I think you're right about the basic design being Graves'. I seem to remember that Bullock modified the stern and the bows slightly when he made the order. The Graves design was more seaworthy than the Army 'David's, but I wonder how sharp the bows were. The sketch I've seen of the Squib in the ORN's shows a very sharp bow, probably to minimize frontal area to the shock wave from the explosion. If these boats were to operate in Florida, then the issue of formation of weed on the hulls could have been a serious one. I suppose the metal hulls had an advantage in that you could careen or pull them up on simple shipways for cleaning and not have to worry about seams drying out and leaks when you put them back into the water.