Speed indicator not working

Johnv

Seaman Apprentice
Joined
Jul 3, 2003
Messages
33
My speed indicator has stopped working ever since the boat released from its mooring and drifted onto the sand for an extended time. The boat has an external sensor which is a plastic wedge at the bottom of the hull. This sensorappears to operate on a vacuum or difference in pressure since it is attached to a plastic hose rather than electrical wires.

I checked to see any obvious signs of sand plugging the sensor, but Is it possible that the sensor is plugged deeper inside.

Are there any other things I can do to troubleshoot the problem, in particular to see if the guage on the dash is working properly?

thanks for any help
 

NBE

Petty Officer 1st Class
Joined
Oct 28, 2003
Messages
354
Re: Speed indicator not working

It basically works on water pressure going to the instrument.

Most external pitots (your wedge) will move to an upward position when bumped such as you hitting the sand. Make sure that the pitot is in the down position. You may have to exert a little pressure to get it to move if it is not pointing downward. The tip or point of the wedge should be below the bottom of your boat usually a couple of inches or so. If it is above or parallel to the bottom of the boat it will not register a reading.

You can unplug the tubing from the pitot and blow into the tubing. You should see the speed reading change slightly. If you don't then you may have some pluggage in the tubing going to the instrument.

Just a couple of simple things to check. Someone else may come along with a few more suggestions.

Good luck!
 

swist

Senior Chief Petty Officer
Joined
Jul 1, 2004
Messages
678
Re: Speed indicator not working

1) Unplug the hose from the sensor and blow out the sensor with compressed air.

2) Then do the same where the hose joins the indicator in the instrument panel.

3) If that doesn't clear it up, throw it away and use a GPS for speed. Pitot type speedometers are VERY inaccurate, in addition to being prone to clogging, as you have seen.
 

NBE

Petty Officer 1st Class
Joined
Oct 28, 2003
Messages
354
Re: Speed indicator not working

Even though they are known for being inaccurate I attribute that to mostly poor maintenance (sediment and/or scale will build up in the tubing partially blocking it) or faulty or poor equipment. Mine is right on the money with the GPS using an external pitot.

Due to the pitot on my lower unit constantly plugging almost every trip I went to the external one. Suprisingly it is actually more accurate that the pitot on the motor was.

I also have to say that I have Yamaha digital guages and that may contribute somewhat to the accuracy. Regardless so far every trip the speedo is right on with the GPS reading. Going to see how long that lasts though.
 
Top