is my speedo bunk

[mike_v2v98]

top speed on my boat is 38 mph by the speedo<br />its a water presure tyoe speedo with a pickup at the rear of the boat<br />on gps my boat does 54 mph<br />what one do i believe

 

[Ross J]

Re: is my speedo bunk

You've almost got the difference between kilometres per hour and miles per hour.<br /><br />I'd be more inclined to believe the GPS.<br />There's another explination but it wouldn't account for such a large discrepancy - the GPS measures true speed tver land. The speedo measures speed over water, if there were a strong current with a headwind it could make a difference.<br /><br />Could there be a break, crack, hole in the tube of the speedo somewhere. Easiest checked by undoing the tubre from the back of the speedo and blowing through it whilst plugging the other end, obviously if air flows there's a fault.<br />Ross

 

[Bob_VT]

Re: is my speedo bunk

Hull shape and location of the pitot tube itself lead to very poor readings. If the pitot is mounted to high the speedo will read lower speeds and visa versa if it is too low it will read higher. Air bubbles in the water will also skew the reading.<br /><br />GPS is far more accurate.<br /><br />Bob

 

[Lark40]

Re: is my speedo bunk

GPS !<br /><br />Forget using water tube speedo readings....GPS is far more accurate.