Shenandoah Whitehall: Steam Bending

     Before assembling the frame of the boat, we need to put a permanent curve into the gunwales (pronounced "gunnles", these are the topmost stringers that run along each side of the boat).  This is because the boat curves up at both ends, and if the gunwales are put in position under tension, they'll eventually straighten out, forcing the hull down at both ends.  Obviously, this doesn't help streamline the boat, so it's necessary to bend the gunwales ahead of time.  There are a number of ways to do this: you can soak them, hang weights on them, pour boiling water over them, or some combination thereof.  We decided to steam them.

     The process is a little more involved than I expected.  You can't just hang the wood over your tea-kettle; it has to be enclosed.  Most people build a box out of plywood, but we didn't have enough ply lying around, so we went with PVC, which is cheaper.  Once we had requisite 15 feet of 4" PVC, the first thing to do was ensure that the wood is held up above the bottom of the pipe, so that it's completely surrounded by steam.  We drilled out holes for dowels every couple of feet, which worked just fine.

     PVC will bend under it's own weight if exposed to too much heat, so we slapped together a wooden frame to support it.  In this picture you can also see the Y-joint we used to connect the steam box to the wallpaper steamer.  Similar steamers are available online and cost a lot less than the big machines you can get at Home Depot, but apparently a tea kettle and a hot plate can work too.

     

     The wood needs to be steamed for one hour for each inch of thickness -- apparently regardless of what kind of wood is used. That seems a little implausible to me, but that's what Google says.  The gunwales are 3/4" thick, so that means 45 minutes.  We waited for the temperature to come up to 212 before starting the timer-- it didn't take long.  A hole drilled for a meat thermometer came in handy at this point.

Gloves are important.

After 45 minutes, we cut open the duct tape and slid the gunwales straight out of the box and clamped them to the wall.  I understand it's important to do this quickly.  We put together a makeshift form ahead of time, so all we had to do was push the cedar firmly up against the pieces of scrap clamped to the wall, and then prop of the ends.  It took a fair amount of force, but it wasn't hard.

Once it cools and dries, it should hold its shape permanently.