing wire
impeller.
>Just as accurate but you have to toss a little sensor on the end of a long
>wire overboard when you are using it. That is what I use and find it
>extremely accurate and easy to use. Since I know how far my motor will go
on
>a tank of gas, it functions to let me know when to refuel as well.

>Geoff [ Lollipop...Lake Tahoe ]

Geoff,

Thanks for the interesting info on the Speedmate knotmeter. Having done
enough " studies " on the water as to speed vs my HONDA 5 power settings [
see special request for information below ]...I think I have enough info
to go on as is. Infact, I never bother with my trailing knotmeter any more
except to demo how it works to an interested passsenger. I am aways in
sight of land...I always have a good nautical chart [ as well as auto
road maps ] of the area...and good binoculars. Since I can " steam "
about 9 hours on 3 gallons of fuel [ and I keep an extra 3 gallons on board
]...and since I'm retired and usually never in a hurry to get
anyplace...I'm not exceptionally concerned continuous speed monitoring.

_ Special Request for Info _.[ RPM METERS ] Do you [ or anyone ] know
of some kind of gizzmo to measure the rpms of my HONDA 5 / 4 cycle ?
Many years ago there was in the model airplane hobby circles a gizzmo that
used a vibrating " reed " that was placed on the motor and when in
resonance with the engine's combustion cycle could enable one to figure out
the rpm. The reed was of adjustable length and at resonace with the
firing rate would give a number. It looked something like a personal
tire pressure guage. With and outboard [ single cylinder, 4 cycle ] one
would have to do a little initial figuring regarding firing rate, gear
ratio to the prop, to come up with an rpm factor. I would like to
develop a rpm vs fuel vs speed curve...just like the " big boys ".

Bill
Wilmington, DE