B & G Sonic Speed, pulses per nautical mile

[Moonshadow]

Can anyone please tell me how many pulses per nautical mile are
delivered by the B & G Sonic Speed system.

 

[Steve Lusardi]

I am very curious why you ask. This system has been out of production for a long time now. I too am a fond user, so I am also
concerned about the availability of spares to keep it running. It is much more accurate than the impeller type because it measures
water velocity beyond the turbulent hull boundary layer and it won't foul and wear out as the impeller type does.. I hope you
realize that it is designed to produce the same pulse train rate of the conventional impeller, as the electronics beyond the speed
box are interchangeable. So it shouldn't be rocket science, once the impeller pitch is measured. Please post your findings when
you have them. Currently, Sperry Marine make a much more sophisticated version for ships. That system measures flow in both the x
and y direction and can have multiple sensors on the hull. Its purpose is primarily used to measure water currents when inshore.
Steve

 

[Moonshadow]

We will be using them to measure water currents past our jetty due to
passing shipping.

I am very curious why you ask. This system has been out of production
for a long time now. I too am a fond user, so I am also concerned about
the availability of spares to keep it running.

They are an old design, but we've just bought two so they are still
available.

I hope you realize that it is designed to produce
the same pulse train rate of the conventional impeller, as the
electronics beyond the speed box are interchangeable. So it shouldn't be
rocket science, once the impeller pitch is measured.

We don't have a conventional impeller to measure, and I can't find info
regarding its ppnm rate anywhere either.

Sperry Marine make a much more
sophisticated version for ships. That system measures flow in both the x
and y direction and can have multiple sensors on the hull. Its purpose
is primarily used to measure water currents when inshore.

Hmmm. Pity I didn't know about that earlier. Too late - I must use what
I've got.

Thanks for your comments.

 

[Steve Lusardi]

You couldn't afford the Sperry unit anyway.......it is very expensive. From your comment, I assume you don't have the rest of the
system (processor and display) How are you going to use it? I will find an impeller measure it and get back to you.
Steve

 

[Moonshadow]

Thanks Steve.

I will design and build a PIC-based interface which will deliver
NMEA-formatted proprietary sentences containing the current rates from
the two Sonic Speed systems. Others will organise for these data to get
to our servers via various boxes of tricks and WiFi. The data from these
will be logged, and probably be made available in real time via the
Internet.

 

[Paul]

Can anyone please tell me how many pulses per nautical mile are delivered
by the B & G Sonic Speed system.

The B&G "Network" paddlewheel puts out a nominal 6.25Hz per Knot (at least
6.25 Hz is the factory-standard calibration setting). That would work out
to 6.25 x 3600 = 22,500 pulses per nautical mile. This is very likely the
same paddlewheel sensor that the Sonic unit is emulating.

 

[Moonshadow]

Thank you Paul.

The B&G "Network" paddlewheel puts out a nominal 6.25Hz per Knot (at least
6.25 Hz is the factory-standard calibration setting). That would work out
to 6.25 x 3600 = 22,500 pulses per nautical mile. This is very likely the
same paddlewheel sensor that the Sonic unit is emulating.

 

[Paul]

Hi guys...

I have/need spares for a B&G Hercules 390 system.

I need to know if possible to interface Dataline/Simrad type speed
and depth transducers into the Hercules computer. Any input? The
post above might be very helpful for speed, what about depth signals??

Is the protocol similar between brands (esp of early 90's vintage)??

For depth sounders it's a lot more complicated. The transducer is a
piezoelectric element, often with a seperate temperature sensor. These are
both analog devices, at least the types I've seen. The electronics in the
display head (or possibly a central processor unit) send a high-power signal
in the high kilohertz range, then listens for the weak echo returned by the
bottom. It is possible to swap out the basic transducer if the frequency it
is designed for matches the old unit, but I don't know what the temperature
measurement interface looks like.

I've seen transducer frequencies of 50KHz and 200KHz, but I don't know what
frequency the B&G units use.