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Old 24-07-2013, 21:57   #1
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Depth Sounder Idea?


I am getting painfully close to completing a 27' sailboat I started building about a year and a half ago and need some advice on a transducer idea I have.

I don't really want to install a traditional thru-hull type depth transducer, and I don't want to use the transom mount style either. What I want to do is take the puck (important) portion transom mount transducer and mount it to the outside of the hull. In this case I would only have to drill a small hole through the boat to allow for the wire to pass through. I cannot use a shoot thru hull type transducer because my boat is built of plywood. I could countersink the puck into the boat without losing any strength because of the build up of keel material.

Anyway, has anyone heard of someone doing this or something like it?

Thanks, Cody

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Old 25-07-2013, 00:57   #2
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Re: Depth Sounder Idea?

You would be taking on quite a task through all this procedure to make an insert and drilled wire access through your plywood hull. It might be a better idea to fare an epoxy plug into your hull that could allow the signal of the interior puck tranducer through the hull. You would end up with the same amount of work and have an opportunity for a clean future refit with no through-hull.

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Old 25-07-2013, 01:04   #3
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Re: Depth Sounder Idea?

Although a small hole sounds attractive it will be very difficult to create a reliable, safe, waterproof seal. This is exactly what a conventional external transducer is designed to do.
It is hard enough to waterproof a wire exiting the deck above the waterline.

I guess you could say I don't think its a good idea.

You also need to be careful that anything you use does not allow moisture to penetrate the plywood.

Is there a particular problem that you have with a conventional external transducer? Someone may be able to suggest a better way of solving the problem.
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Old 25-07-2013, 03:00   #4
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Re: Depth Sounder Idea?

Have you considered a hand held depth sounder?
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Old 25-07-2013, 03:14   #5
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Re: Depth Sounder Idea?

Greetings and welcome aboard the CF, Cody.
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Old 25-07-2013, 03:15   #6
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Re: Depth Sounder Idea?

The conventional approach is to use a fairing piece to mount an external transducer as close to the centreline as practicable (i.e. not through any structural part). Your designer should advise if it is not in the plans.

I understand that it is usual to use a bronze transducer with a wood hull, though an epoxy patch/fairing piece with an internal transducer may have some merit. Again, best to consult with your designer.

A transom mounted sounder is handy as a short term solution. Longer term problems relating to damage due to the exposed location would make it undesirable.

A depth sounder is something that is required at short notice. That is you need to be able to flick a switch and know how deep the water is.

Unless there is a compelling reason to do otherwise why not follow the conventional approach?
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Old 25-07-2013, 03:19   #7
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Re: Depth Sounder Idea?

And I would prefer a transducer nearer the bow than one on a stern bracket, since this will give you the earliest warning of shallow water (assuming you are sailing in a forward direction). In most cases the difference will be negligible, but it could make a difference if you are leaving a dredged channel or approaching a steep shoreline.
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Old 25-07-2013, 05:33   #8
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Re: Depth Sounder Idea?

Thanks for the input guys! As usual, the shortcut idea, turns out to be not so much of a shortcut. Anyway, I think I will either use a traditional thru hull or fair a plug into the hull and use an in hull type transducer.

Thanks for all your thoughts, Cody
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Old 25-07-2013, 06:57   #9
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Re: Depth Sounder Idea?

Have you considered the size of the hole you are going to drill? It's not the diameter of the cable, it's the diameter of the plug that will connect to the display, or the fat part of the transducer (depending on your plan). And while it's possible to cut a transducer cable, it's not a task for the inexperienced to reconnect it. And since the boat is built of plywood, what's the issue? Glue in a butt block, drill your hole and mount the transducer. Want to change? Remove the transducer and butt block and install a new butt block and transducer. Much simpler than on other materials.
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Old 29-07-2013, 04:33   #10
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Re: Depth Sounder Idea?

You should go for the normal through-hull install. Mounting the transducer anywhere but in the bilge will give you problems as the boat heels and pitches. A stern mount is a waste of time as you'll get continuous errors and lost signals. (And it's 15 feet behind the point that goes aground first.) The bronze through-hull is needed if the wooden planks in the hull swell and shrink with water intake although a thinner plywood hull isn't likely to have the same effects. (Will you haul out in the winter?)
There are only two wires for the average depth sensor if it doesn't have a thermometer installed. Almost all are Airmar manufacture with blue and black wires usually 18-24 gauge in a 1/4" shielded cable. Cutting and re-connecting is a no-brainer. Making a fiberglass "window" for the unit in the bilge is just asking for problems. You're better off falling in line with everyone else.

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