H. I. McDunnough
Regular Contributor
I recently spun the prop on my 1979 Mariner 40B outboard, and am currently shopping for a new one. It was a Black Max (extra surface area) 10 1/2 x 13P. It worked perfectly for my rig ; I got 29 mph at a max rpm of 5500. My spare is a Vengeance 10 1/8 x 14P, which I am currently using. It runs at 26mph at a max rpm of 5000. I am currently looking at a Yamaha 10 3/8 x 13P. I know my motor is a Yamaha and had always wondered if it should have a Yamaha prop for a few reasons. First, I have always had trouble torquing Mercury props on. The castle nut's machined surface never comes in contact with the prop. Instead, the tapered sides grind into the prop. Second, the castle nut turns onto the shaft so far that there is barely enough nut left to contact the cotter pin. I also noticed that the pictures in the service manual show a white prop, but it has recommendations for Mercury prop numbers. I'm thinking that Mercury just wanted to sell their props before they actually changed to a Mercury prop shaft. Does anyone know if this is really the case, and if I can or should use a Yamaha prop? Thanks.