After making sure my old speedometer worked on my Seacoaster (1960), I recorded about 32 MPH or so, with four guys (maybe 160 each) and two tanks of fuel... the lake had a small chop, but was pretty smooth. I didn't check it a bunch of times in different directions, but figured I was doing OK. The boat is 15' 10", and I think I was using a 10x12 prop.. 75HP 1961 Johnson.
Later I was riding in another boat, slightly larger, with four guys and the same motor, and that speedo showed 37+... That speedo was a digital one run by a spinner in the water. Mine is driven by the compression of the air in the tube from the speedo arm mounted to the transom.
Since I think the scenery was flying by as much when I was in my boat as the other, I am wondering how accurate these old speedos are... The mechanism looked good, with no corrosion when I looked at it..
And John P.... you regularly mention that you are moving x mph via GPS... Does your GPS really have the resolution to pinpoint the speed that closely?
John Hart
How accurate are speedometers
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johnpthompson
- Posts: 32
- Joined: Tue Jan 03, 2006 2:48 pm
John,
I have a speedo which looks to be part of the original 1963 guages added at the dealership--or could have been with the new motor in 1969--on our Super Lancer. We also have a GPS in the boat. The original speedo reads about two MPH SLOWER than the GPS speed. In our 1953 Super Deluxe we installed a vintage speedo last year. It also reads about one or two MPH SLOWER than a handheld GPS we carried on the same boat. We also have a 2003 Regal, the Faria modern speedo reads about two miles per hour FASTER than the handheld GPS. All three have a pitot (sp?)tube pick-up on the transom.
John Thompson
I have a speedo which looks to be part of the original 1963 guages added at the dealership--or could have been with the new motor in 1969--on our Super Lancer. We also have a GPS in the boat. The original speedo reads about two MPH SLOWER than the GPS speed. In our 1953 Super Deluxe we installed a vintage speedo last year. It also reads about one or two MPH SLOWER than a handheld GPS we carried on the same boat. We also have a 2003 Regal, the Faria modern speedo reads about two miles per hour FASTER than the handheld GPS. All three have a pitot (sp?)tube pick-up on the transom.
John Thompson