bidata paddle wheel

jimh

jimh

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The speed reading from my bidata does not match the SOG from my gps - not even closely (taking into account tide!) . During the hand-over when i took delivery, the guy mentioned that the 'paddle wheel' may need cleaning, quite frequently. Question is, can this be cleaned with the boat in the water. ? Can I safely remove the paddle wheel assembly without risk of flooding.? I have a blanking 'plug' with a threaded flange - just curious as to how much water and how quickly it will enter the boat if i unscrew and remove the sender unit and try to screw in the blank.

TIA

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If the bidata is a Raymarine, I would suggest to check the model on their website for a "rubber pad" which blocks out most of the water when you remove the paddle wheel unit.

I have a ST50 unit and on average I would estimate the amount to be 2-3 litres (first time about 5...) The splashing is more disturbing than the 2-3L indicate.

But check whether you have this rubber thingy, some models do not, than it may be much more water and the speed with which you bring in the blind plug is more important!

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a bit of fouling on the rotator will make a huge difference so i find i need to clean it every couple of weeks. less obvious is that a bit of fouling on the hull in front of the transducer will disturb the flow and make it misread. i have resorted to re-callibrating to the GPS when i can't get at the bottom to clean it for a while.

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I recently purchased the NASA unit, which reads a little just over a knot low when I first fitted it. The NASA unit has a calibration where you can alter up and down approx 50%. I also contacted NASA who gave the following advise.

The paddle wheel should be in a clean flow of water, this was possibly a problem for me as I had removed and old sowester propellor log and used the same hole as such, this meant I was stuck with the origional position.

He said to move the boat, release off the paddle wheel assembly and turn gently until you get maximum speed registered on the log, this will then take into account the flow of water across your hull.

Using both the calibration and tuning the paddle wheel I have now got my log to read IMO fairly accurately.

This method may cross over to your log set up, good luck.

<hr width=100% size=1><font color=blue> Julian </font color=blue>

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I have a Raymarine bidata unit. It came with a spare "plug" to place in the through-hull fitting when I remove the paddle wheel. It recommends keeping the paddle unit out when you don't need it - I have ignored this advice. I also accidentally ignored the advice to antifoul the paddle wheel and the through hull fitting - with the result that the thing does not work even when the paddle is clean. I suspect there is a small wall of mussels around it protecting it from flowing water.

Anyway, very little water comes in (say 1 - 2 litres) when you take out the paddle unit or the plug as the through-hull includes a slam-shut valve. This valve does not stop the flow entirely but it does reduce it to a trickle. My through-hull is about 500mm below the waterline.

When the unit is out of the boat it is easy to push the "axle" out of the paddle so it can be taken apart for cleaning.

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Dear Jimh,
Reading the comments already given to your question,
I suppose the difference in reading is not because of watercurrent? Your GPS gives an absolute speed, while the log reads a relative on in the water....
Kind regards.

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