Transom Mounted Transducer

[RestlessL]

I have decided to replace my NASA depth and speed transducers with a transom mounted unit feeding a Garmin multifunction display. When the boat next comes out of the water (next winter) I will install a thru-deck transducer, but in the mean time I will use a transom-mounted one (Airmar P66).

Can I seek the wisdom of the forum in helping me decide how to fix the transducer. I am on a drying mooring, and estimate that I will have about 4 hours when the transom is dry to complete the job. The transom is balsa-cored, and Airmar suggest mounting the transducer with 3 self-tapping screws to a depth of 22mm (i.e. all the way through). The front edge of the transducer is ribbed, so I do not have a flat surface to glue to, and the transom is, at that point copper-coated.

I am tempted to use shorter self-tapping screws, drill only through the outer skin, and fill the holes with Silkaflex. I might also put a thick layer of Silkaflex on the deeply ribbed front of the housing to keep it all water-tight.

Is my method sound, or should I re-consider?

John

 

[damo]

Why don't you stick it down to the inside of the hull - no holes in the transom, no worries about the tide coming in? That's what most of the rest of us do! Mine has worked fine for the last 4 years bedded on car-body filler.

(Loads of threads about this in the past - use silicone, stickyflex, bluetack, whatever; make sure there is no air trapped in the "glue"; don't put it above a keel etc )

 

[RestlessL]

It is a combination Speed and Depth transducer (triducer), so internal mounting is not an option.

The NASA depth unit I am replacing is internally mounted, but it failed on me last weekend (at low water springs with an estimated 0.2m under the keel).

John

 

[holly1]

Yes thats what i did

 

[damo]

OK, sorry /forums/images/graemlins/smile.gif

 

[roly_voya]

For temporary monting why not fix it to a board and then clamp the boad to the rail with a couple of U bolts. Don't need to dry out and no screw holes in the hull. The alternative would be a lead line...

 

[Rabbie]

Thats a very interesting idea. I have just bought a Garmin fishfinder with transom transducer to replace my Duet sounder/log. I didn't fancy drilling holes back there and wondered if it would be possible to stick it inside as you suggest. The thing is - will it give the same results or will the hull inhibit a true reading on a transducer designed for transom mounting?

 

[JKay]

yes it will work on single skinned grp boat.I used silicone

cheers Joe

 

[Pete7]

[ QUOTE ]
Thats a very interesting idea. I have just bought a Garmin fishfinder with transom transducer to replace my Duet sounder/log. I didn't fancy drilling holes back there and wondered if it would be possible to stick it inside as you suggest. The thing is - will it give the same results or will the hull inhibit a true reading?

[/ QUOTE ] Same results as despite the manfacturers advice not to ordinary sealant works well.

Pete

 

[Rabbie]

Thanks both - that makes life a lot easier and saves me sploshing around in the mud to fix it!.
Cheers.

 

[Chris_Mangion]

I have fitted my transducer for the Garmin 140 on the inside of the hull. You have to submerge it in epoxy in order to eliminate airbubbles which would otherwise give false readings. It also prevents the beam from 1) being bounced about the inside skin of the boat 2) the beam goes thru the epoxy holding the transducer and the epoxy on the skin,as these have the same consistency (more or less).

Take off the bottom of a butter tub, fill it with epoxy, and press the transducer against the bottom. Twist the transducer against the bottom to eliminate all airbubbles.

Mine has worked fine for almost a year now, accurate readings with around 60% gain. If I increase this to 75% it will pick up even small fish

 

[RestlessL]

[ QUOTE ]
For temporary monting why not fix it to a board and then clamp the boad to the rail with a couple of U bolts.

[/ QUOTE ]

Thanks. I am not sure that I could get sufficient rigidity in a board, but may be able to attach siomething to the transom ladder.

And yes, I do have a lead line - but trying to get swmbo on the foredeck using it is a different matter!

John