Posted by David Hurd on August 08, 2003
This must have been discussed before. I am slightly disatisfied with some answers, largely becaus if vagueness in the definition of "devil". Also on another board the nautical origin was rejected because citations in print exist containing "pay the devil" which considerably antedate any nautical references. As an engineer and vessel constructor I am satisfied with only one definition of "devil", which is "the seam between the deck planking and the sheer strake of the ship". The reason is simple, from an engineering stand point. The ship's hull is in effect a beam which is bent(flexed) by waves, and when a beam bends the highest strains (displacements) take place at the top and bottom, so the deck attempts to stretch when the vessel is "hogged" by a wave peak in the middle and shortens when the vessel is "sagged" by wave peaks at the ends. The worst conditions occur when the wave length equals the length of the ship on the water line. Now in the center of the vessel, there is relatively little motion between adjacent longitudinal planks, because they can take the stress and yield almost exactly the same amount. The situation at the side is different, since the side planking is relatively stiffer and must accomodate it self to the deck planks by buckling or bowing out if the ship is to maintain its overall geometry. This buckling makes this seam the leakiest in the vessel. The sides would fail due to instability if the internal framing was not set up to resist this. The seam is known as the "devil" because of the difficulty in keeping it "payed", in consequence of which it leaks all the time. We are speaking of wood hulls here, in a welded steel vessel the situation is somewhat different.
So in my view other seams which are mentioned in the archives are probably not the "devil" in question. I don't for example understand the reference to a beam under the deck supporting the great guns. Why would anyone have tried to pay(caulk)this? Also reference is made to "garboard strake" and the deck. I think the garboard strake is the planking in contact with the keel at the botom of the vessel.
With this definition of "devil" in mind, the phrase "between the devil and the deep blue sea" becomes the vertical distance between the sheer line and the water line, an area of especially high vulnerability in wooden ships, hence by extension something which is at high risk.
One thing I am curious about is the use of "pay" for caulking. Can anyone cite how this came about?