cedar planks and principles of physics

[JMAC]

I am wondering if a dried out cedar plank, when wet out fully with water will swell to the maximum size it is capable of attaining, or if it will swell to the point where it reaches a certain level of resistence from its neighbor planks on either side. Is it more like a light bulb- on/off? or more like a sponge that when slightly squeezed will hold less water. This is not an intellectual excersize...I have practical concerns...planking issues as it were. I also need a summer extender, I think Black and Decker used to make them...

[Noah]

Well, my planks are made out larch.

Some of them are split down the middle. In the winter they open up from between 1/2" - 1". When they hit the water it takes about 24 hours for a 1" crack to swell closed. It will crush some stuff, but not everything. It will become water tight, which means that it swells enough to compress wood.

Take this to mean what you want. The pressure is enough that you can't open the crack back up. It is essentially like there isn't a crack there.

Noah

[Bruce Hooke]

It will swell until it hits its neighbor, at which point, if it still wants to swell more, it will do one of two things:

1. Dislodge itself or its neighbor if one or the other is not attached firmly enough. This is highly unlikely in a boat that is in anything like useable condition.

2. The wood fibers will get crushed along the seam.

It should be noted that in the latter case much of this crushing is permenant. So, if a plank wants to swell to, say 6" wide and is constrained to 5 7/8" then in the future it will only really want to swell to 5 7/8" (or a little bit more because there is some rebound). This is what is known as "compression set". So, the short answer is that the wood will keep taking up water even if it can't expand any more, although the crushed wood will probably not hold as much water as it would have if it were not crushed, so it is not a black-and-white issue.

What is your underlying concern?

[RGM]

Back to basics. Is this planking "in question" flat sawn or quarter sawn/vertical grain. Wood will come and go more in the direction parallel to the grain, less across it. So, which scenario are you looking at? As Bruce asked, what is your underlying concern?

[JMAC]

My reason for asking is that I'm considering replacing my port garboard. It has two planks with the forward one looking sound and the after one a bit tired. This is cedar on oak. The hull has been out of the water on its third season, and I'm wondering how the area between new and old plank will behave when the water hits it.