2000 digital speed sensor mount

Thru hull speed sensor came loose.Tried to remount with silicone between face and hull.Wrong speed readings?Any one know what to use?
Thanks SLR

[boats.net]

Are you talking about a speed sensor for a depth finder?

no but it is a similar type transducer.Unless I have the wrong device.I do not have a depth finder that uses this transducer that was mounted as a thru the hull type.I found this one loose remounted with silicone and it reads wrong now as opposed to no reading at all when it is not mounted to the hull.What else would a 250ox66 use as a speed sensor for digital guages?
thanks,
Steve

[jb123]

you can either use a transom mounted pitot tube OR the yamaha factory speedo pickup that runs from leading edge of lower unit, up thru midsection and up/out thru underneath intake. look for an 1/8" tube.