Checking F25 with Moisture Meter

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Wilfred934
Posts: 19
Joined: Sat Dec 13, 2008 4:52 pm
Location: North Yorkshire, UK

Checking F25 with Moisture Meter

Post by Wilfred934 »

Hi Guys,
For some time now I have been seeking a sound Freedom 25 here in the UK to replace my twin lift keel Freedom 21 DAYDREAM and I have been concerned about the condition of the balsa-cored F25 hull on boats that are now approaching 25 years old or so. My key concern is the integrity of the balsa-cored hull & deck/coachroof mouldings - everything else I feel I can fix fairly easily.

I rented a TRAMEX Skipper Plus moisture meter to check out a 1985 F25 which had been kept afloat all year round for the last 10 years and although there were no significant signs of blisters and with the exception of one limited area on the transom all of the hull & deck/coachroof zones sounded-out fine when tapped with the plastic handle of a screwdriver as a crude “acoustic” check for core–to-skin disbonds, the hull moisture meter readings gave me some serious concerns.

The second part of my posting gives details of the TRAMEX readings – has anyone out there got first-hand experience of moisture checking a balsa core hull – what concerns me most I guess is how to interpret this information? Do high moisture meter readings mean a “wet” outer skin with “dry” balsa core or “wet” skins and core – or whatever? I am an experienced aerospace composites engineer familiar with composite sandwich structures and I have read almost everything published about this problem but I am still puzzled about how to interpret the moisture level data. Can anyone help?

Brief Summary of the TRAMEX Readings: The instrument manufacturers advise that the best option for surveying the overall moisture levels is to use their unit set to Range 1 & the Comparative 0 – 100 scale. One prominent UK surveyor uses the following assessment criteria:

• Low to Medium-High Moisture Levels: Readings from 15 to 45
• High Moisture Levels: Readings of 50 to 80


When the underwater hull area was checked by this surveyor in 2006 there were 22 readings taken and about 95% were in the 15 to 45 zone and about 5% in the 50 to 80 zone.

When I checked the underwater hull area November 2009 I took 34 readings and only 15% were in the 15 to 45 zone and 85% were in the 50 to 90 zone.

The deck and coachroof areas were mostly OK but there were some very high moisture level readings around one stanchion and the coachroof mounted winches, which I assume show moisture ingress into the balsa core but I feel this can be fixed and if necessary core replaced.

However do the high underwater hull readings mean that the hull has an unacceptably high moisture level and can I infer anything about the condition of the balsa core in this area from this set of readings? Has anyone got any experience of these matters please?

Wilf Bishop
Freedom 21 UK DAYDREAM

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Michel
Posts: 546
Joined: Sun Dec 07, 2008 5:48 am
Location: Zaanstad, the Netherlands, EU

Re: Checking F25 with Moisture Meter

Post by Michel »

Wilf,

I read a few articles a long time ago the drawing conclusions about core wetness is not so straightforward as reading the moisture meter's output. Here's one such an article. http://www.marinesurveyor.com/meters.html

I remember that the hull has to dry out for a specified time when you do moisture readings and you have to take account of air and surface temperature, humidity and thawpoint. All of these points influence moisture readings that are taken from the surface of the laminate.

A wet core does not mean that the integrity of the laminate is compromised. Delamination and rotted core do comprimise the integrity.
Michel Capel, Freedom 44 #4 1981 'Alabama Queen', NED8188, cat ketch with wishbones, home port Enkhuizen, the Netherlands, 52*42.238'N 005*18.154'E.

AlanK
Posts: 127
Joined: Wed Dec 10, 2008 6:59 pm
Location: Freedom 33 Boston, MA USA

Re: Checking F25 with Moisture Meter

Post by AlanK »

I use a moisture meter and check my hull, deck and rudder each winter (F-33). Generally from my experience and from what surveyors have told me using soundings from tapping seem more dependable for identifying structural issues.
I have had numerous false readings due to backing plates, water tanks etc. I have also drill pilot holes from the inside in a few small areas that read middle range and always found things dry.
In a few spots in the cockpit sole, around a stanchion backing block and on the rudder I had some very high readings. These very high readings did actually turn out to be wet balsa core which I then repaired.
You seem to have a lot of high readings. I would try drilling a few small pilot holes through the inside laminate into the core and see what's going on if anything.

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