Help me understand Keel Rabbet and Garboard interaction near the Stem and Stern

[rtwpsom2]

I am trying to figure out how the garboard interacts with the keel and deadwood, in this case of a Philadelphia Clipper from the 1850's. On the left you see a rough approximation of the cross section of the keel at midships. It shows how the rabbet should be cut into the keel and the garboard and second strake. The garboard is 7 inches thick and 14 inches wide, the second strake is slightly thinner and transitions down to 4 inches thick, the thickness of the follow on strakes. The keel is 15 inches thick and the keel timbers or keelson is 16" thick. On the right is my rough understanding of how the cross section would look at the bow. The outside surface of the garboard and second strake have turned vertical to match the outside face of the keel. If the garboard remains 7 inches thick it would only leave 1 inch of deadwood between the port and starboard garboards. Is this correct or should the garboard thin down to 4 inches at the stem and stern? Or is the solution eluding me altogether?

 

[AllanKP69]

This is really interesting. For the thickness of the garboard, where did the 7" figure come from? Looking at contemporary drawings earlier in the 19th century, they appeared to be slightly thicker at the rabbet but not by much if at all. The contracts I checked call out the thickness of bottom planking without a specific description of the garboard thickness being any different. The plans below are from a lot earlier than your ship, but would it have changed that much within the century.

1811


1833

 

[rtwpsom2]

The info comes from an article written for the Boston Daily Atlas by Duncan McLean dated 5-19-1851:

Her garboards are 7 inches thick, cross bolted, and the strakes outside of them are graduated to 4 inches, the substance of the planking on the bottom,and her wales are 5½ by 7, carried up flush to the planksheer, and outside, from the water to the rail, she is finished as smooth as class. [sic]

McLean's articles are heavily referenced by Crothers in his Clipper books and are generally considered fairly reliable. Here he gives a generic cross section of the bevel type rabbit that was common in George Rayne's ships.

 

[rtwpsom2]

I just found this generic clipper stem diagram from The American Built Clipper Ship which doesn't say anything definitively, but it would seem the garboard would need to be tapered at the front (and probably rear) in order to work well.

 

[DAWarden-(Jaager)]

My dissection of this:

If shipbuilders were anything, they were practical.
The extra thick garboard - one of several methods tried to resist hogging or sagging? The clipper craze was pushing the physical limitations for the length of a wooden hull. The garboard extra thickness would serve no advantage where the deadwood became deep at either end. It would become adz bait there. Narrowing deadwood to "a snap in two thickness" where running aground, hitting floating debris, resisting major sized oblique wave would need strength? Would you risk your savings to provide insurance on a vessel so constructed?
However. with a model, where the thinning is done is hidden. It is a matter of ease of construction. I think that a few snicks with a sharp miniature block plane on inside of the garboard would be faster to do than chiseling down the deadwood.

Mind that the outer edge of the garboard stays parallel with the keel rabbet all the way at both ends. It does not bend up where stem rabbet curves up and the sternpost rabbet requires increased plank width. Any additional width comes from the more prosaic planking. This is buffered by subdividing into gores that all aim at a sweet run of planking. Within a gore, each planking strake means that a new subdivision measure must be made. If the number of strakes within a gore is six, after the first stake is laid, the next strake is 1/5 of the remaining gap. Then 1/4, 1/3...... Subdividing an entire gap into equal widths at the beginning and expecting it to hold true is the epitome of foolish optimism.