This is an example of a bone dry core on a J Boat. Refer to the chart on page 1.
This is an example of a "high moist" range reading on an O'Day. This deck is not destroyed but any further leaking needs to be curtailed asap or it will be ruined shortly. Because of the location, next to a chain plate, however this should be attended to and the core removed and repaired. There are some ares of a boat that you certainly don't want wet or even "high moist".
This is an example of a "high wet" reading on a Tartan 37. This port light has likely been leaking into the decks core. While this is not in a totally critical location the genny track is only a few inches away and was reading in the high moist range.
A high reading bellow the port light and a moist reading near the genny track leads one to believe the port light is the likely culprit as the moisture diminished the further away you got from the port light. The moisture had traveled a good 7-8" towards the genny track through capillary action though and about 12" side to side.
This is a very bad example of exactly what you don't want to see, a totally saturated core. This boat lives on a mooring and this is one of the primary mooring cleats. Perhaps there is likely some serious delamination going on and degrading or degraded core as one would assume. This core however was routed out around the bolt holes and found to be dryer than would have been expected. Meters can read metals and perhaps a backing plate so this reading was not as accurate as one would like it to be.
Remember the degradation and physical rotting of the core begins around 20% on the CT-33. The longer it has been above 20% the more likely are the odds for a total failure and delamination of the skins but this can still take a long while. I have seen decks with 25% readings going back 10+ years be taken apart only to find that they were damp, but still very, very structurally sound. ALWAYS incorporate spot soundings and core samples BEFORE digging into a deck.
Here's is another example of total saturation this time on a C&C. This is a must do fix and this boat is not one I would like to set out to sea on. Remember, the chain plates hold up the mast and the deck is an integral part of the support system for the chain plates. This particular boat had moisture in lots of critical places though she looked very presentable. Unfortunately without a meter you'd likely hire a surveyor, based on cosmetics, and pay them $600.00 to find this! Save yourself $400.00 and buy a meter.
If you still don't feel comfortable using a moisture meter, even after reading this, please do not buy one. If on the other hand you are competent with a wrench, have common sense, enjoy DIY and have the desire to read beyond these pages and do your home work the moisture meter will be one of your best boating investments!
This is an example of what a saturated core looks like during the rotting process. If you look ahead of the chisel you can see how the balsa just turns to mush when you touch it with the chisel. This was a deck penetration under a teak hand rail.
Saturated Core 2
Here's another view of a saturated balsa core. As you can see the balsa actually looks wet and you can physically see the moisture.
One should note that this balsa, even in the present condition, still adhered quite well to both the top and bottom skins and required a screw driver to pry this square from the rest of the deck. At some point this would have failed. Even this wet, the deck was still sounding out with minimal differences in tone. To the untrained ear, without a moisture meter and only a hammer, one might assume this deck was in A1 condition.
This is a good example of why spot soundings and moisture readings should always accompany one another.
30% Wet Core Reading
This is the adjoining deck section to the photo above with the chisel. As you can see the color of the balsa is telling you how wet it is. If you scrape out this core and compress it between your fingers it drips water like a sponge would.
It should be noted that at this stage of rot (early) the core is still tightly bonded to the skins. If this moisture were allowed to continue the color of the balsa would continue to darken and literally rot away leaving no strength.