Builders' Forum Archives
Re: Flush Hatches - M.C.
Posted by John Beck on May 17, 2007
Chris, To scribe the shape lay a piece of cardboard transversley aross the hatch (laying on the floor, concave side up) at the location you want the rib. The take a compass (bow-pencil) and open it up at least to the max distance between the hatch and cardboard. Starting at one edge tranverse across the hatch curve to draw the same curve onto the cardboard. You must keep the imaginary line connecting the two compass ends verticle during the whole traverse to get an accurate shape.
As an alternative, here is a way to use the ply stiffener without the worries of spring back, or building a clamping form. I did this for the rear hatch of my SW17 hybrid. Note that the ply was smaller than the hatch to allow about 3/4" rim of single thickness around the edge of the hatch. I cut kerfs (fore-to-aft) into the 4mm ply stiffener using the tablesaw with depth about 2/3 way through the ply. I spaced the cuts about 3/8" to 1/2" apart (depending on the radius of bend). The result is like a rolltop desk that lays on the curved hatch with no stress. Pick it up at the edge and it bends like a piece of paper. Fill all the cuts with plenty of thickened epoxy (thick enough that it doesn't drain out of the cuts) and hold it all together with minimal clamping. It will be heavier, but stronger than ribs.
I'm sure CLC is getting tired of my comments lately on the SW17 hybrid flush hatches, but here it goes. The flush hatch installation from CLC that you referenced appears to yield the same outcome as the SW system; that the hatch sits flush WITHOUT the gasket tape installed. It is possible to squash the gasket sufficiently if the hatch is held down with toggles, but no way will bungee cords pull the hatch flush. I ended up removing the 4mm thick rim, and now my hatches are flush with bungee cord system. John Peck, of CLC, mentioned he plans on flush deck on his hybrid MC16.5 and (John, jump in any time ...) we discussed adding an extra spacer such that the top of the hatched is recessed 4mm below the top of the deck before the hatch tape is installed. The bungee system can handle that.
Good luck, John
In Response to: Flush Hatches - M.C. 16.5 by Chris J. on May 16, 2007