What could cause your boat to lose 10mph?

[NickF]

i bought my 2017 21ft limited S last year and when I first brought it out I was seeing speeds of 55-58mph. This year I was only seeing about 47 (yes I know it depends on gas levels, weight, and water conditions). However I had the boat on glass water, three adults and a half tank of gas and couldn’t go past 45. Yesterday I was on the lake against by brothers 2008 Ar23 (same weight on each boat) and he was pulling away.

I checked the clean out plugs and there was nothing along with the intake grate.

I was going to pull the boat next week (it stays in the water) and give the hull a good cleaning and seeing if that might help, but kinda at a loss right now.

Just looking for some suggestions.

 

[Hilario Perez]

That happen to me last week I checked my air filters and they were moist and a little dirty so I went ahead and removed them. I had the boat on the water yesterday with 6 people on it and I was get 50 mph at 7600 to 7800 RPM check your filters I was looking on line to buy new ones the cheaps I found we're 150 I think his to much now I want to know if I really need to put new ones back can anyone give me some feed back the boat runs awesome without them back I don't want my motors to damage because I'm looking to sale the boat very soon going to purchase a new one.

 

[bronze_10]

If it stays in the water may be a dirty hull but that original speed seems high.

 

[Hilario Perez]

Boat don't stay in the water yes i5bwas running really open and good.

 

[haknslash]

If your boat stays in the water you need to pull it out and clean the hull once or twice a season. Your hull develops grime and even organisms living off it if left in the water. Some boats can have what looks like mossy carpet growing off them. All of this slows down the boat due to the drag from a non-clean hull. Pull your boat out, clean the hull (I bet it looks nasty and discolored) and I'm sure your top speed (and fuel consumption) will return to normal.

 

[Betik]

You probably want to clean the impeller and the housing as well. I bet you have a micro cavitation there regardless of the hull condition ( which probably is nasty ) .

Maybe you should consider buying a lift ...

 

[PaulyB]

Too many fat chicks?

 

[merlinjet]

Is the gas you're using from last year? If it is and it wasn't treated, you may have some loss of power there. Just make sure you have fresh fuel.

 

[OrangeTJ]

It’s buildup from being in the water. Same exact thing happened with my SX210, but I lost more like 12 mph. I’d recommend starbrite boat hull cleaner. Nasty stuff but makes the job super easy. Your speed will come back.

 

[swatski]

Let's not forget, @buckbuck 2008 (?) 212X pulled from a brand new (2017?) 212X last year - he likes to drag race, apparently.

Those MR-1 HOs had been built as basically racing engines strait out of the factory. 1.8s - not so much.

--

 

[seanmclean]

55-58MPH seems pretty suspect to start with. Running with a ripping tide and a tailwind?

Boat staying in the water is a real culprit though. I haven't pulled mine in a month, and I'm down about 7MPH from top speed. Should pick it all back up when I clean the hull next week.

 

[seadude]

I agree, boattest saw 52 on that model which is about as fast as these yami's go.
Those old 230's with properly running HO MR1's were no slouches either!

 

[GTBRMC]

I am assuming 55-58 mph was from the dreamometer, not a GPS speed.

Cause of speed drop could be a few different things, but dirty hull is very easy to diagnose and straightforward, although not a lot of fun, to fix. Start there. If not it, come back and post on this thread.

You'll get it resolved quickly with help available here.

 

[djetok]

I am assuming 55-58 mph was from the dreamometer, not a GPS speed.

Cause of speed drop could be a few different things, but dirty hull is very easy to diagnose and straightforward, although not a lot of fun, to fix. Start there. If not it, come back and post on this thread.

You'll get it resolved quickly with help available here.

2017 is a connext boat? I think all those are gps speed . I do agree 58 wow

 

[YamahaCC]

As stated from others, growth on the bottom. I launch mine around June 1st on a lake and by mid July I already notice a reduction in speed/rpms from when it was 1st launched. It happens every year. I never have pulled to clean as the difference is not enough to bother me as most of the activities is water sports and not long high speed runs.

 

[Betik]

@blacksapphirez i think had seen such numbers although for me personally anything above 50mph is science fiction

 

[swatski]

Sure it possible, cool weather etc.

I don't think he ever showed a video though. But it doesn't matter as those are not sustainable speeds in reality with 1.8 N/As
https://www.youtube.com/watch?time_continue=5&v=LeLbSrppe98

--

 

[J-RAD]

1) hull growth
2) air filters (cleanliness & oil saturation)

- if oil then levels may be too high​

3) spark plugs (I would think maybe more likely to only effect 1 engine at a time).
4) impeller obstruction (I would think maybe more likely to only effect 1 engine at a time.)

55-58 won't happen in my world... impressive!

 

[GTBRMC]

2017 is a connext boat? I think all those are gps speed . I do agree 58 wow

Ah, saw "2008 AR23" in original post, obviously did not read it closely enough. That 2008 AR230 was his brothers boat, not his, etc. Thanks for correcting me.

 

[blacksapphirez]

my max it appears to be 54mph...