Ultrasonic speed sensor. Any good?

[runningman]

Speed through the water. We want it!

Our floating condo currently has a conventional paddlewheel log sensor and I'm thinking of upgrading to an ultrasonic speed sensor to avoid the fouling/not working/maintenance issue. One of these will fit/connect to my Garmin NX2 display http://www.nexusmarine.se/products/marine-instruments/transducers/ultrasonic-speed-sensor/

I've heard/read differing things - some say they work, some say they don't work so well. Does anyone have any practical first hand experience of fitting and using an ultrasonic speed sensor instead of a conventional paddlewheel log sender unit?

 

[pvb]

I'm thinking of upgrading to an ultrasonic speed sensor to avoid the fouling/not working/maintenance issue.

Have you tried antifouling it 2 or 3 times a year? Doesn't take long.

 

[FWB]

I've had my ultrasonic speed transducer since 2004. A Raymarine one, presumably Airmar. It's fit and forget just like the depth transducer. I guess the only reason why people fit paddle wheels is the cost, but over the years the cost is not significant.
For the first 2 years of the launch of the boat I had an Echopilot ultrasonic transducer. It wasn't reliable and I changed it for the Raymarine one, but this was back in 2002-2003.
I was told that the underwater profile of the boat is a factor in how good they are. My boat is long keeled and the speed readout appears to be extremely accurate.

 

[mixmaster]

We have a B&G ultrasonic. 21 years and still working (all fingers crossed).

 

[johnalison]

I had a Seafarer "electronic" sensor back in the '70s which worked fine. I think there was a B&G version before that. It wasn't ultrasonic but detected movement by some clever trickery. I don't know why they didn't catch on.

 

[mjcoon]

I think there was a B&G version before that. It wasn't ultrasonic but detected movement by some clever trickery.

Perhaps it was magnetohydrodynamic. Maybe didn't work well in fresh, poorly-conducting water?

Mike.

 

[runningman]

Thanks all.

On the basis of the replies I'm going to bite the bullet and go for the ultrasonic sensor. I'll post feedback on its performance in due course for anyone interested.

 

[Blue Sunray]

Thanks all.

On the basis of the replies I'm going to bite the bullet and go for the ultrasonic sensor. I'll post feedback on its performance in due course for anyone interested.

That would be good as I for one am interested in what does seem like a good idea,

 

[pmagowan]

That would be good as I for one am interested in what does seem like a good idea,

+1

 

[runningman]

I finally got someone to quote me a price for a compatible ultrasonic speed sensor. £995. WTF!!! Then an email arrived with another price of £1099 + VAT.

That's put the kibosh on it. I expected the price to be quite a bit more than a conventional paddlewheel log transducer but I hadn't expected those figures. So I have Plan B and Plan C:

Plan B is to stick with a conventional paddlewheel log and curse the damn thing when it fouls up and stops working, again, and again...

Plan C is to rip the damn thing out and glass up the hole (one less to worry about) and then just rely on GPS SOG (yeah, I know!)

What would you do?

 

[pvb]

What would you do?

What I said in post #2 - antifoul the impellor and housing 2 or 3 times a year. I use Trilux on mine.

 

[FWB]

Depends upon how long you intend to keep the boat. I can't remember how much mine was, prob £500-600 twelve years ago. It has been worth every penny.

 

[marklucas]

Let's look back at the problem.

What is my speed through the water?

And then ask do I really need to know it?

 

[runningman]

Let's look back at the problem.

What is my speed through the water?

And then ask do I really need to know it?

Don't know.

Yes, preferably.

 

[runningman]

What I said in post #2 - antifoul the impellor and housing 2 or 3 times a year. I use Trilux on mine.

As it happens, I have an as yet unopened can of Trilux 33...

 

[pvb]

As it happens, I have an as yet unopened can of Trilux 33...

It's easier to do it if you just take the axle out so you can paint the impellor separately from the housing. Lightly sand all parts before antifouling.

 

[runningman]

Depends upon how long you intend to keep the boat. I can't remember how much mine was, prob £500-600 twelve years ago. It has been worth every penny.

That was a lot of pennies twelve years ago and a lot more pennies now. 100+% more in fact!

As much as I dislike paddlewheels and all the negatives that go with them, an ultrasonic log will have to remain some way down the 'would like to have' list, unless the price drops substantially. Interestingly, the price of ultrasonic logs has gone up quite a bit over the years, not come down, as most new tech seems to. Must be a marine thing...

 

[runningman]

It's easier to do it if you just take the axle out so you can paint the impellor separately from the housing. Lightly sand all parts before antifouling.

Noted. Thanks.

 

[maxi77]

I presume you are looking at doppler logs. The big problem is they use rather expensive technology compared to a paddlewheel. Very many years ago NASA produced one but it had little success. Big ship ones are very common and very accurate and dual axis ones are used for docking very big ships. I have heard of people using pipe flow meters but have no personal experience of this. They work by measuring the doppler shift in sonar echoes reflected from particles in the water a few meters from the hull. This gives a 'true' water speed where as paddle wheel types are affected by the water being 'dragged ' along by the hull. Some can also 'bottom lock' to give true ground speed.

 

[lydiamight]

Have you considered buying one in the USA? These people http://www.p2marine.com/marine-electronics/airmar/airmar-cs4500-speed-transducer.shtml are selling them for less than £450.00 even at today's poor exchange rate. Even with a bit of delivery and VAT its got to be cheaper than the prices you have been quoted