Moisture meters

[zoidberg]

....and the use of them, following a discussion in the club.

It's my understanding that they provide only 'relative' reading information i.e. one spot compared with another. There is no absolute and specific reading that concludes a 'sound' or 'unsound' situation. Such comparative readings can indicate, for example, an area of 'wet' core where screws penetrate or around a skin fitting or that a rudder is progressively 'wetter' at one end compared with the other. This can suggest further physical investigation by e.g. boring holes and examining the removed chips.

Moisture meters range in cost from ~£500 to ~£15 ( Amazon )

Some yacht surveyors pay more heed to 'tapping' a hull, rudder or deck than to 'moisture readings'. Others invariably include a generalised 'range of readings' including mention of the meter's trade name, but stop short of offering any conclusions based on such readings.

What conclusions have readers determined from their use - or their surveyors' use - of moisture meters readings?

 

[typhoonNige]

Our recent survey failed to pick up a water saturated foam cored stringer, but a Sovereign meter used by the boat yard showed it clearly. Not sure if this is a reflection on the surveyor or the meter he chose to use, but the problem may have been missed without the second check. The sovereign meter also confirmed the dryness of all the other stringers and ribs.

 

[VicS]

....and the use of them, following a discussion in the club.

It's my understanding that they provide only 'relative' reading information i.e. one spot compared with another. There is no absolute and specific reading that concludes a 'sound' or 'unsound' situation. Such comparative readings can indicate, for example, an area of 'wet' core where screws penetrate or around a skin fitting or that a rudder is progressively 'wetter' at one end compared with the other. This can suggest further physical investigation by e.g. boring holes and examining the removed chips.

Moisture meters range in cost from ~£500 to ~£15 ( Amazon )

Some yacht surveyors pay more heed to 'tapping' a hull, rudder or deck than to 'moisture readings'. Others invariably include a generalised 'range of readings' including mention of the meter's trade name, but stop short of offering any conclusions based on such readings.

What conclusions have readers determined from their use - or their surveyors' use - of moisture meters readings?

It's a year or two since these articles were written but maybe worth a read

http://www.passionforpaint.co.uk/downloads/sovguide.pdf

http://www.passionforpaint.co.uk/downloads/skipperguide.pdf

 

[savageseadog]

What I can tell anyone interested to know is that the much used Tramex Skipper moisture meter is identical to the Moisture Encounter meter, save for the labels, which is available second hand for much less money,

 

[pcatterall]

I forget which meter I bought specifically for my hull but it was well regarded at the time.
As a ( land) surveyor I was sceptical about the way 'yacht surveyors' did their readings.
On my own yacht I started to find 'odd' areas of high or low readings. As a result I covered the whole hull with a 12" grid of readings.
When plotted against the hull lay up and fittings there was a consistent match with areas of thicker lay up, stringers, internal tanks etc etc.
In other words a high or low reading was meaningless in isolation.
Out of interest I repeated the readings before and after epoxy treatment, before and after primer application and before and after antifouling. There was no noticeable difference in these sets of readings.
In my opinion just scraping off a bit of antifoul and testing in 3 or 4 random places will not give a meaningful moisture survey.

 

[jwilson]

Cheap meters generally are useless for GRP unless you stab holes in the hull for the spikes. Tramex and Sovereign meters etc don't have spikes. Yes, they are all comparative readings, and it's not moisture they detect, but electrical conductance. If the gelcoat high up the topsides and/or on the cockpit coamings gives high readings a similar high reading on the underbody is probably not a problem. They do have their uses though.

 

[Keith-i]

Definitely only relative readings from the usual non-damaging meter modes even though the display might show a percentage reading. There is therefore an element of experience required to correctly interpret the results and establish whether you do have a damp problem or if it's a false reading.

 

[matthewriches]

When my purchase survey was done, the guy used a Tramex meter, carried out “hammer” sounding whatever that was then also took measurements with something from 2 open holes where sea cocks had been removed before filling. There were patches scraped in the antifoul all over, big chunks scraped off around the rudders and P brackets and around the thruster tunnel.

A good job done I think as I had a survey book of about an inch think given to me with the all clear.

 

[Pasarell]

Nigel Clegg, whose company Passion For Paint is referred to by VicS above, is definitely the expert. He wrote the course and book for surveyors and those surveyors who bothered to take notice have far more knowledge than their many less informed colleagues. Nigel is frequently called on as an expert witness and has, occasionally appeared on here. He also rents out Tramex and Sovereign meters, which saves the high cost of purchase, and will brief you on how to use them.
Probably fair to say that any surveyor with a genuine understanding of osmosis and moisture in GRP learnt it from Nigel!