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Top speed 70 hp seem low?? (sorry if wrong forum)

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Jeni0909

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we just bought our first Bennington in July. We are 2nd owner of a 2013 20SL with 70 hp Yamaha
With just 2 adults and 2 young children, light load (anchor and small cooler, towels etc) we are at max speed at 14-15 mph.
Based on everything I have read we should be getting closer to 20 mph. Am I way off? Putting up for winter soon and will have engine winterized and checked out.
We are happy with our boat! Just curious if we can get or should get any more speed out of it.
Tubing is possible but not real fun for the kids, towing tube MAX mph is 9-10.
I see other people posting the near same boat a hp they are getting much higher top speed.
Any response is appreciated!!!
 
Jeni0909 said:
we just bought our first Bennington in July. We are 2nd owner of a 2013 20SL with 70 hp Yamaha
With just 2 adults and 2 young children, light load (anchor and small cooler, towels etc) we are at max speed at 14-15 mph.
Based on everything I have read we should be getting closer to 20 mph. Am I way off? Putting up for winter soon and will have engine winterized and checked out.
We are happy with our boat! Just curious if we can get or should get any more speed out of it.
Tubing is possible but not real fun for the kids, towing tube MAX mph is 9-10.
I see other people posting the near same boat a hp they are getting much higher top speed.
Any response is appreciated!!!
Click to expand...

Is your pontoon kept in the water seasonally? Maybe there is film or build up on the toons. That always seems to be a common theme in a pontoon going slower than expected when all else seems to be running fine.
 
Jeni0909 said:
we just bought our first Bennington in July. We are 2nd owner of a 2013 20SL with 70 hp Yamaha
With just 2 adults and 2 young children, light load (anchor and small cooler, towels etc) we are at max speed at 14-15 mph.
Based on everything I have read we should be getting closer to 20 mph. Am I way off? Putting up for winter soon and will have engine winterized and checked out.
We are happy with our boat! Just curious if we can get or should get any more speed out of it.
Tubing is possible but not real fun for the kids, towing tube MAX mph is 9-10.
I see other people posting the near same boat a hp they are getting much higher top speed.
Any response is appreciated!!!
Click to expand...
I have a 2017 20slmx w 90 mercury ct / 25" toons w lifting strakes and top out around 25 w 4 people in good conditions for another perspective
 
Vikingstaff said:
Is your pontoon kept in the water seasonally? Maybe there is film or build up on the toons. That always seems to be a common theme in a pontoon going slower than expected when all else seems to be running fine.
Click to expand...
All clean as a whistle. :/
 
Allan56 said:
I have a 2017 20slmx w 90 mercury ct / 25" toons w lifting strakes and top out around 25 w 4 people in good conditions for another perspective
Click to expand...
Thank you for your reply. Still seems like mine is running low. I don’t expect high speeds but more than 14-15 mph.
 
I have the 2014 20SFX with a 70 Yamaha and the best I have even done was 16 mph as measured by gps. But boy is it good on gas.
 
Thank you for your reply!!!! Previous owner said he had it at closer to 20 mph and it just doesn’t get close. I measure by gps too. And yes. Gas mileage is fantastic.
 
RPM's at WOT? should be around 5500 or so.

My Yamaha 50Hp 4 stroke pushes my 22' SSRXP at 17, two adults both Bimini's open, no lifting strakes.
 
What size is your prop ?
 
Jeni0909 said:
Max rpm at full throttle is 4000, never higher
Click to expand...

I am certainly no expert on props and such, but it could be motor too low and/or prop too big. I don't even know what my prop. size is on my 50, but I run 5500RPM and the cav plate is just visible at WOT, so I assume I am setup correctly but who knows???
 
With clean toons, I agree with one of the comments above: checking prop situation and engine hole mount due to your lower than expected RPM at WOT. Making adjustments there would hopefully result in better RPM at WOT, and translate into a few MPH to boot.
 
My WOT is around 6200 RPM. I don’t push it to that. I usually run about 5600 RPM and that gets me 15 mph. So if you are only getting 4000 RPM, I would say you still have some investigating to do
 
I will second what has been said above. You should be running close to 6,000 if all is well.
That additional 2,000 rpm should be worth at least 5 mph give or take and you should be running a tad over 20 loaded light.
 
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