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2014 SF20 70HP Yamaha Top Speed

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jimw

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I purchased a new 20 ft' Bennington a month ago and am new to boating. It is a 20 foot model with a 70HP Yamaha. My question relates to top speed. I expected that it wouldn't be very quick, but mine really seems slower than others. At 5800 to 5900 rpm it is only going 17 mph. That is just about full throttle. At full throttle it goes 6000 to 6100 and the tach oscillates..it doesn't seem happy so I back off just a bit. It seems I cannot keep up with other pontoons, many with smaller engines. Is this a normal speed for my combination? Any suggestions to get to 20 or 22 mph. Maybe a prop change? It did originally have a 50HP engine. I sure am glad I had the dealer change it to 70HP when I purchased. I wish I had gone to 90HP which I believe is its max approved hp. Dealer told me it really wouldn't make a difference going to the 90HP. He also said it would go 20 to 25 mph with the 70HP. I am seeing other posts with other Bennington pontoons that are going 30 to 35, not sure what they are but they must be very different boats from mine.
 
Can't say for sure about a 70 only going 17 but our old 22' crest pontoon had a 50hp johnson 2 stroke on it and 17-18 was about all it would do with just the 2 of us on board.  The new bennington is a tri-toon with lifting strakes to help get the boat out of the water and up on plane (more like a V bottom boat) which helps with speed quite a bit.  Well that and the fact we now how a 150HP yamaha on the back of a 22' boat (is almost 26 foot bow to extended stern/back of motor) we can get up to 38-39 mph range with just the 2 of us on board......40 is possible if the water is pretty flat.
 
The "right prop" question is a controversial one, because there is no one answer that will be the correct answer for everyone.

In a perfect world, your WOT RPM would be approx. 5900 regardless of the load.

In the real world, you need to decide if you want your boat to be propped correctly for no load, max load or somewhere in between.

While you are able to over-rev, for many that is desired so that they have a closer to ideal gear ratio when loaded.
 
We were on our neighbors pontoon boat w/a Yamaha 70 HP last week and with 4 people and a couple coolers..........WOT was 11-13 MPH...........
 
jimw said:
... Dealer told me it really wouldn't make a difference going to the 90HP. He also said it would go 20 to 25 mph with the 70HP. I am seeing other posts with other Bennington pontoons that are going 30 to 35, not sure what they are but they must be very different boats from mine
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This is just bad advice as the F90 is a definitely more engine than the F70. Those pontoons doing 30+ usually have a 115hp or better, but typically 150hp is the sweet spot for consistent mid-high 30's, loaded or not. They may also have 3 pontoons and/or lifting streaks to get them up and planing instead of plowing.
 
My 20 SLX does about 20 mph at 5000 rpm. I don't really push it any harder.
 
ErinnDan said:
My 20 SLX does about 20 mph at 5000 rpm. I don't really push it any harder.
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You need to push it once in a while, they're made to run at WOT.
 
I have a buddy with a new Monterey. He got past the 10 hour break in but still hasn't given it full throttle. I don't know how you guys do it not throwing the hammer down! And 17 does seem slow for a 20 footer and a 70 horse. Does the boat stay in the water full time? (growth on toons?)
 
CWag is correct about they are designed to run at WOT.  If you are a slow cruiser like me then I would suggest using Yamalube on a consistent basis
 
My old boat was a 24' Aquapatio with small 19" toons and a 2013 70hp Yamaha. It would get about 16 MPH WOT with 4 adults on board. I would easily loose 50% pulling a tube. My new Bennington is a 22' SSLX with the 25" toons and a90hp Yamaha with a 15 pitch prop. I get 29 MPH with 2 people and about 26 MPH with 4. I have pulled the grandkids and friends on the tube (3 at a time = 1 @160 lbs and 2 @100 lbs) with 3 adults on board and get 22 MPH WOT. I tried several differnt props and got a little more speed with a 13 pitch but lost almost 50% speed pulling the tube. The 15 pitch was the all around best for cruising and pulling the tube with the least amount of speed loss. I would suggest trying a couple differnt pitches up and down to see what works best for you. My dealer worked with me when I bought the boat and let me try several differnt ones out before settling on the 15. I found that my boat did not match all the information I saw regarding speed and power with various pitches. In talking with others I realize that every boat seems a little differnt and trial and error is the best approach. I can tell you there is a big difference of the 90hp and the 70hp. I started to use my 70hp on the new boat but decided to get the new 90hp and I am very glad I made the choice. Good luck and happy boating
 
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The op didn't say how much weight he's carrying and I've found it makes a huge difference in speed on a 20' boat. The wife and I are a combined 310 lbs. and we can just touch 21 mph on flat water with no wind. One day we took out two additional adults and a big dog which added another 450 lbs. and we could only do 12-13 mph. The extra weight really kills a 50 hp engine and 23" logs, we were just plowing through the water.


But yeah jimw, something isn't right there, you should see at least 21-22 mph with a light load. What prop do you have? Mine came with a 14 X 11 Quicksilver and it seems to work well.
 
cwag911 said:
You need a different prop.
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Suggestions? Maybe Bennington should start providing the best available props, for their industry leading boats.

I would have appreciated, at least, to have been offered the option of an upgrade.

What kind of performance could I expect from a better prop?
 
What brand and size is on there now?
 
Benningtons are most often delivered with engines, however it is up to the dealer to provide the props. I was thinking that the boats came with a checklist that had the prop size suggested.


My dealer put a 14 pitch prop on my boat, even though the sheet said 15 pitch. It over rev'd and hit the 6300 rpm rev limiter, and was about 4 mph short of what I expected. I got them to order a Yamaha 15 pitch, and it performed much better.


It should be up to the dealer to make sure that the boat's propped right.
 
Based on your suggestion to run the 15 pitch Bama that is what I told the dealer I wanted. Never gave them an option!
 
Bamaman said:
My dealer put a 14 pitch prop on my boat, even though the sheet said 15 pitch. It over rev'd and hit the 6300 rpm rev limiter, and was about 4 mph short of what I expected. I got them to order a Yamaha 15 pitch, and it performed much better.

It should be up to the dealer to make sure that the boat's propped right.
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Part of that is determining the customers desires & expectations.

In your example, if you frequently towed or had a boat full of people, you were better off being "under propped".

But if a higher speed while boating with minimal load is more important, than the higher pitch is indeed better.

Without knowing customers desires & expectations, it  is nothing more than a shot in the dark & hope for the best.
 
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My 2013 20SF with a 50HP Yamaha will hit 18-19 with just me and the dog. That's WOT at ~6100 RPM. I took the restrictor plate out of the intake. Prior to removing it, I could only hit 16-17 at 5600 RPM. Boat has 25" toons that are pretty scaled up from being in the water for two summers.

According to the performance bulletins on Yamaha's site, they got 19.1 MPH on a 22SLi with a T60 in 2009.

If your RPM's at WOT are at or near the redline, then the prop is properly sized. You could try a higher pitch prop, but you'll lose bottom end pull. Which is kind of important with a heavy boat.
 
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I have a 20sl with a 70 Yamaha and a 14x11 dual thrust prop. Unloaded just me I run 21.8mph and loaded run 16-17 mph. At 6000rpm.
 
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