What are these things?

[Bigjim]

I'm replacing my wind, speed and depth sensors and instruments and made some progress last weekend.

I removed two dead sensors from the hull and installed my new speed sensor.

There were two sensors attached to the inside of the hull but had no thru-hull. I'm assuming they are depth transducers, but why two of them? Anyone have an idea why there are two? Sender and receiver?

[Cheechako]

Many boats have two. One may have been a fishfinder. I have had two a few times. The fishfinders read very deep. I will say though, I usually separated my two, usually one near the bow, even though it was reading at a bit of an angle it gave good trending data.

[Bigjim]

Originally Posted by Bigjim

I'm replacing my wind, speed and depth sensors and instruments and made some progress last weekend.

I removed two dead sensors from the hull and installed my new speed sensor.

There were two sensors attached to the inside of the hull but had no thru-hull. I'm assuming they are depth transducers, but why two of them? Anyone have an idea why there are two? Sender and receiver?

I doubt it was a fish finder, this is from a sailboat...

[Jammer]

Originally Posted by Bigjim

I doubt it was a fish finder, this is from a sailboat...

It is possible that one is the "new" and one the "old" that was abandoned in place when the "new" was added.


If they were both used at the same time, as posted upthread, it is likely that one was used for a depth-only device and the other was used for a "fishfinder." The "fishfinder" is useful for more than finding fish, as it provides clues to bottom composition and presence of structure, both important when anchoring.


Though less likely, it is also possible that they used different frequency ranges. There's a good article here on the reasons for that.

[Bigjim]

The depth finder was not working when I bought the boat, so it is a mystery as to what either one did.

They are both very heavy and dense. One had wires connected to it, the other had one wire and a thin plastic tube. It looked like they were not installed at the same time because they used different methods of adhering.

[OS2Dude]

We have an in-hull depth transducer, and it looks nothing like those. With the threaded rods, I wonder if someone tried to used a thru-hull transducer as an in-hull. Our sailboat has only one transducer, a 'fish-finder' type as it gives an image of the bottom conditions.

[Scorpius]

They look like abandoned depth sounder transducers. I'd say previous owners installed a new transducer each time they installed a new depth sounder and simply abandoned the old ones rather than removing them, filling the holes, etc. And I expect you are right: the one with the threaded rod was supposed to be installed through the hull - but that's more work and involves a haul-out - so they just glued it on the inside of the hull. When it didn't work they abandoned that one too and installed another one, this time perhaps properly.

I have two because we have an awful lot of rock around here and I always want to know the depth. If one fails (which happened last summer) I don't want to be in the dark while I try to fix it or install another.

[Cadence]

Originally Posted by Bigjim

The depth finder was not working when I bought the boat, so it is a mystery as to what either one did.

They are both very heavy and dense. One had wires connected to it, the other had one wire and a thin plastic tube. It looked like they were not installed at the same time because they used different methods of adhering.

Can them and go with new. They look ancient and if you have no readout connected to them?I would guess they have just been left.