Learning to sail
Join Date: Aug 2010
Location: San Francisco Bay Area
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Re: Boatyard transducer installation mistake
Yeah, my temporary solution was the transducer glued with silicone to the inside of the hull at an appropriate place. I had upgraded from an ancient early 1970s neon tube-based Raytheon system to a networked, digital system, that had a fishfinder built into the chartplotter. I don't actually fish, but it seemed at the time that more data can only be good, and I took a gamble on the extra cost. I've decided it was totally worth it; I frequently switch into fishfinder mode in depth-sensitive spots, and now I'd never go back to having just a depth number. (Most of the SF Bay is relatively shallow, and while mostly being full of thick mud, running aground is basically something I'd like to avoid at all costs.)
It worked reasonably well. One challenge is that I don't have an especially good flat spot, so it was glued right at the keel, forward of the fin. I had to experiment quite a lot before I found a good spot, using the bag-of-water trick. One thing that freaked me out unnecessarily is that the silicone did not seem to conduct the pulses until after it had set. So basically, right after putting everything into place, the fishfinder couldn't really track the bottom, but the next day, it worked. I don't have a clear idea of why this was.
The main trouble I had is that there's a lot of noise, all of the time, as well as a good amount of 'surface clutter,' which I assume are sonic reflections within the hull itself. I constantly see things that look like fish or other submerged objects, and I basically ignore them. The depth number works fine the majority of the time. But it doesn't some time, apparently when the bottom is funny or the conditions are a little sketchy. I think it's always been when I thought I was in deeper water, but it's disconcerting to not know for sure, especially when I know my course comes near to a known shoal.
The main thing I'm trying to accomplish upgrading to a through-hull is to get additional display clarity, and eliminate the noise and phantom fish. I'm speculating that the "shoot through" is less shoot-through and more "vibrate large portions of the hull." Certainly a through-hull isolates the sonic element, since it's encased in a fairly heavy bronze fitting, so I think this a reasonable thing to expect, if not especially scientific. But something a little more concrete is that I'm definitely going to get a significant improvement in signal gain, which should add clarity even if the isolation effect isn't as significant as I think.
So I think if you merely wanted the depth number, in-hull is totally OK. But I think anyone installing fresh electronics should strongly consider an integrated fishfinder (if they're going to get a chartplotter anyway), and if so, maybe the through-hull will make a noticeable difference.
Of course I'll update once they get the thing installed correctly, and it gets back into the water. (Who knows when that will be.) I won't be able to make careful comparisons unfortunately, because I didn't have the foresight to capture some of the old soundings, but I'm hoping for a pretty significant objective difference. We'll see if it pans out!