Depth sensor in "foot"

[Calypso Poet - CR38 #116]

Hi All

I am starting to put together the "list" for a planned maintenance haul-out later this year, and as I dont have a speed log on the boat, I will be installing a new DST type sensor on the boat.

The current depth sensor is at midships on port side. With the curve of the hull - even with a -22 degree sensor - i feel that depth info when heeling is never really accurate, and installing a speed log at the same spot, will make speed just as bad.
My boat (hull #116) has a sensor - I presume the original - in the "cut-out" in the forward part of the keel though that is not used, and I think this would be a much better place to install the new sensor.

Question is however, how do I get to this thing? Any info or guidance on how to get to it to take it out. What is the arrangement of that original sensor - how is it mounted? Can I install a thru-hull sensor in it's place without making any modifications?

Thanks

Pete

[N C]

Pete,

Having the depth sounder at the forward cut-out makes the most sense and a zero degree angle installation seems to be the most logical. Getting into real shallow waters is always "dicey." Having the depth sounder at the cut-out to alert you a little sooner than one located amidships may save you from a potential grounding. My speed sensor, the paddle wheel type, is located amidships and seems to be fairly accurate even when heeled over. (I find I'm always comparing the GPS speed over ground with the paddle wheel anyway). I replaced my transducers with retractable ones that give you the ability to replace them without having to haul the boat out of the water. It's a nice feature especially if your transducer begins to malfunction during a trip. They come with a blanking plug. Does the new combination transducer that you are looking out make mention of installation location for the speed sensor?

I have a hatch in the forward cabin that gives easy access to the depth sounder. Different models or production periods may have changed ease of accessibility. It may be the reason why your transducer at the cut-out was never replaced. 

The diameter of the hole through the hull is pretty standard for the transducer so you ought to be able to swap out the thru-hull with relative ease. You may want to measure it beforehand just to be sure. Also,  make sure that the new transducer is long enough to go through the hull and have enough exposed thread to enable you to put on the washer and locknut. Changing out a through hull is relatively easy, other than wrestling with the bonding material. I've never used de-bonding agents so I can't speak for their effectiveness. I used a heat gun to warm up the old thru-hull and wiggled it out with a pair of channel lock plies. Once out, clean all of the old bonding material off of the hull. Apply the new bonding agent, install the new thru-hull and have an assistant out side to prevent it from spinning while you tighten down the washer and locknut from the inside. Tighten it down as recommended in the installation guide, don't over tighten it. The actual transducer itself has an O ring on it and just slips into the thru-hull and is locked down with  plastic nut. There should be some tabs on the locknut for seizing wire.

Hope this helps.

Good Luck,

Nick,

CR 38 #190 "RONIN"

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[Alex Tarlecky]

We installed a DST-800 long stem in the forefoot last year. The paddlewheel quickly stopped working and it turns out this particular device has quality problems. The depth and the temp still work fine and that is enough for us. We don't really need water speed anyhow - just SOG.

We also have a ST model on the port side which we don't even have in. Its been plugged since we installed it. 

If anything.... I would want a panoptix in the forefoot.

[Chuck Batson]

My vessel came with a thru-hull-less depth sounder. There's a plastic tube that's bonded to the interior of the hull, in which there's a small pool of liquid (water?). The depth sounder then screws onto the top of the tube, such that the transducer element is bathed in the pool water. Presumably the acoustic waves just travel through the hull. I don't have any experience with how accurate it is - there's also a traditional thru-hull depth sounder, and that's the one that's wired to the display at the helm. I haven't yet looked to see where the thru-hull-less one is wired.

There's also now solid state speed gauges. Still requires a thru-hull, but there's no paddlewheel to get fouled!

Chuck

[Tom Fuhs]

Hey Alex, how were you able to fit the DST-800 long stem into the fore-foot location.  The original transducer (a Radarsonics transducer seen here: http://www.radarsonics.com/Model_205.htm) had a stem that was less than an inch in diameter.  The DST-800L  stem is 2" in diameter.  Were you able to bore the existing hole out?  Was the new mushroom head over sized for the flat in the fore-foot?  If the DST-800 will work in the fore-foot, that would be good news for me as it would simplify my planned install a bit.  I had been planning to use the existing Radarsonics transducers with an Actisense DST-1 module.  The DST-1 will run the transducers and give NMEA-0183.  Then I'd need a NMEA-183 to NMEA-2000 converter to get the data on the ships NMEA2K bus.  If I can fit the Airmar DT-800L in the fore-foot location, that would be best. The DT-800L is like your DST-800L, but without the speed  paddle wheel.  I'd use a separate speed paddle wheel 'ducer further back on the hull.

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[Alex Tarlecky]

Tom,

I had the yard install it when my DT-800L was fried from lightning... so I can't say for sure if they widened it. However, I don't believe so as I was there and didn't see or hear them drill anything. They did punch out the old tube and replaced it with the one that came with the sensor. They used an air tool wrench to get in where it was hard to reach to screw it down tight. There are many many variations available of these DT/DST. I went through Gemeco to find the right replacement since they are the main national distributor for almost all these sensors (Debbie Sullivan - dsul...@gemeco.com)

And here is the model I used...

airmar-nmea-2000-transducer-dst800l-235-n2-44-166-1-01

I wouldn't bother again. I haven't used my speed sensor since it failed and I have not even used the other speed sensor either. GPS handles all of that. 

- alex

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[Alex Tarlecky]

BTW - the sales front that Gemeco recommended to me for all these parts:

https://www.blueheronmarine.com/

On Thursday, May 25, 2017 at 8:23:01 AM UTC-4, Calypso Poet - CR38 #116 wrote:

[Tom Fuhs]

Alex, so from what you wrote, it sounds like there was already a DT-800L installed in the forefoot, and you had it replaced with a DST-800L. It makes sense that there would be no drilling necessary since they have the same housing. Your boat is about the same age as mine, so it likely had the same skinny stem transducer in the forefoot. Perhaps a PO replaced it. Did your boat still have the Datamarine instruments when you bought her?  If she had the NMEA-2K transducers and instruments when you bought her, The PO must have done the switch and drilled the forefoot. Did the mushroom head fit ok on the flat of the forefoot, or did the edges hang over a bit?  

  -Tom

Sent from my iPhone

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[Alex Tarlecky]

Yes, same datamarine instruments. I guess when we originally installed the DT-800L its possible they widened the hole - that was also done by the yard.

There is plenty of room for the mushroom head. There is also maybe 1.5" or more of fiberglass so if you wanted to countersink an instrument I bet you could. If I had my way I would use a chirp sonar with a long stem instead of the DXX-800L for all the reasons why fishfinders and sonar are so useful. 

If I had given all my through hulls more forethought I would have countersunk ALL them to make them flush when I replaced them.

- alex