Speedometer issue (going backwards at speed)?

[zagger]

I posted this in VP section and I'm hoping for little better response here. I had a strange thing happen the other day when doing some sea trials with my 08 Regal bow rider. The speedometer started going backyards way below 0. At first I thought the tube separated from the drive and was dragging in the water creating vacuum at speed. Once home I checked all fittings and all was OK. I blew little air into the pick up hole and little water came out, no other obstructions or chunks of seaweed. Did that three times till no more water came out and the spedo started to work again. My question is if I have a hole in the line and it fills up with water I would think the gage would simply stop working, what would make it go backward?

 

[zagger]

Re: Speedometer issue (going backwards at speed)?

Anyone have any ideas?

 

[haulnazz15]

Re: Speedometer issue (going backwards at speed)?

You sure the front of the pitot pickup isn't blocked? That's about the only way to create a vacuum that I can think of. Normally if you get a hole in the line, or am object stuck, it will quit operating or freeze at whatever speed it was indicating when the pitot became blocked (speaking from aircraft experience).

 

[zagger]

Re: Speedometer issue (going backwards at speed)?

No obstructions, this one has me baffled that is why I'm asking the forum. Maybe someone had similar experience. Flying SoCal never had freezing problem even in high altitude but I applied same logic to the boat speedo. It should stop working or get stuck at whatever speed, never go backward. Maybe I entered Point Loma triangle????