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Moisture Meters - A Love Letter

Updated: Jun 17

[Note... this is one of two notes written together and originally intended to be posted together to answer someone's request about surveying a boat he's considering. The other is called "Relying on 3rd Party Judgment - Some of the Hidden Factors that Impede Good Decisions and Increase the Likelihood of Decision-Driven Harm". Derived from some writing I did a few years back intended to describe from a technical decision-making perspective where/how the process of hiring experts (mechanics, doctors, surveyors, etc) to help with decisions often blows up or disappoints. I decided to just post this one though this refers back to judgment note in multiple places and I can't afford to find and clean up the references. Maybe later.]


As the initial subject is surveying, I want to conclude on a related point... the (naively) ignorant misuse of measurement as the basis for decisions, and the fact that so much rigor remains withheld and so much amateur unearned trust is quietly granted it. Know going in that I am representing all of this is just my opinion.

Full disclosure - Part 1: I have zero experience operating things that call themselves moisture meters beyond occasionally using the resistive type for selecting wood for woodworking projects. I have observed surveyors up close operate them on other people's boats and a hobbyist operate one on my boat, and engaged in discussion with all of them. I also did what hobby thinkers call "research" (Google) and could not find a single source that rose to what I would consider a responsible, credible, professional and correct explanation of either the theory of operation or the associated measurement cultural practices that would to convince me to take them seriously.

Full disclosure - Part 2: If my disclosure ended with Part 1, I'd say I can't point to anything useful I might have to offer on this subject. However, I do have about 40 years of serious professional daily involvement with precision measurement of analog signals with abundant RF content that demands constant awareness and use of the best known measurement cultural practices.

My reloading bench invaded for a few weeks by some of my measurement gear while writing a paper - mid-90's


  • Every single one of the 131 rescue consults referenced in the "Third Party Judgment" post involved this kind of measurement, and not by luck but because I invented ways of "peeling open waveforms" and finding important pathological behaviors invisible to the test instruments of the time. The rescue consults were fun, but the serious money makers for my company were selling measurement tools based upon patents I was granted for those measurement methods, and in licensing those patents to other measurement companies.

  • Whenever I have had to fill out a form as to what my company does, it has said "measurement tools".

  • That experience has resulted in up-close exposure to maybe 1000's of trained electrical engineers and techs doing measurement, and coaching/critique/correction of faulty measurement cultural practices of many of those.

  • I've been hired several times to write measurement application notes for brand name test and measurement companies.

And to be clear, not one second of that 40 years involved low/any cost moisture meters. But there may exist enough overlap with serious measurement that some commenting on this subject is not unreasonable. So, to steal from Darwin... I hope that I may be excused for entering on these personal details, as I give them to show that I have not been hasty in forming my advice.

The "research" - Firstly, please excuse me for this one time labeling the asking of google anything as research. But honestly, in this case... each sentence/comment I read from any source did more to discredit itself with me than to pull me into the circle of true believers. Vague unknowns and misunderstood concepts piled on top of more unknowns and misunderstanding piled on top of still more. Consistent past experience leads me to view that sort of thing through a particular lens. And further, to notice that I've never seen genuine credibility make you work that hard to find it. I know I didn't read everything. I just never read anything that encouraged me to set aside my training and experience and trust it. Such writing might very well be out there. Maybe these things are actually the M1 rifle of hand-held test instruments and I'm all wet... LOL... wet.

Pilot error from unwarranted confidence - Measurement is not the simple mindless pushbutton act I have seen many think it is when they first jump in... MONSTER rookie mistake. Though actually, what isn't like that? (Unfortunately), that is just the hard-wired standard-issue human response to new things. You don't know what matters, so nothing matters (see other note). Measurement science and measurement cultural practices are big spaces that are assumed by new guys to have been installed in their minds the day they got accepted into an electrical engineering program. I'm not being a smart ass... I have had at least 100's of encounters with engineers.. as in guys who actually know something about electronics and related physics though who probably don't often deal with measurement... who walk up to some test instrument, poke their DUT with whatever probe was hanging off it, and confidently/fully accept the number on the screen. Without thinking. "Oh look... a number on a high-tech looking screen. Must be totally valid!" They then often go on to initiate actions/decisions/spending based on that number they have just MINDLESSLY created. Absolutely common, though one part of this typical farrago IS just pure stupidity on stilts... starting off with the idea that some new thing with a name that sounds like exactly the miracle solution you need ACTUALLY does what the name tries to imply.... not how people who think for a living apportion trust in consequential settings.

Now extend that prior paragraph to people who have no training or experience or even partially developed intuition in electrical engineering (i.e. the domain in which moisture/capacitance measurement lives) or measurement, and who cannot even imagine the innocently minor/stupid maneuvers which can steer or otherwise ruin the measurement... like how what you do measuring AC differs from DC... how the conduction path/structures with which the measurement signal interacts shapes the ultimate measurement values... how probing affects the measurement... understand that there is such a thing as measurement cultural practices and that incorrectly employed even slightly they ruin a measurement very easily... who are pathologically comfortable accepting the first technical explanation they hear that COULD be true under their simpler-than-reality world view. And who pluck how aspects of physics works from thin air, and conflate/smear concepts to explain to others how their "measurements" work. Will not end well.

The measurement effect-ambiguity factor - This is the reality effect that any given number displayed on the measurement instrument can often be explained/affected by a range of disparate things, ranging from what the guy holding the instrument thinks it is, to things that are the opposite of what he thinks it is. Probing angle.. probing pressure.. proximity to surface and subsurface features and voids... material differences.. temperature... Incorrectly interpreted effect-ambiguity is a moderately common problem in my world with professionals from the general population vs specialists, and I assume hopefully reasonably it is more common for those with less relevant background.

About capacitance measurement - Right this moment, there's enough extremely well-used professional electronic test instrumentation in my basement under my hockey gear to fund an order for another 42. In addition to the good/professional stuff, I own a few cheapie Chinese capacitance meters.. oh.. and a 950B I restored just because those were cool. My limited-because-I'm-selective research indicates capacitance measurement is how things called moisture meters work. But I don't use mine to test half-million dollar boats through conduction structures that I can't see or know and which could be anything. I use them to check certain parametrics of 85-cent capacitors when recapping vintage audio and such (hobby stuff). And the physical conditions under which I'm testing that 85-cent cap are extremely controlled as compared to the vastly more complex tangle of dimensional/material/geometric variation of a boat. I have seen serious professional capacitance meters in labs many dozens of times. They cost mid-4 to low-5 figures but I've never needed to or have used those.


I could easily go on but I think I'll kill this too-long thing right here. This was my opinion springing forth from unacceptable-to-me unconvincing/lazy/misinformed writing and awkwardly physics-unaware live discussion (again.... NICE GUYS), through the lens of considerable actual formal electronics training. And experience across 40 years of daily analog measurement, and exposure to trained engineers/clients trying, and not infrequently failing, to solve problems using measurement. In case any of the three people who will read this think I'm knocking some particular instrument/brand... or even the industry, please try again. THIS IS ABOUT PEOPLE... casually accepting something upon which consequential decisions will likely be made... without the SLIGHTEST ability to credibly explain using the same caliber of standards/thinking other measurement domains with life-critical consequences do for how the test works or what the measurement cultural practices must be.. with NO measurement background... and... 3 for 3 for in-person interaction with moisture-meter operators... remorselessly assuming they have absolute missile lock on what is happening inside that complex tangle of dimensional/material/geometric variation of a boat because their high-tech display flashed a certain number. Furthermore, before anyone gets the wrong idea I think every marine services guy (and car mechanic, doctor, etc.) is useless.. that is not even close to true, though literally everyone knows sometimes it absolutely is true. All things human are stochastic (cf third party judgment note) and there exists in all things human a broad range of skills, education/training, experience, conscientiousness, respect for physics, etc. From sharp, experienced and ethical to the other kind with most piled up about half way between. At least we try harder on aircraft and nuclear reactors.


I began typing this to answer one guy who asked innocently how does he get a good survey of a boat he's interested in.. sorry it's so long.

Oh.. and about interpretation of any measurement result. After the measurement is done (to assume an ideal linear model which isn't reality either), how that result shapes the course of thinking and action. That's it's own monster subject, at least away from the docks. More "third party judgment" stuff. The surveyor referenced in the above list with whom I spoke and who represented his work as focused 100% on moisture surveys told me something after a good survey of my boat with some slight moisture when I asked how the average boat performs on one of his surveys. We were sitting on the bow of my boat talking and he pointed along the dock and said something like "every boat on this dock that's more than 2 or 3 years old will show moisture, and the only time it will matter is if it's in a critical area. And trawlers have many fewer critical areas than sail boats. Most boats are overdesigned to deal with moisture." Find the paragraph about judgment and wisdom in the "third party judgment" note.



[End Note - Pasting a section from the judgment note as it relates moisture measurement experience]


I've used 5 or 6 surveyors over time. I feel two were good, one ok, and the others... pretend I figured out a polite way to say "useless". (Notice the Gaussian aligned shape of that curve).

  • My first engine survey of my boat was by a guy my broker swore up and down would be good. That alone soured me on buyer's/most brokers... and Larry, Darrel and Darrel's 4th brother who half-assed his way thru the survey. He LITERALLY hand wrote the result up on one of those guest check's you get in diners. I do a lot of oil testing on all my machines and watching him do the sampling reminded me of that Seinfeld episode where Kramer's Junior Mint ended up in the surgical opening.

  • My hull survey guy was fine... he tries when he wakes up in the morning. Yea.. he missed some things. And he missed them.. he didn't see them and call them out as nothing. But I don't expect perfection because perfection is impossible and the things he missed were not biggies (i.e. "my pen is out of ink" vs "you have a number of hot spots on your brain MRI").

  • I came to understand that the first engine guy was supposedly recommended by the engine manufacturer. Remember... I held out for THAT ENGINE model for 18 months because of it's incredible reputation. Nothing about THAT guy went with THAT engine. I went straight to the manufacturer's service division office with a letter to its VP saying that and which clearly came from someone who knows engines and engineering. The VP called me himself the next day and told me he was having "the best guy we have for the 6CT" contact me. He'd done 100's of them. That guy... fantastic. And I bought the boat.

  • At one time I was curious about moisture and one guy in my marina's yard was urging me to hire "his guy" because he had a flir setup. For years.. damn.. 55+ years.. I've done "fine" art photography (mostly fine crap) and that included more IR photography than most ever play with. I tentatively hired "his guy" but bailed after minutes of stumbling and hand waving. ** See note

  • I did then hire one reputed to be and who carried himself more credibly. There's a section coming up where I am going to utterly crap all over anyone who believes moisture meters operated by people who have no awareness of the measurement cultural practices required by RF gear. I loved that he used a hammer and despite using a hammer, spoke in very precise terms. He approached consulting the same way (at least trying to be a scholar) I do and he took the time to get into the technical advantages and disadvantages of his approach.

  • I became concerned when routine measurements I do almost any time I'm in the engine room revealed episodically re-corroding connections to the bonding network, going resistive which had to be cleaned up repeatedly after short periods of time. Ground and bonding are huge in the signal integrity/RF work I do in my job and I do subconsciously focus there out of habit. I brought a guy in and I felt I was mostly hearing made up on the spot banter so I had a beer with him and sent him on his way.

  • Another was then brought in and if I recall, I wanted that to expand the scope to also address the interface between the networks.. terrestrial and marine AC, terrestrial and marine DC (I still struggle to believe half the marina isn't on fire every night), comm and lightning grounds. 10 min in the saloon didn't have me feeling good about that guy either. Still had at least two beers left so also parted on good terms.

  • A potential buyer came aboard this year and got what read to me as "atypical enthusiasm" for this well-known (he said) surveyor... he worked too hard to praise every microscopic aspect of his guy. His use of his personal moisture meter he showed a guy with a huge and formally trained RF background (me) left me concluding he really had no idea. Lots of enthusiasm though. His demo to prove his method accomplished the opposite. GREAT guy. Liked him. But in the end, another guy with a snippet of knowledge wading in over his head doing something for which he has no training or experience. GOOD GUY though.

  • I have twice been allowed to hang with surveyors while they moisture-metered boats on my dock and enjoyed a cordial and respectful conversation (I know my writing reads as no prisoners but right and wrong physics is brutally simple in the no-BS zone in my head. Friendly in person though and can smile and nod all day when anyone's obviously naked emperor passes by) on the subject with both. I respect many aspects of what they do and wish I had much of their [non-measurement] experience, but their explanation of moisture measurement was pure smoke and mirrors. No thanks.


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