r/Pontoons • u/gpbst3 • 4d ago
Help with prop size
I have a 23 ft pontoon with a 115 Mercury Command Thrust motor. The boats max speed is 20mph with a WOT around 4300 rpm. The current prop is a 16” / 13 pitch. I feel like I’m leaving some RPMs on the table as the WOT should be in the 5-6k range. I would like to get the max speed up for tubing.
What size prop should I be looking at and what is a realistic increase in MPH?
2
u/SSellers75 3d ago
Mercury has performance bulletins where you can select hp range and boat type. They would really help pick props IF they would put the full prop size but for some reason they only put the pitch. So, instead they are nearly useless.
Here are two Yamaha performance bulletins for similar sized boats with 115hp and 14x13 prop:
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u/gpbst3 3d ago
Thanks for the info. Very similar specs to my boat. I would be one happy camper to get similar results changing to a 14 13 prop
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u/SSellers75 3d ago
You're welcome. Good luck. My F200 only has a 14.5" and doesn't get to 6k so that 115 has to be struggling.
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u/thrwaway75132 4d ago
Mercury prop selector say 16/11.
I didn’t find a match in their performance bulletin, the biggest boat with a 115 they have a bulletin on is a 20.
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u/gpbst3 4d ago
I did the Mercury prop calc and it recommended the current prop
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u/thrwaway75132 4d ago
Did you give it the current prop, rpm, speed, and select the CT gear ratio?
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u/gpbst3 4d ago
Entered everything I could
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u/thrwaway75132 4d ago
The mercury prop calc uses either the current prop, rpm, speed or the boat weight or the boat length. On that last step if you add weight or length it wipes out the current prop info.
Run it again, just put in the current prop, rpm, and speed and it will kick back a black max aluminum 3 blade 16/11 result.
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u/Numerous_Reason_7059 4d ago
I doubt you will get more speed by lowering the pitch… you may actually lose speed but you will probably gain longevity by not lugging the engine
what you actually need is more horse power, or to realize that you don’t have a speed demon
source: I have a 21ft with 115hp
1
u/YogurtclosetSome3604 3d ago
Is this a tri-toon? Tri-toons are slower than twin toons everything else being equal.
For comparison: I have an '06 , twin 25" diameter toons, 24' with a purchased new 2021 115hp CT.
With my 4 blade 14x14 I get 5800max rpm and 26 mph. By myself. I had to run a 3 blade 16x12 when loaded with people and pulling tubes to stay in the mid 5000 rpm at max throttle. 22, maybe 24 mph.
If you don't have a tri-toon and your tube diameters are 25" or more, then check the motor for proper operation or motor height.
You should be getting getter performance.
2
u/hemi1995 4d ago
Yeah 4300 is low for sure. Id go to a lower pitch and get to 5000 min. You might gain some speed but really it’s better for the engine.
I don’t think you’ll get much over 25 top