What is the purpose of the ridge on the back of turkish bows
Just like it says up there. Why are there ridges on the backs of these bows near the siyahs, while pretty much all other bows are flat or crowned? And does that ridge make the area stiff and non-working?
The ridge is where the splice between the siyah and the limb occurs. In different bow designs, this splice is treated differently. But in general, it is better to leave the spine where the splice occurs sticking up, and applying a thick layer of sinew to it. The strands of sinew work a bit like the cables on a cantelever bridge.
It is probable that the triangular cross section appeared before string bridges. Aside from being the site of the splices as Stephen correctly points out, it is the place of transition between the broad bow limb and the narrow, but deep, siyah.
The scooped out sections either side of the ridge reduce weight without compromising strength thanks to the sinew on the back of the bow. At the same time the broad belly gives a large area for the splice.
Possibly in early bows where only about of third of the siyah recurved, the triangular cross section was not fully supported by the horn belly and it contributed to further weight reductions in the tips like in the Omnogorov bow from Mongolia.
In some Turkish bows the triangular part is straight sided on the back and in others it is concaved sided on the two back faces.
The scooped out sections either side of the ridge reduce weight without compromising strength thanks to the sinew on the back of the bow. At the same time the broad belly gives a large area for the splice.
Possibly in early bows where only about of third of the siyah recurved, the triangular cross section was not fully supported by the horn belly and it contributed to further weight reductions in the tips like in the Omnogorov bow from Mongolia.
In some Turkish bows the triangular part is straight sided on the back and in others it is concaved sided on the two back faces.