Hull Moisture?????????

[swanny]

Having stripped back the old, old antifouling and old, old VCTar - 'The Passerby' commented that my hull might not be dry enough to re-epoxy by the spring! Soooo, I tape on the hull in two places a square of transparent plastic to see what condensation I could muster. After five days, nothing. The boat is in a hall and the temperature has ranged from a max of minus 2 at night to five degrees during the day. The boat did of course attract condensation all over the hull as the air warmed during the day but none inside the plastic. Is this proof that the hull is dry???? Should I because it's winter time apply some heat to the plastic to encourage more drying of the hull underneath or wot? 'Passerby' will be back no doubt, along with his equally unhelpful friends and I would dearly love to be ready for him this time.........?

 

[Phoenix of Hamble]

Professionals will dry the hull with lamps.......

I wouldn't have thought that moisture could really be tested so easily, and probably needs a proper moisture tester...

No doubt one of the surveyors/boatbuilders will give a more informed opinion....

 

[yoda]

Use a proper moisture meter, it's the only way.

yoda

 

[woody001]

I have done epoxy coatings over the winter...dont bother, you will trap in more mosture. Unless you are very lucky and do it on a 12c + day.
The only true way of finding out is with a mosture meter.
It's almost impossible to get water out the hull unless you have heaters...it's trapped in....

 

[BrendanS]

the amount of water in a hull is not going to show up on a bit of plastic taped on it in cold conditions. It takes time or heat or both to dry out something where the water is deep in the material.

Heat would be good, it will accelerate the process

 

[swanny]

....all very good chaps but that is of course assuming the hull is full of water. From what I have read about moisture meters, they are pretty inconclusive too and used as a 'guide' rather than a definitive tool. Also, from what I read (extensively at the moment) If you want to dry a hull 'quickly' use heat, but if you have a few months to wait, it will dry anyway.........what say ye now? Surely someone has heard of this method of testing if a hull has moisture within it. Incidently, the boat was only in the water for three months last year after nine months ashore and has been out now drying, free from any coatings or, importantly, any Gelcoat, for three months. Perhaps if I'm lucky she is on the way to being dry for spring???????????? No, I'm never that lucky.

 

[BrendanS]

the method of using plastic taped over hull may well work, but won't work at low temperatures.

Diffusion of water is heat dependent, and when the hull is at near zero degrees over night, and slowly heating to just 5 degrees during the day (odn't forget it will get there far less quickly than the air around it), you will get very little movement.

If the temperature was 15 or 30 degrees consistently, then yes, more likely to show a result.

If most of that three months was substantially above zero degrees, then yes, quite likely to have dried out substantially. If you can't arrange for heating, then a good breeze is a good alternative

 

[ashanta]

Take a moisture reading and only apply the epoxy if the hull is at the /or below the recommended water content level.
I can't remember but I think the suppliers/Manu's worked around the figure 3 from the soveriegn scale but i could be wrong?

 

[oldsaltoz]

G'day swanny,

Read your post and have to advise that one 28 foot monohull I treated took 14 months to dry out, hauled out in the middle of our wet season here in Oz and did not dry out enough during the summer, we coated just weeks before the next wet season sent us buckets or rain. That was a many years ago and no problems since; so please take care, its a lot of time and money and will cost a lot more the second time around what having to remove all the new [and very hard] resin. but there is hope, and i hope the following will help.

Have a look for your local Vinyl layer, they all have moisture meters, it will at least give you an indication.

Don't apply epoxy resin till you are confident the thing is dry or you may make the problem worse; also take note of the manufacturers recommendations, most will tell you not apply below 20c and with humidity below 73%. Never start too early in the day as humidity will be higher and finish by 1430 or run the risk of condensate forming on your uncured coating.

Avagoodweekend......

 

[swanny]

Mmm, food for thought guys, thanks! Incidently, the first three months out of the water at end of season last year was outside while I scraped and scraped. I have no facility to apply heat where she is so I have to rely on natural drying. I intend to put the boat back outside in middle of March to assist drying more. But, I guess I am also prepared for it not drying sufficiently. I will source a moisture metre! Preparing myself for yacht charters instead....just in case! Hey 'Oldsaltoz' where on the east coast are you? I should be over there at this time of year working but not enough Hail in Sydney as yet!!!! (I fix hail damaged cars without painting). Was on Central coast last year, Terrigal, Taree etc. Nice place (not Taree though!) See ya.

 

[oldsaltoz]

G'day swanny,

I'm on the coast close to the Whitsunday islands, great sailing. I had the pleasure of sailing a 40+ foot cat [Stevens/Lees design, USA production cat] from Airlie Beach to Cairns. Great trip south to southeasters all the way.

There is large storm cell about to hit Ipswich on the south side of Brisbane as I post this, just called my youngest son, he lives there, to warn him; he got the alert and was at home with both vehicles under cover.

Perhaps the revised storm warning will reduce your work load?

Avagoodweekend.

 

[stephenh]

I am a building surveyor, not a marine surveyor, I use a simple moisture meter (m.m.) quite a lot.
So here goes :
"m.m."s are only a guide - yes very much so.
Therefore everything is relative -
so - get a simple m.m. and a small notebook.
Choose a few areas that you can assume to be dry - e.g. coach roof, topsides, clean them with fresh water ( salt will affect the readings) let them dry, mark and number them with a pencil, take readings and write them down with the date and temperature. These are your base references.
Now do the same with the underwater areas of the hull.
The bottom of the rudder and keel are areas that could be holding water easily so include these.
Do this on a weekly (?) basis and plot the results on a graph - I use a spreadsheet.
You are looking not at the actual readings but for movement of the graph line - you should get the "dry" areas as a straight line and the "wet" areas as a sloping line.
Eventually the sloping line will flatten - probably will never get totally flat - and there you are....
You must use the same m.m. for all readings as each one has a slightly different reading.
Hope this helps.
I expect to get shot down by any marine surveyors......!!!!

 

[Guest]

the plastic patch was an old method used years ago before more reliable meters became available. It is actually quite a sound method if the ambient temp is reasonable. It is doubtful in the "cold" conditions you quote.

Second you say Gelcoat is removed from your hull ... first post said VCTar etc. - no mention that Gel had been removed. If Gel has been removed - then I am feeling something is not quite right here ... who removed it, how was it removed and why ?
If boat stands outside free of antifoul, VCtar etc. this is NOT the answer to remove moisture from hulls and others who just blandly say - apply heat are also incorrect.
Application of heat alone and in uncontrolled environment can actually induce a "sponge" reaction of the hull on removal of the heat ... as it cools down it literally sucks in surrounding moisture from the air ...
You have to do it in conjunction with controlled air - such as Hot-Vac system or with De-Humidifiers placed into an enclosure around the hull.

Your "passerby" ... the way you put it seems to be known to you ? Is he knowledgable in this arena or just some "amatuer" expert ?

Building meters are useless as they are looking for moisture in much higher concentrations ... Soveriegn Meter is c...p - sorry boys - but it literally only gives a surface and limited depth reading ... even though other surveyors swear by it .. the real machine to get a real depth answer - but would frighten 99% of boatowners if put near their "pride & joy" is the Tramax .... this will show right literally the whole depth when reading ... in fact you can find damp bulkheads behind !

I don't like sealing up a hull without finding out whats there ... but I'm lucky - I'm a surveyor and I have two meters ... general and Tramax for Osmosis repair supervision.

Sorry if I can't be more helpful - but its not something that can really be answered in a post ... it needs checking out actually face to hull !!

 

[Guest]

Stephenh approach is good ...

This has a lot of good sense in its approach - the only question I have is the meter used ...

Simple Meters such as Protimeter etc. as builders would use are designed for moisture in walls etc. - a lot higher than GRP and therefore are unsuitable.

But the graph and regular readings etc. is excellent and actually agrees with my methods ... etc.

Remember the readings are NOT %age true ... they are relative ... and have to be viewed as indication - not fact.

 

[mikebees]

Protimeter & Small Boat Champ

You say the Protimeter is designed for surveyers measuring moisture in buildings which surprises me as the manual for my Protimeter Mini gives the impression that it was really designed to assess whether timber has dried out sufficiently - it lists about 300 different species of tree with tiny variations in percentage between 8% and 28% for calibrating use on each species. No mention is made of buildings in the manual. Would this not indicate that the instrument is very suitable for GRP hull moisture measurement where high accuracy is presumably not really required? Can you tell us in fact what percentage of moisture in the hull would be acceptable for the hull to be regarded as dry?

 

[BrendanS]

he quite clearly stated that the boat is inside, and that the temperature is near freezing most of the time. At near or below freezing, no diffusion is going to happen (simple physics, frozen water does not move), so we did not 'blandly' state heat would help.

The comment you make about reverse diffusion when heat is removed is also erroneous, unless the humidity of the surrounding air is extremely high, and the fibreglass very dry. Again, simple physics

 

[Guest]

Re: Protimeter & Small Boat Champ

I have a Protimeter for use on timber hulls and other structures ...

On GRP - it has use only when readings go off-scale on the Tramax ....

As to actual % in vol or mass .... this is a loaded question as it is not a simple answer and one I would be extremely careful about stating ... Why ?

The hull can be in an environment that high % can be tolerated and blistering not evident. Put the boat into a different environment and over a period with same % the hull can blister - due to its change of surroundings.

 

[Guest]

Brendan ... I respect your posts but ....

In answer to Brendans ... inside or out makes no difference as applying heat without controlled air-space also is wasted effort. Second in fact water / moisture transfer occurs even well below freezing ... witness the tests we do on LPG gas where we have to state moisture in the LIQUID and also Gas states ....

Anyway - if the post is read properly - it is advising that proper measures widely understood and respected are observed ... BUT posts prior to mine had advised applying heat with no other info ... I was supplying info to supplement and correct.

High horse ? Why not - I'm tired of being berated for helping - if others know better - then I bow to them ... otherwise - enough.

 

[BrendanS]

Re: Brendan ... I respect your posts but ....

for gods sake nige. How can you compare water diffusion out off fibreglass, to water diffusion when it is being carried in LPG. 2 entirely different sets of physics, as you should well know.

 

[mikebees]

Very good article by proper marine surveyer here : http://www.yachtsurvey.com/moisture_meters.htm