Depth Sounder Transducers

In finalizing the electronics for our new Ocean Alexander 54T, I'm struggling with the choice between "through-hull" and "shoot-through" transducers.* We are only using our sounder for depth, not for fish finding.

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I'm told the "shoot-throughs" loose accuracy beyond a few hundred feet or will not read accurately through*a silt/soft bottom, however I*like the idea of reducing another*hole in the hull.

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I would love to hear others experiences..

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I agree with the fewer holes the better. I haven't used a thru-hull myself but from my experience as a Merchant Marine, the margin of error is negligible. N.O.A.A. surveillance ships typically use a thru-hull set up for accuracy as do most of the other ships I sail on but these are steel hulls. I never had a problem with my shoot thru hulls nor did I ever feel they were alarmingly inaccurate when compared to a chart.

I have not been to the factory.* With limited time off right now, we decided we'd rather take the time it would have taken to visit the factory and use it on the boat when it gets here.* It's due into Norfolk, VA the end of June.* O/A has been sending us pictures about once a month, so we've followed the build pretty closely.

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It is has twin John Deere 6068*M3.* The hull is solid fiberglass, the finish is a combination of gel coat and Awlgrip.

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Below are a few shots of it under construction as well as a few of a finished model like ours.

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Thanks for the other thoughts on the through hulls.* After several boats, I can't say I've ever had a problem with a through hull transducer either, but this boat is going to see a lot more open ocean than our previous ones, so I'm trying to be more conservative.

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Yes*it has*ABT TRAC stabilizers on it.

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The hull is a semi-displacement hull but I did not plan on pushing the boat to 16-18 knots.* I wanted a 8 1/2 to 9*1/2 knot cruise with a top end of 12 to 13*and I wanted the fuel efficiency of smaller engines.* CAT does not make a small Tier II compliant engine, so John Deere became the next most logical choice.* I also noticed Deeres in most of the Kady-Krogens and Nordhavn's runing around the globe, there had to be a reason these manufacturers/owners kept using them.

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Here a few shots of the bottom.* These are not of my boat, but they are of the same model.* These are photos they sent me when I wanted to see the bottom when still deciding to buy it.

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This is an Ed Monk Jr. Design, he and O/A did a lot of tank testing on this hull, especially*on the*bow bulb and prop tunnels.



-- Edited by Just Bob on Saturday 14th of May 2011 06:21:38 PM


-- Edited by Just Bob on Sunday 15th of May 2011 10:07:36 AM

Is there a way to move a thread as this would be good on the O/A page under brands.

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Yes this is the "S" hull.* Several folks have tried bow bulbs on this size boat boat they have not worked well.* Monk and O/A think they've overcome the problems with this design, I sure hope they're right.* We did fairly extensive sea-trials before deciding to buy.

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We*made K-K and Nordhavn comparisons early on when still deciding on a displacement or semi-displacement hull, but once we decided we did not need the full displacement hull they fell off the list.* I think they're both fine boats but we're not doing trans-oceanic crossings but rather extensive coastal cruising.

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Which O/A do you have?* O/A just signed up a dealer in the Mid-Atlantic and Newport RI so they are just now starting to get some attention on the East Coast, there are not many of them around here.* O/A is better known on the East Coast from there ads for their motor-yachts more than they are for their great line of mid-size cruisers that are so plentiful on the west coast.

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Our boat will be in Trawler Fest Baltimore and The Annapolis Boat Show, both in October.* The dealer hopes to draw some attention to it.

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"We are only using our sounder for depth,"

Then a recording unit that will measure while still on the on the shelf in the brown water will do what you need , as well as being a navigation backup .

Personally the "I hate holes in my boat" religion is easy to understand , however I have never heard of a properly installed bronze thru hull putting a boat at risk.

IF you are running with no charts , the front looking sonar might be a better choice, Going up the Amazon?

"I hate holes in my boat"

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So do I which is whats fueling this struggle.

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"I have never heard of a properly installed bronze thru hull putting a boat at risk."

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Nor have I but if I can get accurate readings with a shoot-through than why do it.* Which goes back to the original question, can I rely on the shoot-throughs?

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"If you are running with no charts"

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Wouldn't hit the start button without them!

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"Going up the Amazon?"

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I'm blessed to have an adventuresome 1st Mate, but that would probably push the limits.

Where I cruise, anything that works down to 20 feet is all I need -- two fishfinder transducers epoxied to the hull, one for the flybridge and one for lower helm.

It would seem to me that questions about thru-hull vs. in-hull transducer would be best addressed by the manufacturer. And I would want more than one if I were counting on keeping that $$$ yacht off the rocks!

The shoot through solution will work just fine as long as you are just dealing with a straight beam. For simple depth - no problem. The thing is the transducer can not be allowed to have any air between it and the hull. Sound does not transmit though air well enough to be of any use in this application. Mineral oil in the box that the transducer is mounted in will not evaporate. Water will need to be topped up regularly.

The difference in readings will exist. It will be constant. It will be so small that it will not have any effect. In other words it may be off by about a couple inches no matter the depth of water.

You will have interfaces of a transducer to the mineral oil, mineral oil to fiberglass,(maybe fiberglass to any core, core to fiberglass), fiberglass to the water. The only possible problem is the interfaces from fiberglass to core and core to fiberglass. As long as there is no air between any interface - no problem. As long as it works initially it should not ever give you a problem. If you did not get a good response initially the location would need to be changed. If the boat is in the water you can use some plummer's putty to build a dam around the area you want use and flood that with water to see if you get a reading on the bottom. I doubt that you will have any problems.

Thank you very much for your thoughts on this!

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The hull is solid, so there is no "core" issue.**The unit I had in mind is the Airmar M260 http://www.airmartechnology.com/uploads/brochures/M260.pdf* which is filled with propylene glycol to address the other interface issues you raised.

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So with all this in mind, one of the other comments was to have redundancy, with which I agree.* My original*concept was to have one "through-hull" and one "shoot-through".* So now I question - do I get two Airmars?

Redundant and share the spares is my way of thinking.

Nor have I but if I can get accurate readings with a shoot-through than why do it. Which goes back to the original question, can I rely on the shoot-throughs?

In a word DEPTH.

THe shoot thru will work just fine if not touching the bottom is the reason for the sounder.

IF you desire depth readings while still on the shelf DEEP is required.


Be sure the yard epoxies the edges of the cut hole , preferably with thickened epoxy ,

rather than praying some goop like 5200 might seal the laminate.

I have not proved this, but using the transmitting of sound theory has no reason to believe that depth would be a problem. The attenuation of the small distance of fiberglass is so minimal as to be a non factor. The frequency of the transducer will have the noteworthy affect on the depth readings. Dual frequency transducers take care of this.

I understand you are not looking to use the sonar for fishing, however the technology is developed with "fishing money" and hence good fishfinders typically are good depth sounders.
Personally I did some research on this topic and found that the M260 is a VERY good solution.
If you want redundancy i would get two of these units.
IMHO no reason to drill holes in the hull, technology have prevailed.

Thank you all for your experience and comments, they have been very helpful.*

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I'll send a picture of the installation, then let you know how they're working.*

I have 2 shoot thru sounders at the moment, and at least 3 thru hull transducers from obsolete or dead sounders. I have good returns to 1000 ft with the present setup. I don't recall any of the old thru hull units doing any better than that.
One of mine from Garmin, I bought the shoot thru adapter, so it has an angled pipe with a cap on it, in which teh transducer is firmly mounted. a little 10w hydralic oil when it was installed and it hasn't neede a fillup since. 6 to 8 yrs (can't recall, so I am guessing).
The other, from Humminbird, came with a transom mount transducer. There was a thru hull available, but no shoot thru, so I put the transom mount in a 4"ABS pipe that I cut to the hull angle and epoxied to the hull. I put a cap on it and poured in a little 10w oil. It has been good and maintenance free for 4 yrs or so. One day I might get rid of those old thru hull transducers.

Thank you for the compliment. So do I when I look at the other guys Outer Reef and so does he when he looks at the other guys RealShip and does and so does.........the key is to be happy with whatever gets us out on the water!


-- Edited by Just Bob on Tuesday 17th of May 2011 01:48:37 PM

Just Bob wrote:*So now I question - do I get two Airmars?

Click to expand...

*** Will you have any need for knowing the temperature of the water? How about your speed through the water? A thru hull transducer is needed to get information on these to subjects. Maybe one of each? (1 thru hull and 1shoot thru as a back up?)

Thank you, these are good questions that I had thought of but had not come up yet.* I am aware that I'll be giving up temperature by choosing the shoot-throughs.* Maybe I'll shoot the IR temp gun over the side if I feel like I need the water temp.* I have it now and it certainly is nice to see it on the display but I think I could live with out it.

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Speed I don't get from the water, GPS is good enough for me on with that one.

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Thank you.

You don't give up temp with a shoot thru, only accuracy. If you put the shoot thru outside the ER, the temmp of the inside of the hull will be the same as on the outside. If in the ER, you will see an increase in water temp consistent with the higher ambient air temp in the ER, but it isn't a lot higher. If you are not interested in absolute temp, but only interested in changes, you will still get the information with an ER shoot thru. That is where mine is. When I really want to know the absolute water temp is when I am considering jumping into the water myself. That happens occasionally when the ER is still hot, but more frequently after it has cooled, or before the engines are started.
I used to have a temp on my dinghy sounder, so could compare reading with the ER shoot thru. I never saw a huge difference, maybe a couple of degrees at the most, just after shutting down after a full day's run.

Now this is very interesting, I wouldn't have thought that.* I have*few places I could put it outside the ER - thank you this is a very good thought.*

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My current through-hull has the temp prob built in, I wounder if these shoot-throughs do as well or will I have a separate prob for that??* I'll have to investigate that with Garmin/Airmar.

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Thank you again!

Is the water temp to plan on the survival time , if someone goes overboard with out a survival suit on?

No it's to determine if I want a cup of hot chocolate or an iced tea while floating on*my blow up raft.

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Seriously though, it's why I said*I think I could live without it at the helm.* If I can get a reasonably accurate measure*through the methods described above than great.* If not it's easily attainable by other means.

Water temp is a serious matter if you are a fisherman.
One is allways looking for thermoclines and currents. The sea temp will be your friend and fill your freezer.

Water temp is a serious matter if you are a fisherman.

And if your not a fish guy, having the water temperature gets you???

FF wrote:
Water temp is a serious matter if you are a fisherman.

And if your not a fish guy, having the water temperature gets you???

Click to expand...

*I can see your not a fan of water temp FF.* LOL

When you*buy*a speed transducer, temperature is usually included,*so why not.* On our last boat we had two separate depth finders that also had speed and temp.* One set of transducers were*located in the engine room.* The paddle wheel on the speed transducer was difficult to clean so I just pulled it*and put the plug in it's place.* I now had an engine room temperature sensor.* What I found was that if I did not*run the engine room blower, the engine room temperature would rise as much as 20 degrees when we were in the tropics.* Since our alternators charging efficiency and life span is affected by temperature, we tried to run the blower all the time.* It was easy to see when the blower was on or off.* For us the temperature sensor is just another tool.*

FF the water temp also indicates the currents and this is what we chase on when we are at sea on tankers etc.
Knowing the temp gives you the current direction and weather you are in the right current for your diorection , it is all about fuel saving.

Bingo! Benn nailed it.

Here's a recent photo and comment from a sailboat delivery I did this spring from Ft. Lauderdale, FL to Barnegat, NJ. Find the strongest currents by the water temps and ride them north.

"Hello Gulf Stream. Water temps in ICW and along the Florida coast were in the lower 70's. Once the strongest part of the stream we saw water temps of 86 F plus. I was on watch when we rounded Hatteras and left the stream. Water temps went from 81 to 56 F in 3 miles."


-- Edited by Anode on Saturday 21st of May 2011 08:53:45 AM

With speed thru water, gps speed, heading, and course over groung my Raymarine e displays will figure set and drift.

And add the wind transducer it shows ground wind.

For me all interesting and useful things on a long passage.

I would recommend the thru hull(the one you have to put a hole in the hull for) with paddlewheel and temp sensor.

If you want real accuracy Airmar makes a ultrasonic speed sensor, no moving parts to foul.


-- Edited by millennium on Saturday 21st of May 2011 12:08:22 PM

a paddle wheel only give you the speed over the water, not over the ground.if you are stemming the current you have to alow for it?