Vacuum Bag the whole boat?

[A Fn Noob]

Ok, sometimes I wake up in the middle of the night with ideas.

I am re-doing a 30y/o boat that had saturated foam, wet stringers, etc. Each stringer had some rot in the middle sections of the boat, but rather than patch, I gutted everything. One reason was that I was not about to wait 6 months for everything to dry out.

Tonight I was reading about vacuum-bagging, and it made me wonder if a person could dry out an entire vessel by pulling it into a deep vacuum. Im talking about down to 15k microns. Depending on the amt of water, it could take days, but thats better than months. Wet foam could be dried completely without ever touching it.

I am an HVAC guy, we use 6-7 cfm pumps to evacuate refrigerant lines before charging systems. The primary reason is to remove non-condensibles (air), but also to boil off any moisture that could be in the system. Any service guy that cares about what he is doing carries a micron gauge to "see" when the moisture is gone. (You are lowering the boiling point of the water by having it in a vacuum...Water can boil at room temperature, and removed by the pump)

I think that plastic sheeting may be too weak/porous to pull and hold a deep vacuum, but I think this could potentially be a viable way to (relatively quickly) dry a waterlogged hull without destroying the boat to scoop out wet foam. If you had a comletely airtight encapsulation of some kind, it would work without a doubt.

With all the fiberglass-composite "No-Rot" boats out there, the repair of the future is gonna be removing the 400lbs of water they have swishing around inside that foam.

Drive-in boat drying.

[yokebutt]

Can and has been done. Use real vac-bag film and sealant tape.

Yoke.

[ondarvr]

Many times they put the hull (new construction) under vacuum and leave it that way over night or longer to get all of the moisture out of the glass and core before infusing the resin.

[jimslade]

Your better off setting up fans. Drying out with vaccum pressure could cause a warping effect in the wood. The wet wood would compress under vacuum pressure. It can be done it with properly placed fans in about 30 days.

[samhales]

I am up against the same problem but on a smaller scale by the sounds of things.
I am refurbishing and customizing a small 15 foot fibreglass runabout. I love the boat hull design as it has some nice lines and looks great for a 1980's model. Some of the wood floor was quite spongy so i cut it away only to find a lot of wet soggy foam. A couple hundred pounds I would say. I have remove just over half of the foam and found wet spongy stringers and a rotted transom. the transom was removed and is waiting for replacement. My questions are??????
Can I use laminated fir plywood to replace or attach to the outer sides of the existing stringers now that they are dry in order to give more structural support? Also, can regular fir plywood be used to rebuild the transom? The boat is being converted from outboard to inboard so, I will be filling in the transom area that is presently shallowed out to handle an outboard. The boat will be propelled by a custom surface drive so I am just not sure how much reenforcement to give to the hull near the transom and the transom itself.
Wow, that was a long winded story!!!!!

[jimslade]

Replace all rotted wood or you will be doing the job again. Marine ply or core material works best.

[samhales]

Thanks Jim, but is it okay if I use fir plywood that is of good quality rather than marine grade?

[samhales]

Woops, what is core material?

[jimslade]

You could use exterior grade ply. it will rot faster. Core material is material used in between layers of glass for structural strength.ie balsa core,divynicell nidacore, klegecell,airex and many others. Most will not break down or rot except balsa.

[samhales]

Thanks Jim that information is very much appreciated by a newbie like me.
have a great New Year!!