Speedo accuracy
 

Does anyone know if a speedo is any more or less accurate with a stainless pitot tube rather than the pick up in the drive? Yes ,this is a trivial question, but inquiring minds need to know. Thanks:rolleyes:

Should not make a difference, except that the drive mounted pickup has a better chance of staying in the water. A speedo is just a pressure gauge with a face that reads in MPH instead of PSI. Speed in MPH is 8.31 x the square root of the pressure in psi.

I was told once by a few friends that own a radar gun, that when the drive is trimmed up the accuracy goes away.. I can see what they meant. Take a pipe and hold it straight at a stream of water then tilt it at an angle and see what happens..
I never did any testing on this but it made sense to me..
Go GPS and dont worry about it.. that is the best way to solve the problem..

Dick

That last argument sounds just like the "angled tips vs the Simrek 90 degree tip on drive shower principle...... also since we are talking about line pressure on the pitot tube & reading it in mph rather than PSI, would this not need to be adjusted for altitude? In other words, does a boat traveling at 100 feet per second indicate the same speed at sea level that it would at 3000 feet? Inquiring minds want to know!! :rolleyes:

I think we are measuring water pressure not atmospheric pressure. It would be considered guage pressure not absolute, I think:confused:

My reference was to the statis atmospheric pressure present in the gauge tube which will be compressed by the constant water pressure when under way. This is really just a rhetorical question as we all know the gauges are inaccurate......maybe this is a contributing factor?????:confused: