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Old 22-09-2021, 14:25   #1
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Need transducer advice - depth, in-hull

I've built a 30' cruising catamaran (Kurt Hughes design) and am finishing it hopefully this winter/spring. Knowing nothing but what i can find on the internet, I'm looking for advice on which depth transducer will work in my particular case.


The designer doesn't like thru-hulls for his reasons and thus I followed that advice. I followed the build of a trimaran on facebook where he cut through his composite hull and faired in a solid fiberglass patch and used a 3" diameter ABS pipe from hull bottom to above waterline, should the patch be compromised at a future date. So I did the same - seemed reasonable. Not sure what transducer he used, though. My photo shows the pipe forward in the starboard hull. The fiberglass is probably a bit on thin side.. 4 or 5 mm thick.


At this point I have no electronics in stock, except the vhf. I'm thinking of perhaps using raspberry pi for some stuff, maybe the sense-esp? boards for water and gas tank levels, etc. Can't afford a full blown chart plotter at this stage (hopefully later - still need basic running, standing rigging, sails, etc.) but for the depth, was considering something like a Maretron DSM410 display (good for displaying 2 depth soundings should I later install a transducer in the port hull as well), or a Furuno FI70, ala https://panbo.com/dedicated-depth-display-n2k-best-way/ If I could get the depth readings into wifi I could also see them from ipad/laptop type screens. The wiring perplexes me at this stage - most transducers I've seen have anywhere from 4-8 pins, and many cable connectors are proprietary.



So with that background, what I seek is a transducer that will fit down into the 3" ABS pipe - I can either glue it down or wedge it and fill with liquid and cap. I've been recommended the P79 but it looks like that top plate is too large in diameter on it - more than 3".. not sure. I've also heard that one could just use a thru-hull transducer (of less than 3" dia.) inserted into that pipe as well, but again I'm not sure and don't know which to try. Wiring would be great maybe to go into N2k, though maybe unless I go a proprietary display I would need the actisense dst? device to read the data. I'm good at following recipe style wiring to hook stuff up.


Sure appreciate it if you've read this. thanks! Jim





Image shows pipe for transducer just left of the hanging light bulb.
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Old 22-09-2021, 15:09   #2
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Re: Need transducer advice - depth, in-hull

Pretty nice work.

Tour through go2marine and Hamilton Marine and see if you find the transducer you want.

Really, for most purposes, what is marketed as a fishfinder and transducer is quite adequate. They will read to 600 feet and will show you a trend and something of the bottom composition. A cheap one without a bunch of bells and whistles is just fine.

Try this one at $110:

https://www.amazon.com/Garmin-Strike...s%2C231&sr=8-3

A chart plotter is pretty basic. If you're trying to contain costs, OpenCPN (free), a refurbished simple laptop ($150 or less) and a generic GPS antenna ($20) does the job. That's what I use, with only the addition of a small monitor ($110) at the helm.
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Old 22-09-2021, 15:18   #3
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Re: Need transducer advice - depth, in-hull

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Originally Posted by tkeithlu View Post
Pretty nice work.

Tour through go2marine and Hamilton Marine and see if you find the transducer you want.

Really, for most purposes, what is marketed as a fishfinder and transducer is quite adequate. They will read to 600 feet and will show you a trend and something of the bottom composition. A cheap one without a bunch of bells and whistles is just fine.

Try this one at $110:

https://www.amazon.com/Garmin-Strike...s%2C231&sr=8-3

A chart plotter is pretty basic. If you're trying to contain costs, OpenCPN (free), a refurbished simple laptop ($150 or less) and a generic GPS antenna ($20) does the job. That's what I use, with only the addition of a small monitor ($110) at the helm.

Thank you! The problem I have with some of these Strikers is figuring out what the dimensions of the transducers are that are included.. no pictures of it. I can do some more googling and maybe find out.
Oops... looked at the install manual and it looks like the transducer of the striker is not going to fit.
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Old 22-09-2021, 15:51   #4
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Re: Need transducer advice - depth, in-hull

I think you may be overcomplicating things. If your hull is FG and is not cored, you can put in almost any "in-hull" or "shoot-through" transducer. In fact, you can even run transom mount transducer puck by simply attaching it with toilet ring wax, epoxy or other similar compounds.

I run a CHIRP transom mount transducer in hull of the boat for both - depth and fish finding purposes. You can glue one in anywhere where the hull is not cored, uniform thickness, away from keel and has space. It's embedded in wax and I can remove , replace or move it easily.




Here it is marking fish

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Old 22-09-2021, 16:30   #5
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Re: Need transducer advice - depth, in-hull

As George SD describes, the in hull may work fine for you and trying out is easy without major changes or investments.
I have been using in hull depth finders for many years on different boats.
Any goo will do, the idea is to make sure the contact between transducer and Fiberglas floor does not have any air bubble that interfere with the transmission.
You can play with different locations until you find the best transmission site.
Many years ago like 25 years ago when people started to experiment they recommended having the transducer immersed in mineral oil , I tried and replaced it with regular drinking water and did just fine, my last transducer I applied used butyl tape, made a ball and flattened against the floor, applied the transducer with enough pressure and done.
I liked better than silicone, for obvious reasons, and not yet ready to commit to epoxy, may be will do in the future.
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Old 22-09-2021, 17:12   #6
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Re: Need transducer advice - depth, in-hull

I guess I wasn't clear in why I went to all the work of fairing in a fiberglass patch into the bottom of the hull. It is because if is a wood hull. It is probably about 1.5" thick at that point with wood hull, thickened epoxy and timber inside "keel".


I am looking for a transducer that will fit inside a 3" ABS pipe as I did state. I am hoping to be able to use whatever display I want, not a proprietary one - so maybe that is an unreasonable request. But it seems I should be able to find one that could be adapted to N2k or 0183 readability, even if having to purchase something like actisense-dts.


thanks for the replies! Jim
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Old 22-09-2021, 17:35   #7
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Re: Need transducer advice - depth, in-hull

Here's what I did in images. I fiberglassed the bottom of pipe before inserting it in the hole I drilled, then I fiberglassed over that and the hull on the outside, knowing that the glass to ABS join is weak. The pipe is also fiberglassed to the floor as well as the bulkhead should the glass on the hull bottom fail in some way.
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Old 22-09-2021, 17:52   #8
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Re: Need transducer advice - depth, in-hull

In another transducer thread, someone mentioned nasamarine depth packages. I took a look, and they have a cheap transducer that looks like it would work : https://www.nasamarine.com/product/d...7-metre-cable/ , and to get it working into nmea 0183 you have to go through some pyrotechnics: De:NASA Clipper Range – OpenSeaMap-dev . I'm a bit worried about the cheapness of the transducer and being able to figure out the openseamap wiki on it.. so still looking. But maybe something to fall back on.
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Old 22-09-2021, 18:30   #9
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Re: Need transducer advice - depth, in-hull

Hi
Please disregard everything I posted
does not apply
take care
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Old 22-09-2021, 18:36   #10
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Re: Need transducer advice - depth, in-hull

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Originally Posted by davil View Post
Hi
Please disregard everything I posted
does not apply
take care

Well, I appreciate all responses.. yours for instance I found interesting on the use of drinking water rather than mineral oil. I may use propylene glycol (antifreeze) as I live in freezing conditions... Also the use of butyl should I find myself in such a situation. It all adds value.
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Old 22-09-2021, 19:11   #11
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Re: Need transducer advice - depth, in-hull

Buy any old transducer that will fir your pipe, and fill it with propylene glycol....you’re done
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Old 22-09-2021, 19:27   #12
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Re: Need transducer advice - depth, in-hull

Quote:
Originally Posted by mlydon View Post
Buy any old transducer that will fir your pipe, and fill it with propylene glycol....youre done

Thanks.


You make it sound pretty easy. I don't live where I can go to any store or marina and look at transducers.. so my question would be mostly on wiring these up I suppose. Mostly I assume the old ones are proprietary so you lock into a display. I suppose I could do that - was hoping to get the readout into maybe N2k or 0183, but perhaps the proprietary way is how to go.. If only these systems would usually picture and dimension their transducers.
I won't sweat it.. if I hear more input great, otherwise this has been fun.
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Old 22-09-2021, 19:59   #13
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Re: Need transducer advice - depth, in-hull

Hunky - it is actually pretty easy. Go to airmar.com and look at their transducers - includes dimensional drawings.

https://airmar.com/productinfo.html?...T&name=Marine%

Most manufacturer’s transducers are actually rebranded airman’s - they just have proprietary connectors

The p72 and p74 look perfect for your application . The 74 is offered by cabella’s for just over $100

A raymarine itc-5 will take analog wind, speed, and depth t4ansducers and convert the signal to nmea2000 for you - I have had 2 of them in my last couple of boats and have been pleased with them. A much more cost-effective route. than buying ‘smart transducers.

Matt
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Old 22-09-2021, 21:30   #14
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Re: Need transducer advice - depth, in-hull

Ok, this is interesting. So there are plenty of transducers that will work for you. I personally would look at a "puck style" like the P79.

Having said that, we need to know more about your needs and plans. Here is why
- transducers have various levels of power, resolution, sensitivity. Decision on which one to go with depends on what you need it for.
- to what max depth do you want to measure?
- do you want fishfinder capabilities
- do you care about frequency range (some are better for deep water, some are better for shallow, especially if you want to use it as a fishfinder).
- the more powerful and sensitive ones are bigger
- the smaller and less powerful ones are much smaller
- any liquid will do, as long as there are no air bubbles suspended in it. This is why in many cases in-hull transducers come with their own containment box that gets filled with oil or antifreeze.
- the reason why oil or antifreeze are often recommended, is because water can go bad (bacteria gets in, starts to grow, it gets stale, etc). You want to use a liquid that you can leave there for a long time and not worry about replacing it.
- new transducers come with internal chip that relays information about what kind of transducer is in use (xID in airmark speak i believe). These need to be matched to your instruments as it's like a computer and driver for a specific device - if it can't recognize and doesn't have the drive for it - it won't work.
- transducers usually come with a brand specific plug/connector: Raymarine, Navico, Furuno, Airmar, Mix-n-match etc. Some can come with bare wire, but that's less common. Even within specific brand, the connectors will be different depending on which MFD or sonar box the transducer will need to be matched to. Sometimes you can cut off the plug and use bare wire to splice for a specific system, but if it is an XID transducer and the ID is not present in the MFD/Sonar box, then it may not work.
- high power transducers require quite a bit of power and often their own processing box for the best results. You can't drive them (provide enough power) from a basic depth instrument or a small, basic MFD.
- no contact with ocean water means no water temp readings or at least not very accurate ones (transducer element heats up when it works, so it will always read higher temp when not cooled by the passing water).


Here is what is very important for you - whatever you do,
+ the transducer needs to be horizontal, unless you want to meter what's ahead of you.
+ you need to ensure that there are no air pockets of any sort between the transducer and the water under the boat (no wood, no foam, nothing else)
+ transducer will need to be fixed somehow in your tube, so it doesn't move around.
+ transducer needs to be matched to a specific brand/device, unless you are going with NMEA version.
+ not all transducers work with all MFDs or depth instruments. Software and hardware needs to be compatible with a specific transducer. This means that you way want to go with NMEA if you want universally compatible unit (but will need a more advanced depth instrument that is networked) or you need to decide on the brand of your depth instrument AND MFD before deciding on a particular transducer.
+ location of the transducer is very important. You don't want it to slope, so you need to compensate for the deadrise. You also don't want it to come out of the water when boat is in rough weather and you want to ensure that the water flows without much turbulence under the transducer. If you have turbulent water and the transducer comes out of the water because of the chop - you going to see that it will be losing the bottom and or will have lot of interference.


I think a basic 50/200khz 600w p74 or p79 will both - fit and work fine for you. If you want a networked one - you can get a "smart p79". Keep in mind that you will need to run a wire all the way to the MFD/depth instrument or to the SONAR black box (depending on which route you go). There are some limits on the length of the cables, so you may want to look into this.

I would cut that tube down to where it's essentially flush with the hull on the inside. All you really need is a layer of fiberglass between the water and the transducer since it will be installed inside and does not require any holes.

Here is the bad news - the location you chose may not be good. It looks too far forward and on a slope. You want it closer to the keel (but at least 1.5-2ft in front of it). The goal is to ensure that the installation location is always in contact with the water and the flow is undisturbed.

One more thing - P79 and many other "in hull" transducers are actually 2 piece units. It's the transducer puck itself and the enclosure that you glue into the hull and then fill with liquid. So the p79 is not as big as the enclosure you see in the picture.

Good luck
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Old 22-09-2021, 22:53   #15
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Re: Need transducer advice - depth, in-hull

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Originally Posted by George_SD View Post
Ok, this is interesting. So there are plenty of transducers that will work for you. I personally would look at a "puck style" like the P79.

- to what max depth do you want to measure?
- do you want fishfinder capabilities
- do you care about frequency range (some are better for deep water, some are better for shallow, especially if you want to use it as a fishfinder).

I would cut that tube down to where it's essentially flush with the hull on the inside.

Here is the bad news - the location you chose may not be good. It looks too far forward and on a slope. You want it closer to the keel (but at least 1.5-2ft in front of it).

One more thing - P79 and many other "in hull" transducers are actually 2 piece units. It's the transducer puck itself and the enclosure that you glue into the hull and then fill with liquid. So the p79 is not as big as the enclosure you see in the picture.

Good luck

Thanks much for all the info - very good to know and I'm sure others will benefit as well. You've given me some homework.. some things to chase down I hadn't really considered.



My images in the previous reply don't give a good sense of location in relation the whole hull. Attached shows the placement a bit better.. The location is still visible just forward of the foam blocks.



To address some of your questions and comments, for one I have looked at the P79 - and in the attached image where the arrow labeled "Transducer" is pointing, it looks like that top flange is larger than 3". The flange that looks knurled, but has the angles embossed on it. If that can be removed, then it would fit. Or ground down.. I just don't know never having seen one.


Your first couple questions: My cruising grounds (Norton Sound of the Bering Sea) for now barely get deeper than 100'. If/when I take the boat down to "better" cruising grounds south, then it would probably be only a matter of when I get off or on the coastal shelf. Fish finding would be handy, but wasn't sure I could ask for so much. As I get to know the boat, fishing would be a good excuse to get out on the water.. there's halibut out there as well as cod, pollack, king crab, etc.. salmon of course. So I just don't know... maybe some more research for me. I suppose this would give an indication of my concern about frequency.. something else I'm a bit unaware of. I see it listed for various transducers, but haven't paid much attention to it.


On the other hand, I have been reading various threads and sources about transducers, so am aware of the need not to have air bubbles/pockets, angles of the unit, etc. and installation methods.



I made the pipe the length it is to keep the top of it above the water line. I suppose I could cut it down to height of transducer and put a water tight cap on it, but as for flush - I want a few miles under the boat before I trust the glassing job. I'm sure it is fine, but there's always nagging thoughts.


All in all I think it would have been easier to go thru-hull. But for now it is what it is.


The last image is how things are looking lately.. not the same hull, but shows the bottom paint which is Pettit Trinidad HD - a 53% copper load if that is going to matter.
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