Moisture readings

[paul]

My local boatyard has just taken a few reading from my boat and have given me a reading of 10-12. They said this meant the hull is virtually dry and that expoxying can be undertaken with any reading below 15. What does a reading of 10-12 mean? Is it the % miosture content? If so is this really low? The chap from the yard said the reading was taken using a "trans..." something or other. Any one know what this device is and wheter it's differnt to a nowmal misture meter? Thanks

 

[lezgar]

"Trans" I think that is a Tramex Skipper moisture meter.

If the calibration is ok the readings will be %

10 to 12 is low but depend of the calibration of the moisture meter and GRP boats have different materials and different readings .
Usually you take readings of the upper side of the hull (far away from the water)and compare with the readings in the under water hull.

If the boat isn't new and the hull is ok, Why epoxy? There are no motive that will not continue ok

If you have to remove antifoul you can damage the gel coat, epoxy have solvents that can damage the gel coat and is not totally waterproof (can't avoid the absorption of moisture with the hull inside the water, but can avoid the natural dry of the hull out of the water).

 

[Trevor_swfyc]

A moisture reading of 15% on a boat weighing 1 metric ton would be 150 Kg of the wet stuff, so find it hard to believe it can be % moisture. Could it be parts per million (ppm) but this sounds very low. It may be an arbitary number which only indicates as they said <15 is ok to gel-shield.
Now here's a good posting is gel-shield protection worth doing. My vote is yes it is, this must be better than the hull being in direct contact with the salt water.
Its also a good chance to clean the hull completely and check it over.

All the best.
Trevor

 

[longjohnsilver]

Tramex Skipper

If this si the moisture meter used, it has 3 different scales. If you find out which scale was used I'll look in the instruction book and let you know (it's not a %!). Scale 20 on grp on range 1 = 1.8% range 2 =0.9%. If the hull has been shotblasted then %ages are approx 30% less than above.

Hope this helps.

 

[lezgar]

A moisture reading of 15% on a boat would be that there are a 15 % moisture under the area of the moisture pad (around 4 cm X 4 cm) if the moisture meter is calibrated for GRP and with the correct temperature.

 

[Modulation]

You can always use a solvent- free epoxy, if the hull is indeed dry. I used Blakes SFE2000 - A pig to apply but would have been easier in warmer weather. When the boat was resurveyed 6 years later it was still v dry.

Brendan

 

[paul]

Re: Tramex Skipper

I think it was scale 1 (GRP in saltwater) on the relative scale.

 

[Guest]

All the epoxy paint makers run technical helpdesks that will give you an answer to your question. In my experience, they are helpful and do not try to sell you anything.

Also from personal experience, I would advise you to borrow the meter yourself and run some checks. . Make sure that the meter is zeroed, that the areas you try are first scraped of antifoul and then dried with alcohol. As someone has said, compare the readings with those on the topsides. And if you get a rogue high reading, dont panic - check for things like bulkheads, metal fastereners etc.

Boatyard staff dont have the time to be as thorough and careful as you will be, and the one thing you dont want to do is to trap in some un - detected moisture..

 

[johnlilley]

The Tramex Skipper is probably the meter used. This has three scales. The scale used for GRP vessels is the most sensitive, scale 2. The scale has two sets of numbers top 10-20 which is only a relative scale applied to moisture content in timber, and the lower scale is 0-100 this is a percentage deflection scale, 0 being minimum, again not a specific moisture content.
Neither scale is designed to read the moisture content in GRP but the meter is used on setting 2 and reading the top scale for rough determination of whether GRP hulls are "dry" enough for Epoxy coatings. Generally a reading up to about 14.5 (50% deflection on lower scale) is acceptable. As is common it is easy to misunderstand some readings obtained and over-react. Practice makes perfect. For more info try www.turbolink.co.uk and navigate to survey page
John Lilley

John Lilley, John Lilley & Associates, Web site www.turbolink.co.uk navigate to survey page.