Testing a Gaffrig Speedo ?
 

I would like a quick way to test a Gaffrig speedo.

Seem to remember someone posting a table that
showed PSI to MPH readings. But now I can't find it.

thanks

I shipped mine back to Livorisi. They were more than happy to test the unit. I consider them to be one of the most supportive and user friendly vendors to boaters.

I don't own the boat and was looking for way to tell
work/no-work or if it was anywhere close to actual.

could have sworn I posted this already this am-

MPH = 8.31 * square root(psi)

Hey thanks that is what I was looking for.

So if my math skills are still intact, I come up with the following:

MPH PSI

10 = 1.4
20 = 5.8
30 = 13.0
40 = 23.2
50 = 36.2
60 = 52.1
70 = 70.1
80 = 92.7
90 = 117.3
100 = 144.8

I'm surprized that all of the cheap rubber pitot lines that I see just don't
become balloons.

I'm not sure about the numbers. On the low end of the scale you should be able to blow on the tube and make the needle move if the psi is that low but I can tell you that I can't do that.

Just went over and tested my friends Gaffrig speedometer.

After I blew about a pint of nasty milkish liguid out of the pitot line. (with an air compressor)

40 PSI showed 60 mph. So off it goes to Gaffrig.

Will be interesting to see what it reads after calibration.

Edit: He pulled the speedometer and about a shot of liguid poored out.

I say replace the tubing.