Drying out wet hulls ...

[The Wolf]

Is HOTVAC the go-to preferred method for drying out wet hulls, whether they be fiberglass solid or cored?

It seems that attempts to merely dry the hull doesn't remove the styrene pockets, pthalic acids, glycols and other residues, which are the real enemies of osmosis.

Have any newer methods come to the fore over the last 10 years?

[thinwater]

How would heat of vacuum remove phthalic acid, with a melting point of 405F?


I've designed, built, and operated glycol distillation plants, and I am equally skeptical that you can evaporate that from a hull with any heat that the GRP can withstand without damamge and any vacuum you can actually achieve and maintain.


Not impossible and certainly better than air drying. But I would bet lunch they typically run it just long enough to get it good and dry. The styrene may evaporate. But they don't actually claim phthalic acid in the description.



Water, yes. But this other claims are pretty sketchy. The biggest challenge is actually maintaining enough vacuum to evaporate non-volitile materials at reasonable temperatures. and heating the hull clear through.


And then there is this disclaimer:


There are hundreds of reasons why a boat moulding will not dry. Some causes may be as simple as wet bilges, damp trim linings, water filled closed spaces and damp foam filled spaces.

It’s always important that these are thoroughly inspected for before drying programmes start. The gel ‘flow coat’ applied to the interior may also be as saturated as the old exterior gelcoat. When boats are laid up they commonly suffer from condensation on the interior and also, they often have salty bilges. In these cases, the interior flow coat can never be dried and the moisture will continue to contaminate the structural laminate. Another cause of slow drying is likely to be damp or water filled stiffening frames. These may be hollow or foam filled and should be identified and drained when the boat is first presented for repair.

When the above possibilities have been eliminated, it is likely that the moulding is affected by residues from the deteriorating materials of the moulding. These may be present in friable hydrolysed laminate, between laminations of fibre, or in tiny capillary like cavities caused by erosion. When slow drying is caused by the presence of degraded GRP, the moisture indicated by the meter will be associated with organic acids, styrene and various glycols. These residues can only be removed by either cutting off the damaged laminate, burning off the damaged laminate, or by evaporation under the controlled conditions of the HotVac process.


But it's still a good idea. But perhaps oversold by some vendors.

[Fore and Aft]

The Wolf, the real winner is 10 days for a dry hull which saves you thousands on hardstand fees. The point I think with osmosis is that once you have laid new fibreglass on the hull then you're isolating those pockets of problems from seawater which help cause the problems in the first place. On some badly laid up hulls I have seen its almost impossible to remove all the hull issues. One hull in particular I remember took forever to air dry and was full of air bubbles even after being shaved. So the boat builders screeded the hull with epoxy glue just prior to fiberglassing. Five years later when I surveyed that boat again the bottom still looked like new
Cheers

[pbiJim]

I think that you need to define the problem before you can determine if the proposed solution is appropriate & likely to be effective.


Do you need to dry something out (remove moisture)? Or do you need to remove chemical residues that are not volatile under vacuum?