Chart Plotters for Dummies?

[Bull City]

Hi Bull City - I'm just curious if you tried that test that I suggested in your original thread yet.

I may give this a shot with the current transom-mount transducer.

Epoxy? You could coat the transducer with mold release.

Yes it seems like that should work acoustically. You could also set it in bilge water possibly.

If I decide to try the Garmin in-hull transducer, I'll probably try it out with a plastic bag of water between it and the hull. If that works under power, I should be good to go. If not, screw it, I'll stick with what I have.

Garmin should let you select the transducer. The EchoMap 4" comes with GT-20 transom-mount. I would have paid extra for the in-hull if that was an option. If the in-hull works, I'll have a $100 transom-mount for a door stop. It's stupid.

 

[S35]

I may give this a shot with the current transom-mount transducer.



If I decide to try the Garmin in-hull transducer, I'll probably try it out with a plastic bag of water between it and the hull. If that works under power, I should be good to go. If not, screw it, I'll stick with what I have.

Garmin should let you select the transducer. The EchoMap 4" comes with GT-20 transom-mount. I would have paid extra for the in-hull if that was an option. If the in-hull works, I'll have a $100 transom-mount for a door stop. It's stupid.

I doubt Garmin (or any other manufacturer) would support this claim, but I highly suspect that the only difference between the in hull, and transom mount transducers are how they mount (internally, I bet they are the same).

I think that the main advantage of a proper in-hull transducer is that is is designed to accommodate carious slopes/ angles in the interior hull form.

You definitely want the transducer pointing straight down, otherwise you won't be able to pick up the return signal as the water gets deeper.

S35

 

[ProaSailor]

It's stupid.

With all due respect sir, you know what sounds stupid to me?

"It is mounted in a glob of wax from a toilet seal kit inside the hull"​

 

[billsreef]

Maybe there is something other than toilet wax that could be used? Epoxy? You could coat the transducer with mold release. Or maybe the toilet wax residue will serve as mold release.

I am totally spitballing here. No expertise in this area.

In the days before anyone made a dedicated "in hull" transducer we just epoxied them inside the hull. The tricks were, no core, and no air bubbles. Always worked, though sometimes the no core part was a lot of work.

 

[Bull City]

With all due respect sir, you know what sounds stupid to me?

"It is mounted in a glob of wax from a toilet seal kit inside the hull"​

Two things:

1. I was a little harsh to characterize Garmin's lack of choice in transducers as "stupid." They obviously sell a lot of stuff, and make some nice things.
2. A couple of other anarchists have used a transom-mount as an in-hull, and one used toilet seal wax. Experimenting with that method cost very little. It didn't work 100%. I think calling it "stupid" is harsh.

 

[ProaSailor]

I think calling it "stupid" is harsh.

Yes, but I was using your word for Garmin's policy, which you say now "was a little harsh". More than a little, I would say. How would you characterize not following the manufacturer's installation guidance and then asking why it doesn't work?

Same goes for this proposed "fix" you mentioned, unless you got this advice from Garmin?

I'll probably try it out with a plastic bag of water between it and the hull.

 

[Bull City]

I doubt Garmin (or any other manufacturer) would support this claim, but I highly suspect that the only difference between the in hull, and transom mount transducers are how they mount (internally, I bet they are the same).

I think that the main advantage of a proper in-hull transducer is that is is designed to accommodate carious slopes/ angles in the interior hull form.

You definitely want the transducer pointing straight down, otherwise you won't be able to pick up the return signal as the water gets deeper.

S35

I suspect this is why I lost the signal in deeper water. The transducer is pointing a bit forward.

 

[Bull City]

Yes, but I was using your word for Garmin's policy, which you say now "was a little harsh". More than a little, I would say. How would you characterize not following the manufacturer's installation guidance and then asking why it doesn't work?

Same goes for this proposed "fix" you mentioned, unless you got this advice from Garmin?

Proa, I don't want to get into a pissing contest about this. I experimented, and it didn't work for me.

As for the plastic bag of water, it is an accepted way of testing a location for an in-hull transducer. IIRC, Garmin suggests it.

 

[J_Grove]

ha! just as I suspected!

I wouldn't worry a lot about the transducer pointing "a bit forward". Sure you want it as straight down as possible, but a sailboat heels (your mono a lot more than my tri), so not looking straight down is a common state and it should still give you reliable depth.

So I slightly disagree that the main advantage of an in-hull is that it can be mounted straight down - I think it's more important that it can be mounted solid against the hull without gaps. (BTW there are other major differences between the transducers - the P79 I'm 99.9% sure you are going to end up using is not an imaging transducer). You have a solid fiberglass hull so shouldn't have any issue with core, so it's just a matter of matching the angle on the P79 transducer to the angle of your hull by rotating the transducer. There is also a flange for this that I didn't end up using. Just google "P79 transducer installation instructions" and this will be clearer. Instructions also describe the water bag test, but I don't know if I would completely trust the result if it came back negative. How reliably can you hold an angled transducer/flange against the angled hull when its in a bag of water? Anyway, there is middle ground between the plastic bag and epoxy is to install with a small amount of silicone. Silicone is actually what the instructions call for anyway, and is what I used. If it turns out that it doesn't give you good signal, clean up the silicone and try to return it. If it does work, reinstall with the full amount of silicone.

One other thing. Once I was sure my new P79 transducer was working correctly with the old 4" echomap, I moved ahead with buying the new 9" echomap UHD. As it turned out, the cheapest option was to buy it on sale from West Marine packaged with the GT-54 transducer - also a transom mount - it was cheaper than buying the chart plotter alone. I managed to sell the transducer for $175 on eBay. You're unlikely to get that much for a GT-20 but you'll get something with only a minor hassle factor.

 

[fufkin]

I once tried to chase down the cause of air getting into the fuel lines, gave up, got a mechanic from the yard who was stumped, got an off site mechanic who came highly recommended, who was stumped, almost gave up and then he finally noticed that a bulkhead mounted fuel pump was ever so slightly loose.

Three turns of a screwdriver and the problem was solved.

I haven’t read this whole thread so apologies if I don’t have the location of the transducer right. If it’s close to the engine, which I think it is (?), sure it could be EMI but there’s the remote unscientific possibility that plain old vibration is the culprit.

If you end up installing a proper in hull transducer, move it away from the engine and to a more traditional location further towards the bow.

My one and a half cents.

The other half cent is...a few years ago I was considering upgrading the sun faded read out on my Tri Data. A new one would cost 500 bucks or something. The boatwright who helps me with certain stuff was of the opinion that it was a waste of money...spend a full boat buck, get a multi use chart plotter(I can’t remember the brand). He mentioned, ‘you can just get your depth from gps and you don’t really need a transducer...’ to which I replied ‘yeah but it’s barely accurate to 50 feet(location not depth)’, to which he didn’t even bother answering but just gave me a quizzical look. He’s world class, has about as much modern and traditional experience as one person is likely to possess in both boat building and sailing. Anyway, the faded tri data is still there, the 40 year old transducer is still there and working, and the old girl is still floating.

If and when I modernize my electronics, the transducer will probably be scrapped and the last remaining original hole in my boat filled.

 

[Bull City]

I talked with the electrician a few days ago, and he thinks the problem is that we're using the transducer as an in-hull and it's not designed for that. The experience of dipping the transducer over the side, and having it work under power suggests to him that the problem is not EMI-related.

I sent an email to Garmin Support relating what we have done (including the wax mounting details), hull thickness, etc., and asked them what in-hull transducer do they recommend, can I test it (in a plastic bag of water) and return it if it doesn't work, and how should I install it, given the approximate dead rise angles.

Quote Reply

 

[Bull City]

Garmin recommended their GT15M-IH, an in-hull transducer, which I ordered and now have on hand. Going to test it tomorrow. Fingers crossed!

 

[Bull City]

As they say, "Back to the drawing board..."

I tested the Garmin in-hull transducer today, in accordance with their methodology, and the signal failed when I ran the pod drive, even at low speeds, just like the transom-mount unit stuck in wax.

It certainly seems to be EMI. I added a ferrite bead to the data cable - no luck.

I give up.

 

[El Borracho]

The drive must emit EMI in the sonar band. 50 or 200 kHz? Do they make both?

 

[Jim in Halifax]

Bull, do you know any Ham Radio operators? Those guys are often wizards at tracking down and eliminating interference.

 

[Bull City]

Bull, do you know any Ham Radio operators? Those guys are often wizards at tracking down and eliminating interference.

Actually, I was just talking to a friend who is a sailor and a Ham guy. He didn't have any ideas, but maybe there are others who do.

This problem is a disappointing, but not the end of the world. I can just shut off the motor to inspect the bottom for stumps or snags.

I really don't want to pay someone to chase down EMI rabbit holes.

The drive must emit EMI in the sonar band. 50 or 200 kHz? Do they make both?

That's interesting. Here is the info on the transducer:

TRANSDUCER FREQUENCY CHIRP Mid-band (85-165 kHz)
TRANSDUCER POWER 600 W

How can I find out what the pod drive is doing?

 

[El Borracho]

That's interesting. Here is the info on the transducer:

TRANSDUCER FREQUENCY CHIRP Mid-band (85-165 kHz)
TRANSDUCER POWER 600 W

How can I find out what the pod drive is doing?

Wow, high tech. That might be more immune to interference…or less.

Perhaps a traditional sonar would work better. What a drag for you. We used to call this the “bleeding edge of tech.”

To evaluate the EMI from the pod you will need to find an RF engineer, or like written above an amateur radio expert geek, with a suitable test instrument.

Or use a 0.02 Hz lead line.

 

[Panoramix]

Bull, do you know any Ham Radio operators? Those guys are often wizards at tracking down and eliminating interference.

I wish North Carolina was closer as I find this intriguing. Not saying that I would definitely sort it out but I would definitely come to have a go. In the local (to here!) ham club I think of 2 people who would quite likely sort it out for a bottle of wine! There are lot of hams in the US @Bull City if you search, you might find one that can sort it out, you need the kind that spends lot of time building radios and antennas or bringing back to life old gear.

 

[Panoramix]

Actually, I was just talking to a friend who is a sailor and a Ham guy. He didn't have any ideas, but maybe there are others who do.

This problem is a disappointing, but not the end of the world. I can just shut off the motor to inspect the bottom for stumps or snags.

I really don't want to pay someone to chase down EMI rabbit holes.
That's interesting. Here is the info on the transducer:

TRANSDUCER FREQUENCY CHIRP Mid-band (85-165 kHz)
TRANSDUCER POWER 600 W

How can I find out what the pod drive is doing?

To find out what the pod is doing you need a spectrum analyser. 10 years ago you would have needed to sell a few kidneys to get one but nowadays you can have good enough performance for less than 100USD (google tinySA).

If you still have energy for trialling something, I would try to shield the cables which are between the controller and the motor. They are likely culprits as there are square waves in there (rapid on off signals which are bad for EMI) and temprorary shielding can be as simple as kitchen aluminium foil that you wrap around and then ground carefully (to the sea via the pod?). If that works you can invest in some metallic sleeve designed for RFI shielding (google EMI shielding sleeve) that you would also need to ground.

 

[J_Grove]

I run the Garmin P79 transducer that I recommended to you a couple of weeks ago at 50 KHz with my Echomap. It's not CHIRP so no imaging stumps with it. Ha, Garmin now calls it "entry level" in their Transducer Guide, but it reliably provides depth so works for me. Don't have any idea if it is any less subject to your problems (my guess is that Garmin tech support doesn't either) but it cost less that the one you have now if you are up for one more hail Mary. You did the test-in-a-bag-of-water trick so you could return it, right?

edit: you can pick up a used one on eBay for $50 or less.