I have a 1989 24ft pontoon boat.
1996 Evinrude 115hp
13.25" x 15" prop size
WOT is 4200 RPM @ 19.8 mph (measured with GPS)
I finally checked my speed with a GPS and I'm going slower than I thought. With the numbers above, I calculated a 33% slip. The motor and prop came off a 19 ft ocean fishing boat and so the prop is not made for a pontoon boat. But still, I would expect to get more out of my setup (my mechanic predicted mid to high 20s top speed). If its slipping that much, I would expect my rpms to be higher and thus a little more speed. I just bought this motor a few months ago and the compression was very good, and it seems to runs perfectly.
A couple things to consider --
My boat's been in the water for 6 months and so I probably have dirty/algae-y pontoons.
I had 3 adults on my boat and probably another 200 lbs of 'extra' weight (reinforced roof for sunbathing) - so call it 4 adults.
The existing prop is original for the motor. I'm thinking if I was to get a 14x13 pontoon prop, I'll get more grab (increased diameter, decreased pitch, more cupping), BUT... it seems to me that while I'll probably decrease my slip, I'll STILL be around 4200-4300 RPMs @ WOT -- which would leave me well below my target of 5000 RPM.
This would imply that I should drop pitch even more and go with a 14x11 pontoon prop -- but this simply doesn't sound right to me. An 11 pitch prop for a 115 just seems very small, from everything I've read/seen.
Not sure where to go from here. Is my thought process flawed anywhere? Any thoughts or suggestions?
A key question I have when thinking about this is this - does slip WASTE energy, generally speaking?
1996 Evinrude 115hp
13.25" x 15" prop size
WOT is 4200 RPM @ 19.8 mph (measured with GPS)
I finally checked my speed with a GPS and I'm going slower than I thought. With the numbers above, I calculated a 33% slip. The motor and prop came off a 19 ft ocean fishing boat and so the prop is not made for a pontoon boat. But still, I would expect to get more out of my setup (my mechanic predicted mid to high 20s top speed). If its slipping that much, I would expect my rpms to be higher and thus a little more speed. I just bought this motor a few months ago and the compression was very good, and it seems to runs perfectly.
A couple things to consider --
My boat's been in the water for 6 months and so I probably have dirty/algae-y pontoons.
I had 3 adults on my boat and probably another 200 lbs of 'extra' weight (reinforced roof for sunbathing) - so call it 4 adults.
The existing prop is original for the motor. I'm thinking if I was to get a 14x13 pontoon prop, I'll get more grab (increased diameter, decreased pitch, more cupping), BUT... it seems to me that while I'll probably decrease my slip, I'll STILL be around 4200-4300 RPMs @ WOT -- which would leave me well below my target of 5000 RPM.
This would imply that I should drop pitch even more and go with a 14x11 pontoon prop -- but this simply doesn't sound right to me. An 11 pitch prop for a 115 just seems very small, from everything I've read/seen.
Not sure where to go from here. Is my thought process flawed anywhere? Any thoughts or suggestions?
A key question I have when thinking about this is this - does slip WASTE energy, generally speaking?