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Old 28-02-2010, 15:25   #1
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Thru-Hull Transducer - Design Considerations

When we got our steel yacht, we welded up all the through hulls openings and seacocks. The only one we put back in was the seawater intake for the motor. It is time to get the depth gauge working again, but I just dont like the idea of a plastic transducer screwed through the hull, especially as it is on a steeply angled part of the hull and needs to be raised & leveled for it to sit flat to the seabottom.

Has anyone got any ideas as to how best to install these things to minimise drag and potential failures of the watertight integrity.

We also have a speed unit, but there is no way we will have that inserted through the hull as it is with just a plug unless we can find a foolproof way to install it. A friend nearly had his boat sink due to one of those.
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Old 28-02-2010, 16:52   #2
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I have seen some transducers mounted a short margin off the front of the keel. If you are afraid of the transducers integrity can you use a bronze one? If, not you can build a watertight well and mount your transducer/s in it.

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Old 28-02-2010, 17:02   #3
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I like the watertight well idea. I guess we could incorporate the speed log into that as "well".

Anyone got a photo of one of those contraptions ?
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Old 28-02-2010, 17:08   #4
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Keep that bronze away from the steel!
Lead on the end of a line?
The good old tafrail log?
A gps/current ap for the iphone?
The plastic through hull should seal as well on the steel as any other material with propper bedding, but the thought of such a weak point when you have a steel hull....
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Old 28-02-2010, 17:24   #5
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Can you "shoot thru" steel like you can thru fiberglass?

This is a job for SUPER G!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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Old 28-02-2010, 17:25   #6
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Been using lead on the end of a knotted line (knot every meter).

Got he fancy display for the depth installed, but noting communicating with it.

but the thought of such a weak point when you have a steel hull....
exactly ! There has been 2 yachts sink in our bay due to through hull things failing in the 5 years we have had a boat moored there. There is only about 80 vessels there, so that is not a good ratio.
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Old 28-02-2010, 17:30   #7
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Can't shoot through steel. We had thought of a lexan lense/window in the hull to shoot through but it is probably weaker than a plastic through hull.
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Old 28-02-2010, 17:48   #8
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I reckon you have two options apart from just mounting normally.
1. Bronze unit very well insulated from from the steel hull (epoxies and materials like acetyl - still plastics but they are only providing insulation and are sandwiched between stronger materials).
2. an "internal" well or box section with transducer mounted so that it doesn't protrude past the hull skin with a fiberglass "window" covering it conforming with the hull profile.


But really, most boats have a plastic though hull transducer that properly mounted and sealed does not cause a problem. Try to analyze why the boats in your area had problems and I bet you will find they were either poorly positioned or poorly installed (or perhaps a low quality transducer).
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Old 28-02-2010, 17:51   #9
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I'm with you 100%. Why do you need more than the lead line? It is sort of fun to watch the numbers sceam when you come over the bank, but is it worth it!
All through hulls above the static waterline except for a sea chest for intakes (that rises above the waterline and can be accessed from inside the boat to stopper any malfunctioning or coroded seacock ...or when you leave the boat). And that right there might work for your transducer..I see a portlight as a top to the seachest. Just set it on top....?
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Old 01-03-2010, 11:12   #10
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I guess the problems on the other boats were due to:
- bad installation,
- no maintenance,

We have plastic/plastic - thousands of sea miles, zero problems.

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Old 01-03-2010, 20:28   #11
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I can describe to you what I have on my steel hull.

There are two 2 1/2" OD 1/4" walled steel pipe sections about 3" long welded through the hull on either side of the stem in the verticle position the plastic through-hull transducers mount through these pipe sections. They are very strong, and because they are vertical this compensates for the angle of the hull. the lenght of the pipe sections protects the transducers on the inside of the boat as well as the only visible portion of them is just enough threaded section to snug down the mounting nut.

The real problem with having a recessed trunk with the transducers inside is capturing random air bubbles moving along the hull. Sooner or later enough air collects that it will interfere with the transducer signal unless you provide something to bleed it off.
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Old 01-03-2010, 21:53   #12
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You should also look into the transducers that shoot under an angle, compensating for the dead-rise angle of the hull (tilted element). You find all the info on the Airmar website.

cheers,
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Old 02-03-2010, 12:17   #13
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I remember some time back two transducers for depth - one each side. Then there was a (sort of?) switch that connected only the lee one. Worked very well on a very wine hull.

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Old 02-03-2010, 21:21   #14
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Here is a photo taken from the bow where you can see the transducer pipes welded into the hull just above the level of the keel/hull joint. I do not have the transducers installed at this point.
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Old 03-03-2010, 00:04   #15
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What about hanging transducer over the stern as we intend to try? We are actually planning to install it at the bottom of a self steering blade (Cape horn variant rather than our present Flemming gear) together with the engine intake. This should be deep enough to remain submerged and only draw back we envisage is possible turbulance at speed. However at speed one shouldn't be relying on the depth sounder anyway and you can always slow down to check depth as you would anyway coming into an anchorage. A hinged rod arrangment is another way to get it down deep enough at the stern.


Read on for how we got to this stage.

Ribbony: seems we have more in common. We also recently welded up all the hull penetrations (7 No! including the recessed transducer one) and now only have rudder shaft (new mechanical and orig gland seals) and prop shaft (original inboard PSS seal+new mechanical outboard seal).

Some have called us paranoid (well at least one of us ) but its a comforting thought we wont sink in a common way.

What about the engine intake?

Plan 1 was to install a sea chest opening to cockpit and engine inlet bsically as a pipe within a pipe. Outer pipe being the "hull" kept in a dry state by a noncorroding inner one. Also big enough to push down the transducer as well so we could raise it and clean it easily. We cut out the hole in cockpit but had trouble machining the 100 dia. pipe which was going to form the outer wall of the chest. Time on the slip was up so back we went with plan 2 -a couple of new cockpit drains above waterline thru to transom. As yet we havent got an engine inlet, just a temporary garden hose over the stern. If the bottom of the blade thingy doesnt work we might just have to put in a seacock#!. We already previously bought two apollon 1-1/2" and 1" bronze valves but hopefully wont need them!

Hanging it off the self steer means we can still service the transducer by raising the blade and by introducing a vent valve in engine intake, there is no possibility of siphoning back.

R

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