How does a PWC speedometer work?
bbrad
Just curious, you can be semi-technical. I couldn't seem to find the info
on anyone's homepages or in my manual.
Thanks,
Brad
3cruz
Based on other similar devices, the little paddle wheel in the back drives a
rotating magnet. The rotating magnet passes by a stationary magnet and with
a little elecricity going around, creates pulses that are translated to
speed at the gage. I'm not sure, but I would bet that is pretty close. The
rotation of the paddle wheel is calibrated to the numbers on the gage.
Larry KN4IM
Two types of speedos. Some have little paddle wheels. The wheels
have imbedded magnets in them. When they spin a little coil in the
mounting bracket produces a pulse every time one of the spinning
magnets in the paddle passes by it. The computer in the boat merely
counts the pulses. The paddles are designed so they spin X RPM to
match the speed of the water pushing them around. Unfortunately,
there is so much turbulence under a boat, it's very hard to get it
right....so manufacturers run 'em high. It makes the customer feel
like he got what he paid for and gets the manufacturer off the hook
producing a product that actually WORKS.
The other type is a pitot tube. A plastic "blade" with a hole in the
end of it is dipped DOWN below the hull turbulence into the calmer
water stream. The pressure of the water pushes up into the tube. The
speedo is a sensitive pressure guage calibrated in speed (mph, for
instance). The problem with this type is the "dipped DOWN" part.
Sticking out the bottom, it can get torn off by passing trash, rocks,
bottom, downed skiiers, the dock, the ski ramp, or in some extreme
cases, the grass on the riverbank! So, the mounting bracket is made
to snap back if the pressure on the blade exceeds a point.
Unfortunately, my Sea Rayder's snapback point seems to be about 52
mph. The speedo reads great, VERY close to my GPS, until it snaps
back into its protective position where it reads ZERO the rest of the
day. It's mounted under the port side of the pump and WAY submerged
under the swim platform....so I go without. Some PWC have the blade
type mounted INSIDE the intake grate! How accurate do you think it
will read your speed measuring the speed of the water the pump is
sucking through the grate? Your honor, the prosecution rests.... At
least it doesn't hit anything, much, inside the pump intake!! That's
probably why it's mounted in there....
Larry In Miami
On Mon, 06 Apr 1998 00:05:36 GMT, kn...@mindspring.com (Larry KN4IM)
wrote:
Damm Larry, ya saved from a great post.Perfect
i could not say it any better myself.
But Nothing beats that Gps. ineed to start selling them
think i will check this week.
So, one fell overboard? leaves you 3 right? Dont worry they all come
equiped with floatation devices.
Larry In Miami
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