Dry bottom, wet topsides, reverse of usual - any solutions?

[LORDNELSON]

The problem concerns a 27 foot grp twin keel cruiser, 24 years old, stored ashore, out of the water since last October. Moisture meter shows low moisture content (lowish green sector on the meter) all over the antifouled bottom of boat; when the meter was moved upwards from the waterline towards the deck it indicated yellow than deeply red, that is it was becoming wetter as one moved up and away from the waterline.. The antifouled area of the bottom of the hull was epoxied about 4 years ago. The same pattern of moisture content occurs along both sides of the hull i.e. it is not restricted to one area of the hull. Whilst it seems to be good news that the immersed area of the hull shows low moisture content it also seems worrying that the topsides are so wet. There are no physical signs of osmosis anywhere on the hull. The gel coat of the boat in question is, in a few places, thin to the extent that one can see the grp underneath it as a sort of shadow. The moisture meter was apparently working OK and was tested on several other boats at the boatyard and, on the other boats gave normal moisture distribution and values, i.e. becoming more moist as the meter moved downwards and onto the normally immersed area. Has anyone experienced this type of moisture distribution before or any tenable theory as to why it has happened.

 

[maxi77]

Have you checked inside the boat, I bought a boat where the headlining was sodden, but once removed and the insides allowed to dry it was fine

 

[alan006]

When you tested the section below the waterline, did you rub off the antifoul where you tested it? It might be damp behind the epoxy coating that went on four years ago, but the coating is hiding this from the meter.
However, I think you will find that as long as there are no other problem signs you can probably leave it alone and perhaps monitor it next year went it comes out again.
Hope this helps.

 

[deisel]

When My Bottom Was Dry I Got Some Cream From The Chemist!!!!!

 

[LORDNELSON]

Maxi, thank you for your answer, the side of the hull is covered with thinnish lining material held on with what appears to be contact adhesive. Whilst the side lining and headling did not feel wet thae boat was slightly damp inside (no dehumidifier). Certainly is worth a thought. Many thanks.

 

[LORDNELSON]

Alan006, Thank you for your post. Yes we did scrape through the antifouling but not, of course, through the epoxy. What was notable was the same pattern of moisture distribution along the hull. Thankyou

 

[Lakesailor]

You mention epoxy coating. Have you tried a moisture reading at the same point on the inside as well as the outside of the hull.
Could the epoxy coating be shielding the meter from the moisture in the grp lay-up?

 

[steve_l]

You have capsized!

Solution - right boat, take another beer, relax with the knowledge of a job well done /forums/images/graemlins/smile.gif

 

[saltwater_gypsy]

Are there integral water tanks in the boat??
The type of moisture meter you use is also significant. The microwave/dielectric ones need the same operating environment (ie scrape back the antifoul) to give consistent results.

 

[wotayottie]

solid laminate below the water line and foam or balsa above? interior fabric lining - moisture meters often detect moisture on the inside surface of a laminate or of the wood bonded to it.

 

[jwilson]

Not uncommon, particularly where a boat has had a full 'osmosis treatment' below the waterline, to 'cure' blisters, but as the topsides had no blisters it was left alone.

If you are using a typical moisture meter (eg Tramex) it will read through any barrier coatings, in fact often right through the hull GRP to any damp inside (eg in the foam under stuck-on vinyl linings. You can'y foool a moisture meter into reading lower by a coat of paint, though if the coat of paint is electricaly conductive you can make it read a false high.

What type of boat? Other causes can be balsa core above waterline that has got water in (horribly difficult to fix properly), or leaks into the exposed top "edge grain" of the laminate from badly sealed toerail cappings, but in that case the high readings only usually go down maybe six inches or so.

 

[LORDNELSON]

John, Thank you for your helpful post. The boat is a Mirage 2700. There is no balsa core (thank goodness!). I wondered if it might be leaks down from the deck/hull joint(hidden under a resiliant plastic rubbing strake) but as you mention it would be unlikely to show high moisture for more than an inch or two. I am inclined to the moisture layer on the back of the lining theory even though it did not feel damp.

 

[mormargh]

Do you foam cored stringers running the length of the boat. Over the years, these collect moisture from condensation. Even with weep holes, it is impossible to get out, and would certainly affect meter readings. Unless the readings are the same all over the topsides or there are obvious signs of damage, I would be tempted to say this sort of feature is the most likely cause.

 

[Searush]

Use it to haggle & get yourself a good boat cheap that probably has no problems! Well, no more than normal anyway!

 

[LORDNELSON]

Maxi77
Thank you for your suggestion; yes we did check inside, there were no obvious signs of dampness but the boat had not had a dehumidifier in it nor heating.