How accurate are the old Speedometers

carbineone · Mar 17, 2010

I was wandering if the old style speedos with the old pickup tube in the rear are anywhere near accurate.The kind widely used in the 50s to the 70s. I would almost lean toward them not being very accurate but whats your thoughts...Bruce

Black as · Mar 17, 2010

Re: How accurate are the old Speedometers

I have one in my 1988 Bayliner and it works fine.

carbineone · Mar 17, 2010

Re: How accurate are the old Speedometers

Yes they seam to work fine as far as functioning but you ever checked it against GPS or a game wardens radar.LOL.

JimMH · Mar 17, 2010

Re: How accurate are the old Speedometers

The Old Speedo's are fairly accurate. They are still installing them on boats and the only difference most out drives and out boards have a pickup built into the foot of the gearcase.

Mark42 · Mar 17, 2010

Re: How accurate are the old Speedometers

I have a Teleflex in one boat, and a Faria in the other. Both are accurate to withing a two or three mph, but more importantly, they are consistent. So if the speedo suddenly shows a 5 or 7 mph drop in top speed, I can trust that there is something gone wrong that is causing the boat to run slow. IE, failing spark plug(s), clogged fuel filter or some other fuel restriction, etc.

nola mike · Mar 17, 2010

Re: How accurate are the old Speedometers

yup, my teleflex speedo in my '86 is within 2-3 mph of gps speed @ 50mph--pretty darn good. and yes, consistency is most important. i was actually very surprised at how accurate it was. i'm guessing that this is "water speed" though--so if you're going with/against a strong current, your true speed may be off.

haulnazz15 · Mar 17, 2010

Re: How accurate are the old Speedometers

They are usually pretty close to GPS as long as you aren't messing with major water currents. They lose their effectiveness at high speeds though, so as you get above 50mph, they will usually be farther off. Just for reference, they are pitot-speedometers. (pronounced peet-oh) It works off of air pressure in the pitot tube; aircraft use a similar apparatus to measure speed as well.

carbineone · Mar 18, 2010

Re: How accurate are the old Speedometers

Thanks everyone.I would have never guessed they were that accurate.The system just seemed kinda hokey to me looking at it...Bruce

83Evinrude · Mar 18, 2010

Re: How accurate are the old Speedometers

Checked against a GPS, mine is about 4mph high from 10-20mph, dead on by 30mph and about 1-2mph high at 53mph.

dockwrecker · Mar 18, 2010

Re: How accurate are the old Speedometers

Mine is +/- 15mph...I've tried everything to fix it short of ripping it out of the dash and junking it. Right now it's very useful as a hole plug.

Thad · Mar 18, 2010

Re: How accurate are the old Speedometers

My speedo is worthless. When I turn left it goes up, when I turn right it goes down. I do have a dash mounted GPS that I use for accurate speed, especially when there is a speed limit where I am at.
Regardless, it is the tach that NEEDS to be on the money.
I find that I almost always drive my boat by the RPM's, not the speed.
Just another 2 cents worth.

haulnazz15 · Mar 18, 2010

Re: How accurate are the old Speedometers

There will be inaccuracies from things like hull design, pitot placement, and the angle at which the pitot is hitting the water. In aircraft, if I step on the rudder and hold it, the aircraft sort of skids through the air and the airspeed indicator will read differently because the air is no longer coming from directly in front of the pitot. Same thing in a boat, if you are turning hard or in chop, it can change the angle at which the water is creating pressure on the tube causing inaccuracies. Speedos on a boat aren't really worth much of anything other than a general reference point. Many boats didn't/don't have them since they are not a necessity.

blairjbyrd · Mar 18, 2010

Re: How accurate are the old Speedometers

i would have never guessed that the speedos are that accurate. interesting

Gary H NC · Mar 18, 2010

Re: How accurate are the old Speedometers

I have seen them off by 10 mph in brand new boats...
The original speedo on my ChrisCraft is off by 4 mph...
They vary greatly.

How accurate are the old Speedometers

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