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Jimske 07-08-2006 18:20

Depth Meters
My Brown Searunner 31 has no depth meter and no through hull fitting - don't want any.

I saw some "transome mounted" units and was wondering what they were exactly and if anyone had any experioence with them. Accuracy, power requirements, etc. Thanks in advance.


btrayfors 07-08-2006 18:59


Transom-mounted transducers for fathometers work fine so long as they don't get affected by prop wash (which can cause erroneous readings). You can also install a transducer inside the hull...there are several techniques for doing so ... and this will work OK, too.

Not sure why you don't want a thru-hull transducer. They are perfectly safe and are the best way to go for most boats.


Jimske 07-08-2006 19:13

I mainly want it for getting close in to land so I can anchor in shallows (I draw 32" with board up). Just don't want to go thru the work of drilling thru the hull. I thought it might be simple, inexpensive and portable. Something I would use on occasion when needed.

I am putting in a tiller pilot but don't want permanent electronics on board.


Sunspot Baby 08-08-2006 04:45

West Marine (and others) has a hand held unit that also reads water temp. It's about the size of a flash light. If you have crew that can reach the water, it would work fine for getting close to shore.

I use mine to sound shallow passages in the Bahamas in the dinghy before taking the big boat through sometimes.


GordMay 08-08-2006 05:02

Best use for a sounder is to confirm the exact depth in which youíve grounded.
Slow speeds & eyeballs (or lead lines) work well for getting close inshore, particularly /w only 32" draft.

BC Mike 08-08-2006 08:08

Thru hull
Lets work on some terminology. You want a depth sounder, depthometer and fathometer although used are funny words. Through the hull can be shoot through the hull, or a hole through the hull. You are wanting to avoid a hole in the hull. You can shoot through the hull by glueing the transducer to the inside. More power from the unit is always a good thing, you will realize why after you have owned a depth sounder for a while. The hull needs to be solid for the transducer to shoot throught it. You do not want the transducer on the transom. My transducer is in front of the keel where the hull has a V section. I made a cardboard dam and filled the gap with epoxy and set the transducer in place. Now I can read the bottom depth and see the fish swim by. You can use some silcone to glue the transducer to the hull for a test. If it works you can then glue it with something more permanent like sicaflex. For less than $200- you should be able to find a simple yet good unit from Lowrance or others. By simple I mean that you press the on button and it tells you how deep the water is. Then you press the off button. The unit may have a menu for many options but you do not need to play with those buttons if you do not want to. On the weekend I had the downrigger at 96 feet so I needed to monitor the depth so that I would not hit the bottom.

Sunspot Baby 08-08-2006 10:05

Gord another reason for a fathometer is to know water depth when anchoring so that you know how much scope to let out. Sure a lead line works, but is there a reason not to use the technology that is so reliable and so readily available?


GordMay 08-08-2006 10:51

I was being a little facetious. Perhaps the ubiquitous :) would help.
Although Iíve never felt the need for the luxury of a depth sounder; I have had, and happily used them.
In Jimís case (32 inches, & don't want any thru-hulls), I think donít an electronic ďdepth meterĒ is at all necessary. It may not be much improvement over a yard stick.

Jimske 27-08-2006 10:47


Originally Posted by GordMay
Best use for a sounder is to confirm the exact depth in which youíve grounded.
Slow speeds & eyeballs (or lead lines) work well for getting close inshore, particularly /w only 32" draft.

I use a lead line now. Problem is I single hand mostly and have difficulty checking the depth and driving the boat at the same time when I am near shore.

Jimske 27-08-2006 10:57

Yep, good point. I want accuracy. For going in close to shore and for scoping the anchor. Otherwise I care not about it.

Alan Wheeler 27-08-2006 12:35

I use a fishfinder. No not to find fish. It shows me many aids to navigation. I can see what bottom type I am ancoring in. I can follow bottom contours. I can see Rocks and reefs. I can get an understanding of what the bottom is doing, as in rate of rise and fall. If it is risinging steeply, greater caution is involved. I can follow narrow channels. Yep, I find it a very important and helpful tool. I view the sounder as important as my wind direction and my GPS. You don't need any of them to sail, but they can be very helpful as well.

Charlie 27-08-2006 19:55

I agree with Wheels:

Depth Sounder is a useful navigation tool. Was it Captain's Courageous or some other movie when the ship was sailing back from the banks trying to get back to port first and they through a lead line out found that they were on sandy bottom and used that as there decision as to when to turn.

Ok question on Depth Sounders Howis the depth affected by heel. If you had the boat at a 30 degree heel do you need to use a little trig to figure the actual depth ( are you getting the depth of the water parallel to the keel?) or is it the same depth as if you had no heel?

Alan Wheeler 27-08-2006 22:07

The pattern is not a straight signal. It is in the shae of a cone. Depeding on the frequency being used determines the width of that cone. The deeper the bottom, the larger the area that cone pattern is covering. So even when the boat is on a heal, there is still a considerable amount of pattern going straight down. The returning signal is a bounce. It bounces much like a torch light on a reflective surface. Not quite so accuratly, but much sharper in focus than just audible sound waves. So only the the sounder signal going straight down and then reflecting straight up will hit the transducer and be "heard" by the instrument. Other echo's are filtered out by the processing gear in the sounder.

cat man do 27-08-2006 23:01

Hi guys, I had an apelco fish finder on my last sailing cat that only cost a couple of hundred $. It was great and actuallyworked in about 2 ft of water as the rudders touched the bottom.
Then we had a lightening strke that fried most of the electronics and we could not get a replacement that worked anywhere near as wll in shallow water.
Garmin made one for around $500, but the alarm only made a pittyfull beep and then an icon fashed in the bottom of the screen. If i'm about to hit bottom I want the bloody thing to scream at me.

As I like playing in the shallows, does anyone know of one that still works in 2 to 3ft and has a loud alarm.?????
with the transducer, I routed out the core from the inside of the hull and reglassed to seal the core and get a build up of about 1/4 inch and siliconed the transducer back into this space.

I am half way into a 50ft cat buildig project and dont mind spending a bit more on a sounder this time as a lot of the bars we cross dont have much water over them. cant get off and push off like the last one.


Alan Wheeler 28-08-2006 12:44

Navman have the ability of triggering an ext alarm.

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