Westernlife
Member
Ok so after blowing the bottom end on my 70hp johnson I decided to try and get an 85 I had going, (never used it or seen it run) and I did. So I swapped out motors and hit the water, expecting a little more grunt and speed since I gained 15hp. Well it makes the boat sit slightly lower, eats more gas gets up on plane quicker and holds it alot better (not that the 70 really struggled) but I didn't gain any speed... I actually lost some at times... On Glass like river I had the 70hp doing about 54.5kmh (GPS speed) but the best I could make the 85 do was 50kmh... with one less person then I had with the 70.
So when I got back to the cottage I measured the props since I was sure the 85 seemed smaller and I was right, the 85 prop (no technical "proper" measurments) from hub to the end of the blade (each blade at the widest part) is about 3-3/8" or so, I forget what that measurement was on the 70hp prop but the 85 from the tip of one blade to another again measured at the widest point was 9 something inches. The 70hp was 12-7/8! So can I swap props and gain more speed? Will they interchange? If I'm sacrificing cargo weight and MPG I would like atleast my top speed back preferably a bit more, since it doesn't lose any speed or slow down any like the 70 did in corners and is alot quicker to plane out is it unreasonable to hope for atleast 60kmh? Considering I was getting almost 55 from the 70. The boat is a 1986 fibreglass Thundercraft 16' V-hull Picture is with the old motor.
So when I got back to the cottage I measured the props since I was sure the 85 seemed smaller and I was right, the 85 prop (no technical "proper" measurments) from hub to the end of the blade (each blade at the widest part) is about 3-3/8" or so, I forget what that measurement was on the 70hp prop but the 85 from the tip of one blade to another again measured at the widest point was 9 something inches. The 70hp was 12-7/8! So can I swap props and gain more speed? Will they interchange? If I'm sacrificing cargo weight and MPG I would like atleast my top speed back preferably a bit more, since it doesn't lose any speed or slow down any like the 70 did in corners and is alot quicker to plane out is it unreasonable to hope for atleast 60kmh? Considering I was getting almost 55 from the 70. The boat is a 1986 fibreglass Thundercraft 16' V-hull Picture is with the old motor.