Mine is thru hull. I like that better.

Any transducer which also reads temperature needs to be in contact with the water to be accurate. My thought is temp doesn't need to be that accurate, so it can be mounted in the bilge. As with any sounder it needs to be located so there is no air between the transducer and the water. Either make a box, tube of such and mount to the hull where there is clean water. To find a spot, add water inside the bilge and use a sand bag to hold the transducer in place.

Either that or get another transducer, there are several to choose from
http://www.simrad-yachting.com/en-US...s/Transducers/

Well I opened the instructions and it says my transducer can be mounted inside the hull as long as there is no wood or metal in the hull. I don't think the 98 active thunder tantrum has any wood in the hull. It also says that "down scan imaging" may be degraded if done this way. I think I'm going to use Alldodge's method with the sand bag and water to test it out. Correct me if I'm wrong Alldodge.....the only reason you put some water in the bulge is to make it read correctly for the test. Then when it is sanded and epoxyed it doesn't need the water. Also I should be doing the water/sand bag test and actually taking the boat out for a ride to make sure it's a good placement location

Yes, the water is there to remove all the air so the sound will transmit thru the hull, and yes it needs to be done with the boat in the water.

As for securing to the hull, epoxy is great, but I like to use silicone because if after installing it does work quite right it can be removed and tried again. The silicone will hold forever so long as chemicals (gas, oil and such) don't get around it

Since your recommending silicone would I still need to sand anything smooth or will the silicone filling those voids be good do you think?

I have never sanded prior to install, just made sure its clean

Awesome. Thanks for all the help guys. Love this forum!

Or coring. If there is coring you will have some more work to do.

I'm working on getting my NMEA 2000 setup working too. It's pretty easy with the newer smartcraft stuff. I have an existing NMEA 2000 backbone with my GPS and VHF connected to it. I bought the Mercury CAN - NMEA gateway. One end plugs into the j-box and the other end to the backbone. It was working fine, my engine data was displayed on the GPS. I added a .5 M extension cable to make the rigging cleaner and now I am getting a NMEA 2000 fault on my smartcraft gauges? Does anybody know if a there is a difference in the cables that are used as a trunk line versus a drop line?

From what I'm finding the nema drop and back bone cables are the same. Issues with nema is distance and voltage drop. A .5 M cable isn't much but the connector would be the only item I would thing of. When you remove the cable does the fault go away?

Edit: should mention no cable length shall exceed 20 feet (6 M)

How do I find out if there is wood or voting in my hull? I don't think there is wood. Try and contact the manufacturer?