depth in air = flying height?

[Billjratt]

My boat's been on the hard for what seems an eternity, but that's another story.
Today I fired up the ST60 instruments as part of the electric refurbishment process, and found that the echosounder thought we were in 12 feet of water.
Previously, (on drying grid etc.) I haven't had a reading until the tide came in and covered the transducer, which seemed to make sense. (but could possibly be mud)
I altered the offsets to get a range of readings and noted them, then came home and Googled for relative propagation speeds in air and water. The sums add up - so it does seem to be working.
(343.2m/s in air, 1560 m/s in seawater)
The transducer is a through-hull which will no doubt make a difference, but I'm still astounded, as I remember having to be careful to get oil-and-tube installations just right in previous boats.
I wonder how many more of you have an "altimeter" fitted!

Or could it be that our weather is so poor, the boat thinks it's afloat?

No comments about flee'in already thankyou

Have a good one, when it comes.

 

[BoyBlue49]

Mine doesn't work at all when out of the water, spoke to Raymarine engineer who confirmed they don't give a reading untill in water.

Must be high humidity where you are.

 

[rob2]

IIRC in a previous similar thread, it was noted that the signal in air is weak due to the medium being less dense. Also, some work some don't, a thru hull is more likely to achieve an echo as it doesn't have the attenuation of all the interfaces to pass through.

Rob.