TiggerToo
Well-known member
I seem to remember somthing like this existed: has anyone had any experience?
paddle-less speed probe
- Thread starter TiggerToo
- Start date
AlanPound
Member
B&G did/does a "sonic speed" and "microsonic speed" sensor. Basically an arrangement whereby sonic tx and rx transducers are set in such fore & aft positions that sonic pulses must pass through a volume of (relatively) moving water to get from one to t'other... Speed must be figured by timing, I guess (no Fitzgerald/Lorenz contraction in respect of sound, I suppose).
Sounds like a good idea (no paddlewheel to get fouled up...)
My boat was fitted with one when I got it... It was broken, and it's function had been replaced by a paddle-wheel sensor, so I guess it wasn't *that* good!
(We spend 2 years trying to find the depth sounder transducer... both in and out of the water... Previous owner didn't know where it was, builder didn't know where it was - well, they both thought they knew where it *should* be! In the end we took the boat apart to try and trace the cabling, and lo and behold, that cabling went to the microsonic speed device too! It appears it was a dual function device! DUH...)
Alan
Sounds like a good idea (no paddlewheel to get fouled up...)
My boat was fitted with one when I got it... It was broken, and it's function had been replaced by a paddle-wheel sensor, so I guess it wasn't *that* good!
(We spend 2 years trying to find the depth sounder transducer... both in and out of the water... Previous owner didn't know where it was, builder didn't know where it was - well, they both thought they knew where it *should* be! In the end we took the boat apart to try and trace the cabling, and lo and behold, that cabling went to the microsonic speed device too! It appears it was a dual function device! DUH...)
Alan
G
Guest
Guest
Doppler ...
Pressure ... (Pitot)
small impellor job via bike speedo cable !! (VDO etc.)
Pressure ... (Pitot)
small impellor job via bike speedo cable !! (VDO etc.)
pvb
Well-known member
rob2
Active member
There is a standard Airmar ultrasonic unit which mimics a paddlewheel by giving the standard number of pulses per kilometer. The part number is CS4500, it measures speed and temperature.
There is also a combined paddle wheel and sonar unit DST800 which sounds like what you have!
Measures speed, depth and temperature.
Try Googling "Airmar" and you can check out the possibilities! The European HQ is in the Netherlands and they are great at answering queries in English!
There is also a combined paddle wheel and sonar unit DST800 which sounds like what you have!
Measures speed, depth and temperature.
Try Googling "Airmar" and you can check out the possibilities! The European HQ is in the Netherlands and they are great at answering queries in English!
AlanPound
Member
Can't think Doppler would work - any frequency shift caused by putting the sound into the water would be exactly compensated for on reception.... But transit delay would work...
I think a pitot approach would be dodgy too - that works by pressure difference between a forward facing pitot head, and a sideways facing "static" port (as on an aircraft). I have a feeling that given the relatively high density of water, the relatively low forward speed though the water, and the relatively huge pressure variations due to wave motion, the differentials would be all over the shop...
Alan
I think a pitot approach would be dodgy too - that works by pressure difference between a forward facing pitot head, and a sideways facing "static" port (as on an aircraft). I have a feeling that given the relatively high density of water, the relatively low forward speed though the water, and the relatively huge pressure variations due to wave motion, the differentials would be all over the shop...
Alan
G
Guest
Guest
Doppler and Pitot are used on many ships and other craft ... with good results ..
You will find that many US based mobos have pitot heds fitted to transoms for speed ...
You will find that many US based mobos have pitot heds fitted to transoms for speed ...
AlanPound
Member
Ahhh - doppler, with sound shot forwards, then reflected off the bottom should work...
jwilson
Well-known member
Used a Doppler-type log on a boat back in the 70s: can't remember the make, but worked by reflecting sound of tiny particles of algae/creatures/mud suspended in the water near the sensor. Seemed to work Ok, and didn't get fouled - my current paddlewheel averages 2 days before getting slow, unless you keep moving continually.
pappaecho
New member
Seem to remember that Seafarer made a doppler based log.Also seem to remember that it only sort of worked
G
Guest
Guest
old ones were really unreliable ...
Doppler log uses 2 layers to work ... and you can switch between on older sets a water boundary layer so many metres down ... or in shallow water the actual bottom .. can't remember the depth that the layer is - but its like a thermal boundary in the water ....
Doppler log uses 2 layers to work ... and you can switch between on older sets a water boundary layer so many metres down ... or in shallow water the actual bottom .. can't remember the depth that the layer is - but its like a thermal boundary in the water ....