Electromagnetic log transducer.

[doug748]

I see Nasa have a new transducer on the stocks:

https://www.nasamarine.com/product/electromagnetic-log/

Not a fresh idea, there have been a number over the years but none has caught on, being thought unreliable and certainly expensive. At £159 this might be a winner; it's said to fit the de facto standard 50mm tube and work with any "compatible" 0183 display.

 

[johnalison]

I had a Seafarer version in the 1970s, with a dial readout. It worked very well indeed for many years, though the readout dial broke itself just before I sold the boat. It was far better than the rubbish Navico paddle-wheel on my next boat. I even managed to get the needle against the 10 knot stop in my 26-footer on one occasion. I've always wondered why they didn't catch on. I believe there was a B&G version that preceded the Seafarer.

 

[Ladybirdgaffcutter]

Thanks Doug748, I will be putting an order in, fed up with paddlewheels.

 

[Seajet]

I think the main reason the original ones didn't catch on was one had to be very careful with antifoul; a very good navigator I know rated his Seafarer job excellent.

It did require careful calibration and is still in the boundary layer flow close to the hull so requires respect and a little caution.

Anything is better than a paddlewheel, totally unreliable, likely to clog with wee beasties or weed and vulnerable to the slings when the boat is lifted, if people forget to withdraw them.

I don't understand why people bother with the things, what with the hole in the hull, they're of no use for navigation as I discovered with another boat I had.

 

[mainsail1]

That is good news....if it will integrate with Raymarine etc. kit.
I gave up on paddlewheel instruments years ago and rely on GPS based SOG.

 

[wizard]

You will soon know if its a good idea when all the other manufacturers follow suit.

 

[pvb]

Airmar and NKE have offered electromagnetic sensors for ages. Rather more expensive, but also more sophisticated.

 

[Sandy]

You will soon know if its a good idea when all the other manufacturers follow suit.

Garmin have had one for years. I'm fitting one this summer. NMEA 2000 though. It also gives the water temperature so I will need even less convincing not to go overboard.

 

[GHA]

I see Nasa have a new transducer on the stocks:

https://www.nasamarine.com/product/electromagnetic-log/

Not a fresh idea, there have been a number over the years but none has caught on, being thought unreliable and certainly expensive. At £159 this might be a winner; it's said to fit the de facto standard 50mm tube and work with any "compatible" 0183 display.

Certainly looks interesting, ta for the link.
Not so sure about the blurb though...

the control box converts the sensor signal to boat speed, trip and total distance and sends it to any compatible NMEA-0183 display.

Do such nmea0183 sentences exist?

 

[Ladybirdgaffcutter]

I think the main reason the original ones didn't catch on was one had to be very careful with antifoul; a very good navigator I know rated his Seafarer job excellent.

It did require careful calibration and is still in the boundary layer flow close to the hull so requires respect and a little caution.

Anything is better than a paddlewheel, totally unreliable, likely to clog with wee beasties or weed and vulnerable to the slings when the boat is lifted, if people forget to withdraw them.

I don't understand why people bother with the things, what with the hole in the hull, they're of no use for navigation as I discovered with another boat I had.

You need to know your distance run *through the water* for a few things, so I venture to differ on the last bit.

 

[pvb]

Certainly looks interesting, ta for the link.
Not so sure about the blurb though...

the control box converts the sensor signal to boat speed, trip and total distance and sends it to any compatible NMEA-0183 display.

Do such nmea0183 sentences exist?

Yes, VLW is the distance travelled through the water, and VHW is the speed through the water. The Nasa's "control box" presumably remembers the total distance travelled; the trip distance is reset every time the power is switched off.

 

[GHA]

Yes, VLW is the distance travelled through the water, and VHW is the speed through the water. The Nasa's "control box" presumably remembers the total distance travelled; the trip distance is reset every time the power is switched off.

:encouragement:

Happy to be corrected ta, had a look on here and everything. http://www.catb.org/gpsd/NMEA.html

Must try harder pre posting

 

[doug748]

Thanks Doug748, I will be putting an order in, fed up with paddlewheels.

Good work. It says available first quarter so you may have a bit of a wait. Let us know how you get on.
It will be on my "to do" list for next year, all being well.

 

[johnalison]

:encouragement:

Happy to be corrected ta, had a look on here and everything. http://www.catb.org/gpsd/NMEA.html

Must try harder pre posting

If all else fails, distance through the water becomes an essential tool. I still have my Wlker log but no means of attaching it to my current boat. A paddle wheel should give a tolerably accurate reading of distance but there is one caution. This is that a distance log must not under-read because therein lies the way to go aground and disaster. You therefore need to have a good feel for whether the log is recording the right speed or not. My current one is pretty good; it either reads correctly or way out, but you don't want the log to read 5% low if relying on it to make a landfall.

 

[DownWest]

The one time I used a Walker log, it showed almost exactly the straight line distance between the departure and destination, over five days. Despite one morning finding that the line was slack and 'something' had bitten off the spinner. Fitted the spare, but had no idea how long it had been missing. All night?

Actualy have a Seafarer log kit in the shed. Replaced that and the Seafarer depth sounder recently in a friend's boat. Think I will use the depth in my current little build, but no use for the log.

 

[LittleSister]

I used to like the electric trailing log that I had on a previous boat. Seemed pretty accurate; didn't get fouled up because it was out of the water unless under way; looked like it might be at risk of get caught up in the prop or rudder in reverse, but never did.

The only downside was that people would attract my attention to warn me I had a rope trailing in the water!

 

[GHA]

; didn't get fouled up because it was out of the water unless under way; looked like it might be at risk of get caught up in the prop or rudder in reverse, but never did.

Makes such a mess when it gets caught in tbe fishing line though :disgust:

 

[Seajet]

I used to like the electric trailing log that I had on a previous boat. Seemed pretty accurate; didn't get fouled up because it was out of the water unless under way; looked like it might be at risk of get caught up in the prop or rudder in reverse, but never did.

The only downside was that people would attract my attention to warn me I had a rope trailing in the water!

That would have been a Stowe; how did you get on recovering and coiling the line / cable ?

I imagine a lot less handy than my Wasp trail log I still deploy when out of the Solent, when off watch below I could tell our progress by the gentle thrumming sound through the coaming, a very handy bit of kit for going west / cross Channel even with GPS.

 

[johnalison]

That would have been a Stowe; how did you get on recovering and coiling the line / cable ?
.

They don't take kindly to being reversed over. A friend of mine who was a bright chap found that out.

 

[LittleSister]

That would have been a Stowe; how did you get on recovering and coiling the line / cable ?

I imagine a lot less handy than my Wasp trail log I still deploy when out of the Solent, when off watch below I could tell our progress by the gentle thrumming sound through the coaming, a very handy bit of kit for going west / cross Channel even with GPS.

It was a Stowe. (I'd forgotten the name.) Recovering and coiling the line it was easy. I can't imagine how it would be easier.

I still have one, not in active use, that I picked up at a boat jumble, and have used it a couple of times to check the accuracy of suspect through-hull paddlewheels.

I was interested years ago to read about a tiny Autonnic one, where the trailing spinner (autocorrect tried to say sinner! ) was small enough, it was said, to drop down through the cockpit drain. (I've got what I think may be an Autonnic log instrument head (fixes to pushpit rail) - it came with a boat I bought - but doubt I could find the trailing bit these days.)

They don't take kindly to being reversed over. A friend of mine who was a bright chap found that out.

When I first got mine I was very nervous of that possibility, but after having forgotten several times to haul it in before reversing without a problem, I eventually got blasé about it and never really bothered. It never did come to grief. (It was off to one side, though, as I trailed it through one of the stern quarter fairleads.)