Do underwater plastic logs, transducers have a maximum use date ?

[Fuss]

We all use these plastic components but maybe they become brittle and dangerous after a certain time and no one is telling us.
What type of plastic is used?
Anyone know more or have any experiences to share?

[billknny]

Originally Posted by Fuss

We all use these plastic components but maybe they become brittle and dangerous after a certain time and no one is telling us.
What type of plastic is used?
Anyone know more or have any experiences to share?

You seem very worried about all things polymer and what "no one is telling us". You do understand that a fiberglass boat is made of plastic, right?

[noelex 77]

On many boats it would be possible for the designers to incorporate an area where the transducers can be mounted so that a leak will only cause limited damage and the boat cannot sink.

When the transducers are mounted forward, the waterline is not long way above the floor level so a locker with watertight walls is often all that is needed.

I have have only heard of a few cases where major leaks have occured at the transducers. Thes cases were from collision with debris or ice rather than deterioration due to age. However, boats are sometimes lost when the source of a leak cannot be identified.

If nothing else, isolating the transducers means the number of potential leak spots is reduced. If the water level has risen substantially finding the source of the water ingress is often a significant problem. Reducing the number of potential points of entry, or making them easy to check (if the locker is dry the transducers are not the cause) is a help.

[Fuss]

Originally Posted by billknny

You seem very worried about all things polymer and what "no one is telling us". You do understand that a fiberglass boat is made of plastic, right?

So the logs and transducers are made of the same material, fibreglass, is that what you are saying?
We know that fibreglass does not become brittle with age, so I guess that all is ok then and there is nothing to worry about.

[44'cruisingcat]

I've recently fitted a new plastic depth transducer in the boat I've been working on lately.

There was no "Use by " date on the box.

[Dooglas]

I have owned several older boats (as old as 35 years) with transducers and logs made from plastic. I have never had one fail physically, i.e. harden and break into pieces. Plastic parts I have had fail on a boat have generally been above decks where they have been extensively exposed to the sun (UV). My thought is that transducers really don't see much, or any, sunshine. Heck, many thru hulls and seacocks are made of plastic these days.

[Howler]

After 23 years, our transducer and log look like new. This boat only sails in fresh water however. I suspect salt water might be tougher.

The plastic does well since they're barely exposed to UV light. Just inspect and clean them regularly. Don't forget to have the plug nearby if you do so afloat.

[Mike Banks]

I fitted a window in the hull of 10mm polycarbonate, just below the helm station. Around that I built a box so that in the event it was ever stove-in, the boat would be safe.

To the polycarbonate "Window" I fixed a plastic polycarbonate ship's beaker with the base sawn off. This I filled with light machine oil--(originally water). The transducer fits neatly into this beaker. The polycarbonate window is invisible to the transducer--it has the same sonar characteristics as sea water, as long as it is not painted or antifouled.


That is how ice-breakers keep their instruments from being dislodged by lumps of ice--and it worked for me.

[ramblinrod]

Originally Posted by Fuss

We all use these plastic components but maybe they become brittle and dangerous after a certain time and no one is telling us.
What type of plastic is used?
Anyone know more or have any experiences to share?

I have removed countless old transducers.

None have fallen apart; quite the opposite.

The only issue I have seen is an external teak shim to compensate deadrise and hold a transducer perpendicular to the sea bottom, that had finally started to fail after 35 years. (Bad design that could have been sheared off by a dead head.)

The failure (leak) mode for any thruhull transducer is poor installation or failed bedding / sealing. I generally estimate 2 hours per thruhull transducer removal. Most are less. (We invoice actual labour.)

I recommend depthsounder transducers be epoxy bonded to the inside of the FRP hull to eliminate any risk of leak (for all but high definition sonar).

The deadrise isn't an issue in almost all cases. Most transducers have a 40 degree 1/2 power beamwidth. Even if angled 20 degrees off-axis, a significant amount of energy is still transmitted on-axis, so the system range will not be detrimentally affected.

I don't recommend using lossy bonding materials like silicone, toilet bowl wax rings, silly putty, or bubble gum. These will sorta work but may affect range needlessly, and are prone to mechanical failure. If one wish to move an epoxy bonded transducer, all they have to do is disconnect and short the transducer wires, and give the transducer / epoxy join a sharp whack with a chisel and mallet. Takes only seconds.


Some use a mineral oil or anti-freeze filled still tube inside the hull. These will work, but are more time consuming, prone to mechanical failure.

Some think this compensates deadrise and enables the transducer to transmit perpendicular to sea bottom but it doesn't really work that way. It ends up affecting the ultrasonic beam more than just bonding to the hull.

For cored hulls, the core has to be removed and replaced with FRP.

Neither method will work for wood, metal, or cored FRP hulls. In these cases, a thru-hull transducer is faster than building an FRP window.

(Raymarine Certified Installer)

[Fuss]

does that mean we can use any old plastic fitting beneath the waterline

[Dooglas]

Originally Posted by Fuss

does that mean we can use any old plastic fitting beneath the waterline

No, I believe that means that the plastic composites which are used for transducers, thru hulls, speed logs, sea cocks, and the like are formulated of materials which hold up under this kind of application.

[Fuss]

Do they hold up better than Marelon because this plastic is supposed to be the best composite for underwater fittings?

[Mr B]

I pulled my wind generator apart for cleaning and a paint job, 16 year old, Rutland 913,

The plastic cover and the plastic cone on the back of it, Fell apart in my hands,
It was UV effected,
Plastic rail clamps for Solar panels, Etc, have all been binned,

My davit Hammock is plastic of some sort, No way would I put it back on my boat, Thats another new one to be made,
All the plastic covers and syklights on my 29 year old RV have all reached their use by date,
They disintegrate pulling them apart to clean or repair,

Lots of plastic fittings on top of RV's and Boats disintegrate after many years of UV exposure,
Under cover and not exposed to UV, All the plastic bits, they seem to be like brand new,

No, I dont know what they are all made from, It does vary depending on what it was used for, The plastic bits, They do vary in colour too, White right thru to Black,

The Teflon strips under my house doors have all disintegrated from old age and exposure to the sun,
I have spare Teflon left of the same age for the doors, Kept out of the sun, Its still brand new,
My thru hulls of the same vintage all look brand new, Some sort of black plastic,

Cheers, Brian,

[Fuss]

are plastic underwater logs and depth transducers made of marelon or a similar material?

[Fuss]

As an update to this thread! I just took out a 10 year old white Marelon thru hull fitting and hit it once with a small hammer and it broke in half.
So...they are not so strong as the world would have us believe.
A long time ago I hit a brand new one with a 2 pound hammer many times and it only distorted.
These issues should get addressed by manufacturers.

Therefore in my opinion if you have any plastic thru hulls in your boat more than 5 years old, you have a safety issue.