An impressive video of the nasamarine electromagnetic log.

[mattnj]

See Raymarine ST60 Log transducers

i dont know what you mean.... i spoke to NASA they do a unit to directly replace a raymarine (airmar) paddlewheel....it connects to the back of your ST60/ST40/i60 whatever....no display and not NMEA output (this one is pulsed)

Electromagnetic Log 3 (transducer and data box) - Nasa Marine Instruments

 

[AntarcticPilot]

i dont know what you mean.... i spoke to NASA they do a unit to directly replace a raymarine (airmar) paddlewheel....it connects to the back of your ST60/ST40/i60 whatever....no display and not NMEA output (this one is pulsed)

Electromagnetic Log 3 (transducer and data box) - Nasa Marine Instruments

They do now - I was a beta tester for it, mainly as a result of suggestions on that thread! And it's slightly more complicated than plugging into the back of the ST60; there's a box of electronics between the two. The point is that there's a lot of information about the NASA electromagnetic transducer in that thread.

 

[Refueler]

I have the half speed thing on a NASA log - it is caused by one of the two tiny magnets disappearing from the paddle wheel. Replacement part costs under a tenner! And refrain from pressure washing the paddle wheel next time........

Or just buy the Neodynium magnet itself and epoxy it in. Pennys.

 

[vas]

Have you tried antifouling the impeller and housing?

not really, I suppose I could try using velox plus in a spray can as I do for the props and shafts. next lift...

You could just epoxy the transducer to the inside of the hull if you are solid GRP. I did that to save another hole in the boat and it works perfectly.

plywood hull I'm afraid,, so not really possible. Rather have the only bit of info that works remain as such.

cheers

V.

 

[William_H]

I think it uses magnetohydrodynamics.

Thanks for that. I can't pretend to really understand it all but have got a bit of a feel for it. Does it work in fresh water as fluid conductivity seems important? ol'will

 

[cpedw]

Does it work in fresh water as fluid conductivity seems important? ol'will

I think (you're not the only one with an incomplete undertanding!) the fluid must be conducting so distilled waer probably doesn't work but most fresh water has enough impurity to be conducting. I don't know if the conductivity affects the response so it might need recalibrated moving from sea to river.

 

[Chris Durbin]

You could just epoxy the transducer to the inside of the hull if you are solid GRP. I did that to save another hole in the boat and it works perfectly.

I'm curious to know if your solution still works after a few years. Fixing the EM log transducer directly onto the inside of the hull with epoxy seems like the answer to a number of problems: No hole in the hull, no fouling of the contacts, easy installation. I just want to be sure that I understand your post correctly.

 

[PaulRainbow]

I'm curious to know if your solution still works after a few years. Fixing the EM log transducer directly onto the inside of the hull with epoxy seems like the answer to a number of problems: No hole in the hull, no fouling of the contacts, easy installation. I just want to be sure that I understand your post correctly.

This thread got confused between the EM log and a normal depth transducer. You cannot stick the EM log to the inside of the hull.

 

[tillergirl]

Chris

There are different types of transducers. Speed transducers whether a paddlewheel or EM sensor need to be in the water; i.e. you need a hole in the hull. Some echo sounder transducers will work fine inside the hull. I need a temporary quick fix so I stuck an Echo Sounder transducer inside the hull using a bed of silicon. It worked fine and accurate for 12 months. Personally I wouldn't use epoxy. I was able to prise off the transducer from the bed of silicon and it can be reused. If it was stuck on epoxy the transducer would be there forever. Some combine ES and log transducers and they need to be throught the hull

 

[Chris Durbin]

This thread got confused between the EM load and a normal depth transducer. You cannot stick the EM log to the inside of the hull.

Thanks, Paul. I suspected as much, it just seemed too good to be true! I imagine that's because the electrodes need to be in contact with the water. Otherwise, EM waves can pass through GRP with no problem.

 

[dukeofted]

Sorry for the confusion, I got confused between a depth transducer and a speed transducer. As has been pointed out, the speed transducer needs to be through the hull to work.

 

[tillergirl]

This won't help. I find my EM log works accurately for about 3 or 4 weeks before crud grows on it. I did once clean it (and most of my arm at the same time) but the wrong values continued after cleaning. I suspect it is very sensitive and any growing on the bottom ahead of the transducer upsets the flow.

 

[Andrew_Trayfoot]

I have the EM Log /Owna NMEA repeated running for 2 years now.
CopperCoated the transducer.
All has worked perfectly.