Bronze or plastic for transducers

[capn ken]

I'm replacing my depth sounder and knot meter with a dst multi sensor . Any thoughts on plastic vs Bronze ?

[Emmalina]

Nope just bronze is obviously stronger !

[Statistical]

Not a big fan of plastic. Not sure how it socially seems to get a pass for transducers when most people wouldn't consider a weak plastic thruhull for a seacock.

You can buy the transducer insert separate from the thruhull so bronze vs plastic is a small one time cost.

All this assumes you have a fiberglass boat. Not sure best practices for aluminum/steel.

[b_ohare]

Bronze as I just had this done.

My Airmar DST810 has never worked correctly (e.g., boat speed almost always reading 0 when in the water but when you take it out and blow on the paddle wheel, it registers speed; incorrect boat speeds when they show), even after replacing the transducer once. After speaking with Gemeco, they said they've seen a handful of situations where the plastic housing gets pinched thousands of an inch while in the water (i.e., under stress) and that might cause the faulty readings. I'm getting launched today with the new bronze housing (that won't pinch) so I'll report back if it doesn't fix the problem but they believe that's the issue.

[Dockhead]

Plastic is very widely used for this, and is generally considered to be fine. This is vastly less stress than a through-hull fitting.


I would caution against combined DST transducers if you have a place to mount a separate depth transducer. The consumer grade paddlewheel speed logs are bad enough without being further miniaturized to fit together with a depth transducer.

[Scorpius]

I would go with bronze. A friend's boat in Florida was hit by lightning. It travelled down the mast to the bilge, jumped to the depthsounder cable, and melted the plastic transducer housing. The remains of the transducer fell out leaving a 2" hole in the bottom of the boat. The boat sank.

[Statistical]

Originally Posted by Dockhead

Plastic is very widely used for this, and is generally considered to be fine. This is vastly less stress than a through-hull fitting.


I would caution against combined DST transducers if you have a place to mount a separate depth transducer. The consumer grade paddlewheel speed logs are bad enough without being further miniaturized to fit together with a depth transducer.

Have any recommendations for Speed only transducer that is N2K compatible. When I looked last didn't find much and went with a DST.

[Dockhead]

Originally Posted by Statistical

Have any recommendations for Speed only transducer that is N2K compatible. When I looked last didn't find much and went with a DST.

Airmar make a few of them:

Ultrasonic UST800/850
Paddlewheel ST800/850
Electromagnetic DX900+

The classic speed transducer, what the racers use, is the Signet Blue Top, but it's pulse only, not NMEA2000 (or even 0183).

I've had the UST850, the DX900+, the predecessor of the the UST850 which was the CS4500, and I have a Signet Blue Top on order.

I can't say anything about the DX900+ because it was DOA and I'm waiting for it to be repaired or replaced. It comes in either NMEA0183 or N2K and the 0183 version is supposed to work better, so that's what I ordered.

The old CS4500 was quite good, so far the best I've ever used. It was pulse only but interfaced through an Actisense adapter. It worked better than the UST850, which is OK-ish and what I'm using now since my old CS4500 died.

I have a B&G H5000 system which likes pulse and 0183 transducers and does elaborate calibrations including for heel, so I'll try the Signet with that when I get it. Then I'll decide whether I prefer that or the DX900+.

You may prefer a pulse or 0183 transducer because the plotter has more computer power than the N2K "smart" transducers. Or in my case, with an H5000, far more computer power.

Speed through water is the hardest sailing data to measure. It's complicated by the fact that the boundary layer of water is disturbed and doesn't flow in a linear relationship with boat speed. The non-paddlewheel sensors are supposed to be better because they are suppoesd to "reach" further from the hull into less disturbed water, but I have not yet found one which is really accurate yet.

With paddlewheel sensors you have the additional problem of the measurements changing as the paddlewheels gradually foul. You have to clean them often and calibrate them often, if you hope to get anything like valid data from them.

I keep trying because valid speed through water data is crucial to calculating true wind, which you need for laylines, target speeds, etc.

[Colin Stone]

I switched mine from plastic to bronze.

And a supplementary - how much water comes in past the internal tube flaps when the log transducer is pulled?? Mine is 1.1m underwater.

[Dockhead]

Originally Posted by Colin Stone

I switched mine from plastic to bronze.

And a supplementary - how much water comes in past the internal tube flaps when the log transducer is pulled?? Mine is 1.1m underwater.

Depends on how fast you are.



Mine doesn't have the flap. So there's a small geyser. I have never gotten over the terror of that moment.


The terror inspires to great speed, however, so it's usually less than a liter of water.

[meirriba]

Originally Posted by b_ohare

Bronze as I just had this done.

My Airmar DST810 has never worked correctly (e.g., boat speed almost always reading 0 when in the water but when you take it out and blow on the paddle wheel, it registers speed; incorrect boat speeds when they show), even after replacing the transducer once. After speaking with Gemeco, they said they've seen a handful of situations where the plastic housing gets pinched thousands of an inch while in the water (i.e., under stress) and that might cause the faulty readings. I'm getting launched today with the new bronze housing (that won't pinch) so I'll report back if it doesn't fix the problem but they believe that's the issue.

Sorry but it seems to me as a poor try to avoid the blame...
Anyway, most systems have an option to adjust the log speed output (or should have - our Raymarine using Airmar transducer does).
All I do, is adjust it to the GPS SOG in an area without current.

[Dockhead]

Originally Posted by meirriba

Sorry but it seems to me as a poor try to avoid the blame...
Anyway, most systems have an option to adjust the log speed output (or should have - our Raymarine using Airmar transducer does).
All I do, is adjust it to the GPS SOG in an area without current.

If it's reading 0, you can't calibrate it.


Not all problems with these -- and there are many -- can be solved with calibration.

[meirriba]

Originally Posted by Dockhead

If it's reading 0, you can't calibrate it.


Not all problems with these -- and there are many -- can be solved with calibration.

You are right of course.
But what is strange for me is the fact that it does work (even if the reading is inaccurate) when out of the hull.
So the OP should investigate what is blocking the paddle from revolving once inside its hull housing.
May be it does not stick enough out of the hull?

[meirriba]

Airmar triducers come packaged with a plastic throughhull.
I am using these, for the last 13 years, never had a problem with the through hull (had some issues with the triducer, not many but still...).
As to plastic in general, modern plastic ones (e.g. Trudesign) are strong enough for any purpose.

[SailFastTri]

Originally Posted by meirriba

Airmar triducers come packaged with a plastic throughhull.
I am using these, for the last 13 years, never had a problem with the through hull (had some issues with the triducer, not many but still...).
As to plastic in general, modern plastic ones (e.g. Trudesign) are strong enough for any purpose.

I agree. A fiberglass boat is fiber-reinforced plastic too.