Depth sounder suggestions

[Dmksails]

I'm at the point in my build where I need to make a decision on a depth sounder. I sail in the puget sound a a depth sounder is very helpful when navigating in fog. I'm not sure yet on a thru hull or transom mount. Any suggestions?

[dbeck]

Disclaimer: I don't have a depth sounder with fixed installation, just using the handheld one from Plastimo.

My ideas:
- transom mount is ugly and it might be in the way with motor, rudder or when reboarding after a swim
- through hull: although not an optimal position, I would mount it in the inner forward corner of one of the lazarattes; our lazarettes are sealed towards the area below the footwell. In case of a mishap, just one lazarette gets flooded. Easy access to the transducer.
- in-hull: this is not supposed to work out of the box with a wooden boat; my idea would be to cut a hole, and close the hole with glass from inside and outside maybe with additional layers of glass in between (and no air bubbles). This should be pretty strong and very little risk of a leak. I would be interested if s.o. tried that already.

Dietrich

[Pasi in Finland]

When I was thinking about the same, a fellow builder in Germany also suggested the lazarette as a safer place for installation. I thought it made a lot of sense from a safety perspective while still being far enough from the keel. At least my sender requires a 45 degree cone to be unobstructed.

As a lot of things are thrown around in the lazarettes, I made a small box to protect the sensors and offering added safety in case of leaks. The lid has a gasket made from a motorcycle inner tube, and while not necessarily 100 % water tight, it will considerable slow the possible water ingress. Additionally, the top of the box is at least close, if not above, the water line. Excuse the sloppy fillet work. I did the box in a hurry as "no-one will see it"

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I have both the depth sounder and speed sensors there, as the NASA instrument with both was on sale. Don't expect that the log is really useful or necessary, but did install the sensor anyway.

I have not tried this yet as everything is still frozen for a few more weeks here.

If your trailer is fairly long, it might be possible for the supporting rollers to interfere with the sensor/sensors. My transoms hangs out enough that this is not a problem.

On hindsight it most likely would have been better to have the sensor on the opposite side of the engine. Don't know, we'll see.

Pasi

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My ideas:
- transom mount is ugly and it might be in the way with motor, rudder or when reboarding after a swim
- through hull: although not an optimal position, I would mount it in the inner forward corner of one of the lazarattes; our lazarettes are sealed towards the area below the footwell. In case of a mishap, just one lazarette gets flooded. Easy access to the transducer.
- in-hull: this is not supposed to work out of the box with a wooden boat; my idea would be to cut a hole, and close the hole with glass from inside and outside maybe with additional layers of glass in between (and no air bubbles). This should be pretty strong and very little risk of a leak. I would be interested if s.o. tried that already.

I went with the in-hull strategy, a year after I finished my boat. The sounder is located in the first bilge compartment forward of the centerboard trunk.
I marked a hole of the desired diameter, and used a small router to carve away the upper glass layer and most of the wood. Then I very carefully sanded away
the remaining wood until only the lower fiberglass layer was left. I put a temporary cover over the area and filled the void with liquid resin, and finally covered everything
with a glass patch. This gave me a wood-free opening for the sounder, undetectable from underneath the boat. I am using a Garmin (Airmar) sounder with NMEA2000 output.
It is great for a sailboat (it detected the bottom at the deepest place I have ever sailed: 165 feet), but is useless for fish-finding.

Obviously this would have been much easier to do while the bottom panel was lying flat on the floor, unassembled. It's probably a good idea even if you aren't planning to install
a depth sounder right away.

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One last photo. The actual transducer goes into the black cylinder, which gets filled with liquid to transfer the ultrasonic waves.

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[Dmksails]

Pasi - I really like your idea. I'm planning to install a depth & speed transducer, and this sounds like the ticket. One question - how closed does this come to the trailer supports?

If I read this right, you've placed it against bulkhead 8 on the port side?

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Pasi - I really like your idea. I'm planning to install a depth & speed transducer, and this sounds like the ticket. One question - how closed does this come to the trailer supports?
If I read this right, you've placed it against bulkhead 8 on the port side?

Actually, it's just ahead of the centerboard trunk (or bulkhead 4), offset about 8 inches from the centerline. It is not near any trailer supports, and the front part of
the keel protects it pretty well from grounding damage.

One reason I chose the specific transducer is that it has NMEA2000 output, so it plugs into my chartplotter. The chartplotter is
one of the smaller Garmin Gpsmap units. It is a model that has no depth sounder or fishfinder hardware built into it, and I got a really good deal on
it since 99% of boat owners have no interest in such a thing. But it displays depth data from a NMEA2000 device just fine.

If you want a "real" fishfinder, you can get a different transducer that mounts on the hull the same way.

[Dmksails]

Doug - I like your idea, but I'm planning on a thru-hull transducer with depth and speed. Do you think the speed paddles would be anywhere near the trailer supports?

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Doug - I like your idea, but I'm planning on a thru-hull transducer with depth and speed. Do you think the speed paddles would be anywhere near the trailer supports?

I'm sure it would be safe from damage, but:
1: Double check that there is enough room under the floorboards for your transducer.
2: In my location, it would be a bit of a hassle to clean the speed paddle when the boat is in the water.

Doug