[abrahamx]

The unit was saying 7. something mph while my raymarine unit was saying 4 something. Which one is likely right. I do not have a transducer, it was just sog from the gps. the ray marine has a transducer. The 7mph is closer to my hull speed. If that thing is correct I have been going alot faster than I thought. Whats the deal?

 

[CharlzO]

Not to ask the really silly question, but your raymarine wasn't reading in knots whereas this one is showing mph is it? Granted, I know 4 knots isn't quite 7 mph, but it'd be a closer gap.

 

[abrahamx]

No, both were mph. This was under motor at full 3600 rpm on my beta 20. I always wondered why it would only push me 4.5 mph at full throttle. Maybe the gps is correct and I need a new impeller for my raymarine? I do notice it does not read speed till jarred loose or something. Yesterday it did not start reading till I put up the sails and keeled a tad.

 

[PaulinVictoria]

Currents? The Ray is giving you speed from a paddle wheel (SoW) whereas the Lowrance is GPS speed (SoG). 2-3 kts or more difference between the two is quite common round here. Or if no currents, likely the transducer needs a bit of a service, pop it out (bung in the hole), clean it up, lube it and pop it back in.

 

[SVAuspicious]

I think paddlewheel fouling is the most likely.

 

[abrahamx]

Just got back from the boat at the slip and the lowrance is reading 7.5-11.5 ft of depth and my raymarine is reading 4.5 which I know to be true. at least to the muck anyway. Messin around forever trying to figure out how to switch he raymarine from mph to kts. Going to have to look up a manual. 7 foot variance is not good in lake st clair as the depths are anywhere from 1' to 15'

 

[MarkSF]

1) Speed readings from a paddle can be miles out. Mine varies a knot depending on whether the bottom is clean. It might need calibrating. The display unit often has a calibration routine.

2) most depth displays have an adjustable offset. Someone may have set it to read depth under the keel. I prefer true depth. I calibrated my offset using a bucket with a brick in it, and a line attached.

 

[Capt Len]

Is it possible that the water going past the impeller is not lineal (in line with fore/aft) but flowing up at an angle because of hull shape? Weed on the hull close by would also effect it.