Been following this post as several of my customers (West Marine Associate) ask me this same question each year. While West Marine does train us, and requires that at least once a year we maintain our status, this post goes into far more detail than I was ever taught. I know, that even with a core construction, there is no way you would want any chance of seepage into the transom under any circumstances. Just to be sure I got it right I condensed everything heard and added a few things so correct me if I am off base anywhere or I will be spreading some hate and malcontent among my customers.
1. Read the instructions provided by fish finder manufacturer concerning transducer placement carefully. (I would think this is one thing you would really want to get right the first time)
2. Drill a small pilot hole to guide a countersink to the depth such that the width of the counter sunk hole matches mounting screw's major diameter to prevent gel coat cracking.
3. Counter bore pilot hole with an oversize bit.
4. Fill counter bored hole with structural epoxy putty such as Marine Tex.
5. When cured, drill proper sized mounting holes
6. Coat threads of screws with lubricant such as silicon
7. Mount transducer
8. Paint transducer with anti fouling water based paint or transducer paint
Something is wrong here! What has me troubled is if one countersinks to screw's major diameter, then re-bores it with an over-sized bit, which has to be larger in diameter than the screw's major diameter, what is the purpose of counter sinking in the first place as you would be drilling right over it anyway? Is it possible the term screw's major diameter means diameter of the screw's head, then it makes sense although I am not sure if I got it right just yet? Let me ramble on for a little bit more as you guys got me thinking about this. I like the idea of drilling an over sized hole and filling it with structural epoxy. If one would just drill straight into the transom and mount the xducer, we know that no matter what gunk you put on it there is always the danger of seepage. However, there appears to be something than can still go wrong with Brian's method if not done right. Suppose the length of the mounting screw is one inch. The depth of the over sized hole then should be something greater one inch or else the only thing to prevent seepage would be the 5200 or whatever gunk you stick in there. If Brian's method is done correctly by going deeper than the mounting screw, then even if the gunk fails completly (not likely) there is no way that I can see where seepage can ever occur.
I am also wondering what is wrong with JackC idea of epoxying the starboard directly to the transom. Epoxy takes to starboard, the stuff should last forever, the epoxied surface area would be so great that the strength of the bond would go out of sight, and there is not a lot of structural stress on a Xducer anyway. I can understand JackC's concern as I would not like to put holes into a new $1000 per foot hull. God forbid, but if JackC has to tweak his Xducers position because of some unforeseen cavitation problem, no problem with starboard. From what I read about JackC's ride, it could be around longer than JackC. Sooner or later, the fishfinder is going to be outdated and have to be replaced. Again, no problem with starboard or a xducer change out. I am trying to put myself in JackC's shoes, listen to everyone, but the final decision is yours. What ever you decide JackC, do not listen to me as I have only mounted one xducer in my life and it was a piss poor job. Likely all the suggestions will work out fine, but I am curious what the pros on this form will eventually come up with as the best way of going! |