Appreciate opinions from anyone using fish finder / sonar. Currently dropping anchor is like roulette not knowing bottom conditions, stones, logs or sunken boat. It would be nice to see on screen condition of the sea bed or river before dropping anchor and pray that anchor not be lost if wrap, dig in without possibility of retrieval .
Budget is not big for unit .

A fishfinder will be cheaper and have more features.
The cheapest models on Whitworths/Anaconda/BCF are $230 to $249. They will display depth, temperature and voltage, and compared to depth sounders, fishfinders will provide a running display/diagram of the water profile, showing fish or weed in the water column, but more importantly will show whether the bottom is hard sand or mud with soft mud underneath that, as the echoes penetrate different layers. They usually have a shallow alarm and a deep alarm and night lighting. These 2 alarms are when you want to navigate between 2 depth contours, say on a gently sloping 90-mile beach I sailed between 15m deep (about half a km offshore) to 25m deep (which was usually about 10km offshore). On a rocky coast, the seabed rises more abruptly, so this feature does not give as much prior warning. The night light was reassuring on some lonely nights.

My FF sensor is mounted inside the hull, and goes through about 15mm of fibreglass, It is mounted on a bed of silicone or mastic.
And in terms of your anchoring, if you know the depth, you have an idea of how much rode to put out. You also have a graphic display of the contour, because there might be a drop off section of the sea bed.

I'm not a sailor - yet spend a surprising amount of time on this particular forum.
I do, or have done, a lot of fishing, and like my electronics.
The transducer is likely going to be the biggest issue. Like the fabulous Phill has done, yachts seem to be regularly done 'through hull' in a bed of silicone - but need to be careful not to have bubbles in the silicone/mastic, as it can throw the signal.
Question is - what is "not a big budget"?
The $250ish units will do the job, most likely. My concern would be the transducer going through hull.
If you can extend into the $500-$1000, you'll get a unit with a bigger screen, more functions (like basic chartplotting), and more importantly, a more powerful transducer. Looking at the Lowrance units, which is what I use, the 5" Eagle also has an SD slot for waypoints etc AND updating the software. The downscan imaging is lightyears better than the standard sonar on the $250 units.
Those units are heading towards $600 on sale. Prices will go up from there, surprising rapidly, for larger screens etc.

eagle 4 at bcf for 200 bucks...

Cripes don't drill a hole in the hull - if I have interpreted right that this is a potential action please don't do it. Assume you have a solid glass hull layup. So epoxy or other suitable glue a pvc tube to the hull inside just fwd of the mast. The tube chamfered so it is oriented straight down vertically. 1/2 fill with glycerine. Put the through hull transducer in. Cap it off at the top. Job done. I have done this. It worked perfectly. Glycerine fill the 1/2 tranducer height at least. Some polyurethane adhesive sealants also work with just transducer alone.

R13 - I've always understood the term 'through hull' to mean that the transducer is sending the signal through the hull, not that the transducer itself extends through the hull? Our Fabulous Phill appears to be supporting this, in that "sensor is mounted inside the hull" and is "It is mounted on a bed of silicone or mastic". I understood the statement "goes through about 15mm of fibreglass" to mean that that the signal is transmitted through the 15mm of fibreglass, not that the transducer itself is physically installed through 15mm 'glass?
I don't think anyone is suggesting drilling a hole in the hull. If there was going to be any holes drilled, it'd make more sense to mount it off the transom.

And I can see my poor communication: "My concern would be the transducer going through hull."
To clarify, that would be "My concern would be the transducer signal going through hull with weaker transducer". Apologies for the poor comms there.

Depth sounders are mounted inside a hole cut into the hull. On runabouts they are mounted on a bracket at the transom, but then you have the problem of screwing them there and the attendant leaks.
In practice, placing a sensor inside the hull, with no hole, works. Just sit it on a bed of silicone or mastic or similar liquid/gel, just like ultrasound for pregnant women. Perhaps the signal is slightly weaker, but you could always get a better/stronger FF.
In practice I find my cheapest-model FF works extremely well.

I mounted mine on silicone and it didn't work very well, ended up mounting it in a well of water and it's fine , I think that the silicone was of the wrong density for the distance between the transducer and hull .

Appreciate all info and advice.
My biggest worry is that not knowing seabed configuration i might hook on something where i might cut my anchor chain ( happen before ), as I'm unable to retrieve it.
Last week I drop in nice place on Brisbane River but i could see that when tine changed my position with relation to shore didn't look good.
Power up and go sideways to the current. Yep, the boat stop abruptly pulling now down. Luckily i was able to pull my anchor up but it was struggle finely release with shruder.
Probably some concrete or other solid stuff on the bottom.
Would fish finder show seabed configuration and if some structure on choosen spot ?

Would fish finder show seabed configuration and if some structure on choosen spot ?

Yes.
A fishfinder will show a flat bottom, an undulating bottom, a drop off on the bottom, a large rock or coral head, a structure like the remnants of a pier, a wreck, and a large submerged log or tree.
It will not show a cable or low profile object like a flat concrete slab.

The Brisbane river has flooded so often that there is sure to be debris in the areas that are not dredged, so basically closer to shore where people would like anchor.
To use the fishfinder to be certain that the chosen area (in the Brisbane river) is clear, you would need to do a good sweep north to south and east to west. I am not confident that you would have the room to do that if other boats are around. In the end there is a bit of luck involved.


I used electrical/plumber/ frig mechanic's putty to mount transducer. No problem.
Gary

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damned67 said..
R13 - I've always understood the term 'through hull' to mean that the transducer is sending the signal through the hull, not that the transducer itself extends through the hull? Our Fabulous Phill appears to be supporting this, in that "sensor is mounted inside the hull" and is "It is mounted on a bed of silicone or mastic". I understood the statement "goes through about 15mm of fibreglass" to mean that that the signal is transmitted through the 15mm of fibreglass, not that the transducer itself is physically installed through 15mm 'glass?
I don't think anyone is suggesting drilling a hole in the hull. If there was going to be any holes drilled, it'd make more sense to mount it off the transom.

And I can see my poor communication: "My concern would be the transducer going through hull."
To clarify, that would be "My concern would be the transducer signal going through hull with weaker transducer". Apologies for the poor comms there.

Ok, apologies, my bad.

I installed my Fish Finder / Depth sensor in the bow of my boat on a bed of Vaseline. No way I would add another hole in the hull. Bow location is important if you are sneaking into a bay and want as little water under the keel as possible for swimming or fishing. The bow sees the changes in the depth and bottom first. So it "looks" through the 1mm of Vaseline and 1" of GRP. Its worked perfectly since 2010. We can see fish, the fish size, bottom contours and what the bottom actually is. It can also see through the top layer sof sand and show the rock below if there is any. Cost at the time was $300, monochrome. Its absolutely invaluable for anchoring.

Great advice everyone , appreciate. Just place order for Garmin vivid fish finder 4cv.

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r13 said..

Ok, apologies, my bad.

No need to apologise! My communication was unclear. Plus, I'm regularly wrong.... just ask my wife.

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Jolene said..
I mounted mine on silicone and it didn't work very well, ended up mounting it in a well of water and it's fine , I think that the silicone was of the wrong density for the distance between the transducer and hull .

I mounted mine in a bed of silicone (Lowrance Triple Shot) ensuring no air bubbles. Pretty much used the whole cartridge to make sure the bottom of the transducer was entirely bedded in the silicone. Down low in the solid layup. Works perfectly. Tested it in a plastic bag of water first.

I used a two part liquid silicone and poured it into the well around the transducer submerging it.
Ended up with a very weak signal. Replaced the silicon with water and it works perfectly. May have just used the wrong silicone, I just figured that water was probably less compressible so I stuck with it.

Before any permanent transducer mounting, put it in a plastic bag part filled with water with elastic band round the top where transducer cable exits. Move the bag to different locations inside the hull to identify where the transducer is best located.

I reckon using silicone to internally mount a transducer is wrong because a transducer emits and receives sound waves. The silicon would absorb too much sound there by dulling the echo sounders return signal.

I have used silicon only to create a dam, then fill with water to test the hull suitability at that point. Place the transducer in the water to guage its sensitivity particularly at the depths you prefer to sound.

I have in the past then used epoxy resign to flow in that same puddle of test water with great results.

I now have fitted a multibeam transducer under the bow with a small diameter tube through the hull for the 2 cables. I now know which side to steer to stay in a river channel as I have a 3D sidescan image and a depth profile to see the depth trend changes.

Its all rather expensive but nice to have. Years ago yacht depth sounders (only displaying digits) were 3 times the price of fishfinders which show bottom hardness, sand mud, weed, rock as well as fish all in a nice graph like image with big digits that also only required a glance to know if it was trending deeper or shallower. Mine also measures the water temp which also helps to know where the East Coast current eddies might be on a comparison to the satellite ocean temperature images from the BOM, (Manly Hydraulics Lab issued those previously)

Hope all that helps in the understanding of what you can achieve with sounder technologies nowadays

Very interesting re multibeam transducer and 3D image. Something like this?

chsmith.com.au/Products/Lowrance-Simrad-Structure-Scan-3D.html?srsltid=AfmBOoq3qbxqDtQUdt3vfesrspBDvuB7hhDys1jtEqnFP25B-IKrzjfq

I am digesting the capabilities now - can these give a "forward view" plot of depth which would be incredibly useful when sailing at speed in areas subject to large depth changes and shifting mud flats. I see some can view 180m out to each side - so assume this would also be able to do 180m forward?

That's the one I have. No it doesn't look forward but gives results when tight turning.
They come up 2nd hand for half the price occasionally.

Any system that looks or pings forward in theory sounds good but in practice unless you're travelling really slow, your response time to back out is too late. Explore instead by dinghy.

As far as I know all sounders only log what you have passed over.

You can't beat a person up on the spreaders spotting ahead for coral or reefs in clear water.
Has anyone found a camera or flir thingy up the mast useful?

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Ambler said..
That's the one I have. No it doesn't look forward but gives results when tight turning.
They come up 2nd hand for half the price occasionally.

Any system that looks or pings forward in theory sounds good but in practice unless you're travelling really slow, your response time to back out is too late. Explore instead by dinghy.

As far as I know all sounders only log what you have passed over.

You can't beat a person up on the spreaders spotting ahead for coral or reefs in clear water.
Has anyone found a camera or flir thingy up the mast useful?

Great thanks, much appreciated. A lidar system could do it................spendy............

www.commercialuavnews.com/international/teledyne-flir-introduces-lidar-payload-camera-platform-and-more-at-auvsi-xponential-2023