Moisture in cored hull

[GAJ]

Has anyone any experience of spurious moisture meter readings ( very high unfortunately) on a foam (Divinicell) cored hull. The Surveyor isn't convinced it's water but could be something else........?
Or had experience of curing high moisture content?
Apparently it is a common problem on hulls of this type such as the major Swedish builders boats. I suppose Bavarias will eventually face the same problem, they are cored hulls aren't they?
Help!

 

[arthur1808]

If you're looking at the boat to buy, (Surveyor?) then unless desperate I wouldn't. On the other hand....

You do sometimes get some funny readings from moisture meters: try leaving the boat on the dry for a while, scrape back all the AF / primer in the area of the reading and apply a little heat (heat gun, hair dryer). See if that fixes the problem.

If it doesn't then you will need to find out where the moisture is. You are going to have to drill into the hull to access the core and see / feel if it is wet. If it IS wet then you will need to drill more to establish the extent of the damage, riddle the area with holes and apply lots of gentle heat to dry out the inside, and refill the core with (IMO) epoxy resin fluffed out with some miroballoons.

Not a nice job. I've been there! One of the holes I drilled came out dry, so ground back a little an filled with epoxy - end of problem. The next patch I did needed extensive drying and was a pain in the a**e because above the waterline, which meant I had to access the core from inside the hull (remove and replace headlinings, etc etc). The final "erroneous" reading I investigated when this was me was on the rudder, and as my 6mm drill bit penetrated the skin I had to leap back trying not to let the full bore of water which followed me get on the plugged in and running drill!! Electrocution was not on the agenda that day. There's more, but you may want professionals to help if you find huge amounts of moisture?

Hope this helps

Arthur

 

[harvey]

Yup...sadly mine weren't spurious readings and it took months to dry. It was a balsa cored hull which had delaminated in areas. Hayling Yacht Company did the biz using vacuum heater pads and infra red heating . They did a thorough job but it wasn't cheap. Good luck!
John

 

[oldgit]

You may find Cored Hulls this website useful in explaining the causes and problem.

 

[snowleopard]

The article refers to balsa cores which are a very different proposition from closed-cell PVC foam. Moisture getting into balsa will inevitably cause rot whereas moisture in a foam core should not penetrate beyond the first layer of cells.

There is one potential cause of moisture in foam cores: where the sheet of foam is scored to make it more flexible. The foam looks like a bar of chocolate and if the resin doesn't fill the scores it leaves a channel for moisture to track through the laminate. This type of foam tends to be used in areas of tight curvature to help it follow the mould.

 

[GAJ]

Thank you all for your input, I have already read the doom and gloom on the website link thanks!
Yes balsa is a different situation from closed cell foam, the water absorption rate and permeability are lower in Divinicell according to the manufacturer, unfortunately I don't understand what a permeability rating to ASTM E96 of 2.8 m2/s x 10 (to the minus 8) it's all Greek to me! Is that good?
I think that the water Absorption Rate of 0.100 kg/m2 is 100gram/cc per square metre is that correct? That sounds to be pretty low.

The question I have in my mind is this does water ingress damage the GRP to foam bond or can it be dried out without any consequential damage?
I have spoken to a chap at Transworld the Hallberg Rassy dealers and he said they just drill holes and dry out the affected Hallbergs with heaters until the moisture readings are acceptable. The same applies to a couple of other dealers/yards that I have contacted.
Graham

 

[Birdseye]

[ QUOTE ]

The question I have in my mind is this does water ingress damage the GRP to foam bond or can it be dried out without any consequential damage?
I have spoken to a chap at Transworld the Hallberg Rassy dealers and he said they just drill holes and dry out the affected Hallbergs with heaters until the moisture readings are acceptable. The same applies to a couple of other dealers/yards that I have contacted.
Graham

[/ QUOTE ]

And they would say something like that, wouldnt they?

I can offer no advice on cored hulls, but I have been through the drying out routine with a solid hull. And it was a pain not so much for the difficulty, or even the cost (the seller paid) but for the time wasted. Which was inevitably a lot longer than forecast by the manufacturer.

There are lots of boats for sale - I recommend you find another one without the problem. After all, you are looking at HR for their "quality" and a wet hull isnt very "quality" is it? I think that Malo are solid hulls but I dont know about Najad.