What is this speedo off?

[Bob Moseley (RIP)]

Hi all - a bit of Googling research leads me to think this is a boat, sail or speed, speedometer where one can translate the water speed (knots) to a land speed (mph).

Bob

[Lang]

Yes, a boat was my initial thought but even for a speed boat the ranges are useless. The area of 99% of operations below 20knots is too small a scale to be useful. A race boat maybe?

I am going to buy this on ebay out of interest as I can not see the drive. It could well be an aircraft instrument out of something like an early glider if it is a pressure instrument and not mechanically driven but even then 60mph is a bit light on. Maybe a blimp or early helicopter? If it was a race boat it also will be pressure driven.

I even thought a wind gauge out of a control tower but once again 90% of wind speeds are below 10 Knots so once again useless.

If you look at the scale it is almost certainly pressure driven as the numbers get further apart the higher you go - mechanical is a fixed ratio. Water pressure should be constant too so it looks like some air pressure driven device.