Bedding in new transducers - what's best?

MM5AHO

MM5AHO

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I'm fitting new speed and depth transducers this winter.
What is the best material for bedding them in. I'm removing the old Airmar ones, and fitting new NASA. The diameter of the log is similar, but the diameter of the depth transducer seems different. The NASA much thinner on the shaft though external part similar size.
With fibreglass hull, (quite thick), what is best material to fix these in place?
 
Eyore said:
Just fitted Raymarine ones using Sikaflex, don't much like the sound of silicone.
Click to expand...

Nasa specifically mention avoiding mastic sealants, just to use silicone sealant. Some adhesive sealants can attack some plastics, and it may well be that Nasa's plastics are vulnerable to this.
 
As pvb says, it seems that NASA may have had issues with solvent-based sealants and hence they recommend water-based silicone. Some other depth transducers come with a warning not to antifoul them, presumably for the same reason. I can't say I have ever had a problem with antifouling and suspect the same may be true of solvent based sealants. However, it could be that some modern hybrid sealants are water based as many such products seem to be going the same way.
 
Last edited:
David2452 said:
That's am "in hull" transducer, for which Airmar have always recommended silicone (basically just to stick it down) when it comes to "through hull" transducers the story changes to non specific as to type or manufacturer but "Marine sealant, suitable for below waterline", and that ain't silicone.
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Yes, I was responding to Lazy Kipper's question "What would you use for an in hull Raymarine depth?"
 
To clarify.
Current transducers are completely through the hull - holes in the hull.

I can see that silicone might be OK for bedding a depth transducer to the inside of the hull - perhaps, but surely not for waterproofing the plastic through hull housing that holds the speed log?
In the case of the hole for the depth, the new unit is much smaller diameter than the old. Old about 40mm? new about 15mm shaft with a bigger head.
In effect I need to fill the hole that is left and bore a new hole for the new unit - or attach it inside perhaps?
 
MM5AHO said:
I can see that silicone might be OK for bedding a depth transducer to the inside of the hull - perhaps, but surely not for waterproofing the plastic through hull housing that holds the speed log?
Click to expand...

Yes, that's what Nasa recommend. There's no real water pressure to cope with, and the mechanical strength is provided by the fixing.

MM5AHO said:
In the case of the hole for the depth, the new unit is much smaller diameter than the old. Old about 40mm? new about 15mm shaft with a bigger head.
In effect I need to fill the hole that is left and bore a new hole for the new unit - or attach it inside perhaps?
Click to expand...

It would be easier to leave the current transducer in position and fix the new one in-hull. But you need to test the in-hull position first before finally deciding.
 
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