Moisture readings?


New member
17 Feb 2002
What constitutes a high moisture reading for hulls. When I purchased my first boat the moisture readings were between 20 and 50 which the surveyor described as being 'low to moderate'.
Since then it's been on a drying mooring and has just had 6 months out of the water, it's been surveyed again with moisture readings of 18 and 19 which another surveyor describes as high and is using the dreaded O word.
To confuse matters further, I've just bought a Griffon which was epoxied 10 years ago, hull readings range from 12 (ultra low and same as dry datum readings taken from topsides) up to 40 (nothing to worry about I'm told). /forums/images/graemlins/confused.gif


Well-known member
9 Mar 2003
s e wales
The numbers themselves are meaningless without details of the meter used, the scale, and the reading of a bit of dry topsides as datum. You need to understand that the numbers show relative moisture - they are not absolute measures of the water content. The meter itself has to be zeroed and the surface has to be prepared. Even then, some of them dont work very well on sharp curves.

My last boat was measured with the Sovereign meter (cant remember which scale) but the readings were about 15 for the hull and 5 for the topsides. Osmosis had started - you could just detect very shallow blisters if you knew what you were looking for. A treatment was done.
If your readings are with the same meter then the hull is wet. However, thats not necessarily the same as osmosis. If it dries out when removed from the water, you likely havent got a problem.

But in the end, there's no point in hiring a surveyor and then taking notice of us amateurs on the site. If you are still worried, then best cough up for an expert type like Tony Staton Bevan (must be an expert - he wrote a book!)


New member
17 Dec 2004
Buckland Monachorum
Have a read of this...
its interesting you never hear fishermen on very old GRP boats that spend most of their time afloat having an issue with moisture...or do you...time for a marine surveyor who surveys old fishings boats to answer that one...My suspicion is its totally cosmetic unless the boat has been built very badly, with voids and lots of chopped mat under the gel coat.
And possibly just a good little earner some boat yard thought up?
(I had a new boat all epoxy that had bubbles on the top sides after a racing plastic map had been stuck there for a summer)


Well-known member
30 Jun 2002
Good answer......Agree entirely.
Would add that a high moisture reading may only show the boat has been in he water a long time, not that it has "osmosis".


The O and readings ....

If what the original post gives as detail is the whole story - then I as a Surveyor openly state that the Postee should go back to his Surveyor and demand an explanation.

The readings are totally without reference, no info on which meter etc. etc. Each meter has different scales and one reading with one is not directly related to another meter. Various meters work on different technology as well ... one on RF, another on Resistive load.....

The Surveyor should explain to the client his findings and not leave him in a state of confusion.

I can also say that just because a guy writes a book, another has this and that or letters after his name and belongs to some association or whatever is no guarantee of anything.

I know of cases of boats surveyed by some well-known people and work completed that IMHO was unnecessary and netted the surveyor involved a commission .... the client a bill of course that often is ill-timed and hardly affordable.

Another area that annoys me is the practice of writing up reports that tie the hadns of the client along with Insurance Co. when applying for insurance. How many times have items been changed on aboat due to some silly comment or misguided opinion of some surveyor who wrote it up into the report as gospel ....

Good example .... Westerly Pageant, Gosport a few years ago .... Husband died and Widow who was not into boats put boat on market. She of bcourse did not want hassle and put boat to a broker. That broker had a private arrangment with a well known surveyor .... She was advised to have a report done to help sell the boat.
Ok we have a very nice well cared for Pageant .... I know the boat and would have been happy to have it as mine ... but anyway. His report a) original Volvo engine to be replaced, b) hull to be ground back and osmosis treatment applied to his spec., c) the chainplates had been extended to allow mast up / down in french canals with high quality stainless steel .... he required them to be removed and original design to be fitted.
Now I looked at the boat just prior to the work and was amazed at the list, meter showed hull as good and maybe not 100% dry - but not requiring such drastic treatment ... chainplates werte substantial and far more than required for the job, engine started and ran nicely - with a full log of use .....
My client declined the boat for another reason and I took interest in the boat to see what would happen .... Myself and the subsequent yard who were given the work advised the lady that she should have second opinion - which she declined. The surveyor in question required the yard to pass to him that removed engine .... the hull would be metered by him throughout and yard was instructed to not interfere - just do as instructed.
The boat was duly completed and argument then ensued - as yard refused to hand over engine to him - stating quite rightly that she was legal owner - not him. Oh - I forgot to say that HE sourced the replacement engine of course.

The final part was that he was banned from that workshop - but still claims to be the Expert in Yacht Surveying .....

I know the boat went to a good home and the new owner of course was very pleased. Not surprising really .... the real loser in the saga was the poor widow who knew nothing about boats and was duped by this 'surveyor'.

I have to declare here that I am not willing to Name the person or Boat for good reason - to protect the ID of new owners and also the lady in question ..... all I will say is the Boat was based in Gosport and is still in Solent area now.

Yard involved was mid Solent based.