Hello, new to the Forum. I hope I am posting to the correct section.
I have enjoyed reading, now I hope you can help with a question.
Info:
I have a 1974 Johnson 85hp outboard mounted on a 1978 28' pontoon with a hard roof deck on top, that was purchased two Summers ago.
After the first season I had it, I had my mechanic replace the lower unit fluid as I didn't know when the last time it was done.
The prop is a 13 spline, 3-blade, aluminum, 14x11.
We normally have five adults & five children of normal size at any given time on the boat, along with coolers, ect....
We don't tow any water toys as we have another boat for that. This is more of a cruiser and 'floating island' for hanging out, swimming and jumping off.
Problem:
The first Summer the motor ran great no problems. Ran a steady cruising speed of about 3800 - 4500 rpm.
The second Summer we had it, for the whole season it run fine no issues, same rpm range while cruising. But, at the end of last Summer before storing, I noticed the motor ( or Prop ) would 'slip' at about 4200 - 4300. As in we would be going then rpm gauge needle would 'jump' from 4200 to 4500-4600 for a couple of seconds and you could hear the 'wrrr' sound of high revs, then it would go back down. It did it every so-often, if you know what I mean. We could cruise at 3800-3900 all day with no problem, but once we got over 4000 it would 'slip'.
I checked the prop and there doesn't appear to be any issues with it. I could put it in gear, turn the prop by hand, and the motor would compress as if it were running. No 'slip', but I also know that's not under a heavy water load. I don't know if that's a test, but a fellow boater told me to try it.
So, I was looking for some help as to the proper prop size. I was thinking the pitch needed to be in the 17 range (?).
Or is there another issue?
Thanks in advance.
I have enjoyed reading, now I hope you can help with a question.
Info:
I have a 1974 Johnson 85hp outboard mounted on a 1978 28' pontoon with a hard roof deck on top, that was purchased two Summers ago.
After the first season I had it, I had my mechanic replace the lower unit fluid as I didn't know when the last time it was done.
The prop is a 13 spline, 3-blade, aluminum, 14x11.
We normally have five adults & five children of normal size at any given time on the boat, along with coolers, ect....
We don't tow any water toys as we have another boat for that. This is more of a cruiser and 'floating island' for hanging out, swimming and jumping off.
Problem:
The first Summer the motor ran great no problems. Ran a steady cruising speed of about 3800 - 4500 rpm.
The second Summer we had it, for the whole season it run fine no issues, same rpm range while cruising. But, at the end of last Summer before storing, I noticed the motor ( or Prop ) would 'slip' at about 4200 - 4300. As in we would be going then rpm gauge needle would 'jump' from 4200 to 4500-4600 for a couple of seconds and you could hear the 'wrrr' sound of high revs, then it would go back down. It did it every so-often, if you know what I mean. We could cruise at 3800-3900 all day with no problem, but once we got over 4000 it would 'slip'.
I checked the prop and there doesn't appear to be any issues with it. I could put it in gear, turn the prop by hand, and the motor would compress as if it were running. No 'slip', but I also know that's not under a heavy water load. I don't know if that's a test, but a fellow boater told me to try it.
So, I was looking for some help as to the proper prop size. I was thinking the pitch needed to be in the 17 range (?).
Or is there another issue?
Thanks in advance.