Triducer not flush, is that ok?

[Pub911]

I bought a new triducer and as luck would have it, it fits perfectly in the sleave where my old speedometer was - well,almost.

Everything matches, inner tube diameter, threads for the locking cap, everything but the tube length. The old tube is about 3/16" too short, leaving the outboard end of the triducer proud to the hull surface by the same amount. FYI, this is an ARIMAR DST800 I'm talking about, and it's reusing the sleave of an antique Datamarine sending unit. Fear not, I checked the seal under pressure and it holds.

It this ok? The only think I can think of that might cause me an issue is if the paddle wheel will give true boat speed. Will the fact that the cylinder sticks out a tiny bit create turbulence and throw off its callibration?

Is there anything else anyone can think of that may cause issue?

Thanks!

Thoughts.

[artbyjody]

Depending on your display ability to adjust.


It being shorted/longened means more of a vortex of water at higher speed and I doubt you can calibrate to compensate for it. Thus means higher hull speed - the more inaccurate the speed reading will be (forget calibration at this point). It may be nominal - the only thing you can do is sail and try to figure out of there is a difference.

[r.furborough]

Airmar manufacture these items in different lengths and the difference, apart from the turbulance already mentioned could affect
a) the position of the O-Rings for the water seal.
b) the location of the hall effect device for the speed wheel in relation to the pick-up in the housing.

Here are the Airmar part numbers and specs...

Thru-Hull, TRIDUCER® Spares
20-752-1 (B744V, B66V) 6.81” / 173 mm
20-752-3 (B744VL, B66VL) 9.20” / 234 mm
20-178 (B44V) 6. 32” / 161 mm
33-122 (B44) 5.55” / 141 mm
33-125 (B55) 5.62” / 143 mm
33-127 (B56) 7.65” / 194 mm

[Pub911]

Interesting....

There's more to this story. I bought the Garmin-branded unit online after consulting with AIRMAR asking if Garmin's branded product would talk NMEA 0183 to my Raytheon Chartplotte, which they confirmed.

When the part showed up, I assembled it - putting the triducer into the supplied plastic tube. It slipped in just fine, but the business end of the unit was not flush at the outboard side of the tube - it was RECESSED by about 3/16". I dismissed it, knowing I was going to try to reuse the existing sleave already installed in the boat from a prior Datamarine speedo.

I didn't want to force it to make it flush, so I didn't word too hard to make it flush in the supplied tube, but I did heavily hand-tighten the supplied cap, so that should have done it.

Now I'm thinking, could I have been sold a sensor unit that is incompatible with the supplied tube?

Do you have a x-reference of the part numbers above to the different models of the dst800 (e.g. plastic vs. SS)?

[sailingdog]

One other issue is if you hit the triducer against something, like in a grounding or collision with underwater object... it could damage the triducer or worse—pop the triducer through the hull and lead to your boat flooding.

Originally Posted by Pub911

I bought a new triducer and as luck would have it, it fits perfectly in the sleave where my old speedometer was - well,almost.

Everything matches, inner tube diameter, threads for the locking cap, everything but the tube length. The old tube is about 3/16" too short, leaving the outboard end of the triducer proud to the hull surface by the same amount. FYI, this is an ARIMAR DST800 I'm talking about, and it's reusing the sleave of an antique Datamarine sending unit. Fear not, I checked the seal under pressure and it holds.

It this ok? The only think I can think of that might cause me an issue is if the paddle wheel will give true boat speed. Will the fact that the cylinder sticks out a tiny bit create turbulence and throw off its callibration?

Is there anything else anyone can think of that may cause issue?

Thanks!

Thoughts.

[Pub911]

I thought about that...and I suppose there's an increased chance given the ridge, but the risk is not eliminated even when flush, no?

I know what you're saying though...why play with fire. It's just so enticing to simply screw it in, wire it, and be done. taking the old threaded tube out and dealing with the sizing issues above in the parts received are going to be 2 hassles I'd rather not deal with.....of course, at the expense of sinking? No.

thanks all.

[sailingdog]

The risk is greatly reduced when the triducer is flush, since the impact has to hit the triducer much more precisely...if the triducer sticks out, the chances that it gets hit and breaks the through-hull tube is much, much greater.

Originally Posted by Pub911

I thought about that...and I suppose there's an increased chance given the ridge, but the risk is not eliminated even when flush, no?

I know what you're saying though...why play with fire. It's just so enticing to simply screw it in, wire it, and be done. taking the old threaded tube out and dealing with the sizing issues above in the parts received are going to be 2 hassles I'd rather not deal with.....of course, at the expense of sinking? No.

thanks all.

[r.furborough]

Originally Posted by Pub911

Interesting....

Do you have a x-reference of the part numbers above to the different models of the dst800 (e.g. plastic vs. SS)?

Enter 'DST800' into this page for model and wiring information AIRMAR Cross-Reference Interface

This is Gemeco's PDF catalog, more information can be found here, this is where the initial cross reference information is found. http://www.gemeco.com/PDFs/GEMECO_2009_CATALOG.pdf