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Catalina/Capri 25/250 Sailor's Forums

Catalina 25 Specific Forum

Installing a depth finder - Transom Mount

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gracer
1st Mate

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USA
39 Posts

Initially Posted - 02/13/2004 : 08:43:25

Has anyone installed a transom mounted depth finder? I need some instructions (pictures would be great) on installing one on a C-25 SK. Any hints as to location etc. would be helpful.

Bob

Bob Grace
Castleton, Vermont
1984 Swing Keel "Sara"

Edited by - on

ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 02/13/2004 : 09:45:24

IMHO stuff...

Unless you sail on totally 'flat water', your transom will be out of the water a good portion of the time due to the motion of the boat... I wouldn't mount a depth sounder there. You also have the 'messy' transducer cable to deal with.

I've had good luck epoxying a "puck" style transom-mount transducer inside the hull. I' wager that's how most owners mount them. You can also get more elaborate and build a little containment with a piece of pvc pipe and set the transducer inside it with a bit of mineral oil... that works fine too. There should be lots of info on this topic in the archives.

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lcharlot
Master Marine Consultant

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Antigua and Barbuda
1301 Posts

Response Posted - 02/13/2004 : 12:02:36

I installed the transom-mount transducer that came with my Garmin 168 on the keel skeg about a foot forward of the rudder. I didn't want to drill into the hull, so I fabricated a bracket out of stainless steel sheet metal and epoxied it to the skeg with a couple of layers of fiberglass tape, holding it in place with a large "C" clamp until the epoxy cured. The "C" clamp was isolated with a couple of pieces of 1/8" polyethylene from touching the epoxy (nothing sticks to polyethylene, not even epoxy). The transducer itself I safety-wired to the bracket. The transducer cable lies along the keel skeg and is held in place with small cable clamps (these use the smallest #4 stainless sheet metal screws I could find). The cable enters the starboard quarterberth area through an existing hole in the transom that the PO had made to run power cable to the outboard motor. I had to enlarge this hole to 3/4" to pass the transducer cable connector, but at least I didn't have to drill a new hole. The cable is then routed forward to the instrument head along the inside of the quarterberth, or through the bilge, however you want to do it. My solution isn't real pretty, but has the advantage of putting the transducer in the water, where it was meant to go, and did not require drilling a large hole in the boat as you would have to do with a thru-hull transducer. Some people install the transom-mount transducers inside the hull by bedding them in silicone and surrounding them with a bath of mineral oil contained in a piece of 3" PVC pipe epoxied to the hull. While this usually works, it has one disadvantage in that the water temperature sensing function of the transducer won't work, since of course the transducer isn't in the water. It will measure temperature, but it's the temp inside the boat, not the temp of the water. I also suspect that the maximum depth range of the transducer is reduced by as much as a third when you do the in-hull mount, since the transducer was designed to be IN the water, not trying to beam through 1/2" of fiberglass.
My solution does have one possible disadvantage in that the transducer is literally "hanging in the breeze" and could be smashed off the mount if something like a piece of driftwood were to hit it. But I had the same setup on the old boat for 5 years and never took a transducer hit. Seaweed would be a problem though. If you sail in an area where there are kelp beds or eelgrass, the transducer should be faired somehow so that it can't catch on strands of kelp.

Edited by - lcharlot on 02/13/2004 12:15:14

John V.
Admiral

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USA
559 Posts

Response Posted - 02/13/2004 : 13:12:33

Epoxying the "puck" in the forward locker works very well.
When you mount a transducer all the way aft you get a chance to see the rock you just hit,

rather than get a warning and avoid the hazzard.

my boat came with a signet multi function instrument
it reads depth, water temp, speed, distance traveled and log.

but with a digital depth reading I'm not getting enough information.
I'm adding a Huminbird fish finder. these work great, not very expensive and (you can turn off the little fishy things)when you epoxy in the forward locker you will get a slight tilt forward meaning the aim of the transducer will be a bit ahead giving more warning time for avoidance of submerged objects.

Edited by - John V. on 02/13/2004 13:14:09

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 02/13/2004 : 21:45:46

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by John V.
 ...When you mount a transducer all the way aft you get a chance to see the rock you just hit,

rather than get a warning and avoid the hazzard...
<hr height="1" noshade id="quote"></blockquote id="quote">
In my vast experience, by the time the depth sounder "sees" a rock at three or four knots, you've hit it--no matter where you mount the transducer. It's a depth sounder--not a forward-scanning sonar. The same with a fish-finder--don't plan on it keeping you off the rocks! (For perspective, many rocks around here are these size of tractor-trailers, and some are the size of Rhode Island.)

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John V.
Admiral

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USA
559 Posts

Response Posted - 02/14/2004 : 17:22:19

Well Dave I didn't really mean that you should go crashing through the shallows at 4-6 kts. But the difference of 25 feet in being able to read a trend like sudden shallowing will certainly give an opportunity to make course adjustments at a slower speed. This may be most useful when entering an unfamiliar anchorage.

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