new speedo - existing pitots etc??

hi all and a merry christmas,

replacing guages on my 2001 SAN. any issue with using the existing pitot/pickups for the new speedo? also, would it be possible or even beneficial to use the two existing pitots for one guage? the guage is a standard faria analouge.

thanks,

d.

KRoundy wrote: One gauge per speedometer. Why would you want to use two pitots for one speedo? Besides, it won't work. Your speedometer would read twice the pressure, meaning roughly twice the actual speed (10 MPH would read 20 MPH).

I agree that one pitot per speedo. Try the existing pitot before putting on a new one = I feel it will work.

Regarding the pressure and it doubling with two pitots, no, it will not. You can't get twice the pressure from the base pressure. Kevin,
You need to go back and take some more physics/engineering classes!

Are you certain that the "standard Faria analog" speedo you have is in fact analog? I realize it reads with a needle, but it may still be a digital gauge. I would imagine that its the typical replacement speedo that CC was installing in place of the faulty Teleflex ones ('00-02) but take a closer look.

CC was in fact putting 2 pitots on boats with only one speedo for several years (at least '00-03). I believe the speedo would always read the higher reading of the 2, so it acted just like the old dual-speedo set up in that regard.

Yes, the gauges will read wrong... but they will not read double (which was Pete's point).

Still moot, as I suspect the OP has a very different set up than the one being discussed. The digital gauge systems are not set up like Airguides with pressure lines running all the way to the dash.

Believe 00' was the first year for digital gauges. The 03'+ (maybe even 02' for the SN) has a gateway box (circuit board) in the trunk, which is as far as the pitots run, would assume that is converted to a digital signal from there to the dash. The 00'-02' may be the same/similar.

I'm trying to explain this plainly. Pitots work by measuring pressure, in my business they measure a pressure differential using a pitot-static device. On an aircraft the pitot provides pressure from air being forced into the pitot and then a separate static port reads pressure of the static (uh - natural) air pressure. The difference in static (side) and pitot (front) pressure is used to measure speed.

On a boat the idea is much more simple. The water enters the pitot tube and starts to go up the line. Not very far, but it does. This compresses the air in the system and the Airguide reads this pressure as speed.

As usual, Wikipedia has a decent and simple explanation: Pitot tube

Yes, if water dribbles on your legs while driving you have a leak. Good reminder.

KRoundy wrote: I'm trying to explain this plainly. Pitots work by measuring pressure, in my business they measure a pressure differential using a pitot-static device. On an aircraft the pitot provides pressure from air being forced into the pitot and then a separate static port reads pressure of the static (uh - natural) air pressure. The difference in static (side) and pitot (front) pressure is used to measure speed.

Answering "plainly", it may be beneficial to explain the reason aircraft need to read a differential pressure and what happens to air pressure at different altitudes.