The Electrophysics CT-33 Moisture Meter
I've always been a big proponent of boat owners, and more importantly boat buyers, owning a moisture meter. I don't suggest this because I want every DIY boater to think they are a surveyor, or to try and circumvent the surveying process, that is not my point at all. I suggest it because in all seriousness the meter above paid for its self the first time I used it to rule out just one boat. Essentially, a survey for 30+ footer can run $600.00 or more these days and whether or not the boat passes you pay the surveyor the $600.00+.
More often than not you find a boat and it looks great on paper and on Yachtworld.com. You then meet the broker, bring your spouse and you both get an extreme case of boat buyers lust. "She's just perfect!" Your heart gets racing and you begin to imagine how much fun it will be to own her. But wait a minute, she looks great on the surface but what's underneath? Is she in need of hidden big $$$ repairs?
Any good and reputable broker should offer to bring along a moisture meter, if not just ask. Sadly though many less helpful or thorough brokers claim they don't have one or don't know how to use one. More often than not they don't actually own one. This to me is like going to a family practice doc who does not own a stethoscope. If this is the case ... well.. your choice? I know many good brokers, who have meters, and who go over the deck and cored hull before even listing a boat. Ask all the questions! If you don't ask them, you won't get any answers.
So what can you do to protect your self from paying for surveys on boats with saturated decks or hull core? Buy an Electrophysics CT-33, or its sister meter the J.R. Overseas GRP-33, read this blog and the manual, do a Google search of "moisture meters for fiberglass" and then go for it.
When we bought our current boat I looked at over 50 boats, meter in hand. It did not take me long to rule many of them out due to severe moisture issues. Many times I would not even involve the broker and instead would do a drive by, find a ladder, and at least circle the chain plates and deck fittings near the rail. I don't suggest boarding any boat without a broker, I didn't just leaned the ladder up and did some cursory checking, I have been able to rule out many boats this way without wasting a brokers time. Heck on many "drive by's" I never even had to get out of the car! I saw some nice boats and some basket cases but unfortunately some had some really hidden deck problems even though they were in good cosmetic condition.
The CT-33 is sold by Electrophysics in Canada currently sells for $160.00 and you'll need a calibration block for another $10.00. The US distributor, J.R. Overseas, has an exclusive deal for all US sales and they sell a meter that is slightly altered, has different scale graphics but that is essentially a very similar meter. The J.R. Overseas GRP-33 sells for $325.00. I use the CT-33..
Electrophysics Inc. (LINK)
The photo above shows the first thing to do when you turn it on. Simply flip it on and hold it vertically in mid air. The needle should read zero. This is an initial calibrations check.
Please DO NOT buy a moisture meter if your intent is to circumvent the survey process! To master the use of one takes time and should be used with soundings, something many DIY's don't have the ear for. Using one to rule in boats that may be a good candidate for a survey or to rule out boats that have a pegged meter all over is fine and can save you money.
CT-33, Copper Plated Calibration Block & Acrylic Spacer
In this photo you can see the meter the copper faced calibration block and the acrylic spacer. These two items are used to calibrate the device. Though you will likely never need to calibrate it, the check takes just a few seconds to confirm the calibration is within spec.
Copper Calibration Block
In this photo the calibration block is laying with the copper face down and away from the meter. This face down orientation is what you use when checking the calibration.
Calibration Plate & Spacer
Next the acrylic spacer is placed over the calibration block and it's ready for you to set the meter on. The meter can't see beyond the copper so it does not really matter where you set it to check the calibration. You can even set it on a saturated deck if you wish..
Testing The Calibration
When the meter is placed atop the spacer and copper faced calibration block the meter should read exactly 14%. My camera was slightly off center but the meter does read spot on when you are directly over it.
So if the meter reads zero when holding it in mid air and 14% when placed atop the calibration block and spacer it's ready to use and in perfect calibration.
Test Panel & Meter
In order to display how the meter works I chose to use a known dry chunk of deck skin I had lying around. The deck skin is made of sandwiched balsa and is quite typical of most hull and or deck construction. This piece actually came off of a Maine built Downeast style boat but sandwiched balsa is fairly straight forward stuff.
Meter Reading of Dry Test Panel
Now I know what you're probably thinking "it's already wet"? If you thought that you'd be wrong. This 6% reading is actually about as bone dry as you'll ever get on either solid or cored fiberglass using the CT-33. Using this meter any reading between 0% & 15% is considered dry on fiberglass.
Remember this meter is primarily designed for the many different species of wood. It may also be used on man made materials such as fiberglass. You'll need to reference the scale found at the end of this page for fiberglass interpretations/translations.
Contrary to popular belief moisture meters don't actually read moisture. They actually read capacitance. This capacitance reading is then transposed, onto the analog display, into a relative moisture reading.
Meters Read Metals !
In this picture I am holding a piece of metal up against the underside of the simulated deck/hull. As you can see the reading has gone from 6% up to 7.5%. This cored deck piece is a little over 3/4" thick and still the meter picked up the metal. If the deck were thinner the reading would have been higher.
It is very, very important to know what is UNDER the deck before taking a reading and the approximate thickness. Some new boats, from builders like Catalina, have aluminum plates glassed into the deck under winches, stanchions and other hardware. These aluminum insertions will cause "wet" looking readings as they are only about 1/4" deep at best. Large backing plates can also throw off readings so please do your best to look inside and to be sure your not reading metals through the deck.
This meter is designed to read approximately .5" deep but as you can see it will still, just barely, see a piece of metal at 3/4" depth. This is a good thing especially on cored hulls. Why? Well for one meters will read the copper in bottom paint as moisture so you can't use one over bottom paint.
Secondarily any hull that has recently been hauled will have rather high moisture readings. If the hull is cored, and close to 3/4 of an inch thick, the exterior paint won't throw off the meter by much and you'll be able to take moisture readings from inside. This is why it is best to go around thru-hulls from the inside not outside. On solid glass hulls I would not bother metering and would suggest focusing your efforts on the deck and bulkheads. If everything else checks out, namely deck and bulkheads, bring in your surveyor to do a full bottom examination.
One other area for potential high misreading could be a gelcoat with a high metals content. Some gelcoat manufacturers use titanium dioxide as a coloring/pigment agent and in some cases it can throw the meter off. If you get consistently high readings on a gelcoat find a known dry area and take a baseline reading to compare against.
Reading 5/8" Solid Fiberglass
Here is a piece of 5/8" solid fiberglass I laid up to cut thru-hull backing plates from. It is bone dry and has never left my shop or been wet other than atmospheric moisture. As you can see it reads a little over 8%.
Different materials can have different readings. This piece of known dry 5/8" solid glass actually reads slightly higher than a dry sandwiched balsa core. Both of these chunks have been sitting in my shop for well over two years, stored right next to each other, so the environmental controls were identical. No need to worry though as any reading on fiberglass between 0% & 15% is considered dry with the CT-33..
Water Mist Sprayed Onto Surface
I wanted to illustrate just how sensitive these meter are and to impress upon potential meter owners why the deck surface MUST be BONE dry before using a moisture meter.
I simply used a misting bottle of water and sprayed the surface of the cored deck chunk to simulate dew or rain. I then used a terry cloth towel in an attempt to dry the surface before taking a reading.
Residual Deck Surface Moisture
As you can see, even after wiping it with a towel, the reading was drastically higher and certainly in the high "moist" range.
Please DO NOT use a meter on any deck or interior hull sections that have dew, condensation or where it has recently rained. If you must take a reading after a rain or dew use a rag dampened with either Acetone or Denatured Alcohol to ensure the surface is bone dry before taking a reading. I still suggest waiting if at all possible. I only suggest Acetone with the utmost caution. PLEASE DO NOT use Acetone on a boat you don't yet own if you have even the slightest concern it is a painted finish. Never use Acetone on a painted surface!
Acetone drys surface moisture faster than Denatured Alcohol but both work. I suggest the latter and a little more patience as it is much safer.
Again you can not take a reading with even the slightest amount of surface moisture!.
The CT-33 Scale For Fiberglass
This is the scale for translating meter data. It's is fairly straight forward. The scale on the left is for reading wood, or a wood cored laminate and the scale on the right is for reading solid fiberglass. As you'll notice a 30% moisture saturation in wood or a cored section is only equal to 3% total absorbed moisture on a solid fiberglass with no core.
Core rot, degradation and the physical failure of the core can begin at about a 20% reading on the CT-33, sometimes sooner, which is in the high moist range. A pegged meter is indicating a moisture content in the core of about 35% or more!! If boats were made out of water this would be one thing but a core, with even close to 35% water content is not a good sign.
*Some other important things to remember:
Moisture meters read metals and display it as moisture. If you want to take reading bellow the waterline you'll need to scrape away bottom paint in order to get an accurate reading. This is a bad idea and best left to your surveyor. If you want to check for core moisture bellow the waterline do it from inside the hull on areas around seacocks etc.. I do not suggest that you use your meter for bellow water applications, with a solid un-cored hull, as these readings can be very misleading and are best left to a pro to interpret.
Moisture meters can not read frozen water. There is no benefit in even bringing your meter to a boat in the dead of winter. Along those same lines if a surveyor says he can survey a boat for you at 20 degrees F and get moisture readings walk away! Temps should be well above freezing, for a while, before even considering moisture readings.
Always find the lowest reading you can on the boat to use as a baseline. Many times on sailboats you'll find some dry core right above the wind speed & depth gauges if they are mounted on the cabin.
Look for differences in deck moisture readings. Diminishing changes in readings as you move away from a deck fitting are good indicators that the deck is wet around the fitting and that it is leaking or has leaked.
Most every boat has some deck moisture so don;'t be too alarmed at some "moist" readings. Readings in the moist range are certainly areas of concern but I would suggest bringing in a surveyor if you like the boat. If on the other hand the meter is pegged in multiple areas sch as mast bases, chain plates, genny tracks, bulkheads and other high load areas this is a boat that is probably safe to walk away from and continue looking.
Remember this is not for you to become an expert just to prevent you from spending $600.00 needlessly on a basket case boat. A few years ago I knew of a boat that had been surveyed almost ten times in two years on the market. She had wet decks, a saturated rudder and hull core moisture around the thru-hull penetrations. Each time the potential buyer either paid a discounted rate to "buy" the previous survey usually half price but it varies or to have a new one performed. A simple CT-33 purchase for under $200.00 would have saved these buyers some serious money. Each buyer could have ruled this boat out rather quickly with a little knowledge.
If you don't feel comfortable buying and using a moisture meter by all means don't. A little common sense goes a long way and is all that's necessary. Buying a meter when buying a boat will get you well on your way to saving money on unnecessary surveys. If the $179.00 price tag (including delivery) is still killing you it's very easy to sell it when your done on any of the sailing forums.
How many times do you need to fork over $600.00+ when looking for a boat before you invest in a moisture meter. Don't laugh I know some who have coughed up close to 2k in the search for a new vessel and the surveyors loved every penny of it.
The use of a moisture meter is only to determine if the boat is worthy of spending the money to continue on with a full survey. This is not written, nor intended, as a means for you to replace a professional survey. This article is intended to help you uncover boats which are clear lemons and which ones are worthy of pursuing further.
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