1971 Merc 165 inline 6
I was running a 23 pitch aluminum 3 blade; at 2500 rpm I would do about 27mph with a prop slip of 18-20% using the calculator. WOT throttle rpm was 3900 rpm and around 45 mph with prop slip dropping to 12-15%.
I put a 4 blade 21 pitch stainless on and the prop slip has jumped way up. At 3000 rpm I could hardly get 25mph and would start to overrev around 35mph, around 4300rpm.
I am confused; I shouldn't be getting such high numbers with the stainless. The prop shop said they would let me take it back but I am starting to wonder if a 4 blade prop is going to work with my boat. My boat is a standard V-hull, 1971 Glastron V-174. When I go back to the prop shop should I try to swap this for a 3 blade? Right now my plan is to jump up to a 23 pitch 4 blade. I mainly use this boat for skiing and like the benefits of a 4 or 5 blade prop, but would at least like to get a comfortable 35mph for slalom skiers.
I was running a 23 pitch aluminum 3 blade; at 2500 rpm I would do about 27mph with a prop slip of 18-20% using the calculator. WOT throttle rpm was 3900 rpm and around 45 mph with prop slip dropping to 12-15%.
I put a 4 blade 21 pitch stainless on and the prop slip has jumped way up. At 3000 rpm I could hardly get 25mph and would start to overrev around 35mph, around 4300rpm.
I am confused; I shouldn't be getting such high numbers with the stainless. The prop shop said they would let me take it back but I am starting to wonder if a 4 blade prop is going to work with my boat. My boat is a standard V-hull, 1971 Glastron V-174. When I go back to the prop shop should I try to swap this for a 3 blade? Right now my plan is to jump up to a 23 pitch 4 blade. I mainly use this boat for skiing and like the benefits of a 4 or 5 blade prop, but would at least like to get a comfortable 35mph for slalom skiers.