Moisture in GRP

[Herald]

Hi All

Just in the process of getting rid of the wooden boat and replacing with a second hand GRP 35 footer. More comfortable for SWMBO.....

Surveyor has been round today and noted that the moisture readings taken were high and she was quite wet below the water line. The topsides were also measured and found to be in the medium range. He is not unduly concerned by this and there were no signs of any blisters on any of the hull.

Boat was built in 1986 and has been out of the water in it's cradle since summer 2007. A previous survey was completed in May 2007 and all reading were found to be within the green range on the moisture meter.

Should this change be expected, is it normal or perhaps a dodgy meter? My first GRP boat and concious of the dreaded "O" word and whether to continue with the purchase.

Any thoughts / suggestions much appreciated.

Tom

 

[npf1]

some useful info here: http://www.bluestarsurveys.co.uk/skipperguide.pdf

and here

http://www.bluestarsurveys.co.uk/osmosis3v6.pdf

 

[sterntube]

Its not a princess by any chance is it?

 

[Herald]

No, not a princess. 35' Bolero sailing yacht

 

[matelot]

most likely the result of two different meters possibly two different surveyors. the green sector sounds like a tramex meter. I dont remember the sovereign havinbg coloured sectors though I could be wrong.

some meters will detect condensation on the innner surface of the hull. was the boat damp inside / was it a cold night the night before?

 

[Pasarell]

I wouldn't be too concerned about the variations between meters. You can get that from the same meter on different days as Matelot says. The most relevant point is the variation between bottom and topsides. On a 23 year old boat I would expect the bottom to have some moisture content while the topsides are pretty dry so your surveyor sounds about right

 

[maxi]

At least the surveyor measured the topsides which is wholly sensible - but sadly uncommon.

The topside and underwater areas will be the same laminate, laid up at the same time as each other. Therefore the 'interesting' measure is between the moisture reading of the topsides, which have not been immersed for more than moments at a time, and the underbody which has experienced total immersion.

The meter will not tell you the actual moisture content, but will give impartial indications of variances in moisture content between different areas. These readings must be interpreted, art aided by a little science - but not pure science.

If there are no focus areas where readings are significantly high, then it is "probable" that there is little to worry about.

 

[Herald]

[ QUOTE ]
.some meters will detect condensation on the innner surface of the hull. was the boat damp inside / was it a cold night the night before?

[/ QUOTE ]

It was definately cold the night before as there was a frost yesterday morning. Not sure what she was like internally, but has been laid up ashore for 18 months with the washboards in and little or no ventilation.

 

[seabright]

My last surveyer used his meter on the boat I was thinking of buying with the hul still dripping wet. Gave quite high readings as I recall.

Far what its worth I would believe what you see. If in doubt get it done again by a recommended person whilst you are there so you can also have a chat about it.

Moisture and even osmosis in reasonaly thick hulls is not a big deal unless.....

 

[matelot]

Thats a likely reason for the difference. Was the first survey done in mid summer?

I once found very high moisture on the bow of my Prout cat. Turned out after investigation to be salt on the inner surface of the hull from when I had removed the log whilst afloat. Quick swill with fresh water and the moisture reading dropped like a stone

In the end you employ a surveyor to provide advice. Talk it through with him - he's the expert, not us.

 

[Herald]

First survey done in May.

Thanks for all the comments.

 

[dombuckley]

Yes - both Sovereign and Tramex meters are affected by both temperature and humidity, so readings will vary even during the course of a single day. Cooler temperatures and higher humidity will result in higher readings.

Additionally, the Tramex detects much further into the laminate (approx 30mm), so can be affected by condensation, metalwork and tanks on the inside. I find it good practice to take readings at the end of the survey: this way, the boat has been completely ventilated for 5-6 hours, including lifting sole boards, and you know where all the metal items / tanks are located.

Also, particularly during the summer, it's amazing how a boat that was smooth in the cool of the morning can start showing blisters as it warms up in the late afternoon.