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Where did my speed go?

R

resauter

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2011 2275FSi, Yammy 150
One day, the boat was comfortably running 35 mph at wide open throttle (about 5850 RPM). No prop strikes, or obvious damage to the prop, and next trip out, with just two extra people on board, suddenly I can’t get over 25 mph!
It feels as though the boat is dragging, and the prop is either cavitating, or experiencing ventilation.
I have a hard time imagining that 400 pounds of additional people, same fuel load, all else, and my speed suddenly dropped by 10 mph. By the way, RPMs are still running close to 6000 RPM.
Questions: does the F150 have a rev limiter? I feel as though I’m sitting on the rev limiter rather than the prop holding the rpm’s at the correct place.
Any ideas on what might have so suddenly changed without having struck anything and damaged a propeller?
I checked the boat on the trailer, and we are not dragging a tree stomp, or an anchor, or anything like that!
 
Dirty toons ? Even light slime will slow you down.
 
Any chance you have bad gas? When was the last time fuel and water separater filters changed? Does the engine feel like it is firing as normal or maybe time for new spark plugs?
 
Change fuel water separators just to be sure. My Yamaha 250 SHO is supposed to run 6000rpm max but I hit 6200 without it limiting me. My Verado had a limiter, doesn't seem like the Yamaha does.
 
Fuel water separator changed in October before putting the boat away for the winter. Engine is not misfiring at all. Tunes are not as clean as they could be, but they’re cleanliness did not change from one outing to the next outing five days later.
 
If your prop has a pressed-in hub that is slipping, it won't last long. Stay below the slip point to prolong the use.

Has the boat run a better speed with that load previously? Where was the 400 pounds, if only in the back, that could be the problem. How are you checking the speed? boat speedo or GPS? The problem could be load distribution and a prop not well suited to pontoon operation.

You motor should have a rev limiter, expect it to be more in the 6200-6400 range.
 
Load (400ish lbs of people) was distributed evenly throughout the boat.
The speed is GPS speed, I do not have a in water speedo
As stated in my original post, nothing else had changed from previous outings with this boat, and the speed suddenly dropped by 10 mph. The prop is the power matched Yamaha prop for the boat, and until recently worked fine.
I think NCLakeguy has probably nailed it. I will pull the prop and put our spare prop on and then water test the boat.
Thank you all for your replies. While I have owned boats for 50 years, this is our first pontoon, and only about our 10th or 12th outing with the boat so I am still learning.
 
Solution

Another shout out for Ken at Propgods.
I described the sudden change in performance, and he immediately suggested that it sounded like the hub was slipping. (Sudden big loss in acceleration and top speed).

I told him which boat I have, engine, and options (lifting strakes, etc), and that I wanted to go stainless steel.

He made a recommendation, and it is right on! My acceleration and top speed are both a little better than they were with the stock Yamaha aluminum prop.

The other great thing with using him is that if the prop had not been the perfect prop, for $40, he would have exchanged it for a different one. I have not found anyone else who will exchange a prop once it has been on the boat.
 
NCLakeGuy called it up above. Nice job! And glad Ken got you hooked up. He’s knowledgeable and great to work with. Many in the forum have utilized Propgods!!!
 
I also lost some speed several trips ago. Now my boat lists to the starboard. Using an endo scope I found water in the tube, center section. 2017 so it should still be under warranty.
 
CaptianMark said:
I also lost some speed several trips ago. Now my boat lists to the starboard. Using an endo scope I found water in the tube, center section. 2017 so it should still be under warranty.
Click to expand...
If you are the original owner, lifetime warranty on the structure.
 
CaptianMark said:
I also lost some speed several trips ago. Now my boat lists to the starboard. Using an endo scope I found water in the tube, center section. 2017 so it should still be under warranty.
Click to expand...
Get it into a Bennington dealership service center. They need to diagnose it, and you can go from there. You would still have coverage assuming it’s not collision/insurance related. There are a few options depending for dealing with those situations. Good luck!!!!
 
I will make an appointment with my local dealer. Their procedure is to elevate the boat from the trailer. Drill a hole in the bottom of the tube, drain the water, then weld a patch on the drain hole. Pressurize the tube to find the leak then weld to repair. This is a one day fix. If this dose not work they will replace the tube. This would take much longer.
 
I never really understood dealers drilling a hole in the bottom of the toon - yeah they're welding it back but to me it would be better to drill at the top and leave the bottom in virgin condition. You can still inspect with a borescope and drain using a tube and vacuum pump.

I also think you could use an infrared camera as presumably any water-filled portion will be a little cooler (or warmer) after pulling the boat from the water. Not many dealers have one but are they cheap enough these days to avoid the expense of a welder?

But maybe punching the bottom is Bennington's required procedure.
 
Mine was drilled on the bottom . Drained ,then welded the hole Toon replaced during the off season. Back on the water in one day .
It had factory weld burn through during covid .
 
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