I am new to boating so have no experience to draw on. The boat is a 1968 15-foot Larson paired with 85-HP Johnson. Perhaps a bit heavy, but that's the way we bought it. The prop has three blades, 6.5 inches tip to center, so I guess that makes it a 13-inch prop.
First trip: We had it out last week for two days of tubing on the lake. Everything worked as expected, with lots of starting and stopping as the kids took turns on the tube. Lots of rough water due to boat wakes; the boat pounded roughly through the waves if we let it, which added to the fun.
When starting off pulling the tube, I found it worked well to run the RPMs to 4000 until it got up on plane. Then I could increase the speed to suit the age of the child. 4500 RPMs was 22 MPH and 5500 was 33 MPH. I did not run it WOT at 6000. There is no red-line on the tach, but it seems unwise to run it continually at 6000. Right?
Second trip: Yesterday my wife wanted to go out on the water, but she has no interest in speed. We just putted around the lake in the no-wake zones. When we were ready to go home, I pushed the throttle for a quick trip back the the boat launch, but at 4000 RPM, before the boat was on plane, the prop seemed to lose it's grip on the water. The boat slowed down and the tach shot up to 6000. What's going on? I tried again with the same result, so I walked back to look at the prop. Did it have a bunch of weeds? I couldn't tell in the bright sun and shadows, but it didn't seem to be pulling a trail (and I didn't think to raise the motor for a better look). The cavitation plate had not fallen off.
I tried again and again to get the boat up on plane, but each time, before it got there, the prop seemed to loose its grip while the tach shot up to 6000. I can tell it is a water problem, not gears or motor. Finally we gave up and putted back to the marina.
The motor has tilt-n-trim, but I don't know when to use it, so the motor was full-down all the time, same as last week.
What's going on? Any ideas will be much appreciated, but as the boat is not in the water, I'll have to wait to try anything. --Peter
First trip: We had it out last week for two days of tubing on the lake. Everything worked as expected, with lots of starting and stopping as the kids took turns on the tube. Lots of rough water due to boat wakes; the boat pounded roughly through the waves if we let it, which added to the fun.
When starting off pulling the tube, I found it worked well to run the RPMs to 4000 until it got up on plane. Then I could increase the speed to suit the age of the child. 4500 RPMs was 22 MPH and 5500 was 33 MPH. I did not run it WOT at 6000. There is no red-line on the tach, but it seems unwise to run it continually at 6000. Right?
Second trip: Yesterday my wife wanted to go out on the water, but she has no interest in speed. We just putted around the lake in the no-wake zones. When we were ready to go home, I pushed the throttle for a quick trip back the the boat launch, but at 4000 RPM, before the boat was on plane, the prop seemed to lose it's grip on the water. The boat slowed down and the tach shot up to 6000. What's going on? I tried again with the same result, so I walked back to look at the prop. Did it have a bunch of weeds? I couldn't tell in the bright sun and shadows, but it didn't seem to be pulling a trail (and I didn't think to raise the motor for a better look). The cavitation plate had not fallen off.
I tried again and again to get the boat up on plane, but each time, before it got there, the prop seemed to loose its grip while the tach shot up to 6000. I can tell it is a water problem, not gears or motor. Finally we gave up and putted back to the marina.
The motor has tilt-n-trim, but I don't know when to use it, so the motor was full-down all the time, same as last week.
What's going on? Any ideas will be much appreciated, but as the boat is not in the water, I'll have to wait to try anything. --Peter
