farmer boy 3:15pm, 5 May 2011
I have bought the above and the instructions are telling me to fit the transducer on the bottom of the transom (in the water) - which I don't want to do! I was sure someone had said that it is ok to epoxy, or sikaflex it onto the inside of the hull - or was I dreaming?
I was wondering if the design of transducer has changed and that it has to be on the outside of the hull now?
Anyone done it and did it work ok?

Thanks in advance... John
Skykomish E29 Posted 8 years ago. Edited by Skykomish E29 (member) 8 years ago
You can fix the transducer to the inside of the hull but you have to make sure that there is NO AIR trapped between the transducer head and the hull surface this is why they recommend fixing it in a bed of silicone sealant or traditionally a tube filled with oil. Personally I wouldn't epoxy it in place nor for that matter Siklaflex it as you will never get it out again if you make a mistake with locating it I think I just used frame type sealant when I had one
I know that Norman has fixed his inside.
rothwell_neil 8 years ago
John, your tooth must be hurting so much that you are forgetting things. Mount it under the battery box and against the vertical panel, use plasticine or similar to make a nice pocket, fill with silicon or epoxy, make sure there are no bubbles and push sensor in. It works on ultrasound and so long as the sound signal can pass through combined materials will work. This works inside the boat so long as the interface between them all is air free, hence the gel for a ultrasound scan. In engineering when you run out of the proper stuff swarfega works very well! The offset will need to be set as the velocity through silicon is different to glass fibre or water but this can be set in the settings. Not much has changed since 1922.
NormanKlipspringer 8 years ago
I fixed mine with Solcaflex 291. It may never come off again but hey who wants it to come off. I plan to do the same thing on Klipspringer. The Gramin fishfinder 90 does not have any means of setting an offset (at least I cannot find any), so you just have to be wary and know what the error is. On Archimedes it was about 0.3m high. There is also an error if you mount the transducer away from the centre line of the boat, which is inevitable in a keel boat to get to a reasonably small hull thickness. The error will come when the boat leans and then the reading will be different on each tack.
farmer boy 8 years ago
thanks guys... all makes sense now... I think my brain is full... must get rid of something!
rothwell_neil 8 years ago
Norman I use the offset for the keel on my fishfinder 100 and set this plus .3M Seems to work quite well at all depths and as I only care about anchor depths and getting in over the bar this is good. Calibrated over a hard sandy bottom at anchor with a lead line.
NormanKlipspringer 8 years ago
Fishfinder 100 has keel offset as an option in the calibration section. The unit is now discontinued. 90 and 140 do not have this option - no calibration section. Neither does the echo 100.
rothwell_neil 8 years ago
I will count myself lucky, having said that mounting the unit at front of cockpit locker will be about 0.1-0.2m from the water line and thus self calibrates! Depth shown is depth of water plus need to add a bit anyway, doesn't sound like a big problem. Thing in the solway is that it is rare to see anything over about 10M, 20M is deep deep water, Robin Rigg wind farm is 10 miles off shore and at +0.6M above chart datum!
NormanKlipspringer Posted 8 years ago. Edited by NormanKlipspringer (admin) 8 years ago
Yes I think you are lucky with your unit. Why Garmin have chosen to exclude calibration form their newer units beats me.
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