252 FSH RPMs

[gajb1795]

I really wanted to avoid creating another 1.8L RPM thread, but finally folded in order to check what other 252 FSH owners are seeing.

We've had our 2022 252FSH for about a month now. I'll spare you the long list of issues I've had with this boat because overall we love it despite all the sweat equity I've had to put into it already. Most of the bugs have been worked out, but the one thing that has me stumped is the max RPMs I'm seeing. Both engines are topping out pretty consistently around 7000-7100. I had a 2018 190FSH prior to this boat and I saw 7400 in similar conditions on that engine. I'm under the assumption that 7K is low for these engines in general.

For top speed, I'm getting what most are reporting and pretty impressed overall - 44/45 with 2 adults, 3 kids, and 75% tank on slight wind. The attached picture was me solo with a decent headwind getting 43 MPH (ignore the water spots!). And I'm sure someone will catch this, but yes in this picture I've used cruise assist to max out RPMs, but I get the exact same result at WOT.



I've checked all the usual suspects (oil level, air filter, throttle cables at full stop). Before I drive myself crazy chasing a few hundred RPMs, I wanted to check to see what everyone else is getting with the same rig given I'm getting similar reported speeds.

I'm not as worried about max speed as I am ensuring there's not another gremlin I need to address with this boat.

 

[FSH 210 Sport]

Did you check to make sure the reverse buckets are fully retracted?

I assume you are at sea level?
What are the atmospheric conditions?
How much load do you have on the boat ? Trolling motor, tackle, porta potty etc…
What octane fuel are you running?
Tried a new set of plugs?

Im just a tad envious…those are really nice boats!

 

[gajb1795]

Did you check to make sure the reverse buckets are fully retracted?

I assume you are at sea level?
What are the atmospheric conditions?
How much load do you have on the boat ? Trolling motor, tackle, porta potty etc…
What octane fuel are you running?
Tried a new set of plugs?

Im just a tad envious…those are really nice boats!

For buckets, yes - if anything I need to adjust them down some as neutral puts me at ~1MPH. I hadn't thought about that though - I guess in my mind the bucket may slow top boat speed vs increasing load/limiting RPMs?

~840' above MSL where we normally run. Seasonal Atlanta conditions right now, warm and humid, but again my previous boat saw pretty consistent RPMs on the same lake. We had it down in Tampa over Memorial day and got the exact same numbers.
No additional load beyond the family and enough kids toys to keep them amused for the day. I am running CJS and the boat tracks straight.
Currently, it has 89 non-ethanol fuel in it. I went ahead and put new plugs in at the 10 hr service to see if that made a difference, but no change was observed.

I'm hoping I'm chasing a problem that doesn't exist...

 

[FSH 210 Sport]

For buckets, yes - if anything I need to adjust them down some as neutral puts me at ~1MPH. I hadn't thought about that though - I guess in my mind the bucket may slow top boat speed vs increasing load/limiting RPMs?

~840' above MSL where we normally run. Seasonal Atlanta conditions right now, warm and humid, but again my previous boat saw pretty consistent RPMs on the same lake. We had it down in Tampa over Memorial day and got the exact same numbers.
No additional load beyond the family and enough kids toys to keep them amused for the day. I am running CJS and the boat tracks straight.
Currently, it has 89 non-ethanol fuel in it. I went ahead and put new plugs in at the 10 hr service to see if that made a difference, but no change was observed.

I'm hoping I'm chasing a problem that doesn't exist...

Right on…. I think your boat only requires 86 octane though ?

 

[gajb1795]

Right on…. I think your boat only requires 86 octane though ?

With diesel at what it is, we grab whatever is on the way to the ramp

FWIW its the same thing I ran in my previous boat. I suppose that comparing this boat to the last could be part of the problem, but I'm assuming these engines should operate mostly the same?

 

[FSH 210 Sport]

With diesel at what it is, we grab whatever is on the way to the ramp

FWIW its the same thing I ran in my previous boat. I suppose that comparing this boat to the last could be part of the problem, but I'm assuming these engines should operate mostly the same?

Well, I think if you can find 87, at the very least you’ll save some dough on your boat fill up. I mix 85 and 91 non ethanol in the correct proportions to get 86 octane. It’s about $8 more per 40 fill up when compared to 87 ethanol.

I agree, the engines should operate the same, just depends on the load they have on them.

 

[NateKurtz]

I assume you checked/adjusted the plug gaps? I put new plugs in my 210 without checking the gap and went from 7800 rpm’s, down to 7000. Took plugs out, gapped to Yamaha spec, installed, and got my rpm’s back.

 

[Zackdadams]

My FSH 252 runs at 7000 RPMs max.
45 MPH generally.

 

[Bugslayer]

My 252 tops out at 7K.
Generally 43-44MPH.
I'm on the Sea of Cortez, about halfway down the Baja peninsula for reference. ?

 

[gajb1795]

Thanks @Zackdadams and @Bugslayer - exactly the feedback I needed. I'll stop chasing a problem that doesn't exist.

 

[Sean R]

I have a 21ft but same engines, I hit 7600 to 7700 rpm. Wouldn't think the larger hull would decrease rpms.

 

[gajb1795]

I have a 21ft but same engines, I hit 7600 to 7700 rpm. Wouldn't think the larger hull would decrease rpms.

This is what led me to make the post in the first place. My previous 190 FSH had the same motor and I was under the assumption max RPM is in the range you show.

Based on what other 252FSH owners have posted, I at least feel confident mine is working as designed. I'll let others that know more than me speculate as to why 7000 would be the WOT RPM for these boats.

 

[FSH 210 Sport]

This is what led me to make the post in the first place. My previous 190 FSH had the same motor and I was under the assumption max RPM is in the range you show.

Based on what other 252FSH owners have posted, I at least feel confident mine is working as designed. I'll let others that know more than me speculate as to why 7000 would be the WOT RPM for these boats.

In my service manual it lists the max rpms for my TR-1 motors as 8000. My engines are different than yours, but I wonder if the shop manual lists the max and or rated rpms for your 252? Maybe for the 252 the rated rpms are lower?

I’ve done a lot of impeller testing as I operate at 5000’ above mean sea level, and my density altitude is higher than that. My problem was I was only getting around 7000 rpms with just me in the boat, low fuel load etc.. with several people in the boat and on a summer day=high density altitude I was only getting 6500 rpms. This was a huge double whammy, too much pitch on the impeller, and that too high of a pitch was keeping the engines from reaching their peak hp rpm.

So, I got impellers with a lower pitch to get me up to rated rpm’s so the engines could make the most hp they could at my altitude. As with most things it is a compromise, now that I get rated rpm’s, I turn more rpms to get to my best cruise speed, it used to be right at 6000 rpms and 7.8-8.0 gph and 3.5/3.6 mpg. now my fuel consumption increased about .5-.8 gallons per hour, and my mpg dropped from 3.5/3.6 to 3.2 mpg, but the trade off is worth it. My old max speed was right around 31-33 mph with just me in the boat, and 28-29 mph with 5 or 6 adults on board. Now my max speed is right at 41mph with just me in the boat with a full load of fuel and my gear. With 3-4 adults on board and everyone’s gear, my top speed is 38-39 mph. And last summer when I had 6 people on the boat and towing Big Mable with two people on it, the only way I could get the boat on plane was to go down wind… pretty anemic. I have not been able to test with that load and configuration yet, but I am very confident that it will perform worlds better.

Having said all that, perhaps the impellers and pumps that come on the 252 are the same as the 255 sport E with its 70hp per engine increase in power? Jet pumps are interesting, the only demand hp chart I have seen is one for a Berkley Jet pump, to get 5000 rpm it required 350hp, to get to 6000 rpm it required 725hp, an exponential increase in hp. So, if the peak power of the 1.8L engines is at say 7700 rpm, then the 1.8L is not making peak hp.. Yamaha is very tight lipped with horsepower / torque charts, and as far as I know the only engines they even talk about power wise are the 1.8L. You can look right on the engine and it will list max hp in KW’s but no associated rpm‘s. If you want to know peak power, take the KW number X 1000 / 746 to get the hp. For example, on my TR-1 engines it lists 83KW as max power, 83x1000 / 746 = 111.2 hp. During the summer here at 5000‘ that 111 hp drops to roughly 81.2hp on a hot day.

The other thing to keep in mind is that your 252 weighs roughly another ton over a 21 foot bow rider, and that takes more power to push that the through the water at best cruise.

So, if you are after max power and speed a slight modification to the impeller pitch would probably net you the higher revs, peak power output, and more speed. If you desire that I highly recommend you call Impros out in So Cal and talk with Glen, he is the man when it comes to impellers. I will tell you that swapping impellers is pretty simple, and the first time it may take you up to two hours, but after that you can do the whole job start to finish in about a hour.

Properly “propping” a boat is very common place to get to the rated rpm range of say an outboard engine. So that may be something that all the 252 FSH owners may need to do to get max performance out of their boats.

 

[MillsyMO]

I found this thread bc I was wondering the exact same thing about my ‘22 AR250. 7k RPM’s is all I get and 43-46mph. I watched a YouTube video how to adjust the slack out of my throttle cables (I don’t have TBW) thinking that would help and it did nothing.

 

[FSH 210 Sport]

Looking at older threads this morning and in this one I went and checked around a bit and the 255 FSH sport E uses 160mm pumps and the 252 FSH uses the 155mm pumps, the impellers and wear rings are not surprisingly different as well.

Looking at some of the tests, the 252 uses (23.6 gph) roughly half the fuel at WOT than the 255 does (44.3 gph) based on the test numbers of the 2021 252 SD since that is the closest boat tested. That additional 20.7 gph nets roughly 14 mph.

Sure would be interesting to see what the actual gph / speed numbers are on the 252 FSH are. What the 252 FSH lacks in power / top speed, it gains in better economy.

255 Chart:



252 Chart:

 

[gkallevig]

I previously had a 190FSH. I was concerned with all the usual jet boat stuff and trying to maximize performance. One thing that comes to mine with your rpm issue is how well the pump is being loaded. Any inefficiency in water rushing into the pump will result in a higher motor rpm being able to be spun, because there's less water load in the pump. So if Yamaha made improvement in how efficiently water loads info the pump, that might be causing the same 1.8 engine to run less rpm...but not necessarily provide less thrust. You almost need a dyne chart to know for certain where the 1.8 makes peak power so you have somewhat of a target rpm. And then I'd want to know if the pump diameters, or other aspects of the pump, changed from my fsh190 to your fsh252, or know whether the intake grate was redesigned or how the hull shape might better feed water into the grate. Then of course you're naturally going to get more water flow into your 252 intakes because you're going slower due to the larger hull.
That's the thing with these jet boats, its never ending questions of how to optimize. That's why I went back to a prop. I"m no jet expert, just my $.02.