How dry?

[tomj]

I'm in the process of restoring a 1974 sunfish. I've already had to install three ports to access the backing blocks, all of which became saturated and fell off, and were rattling around in the hull. I also need to re-attach two of the main styrofoam blocks, which also came loose.

So far, no big deal. Here's my question: the closed-cell foam that attaches the styrofoam blocks is TOTALLY saturated with water; it's palpably wet to the touch. I'm assuming I need to remove as much of this stuff as I can reach, even the stuff that fills the gap between the top of the styrofoam and the hull, but I won't be able to reach the outboard side of the styrofoam blocks. I almost certainly won't be able to get ALL of it out.

My question is: how dry does the inside of the hull need to be before I re-attach the styrofoam blocks? Do I need to dry it out for weeks using forced air, etc., or do I merely need to scrape out as much of the obviously damp closed-cell foam as I can and let the fiberglass surface dry out? The styrofoam itself doesn't feel that damp, though it could very well have a lot of absorbed water. Will the pour foam cling to slightly wet styrofoam?

 

[DanB]

How Dry? - Dry Dry - New pour foam won’t adhere well to wet anything.

The pour foam that’s still firmly attaching the styrene foam blocks will dry and you should be able to leave it alone.

Scrape out as much of the pour foam that no longer secures anything. You can get above and below the blocks with something, a grill spatula from the dollar store, something – those are the important areas.

Know of a machine shop near by? Drop in and ask if they have an burnt out industrial hack saw blade you could have - 18” long 1.5” wide. The rounded nubbs of the spent blade make a good removal tool that won’t chew up the fiberglass roving or styrene block.

Weigh your boat to get an idea of just how water logged things are.

Visit the Sunfish Sailors group ( http://groups.yahoo.com/group/sunfish_sailor ) and look up an article on reattaching foam blocks by John Howard. Good pictures of where you are going and what’s needed.

 

[tomj]

Dan, thanks for your reply. I've already the Sunfish_sailor forum article, so I'm pretty sure I know what I have to do.

I'm guessing it'll take more than a few days, or even weeks, to get the old securing foam dried out completely--but if I understand your post it won't matter so long as the new foam won't need to adhere to it. Like you surmised my problem is above, below, and alongside the loose styrofoam, and as long as I completely remove the old foam from these locations, and the styrofoam and fiberglass are dry, I should be good to go.

An interesting observation: the styrofoam APPEARS quite dry, and from what I've been able to read it has much higher water reistance than the poured polyurethane foam surrounding it. I'm guessing 90% of the excess weight in the boat is due to water absorption in the poly foam, not the styrofoam. So I'm thinking of trying to gouge out as much of the soaked poly foam as I can, even where it's still doing its job of securing the styrofoam, with the idea of replacing it with nice, new, dry foam. I know there will be areas I can't get to, and so still plan to give the boat a good, long dry-out in the off season, but I'm hoping that by replacing the soaked foam I can make a big dent in lightening the boat.

Sound like a good idea?

 

[DanB]

Sound like a good idea?

How overweight is your boat? Sounds like you have the Jenny Craig special edition.

I removed some blocks from under the seats of a curiously heavy aluminum row boat that had sat swamped all summer. They felt dry though weighed a ton. When I cut into them it was like slicing a watermelon.

You could go to the charts at US Composites to find the air volume of polyurethane pour foam. From there you could make a guesstimate of the volume of bedding and get a rough idea of the water weight you’ll be mechanically removing. What is it?? Guessing here?? 1 cubic foot of water weighs 64 lbs, 1 lb density foam is 90% air so could potentially hold 58 lbs of water. If all the bedding you remove makes up ½ cubic foot and is 100% water logged you’d lighten the boat by 29 lbs.

From John’s article comments and reading about different grades of foam I get the impression density along with type play a role in plastic film permeability. We can see what the materials are, but I’ve not seen anything about the grade used for either. Point being the 2-part foam Sunfish uses for bedding might only be along the line of 1 lb density which could take up and release humidity quickly compared to a denser grade in the styrene simply as a function of cell wall thickness. If this be the case the bedding could dry more quickly. Unfortunately, we are only left with the empirical method of trial to find out.

I’ll cross my fingers spot drying will let you stick things back together solidly. Let us know come fall.

 

[mike4947]

Before going hog wild hacking away foam that isn't loose I'd suggest weighing the boat first to find out just what water weight you have. The average weight of a bare sunfish hull is 130 pounds.
And I agree the blocks can feel dry as a desert but still hold a lot of water. That's what takes so long to dry a wet hull out. It takes what seems forever for the water in the blocks to migrate to the surface where it can evaporate.