Ultrasonic speed/log/depth

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Gwylan

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I'm fed up with my paddle wheel log and having to clean it to remove all manner of sea creatures that see it as a great place to hide, breed, get a free ride.
It seems to make sense to go for an Ultrasonic log, speed, depth gizzmo.
Anyone got experience? Are they worth it?
Appreciate any input on experience, makes, suppliers etc
 
I have a Raymarine Ultrasonic log fitted to my boat. It has been on for over 4years and works flawlessly. However Raymarine were amazed to hear this. The model I have has been replaced, since it apparently did not work properly on AWB. My boat is long keeled.
A good place to find one is
JG Tech scroll down to AIRMAR, and a quick google will find other links.
 
I was given a Garmin 160C fishfinder for Christmas which I have yet to fit, but it would appear to do what you want AND give you a picture of the bottom as well. Mine came with a transom mounted transducer, but some here have said that it can be bonded inside the hull OK.
 
I would be supprised if it does. The 160C can show speed if equipped with a speed capable sensor, which costs more than the fishfinder does (last time I looked)
 
Just scuttled off to check - you are right - mine is depth and temperature - Oh well!
I was considering getting pukka in-hull transducer in the States in a month or so anyway - if its any cheaper.
 
Not making much progress here chaps!
Await response from JG Tech
Need some real help to avoid a season of nearly running aground and not knowing how far we have gone anyway!
 
Well sorry!
OK - so if you can't afford the transducer then no more ultrasonic suggestions....

but you could try the pitot tube principle....

Stick yer face in the flow with your mouth open and have someone hold a bucket for you to pee in - once you've calibrated the pee/distance ratio you're laughing!
 
Frankly, that's nearing the anatomically impossible.
There is an established technique for counting the time it takes as the bubbles trail away behind the boat, but it sort of breaks down above about 6 knots. Though I might breakdown if the boat ever gets over 6 knots through the water.

Not to mention the difficulty that might be encountered laughing and peeing into a bucket at the same time. Who holds the stopwatch?

How do you compensate for difference in pressure between the early morning rush and pre bedtime drain? Do you have to hold the bucket on the end of the boat hook and hold the boat hook at different distances depending on the time of day, or number of pints consumed?
I can see endless hours of making calibration curves and compensation tables for accounting for the wind direction.

Is wee magnetic, other than to your salopettes when peeing over the stern? Another correction

Not really thought this one through have you?.
This not the level of constructive suggestion I might reasonably have expected from such a learned forum.
 
I occasionally sail on a 1987 built 40 ft with top of the range (then) B&G ultrasonic log. It doesn't seem to have ever given any trouble.
I find it amazing that other manufacturers of logs still stick with paddle wheels. Certainly here in Perth (Oz) a paddle wheel will foul after just a day or 2 with warm water and very keen crustaceans. I gave up on paddle wheel long ago.

An ultrasonic log should be fairly simple (fool proof) with a transmitter transducer mounted forward of a receiver transducer aft. The frequency shift of the signal as transmitted from one to the other via the water is directly related to the water speed.

Why can't we buy one at reasonable cost? (Compared to a GPS which does it all and more.) olewill
 
You are quite right, I feel I have sullied the hallowed cyber-ground /forums/images/graemlins/frown.gif

So here's another method that involves fully immersing your head for significant periods of time.

Vortex shedding frequency - often used in industry for flow measurement, though not perhaps so directly as my next proposal:

The faster your head travels through the water the higher the frequency at which your ears will flap.

Downside is of course, again it has to be calibrated for your particular ears.
I suggest most comfortably achieved by suspending by a rope from the end of the boom by your ankles. Some form of accellerometer or counter will require to be clipped to your ears too.
/forums/images/graemlins/wink.gif
 
Despite my obvious flippancy above - pitot or vortex shedding or even ultrasonic (doppler shift) methods you would have thought should be widely available, instead we usually opt for a cheap and cheerless electro-mechanical device.
I mentioned my fishfinder earlier and had my bubble burst (thanks Mobydick!), but assuming one has a speed facility,I'm not sure how it measures speed, one transducer, or per your description.
I had assumed it ranged whatever returned an echo and calculated speed by the distance moved between echo returns.
 
Now that looks like an interesting site.

Which one have you got?

My (Stowe) depth sounder is getting a bit tired, and the thought of buying a new transducer that also double up as an untrasonic log....

Presume the combined transducers need to be upright?
 
Mine is original Raymarine. I think the Airmar ones are the only ones now,best to ring JG Tech for the right one for you.
 
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