There were a number of other systems of forming the framework for a ship; one of the simplest and easiest, both from the constructional point of view and for the geometrical laying off in the mould loft, was that adopted by the majority of American builders and shown in (21). Here two sets of futtock timbers forming one complete frame are all abutted together up to their extremities, the only gap being between each set of frames, which again was filled with salt in the best class of ship. Ships built of teak, incidentally, as many of the English clippers were, did not need salting, as teak has its own resistance to rot.

  It will be noticed also that the timbers crossing the top of the keel in the American system do so without any notching out, the rabbet for the bottom planking being at the top of the side of keel. This was also the style in British naval ships. British merchant ships, however, usually took the rabbet out of the side of the keel at a lower point, nearer the middle, which meant that each floor timber or futtock had to be notched out over the keel so that its under surface lay in line with the top edge of the rabbet.

   One result of this was that the basic keel in British ships projected downwards less than in American construction. Also American ships sought longitudinal strength through additional keel pieces below the basic one, as well as extra keelsons and side keelsons, these latter also helping to stiffen the bottom under the mainmast.

  The remaining structural differences between British and American ships were in the latter's much larger waterways, spirketing, bilge and , side ceiling, and bulwarks. An additional reason for the greater scantlings of American ships was their use of comparatively softer timber than was used in Europe. Externally, British clippers used a wider plank, up to I I in. as against an average of 7 in. on American clippers, a difference which is very noticeable in contemporary photographs or paintings.

   American shipyards also kept to the use of wooden knees for beam ends and elsewhere much later than the British, because of their iron shortage.
The need for extra longitudinal strengthening oflong ships, in addition to these features, was still apparent, however, and it was achieved by using the earlier naval practice of diagonal bracing with iron straps over the outer surface of the wooden frames. The straps were let into the frames to provide a flush surface for the outer planking. In the later composite construction the straps were outside the iron frame flange, which meant that the outer planking had to be notched out wherever it crossed a strap.

  Another method of construction involving the principle of diagonal bracing was used on a few famous clippers such as the Vision and the Chaa-Sze. This involved two diagonal layers and one longitudinal layer  of external planking, as shown in the drawing of the Vision's structure.