: Interestingly, most of the "olde time" builders I know of
: have adjusted their notions of what scarf ratio to use; years
: ago it was 12:1 or even 16:1, now 8:1 seems to be the norm. The
: reason of course is the use of epoxy.

: I took a look at scarf ratio from a theoretical point of view; in
: theory it should be sqrt(P/C) where P is the parallel-grain
: strength and C is the cross-grain strength. Since parallel-grain
: strength is about 10x cross-grain strength for most woods that
: would indicate an optimum ratio of about 3.2:1. Since figuring
: that out I have worked with ratios down to 4:1 and found the
: joint to equal the wood strength.

: Of course, there are some caveats. A joint with a steep angle tends
: to slide apart when clamped so the clamping arrangement is more
: complicated, and there is always the concern that the glue could
: weaken with time or moisture. So based on that the 8:1 ratio
: makes perfect sense, and certainly wastes far less wood than
: 12:1. I usually use 8:1 below the water line and for wood that
: will be bent after scarfing, and 6:1 for unstressed joints above
: the water line.

I use the 8:1 scarf primarily because it wastes less wood than a longer one. Longer is stronger and bends more naturally.

Bill H.