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Old 22-07-2013, 00:53   #1
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Thru-hull Transducer: Is this a dumb question?

I have a wooden core boat and that rules out in-hull depth transducers, and transom mounted? For a sailboat it seems a bit tricky.
So, that leaves thru-hull--which of course means a hole in the hull.
So, the scary thing with a hole in the hull is of course if the thru-hull fitting fails, the boat fills with water, and you, ah, sink.
So--why can not one build a little solid fibreglass "box" with a watertight inspection port/plug over the thru-hull, meaning that if the little f**ker ever failed, then your "safety box" over the thru-hull saves your boat from sinking, working like a watertight bulkhead does in other areas of some boats.
I did some google searching, and some searching of this forum but found nada about this sort of idea--maybe I was using the wrong words.
This has to be an idiot suggestion right, otherwise I surely would have found something about it?
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Old 22-07-2013, 01:31   #2
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Re: Thru-hull Transducer: Is this a dumb question?

Rather than a sealed box it just needs to be installed in a waterproof area that extends above the waterline. A locker is commonly used.

The transducers have a very low rate of failure (with respect to watertight integrity) so on there are other, more important, priorities. The rudder and seacocks and stern gland are more likely to cause flooding problems and these issues are rarely addressed in production boats.

I think the principle of stopping the boat from sinking from a failure of any component below the waterline is a very valid one which more boat builders could address, but the depth transducer would be low down on my list of priorities. If a locker extending above the waterline is not available a sealed box would work. The main problem would be maintaining a reliable watertight seal on top of the box while making the top easily removable for inspection. The risk of rot in the enclosed space would need to considered on a wooden boat.
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Old 22-07-2013, 01:43   #3
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Re: Thru-hull Transducer: Is this a dumb question?

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Originally Posted by noelex 77 View Post
Rather than a sealed box it just needs to be installed in a waterproof area that extends above the waterline. A locker is commonly used.

The transducers have a very low rate of failure (with respect to watertight integrity) so on there are other, more important, priorities. The rudder and seacocks and stern gland are more likely to cause flooding problems and these issues are rarely addressed in production boats.
Thanks Noelex,
I do not have a production boat, and the thru hull transducer for depth would be my one and only thru-hull.
Rather than a very low rate of failure I want a foolproof backup, hence my idea.
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Old 22-07-2013, 02:28   #4
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I have my depth sounder mounted inside the hull (which you have said you can't do but bear with me...) in a short section of PVC storm pipe which has been cut so that the bottom matches the curve of the hull resulting in the pipe being vertical. The PVC pipe has a threaded end glued on to which a screw-on cap is screwed. I have the transducer actually mounted through the cap and the pipe filled with water, but you could simply have the storm pipe and screw-on cap over your through-hull mounted transducer. The pipe could be glued and/or glassed into place while the screw-on cap will provide a watertight access point.
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Old 22-07-2013, 03:06   #5
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Re: Thru-hull Transducer: Is this a dumb question?

Noelex77 has advised that the rate of failure is very low. I'd put it at zero. Look at the way the thing is constructed; there's now way it can fail unless, perhaps, you so ignore the vessel for so long that rot infests the wood to which attaches.

If it's a carvel construction, you've a far greater chance of springing a plank (again, only if you ignore maintenance), and if you have a motor, the stern gland is also far more likely a problem. And so on; it'd be unwise to assume that eliminating thruhulls would eliminate the chances of sinking.

I suggest install it with confidence; do it right and it will not fail.
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Old 22-07-2013, 03:41   #6
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Re: Thru-hull Transducer: Is this a dumb question?

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If it's a carvel construction, you've a far greater chance of springing a plank (again, only if you ignore maintenance),
Composite consrtruction: strip plank oregon/glassed exterior
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Old 22-07-2013, 05:58   #7
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Re: Thru-hull Transducer: Is this a dumb question?

Standard method with a thru-hull type transducer & wooden boat is to drill a 25 or 30mm diameter hole in the hull, tape up the bottom and fill with clear epoxy. When it sets, epoxy the transducer over the now filled hole.
This guy has a variation on this if you think epoxying the transducer is too permanent.
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Old 22-07-2013, 06:04   #8
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Re: Thru-hull Transducer: Is this a dumb question?

Presumably you won't be wanting to remove the transducer very often if you go the box way. I mention this as I remove my transducer (to prevent fouling) whenever I leave the boat for say a week or more so a box won't work in this case.

How are you going to waterproof the point where the wiring has to exit the box?
Hopefully not with another box on top again

I do think you might be over thinking this but it's your boat and one can't be too careful.

BTW, what sort of boat are we talking about if this is the only underwater throughhull?
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Old 22-07-2013, 06:51   #9
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Presumably you won't be wanting to remove the transducer very often if you go the box way. I mention this as I remove my transducer (to prevent fouling) whenever I leave the boat for say a week or more so a box won't work in this case.

How are you going to waterproof the point where the wiring has to exit the box?
Hopefully not with another box on top again

I do think you might be over thinking this but it's your boat and one can't be too careful.

BTW, what sort of boat are we talking about if this is the only underwater throughhull?
Hah hah, you are right--I could end up getting boxed in!

I follow a lot of the ethos of the Roger Taylor "Simple Sailor" school of sailing when it comes to choosing and preparing a boat for the ocean. It is not for everyone--i.e, 99.99% of sailors don't do it his way, certainly not in a boats this small as mine is--but that is ok, each to their own.
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Old 22-07-2013, 08:06   #10
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Maybe I'm missing something here, but...


My last trailer sailer came with a Hummingbird depth sounder that the PO hadn't yet installed.
The manual said simply "glue the transducer to the inside of the hull" - so i did.

It worked perfectly, with no hole in the hull. Had something to do with the hull material (GRP) being denser than water, so apparently provided there was nothing between the transducer and the water that was LESS dense than water, the puck would look 'through' the hull in to the water.

Would such a thing not work on your boat?

I too am uncomfortable with through hulls, and long term would like to remove all of them.
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Old 22-07-2013, 08:14   #11
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Re: Thru-hull Transducer: Is this a dumb question?

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Would such a thing not work on your boat?
It will not work on a cored, or wood structure. The OP qualifies on both accounts

Its a good for solid glass, although the range and quality of reading are both effected.
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Old 22-07-2013, 08:15   #12
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Found the type of puck i was talking about on Amazon:

http://www.amazon.com/Humminbird-XAP.../dp/B000G644HI

Says hull must be "single layer fibreglass" but surely your core material is more dense than water.

So perhaps for $40 you can afford to experiment.
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Old 22-07-2013, 08:19   #13
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or, perhaps you could replace a small square of your hull with solid GRP, then us a puck transducer.

no hole on your hull then...
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Old 22-07-2013, 08:48   #14
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Re: Thru-hull Transducer: Is this a dumb question?

I too think that the risk is quite low and thus acceptable, but it is your choice of course!

Two points:

You don't need a sealed box to accomplish your aim of not flooding the boat in event of a transducer failure. All you need is an open-topped box that reaches above the water line by a few inches. In the unlikely case of leakage, the water will only flood in until the level equals that of the ocean outside the boat. This stand-pipr principle is used in some boats for through hulls, centerboard cases and so on.

Second, considering that the inside surface of your strip planking is not glassed, I would worry about rot if you closed the box up as you describe. Lack of ventilation is a prime suspect in dry rot infestations.

And for what it is worth, our strip planked hull (glass both sides) has several through hull penetrations that have given flawless service for 21 years now...

Cheers,

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Old 22-07-2013, 15:40   #15
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Re: Thru-hull Transducer: Is this a dumb question?

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I too think that the risk is quite low and thus acceptable, but it is your choice of course!

Two points:

You don't need a sealed box to accomplish your aim of not flooding the boat in event of a transducer failure. All you need is an open-topped box that reaches above the water line by a few inches. In the unlikely case of leakage, the water will only flood in until the level equals that of the ocean outside the boat. This stand-pipr principle is used in some boats for through hulls, centerboard cases and so on.

Second, considering that the inside surface of your strip planking is not glassed, I would worry about rot if you closed the box up as you describe. Lack of ventilation is a prime suspect in dry rot infestations.

And for what it is worth, our strip planked hull (glass both sides) has several through hull penetrations that have given flawless service for 21 years now...

Cheers,

Jim

Ok Jim, 21 years is a good long time. I don't expect you to write a novel, but I would be interested if you could quickly explain when you get a moment how you put yours together to provide such a flawless experience with your thru-hull for such a long time, because I have to say some of the scare stories do not equate with your experience.
I see your boat is in Hobart. Beautiful part of the world, I have been there (as a tourist, not as a sailor).
Cheers mate.
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