Re: Converging ring
Back in the late 60's and early 70's Merc had SS props for their engines along with Alum and some Bronze (Michigan Wheel). Merc flared the end of the barrel of their props to assist in the suction of exhaust gasses from the engine and to help keep those gasses from being sucked up by the prop and causing ventilation with resultant loss of thrust.
OMC comes out in the early 70's with their own SS prop that is Teflon coated and had a Bronze Diffuser Ring. I bought one for my '72 125 Johnny ($185). Well worth the money as the 125 was eating Alum right and left. The idea that OMC apparently had was to first be different from the competition and second do the same job of keeping the gasses from the blades. So they caused the water flowing immediately adjacent to the barrel to "deflect" into the exhaust stream.
Problem I noticed with that philosophy was that the ring could be knocked off by a tree stump or something and you were without it. Saw several boats over the years with it obviously missing Then there could have been some incompatibility issues with the materials and the mfgr. cost of the extra processes associated with the ring. Have no idea as to whether or not any "drag" was associated with it.
I am not currently aware of what they offer but I have seen some OMC's with what looked to be Merc flared barrels and some with no flare at all....just the barrel seemed to be a bit longer.
My 2c.
Mark
