Speed Plateaus at 5200rpm

[jimmbo]

I pushed past 5,200rpm and maintained for a little longer. The speed peaked at 35mph at 5,800rpm. If I pushed throttle forward further, rpms seem to stop climbing.

That last sentence appears to indicate that a Rev Limiter has been activated. More Pitch will bring the Rpms down

 

[jakec]

I don't know if that's a feature, I'll need to look at the manual .I thought it may mean pitch was too high.

 

[jimmbo]

More Pitch means more load and more load, results in lower Rpm.

What year is your Suzuki?

 

[jakec]

It is a 2022. I just pulled the manual out to flip thru later, and see if there is such a thing as a rev limiter. I don't think there would be tho, not at that rpm, as the stated max rpm is 6,200.

 

[jimmbo]

Okay, but if there is spare Throttle Movement, which gives no increase in Rpms, something is not Kosher.
I am not familiar with current Suzukis, so... Is there an actual Throttle Cable going to that engine, or is it a Fly by Wire Electronic Throttle Control?

 

[jakec]

I got the simple mechanical throttle unit, so I am guessing it is cable. When I ride my motorcycle up a steep hill, I can open the throttle with no increase in rpm and we just call it lugging it. I would think this would be the same here.

 

[jlh3rd]

well, max manufacturer engine rpm is 6200, you say...every engine has a max throttle operating range ....so I'll take a guess that min rpm at max throttle is around 5200 (my 2021 merc is 5000-6000 at max throttle). So operating range wise, your not lugging the engine with max throttle and 5800 rpm....technically....
I re-read your first post and basically nothing has changed.....except you are not ventilating now?.....
So a reduction in pitch can bring you higher rpm's...basically a 1 inch reduction gives around a 200+ rpm increase...
There's more general rules of thumb concerning propping....with everything else being equal.....
A 1 inch decrease in prop diameter can increase rpm's
lower blade #'s increase rpm's....
and ,supposedly, a 4 blade works better at countering ventilation issues than 3 blades....
of course this works the opposite......
It can get expensive trying to fine tune....I've got two props on my shelf, learning curves....

 

[jakec]

Just found this passage in the manual. So I am probably just fine having my max speed achieved between 5,200-5,800 rpm.

And yes, you’re correct nothing has changed except I stopped trimming it so much, when I first had the engine I was ventilating but now I’ve realized the speed increase stops after about half trim. I haven’t made any other changes to the setup, just trying to pay more attention and look for different behaviors I didn’t notice before.

So.. if my rpm is fine, I still have the question of how to squeeze more top speed. Since it seems one way to get speed up is to lift the boat more, maybe a 4 blade is the correct move as people have suggested here.

 

[jimmbo]

A 4 blade will likely drop the Bow. A prop with more Rake will help raise the Bow. Enertia is such a Prop, actually it will lift the entire Boat Vertically, as well give a completely different feel as to how the boat handles.

 

[jlh3rd]

so now there's rake, blades , diameter, pitch, motor height.....I should've added cupped props in addition to all the others...good luck....
....remember, your almost ,if not, there

I disagree...trim raises or lowers bows....props can help with added bite...but you can only raise a bow so much....
you can go get that enertia prop....and start all over again.....

 

[jlh3rd]

Just found this passage in the manual. So I am probably just fine having my max speed achieved between 5,200-5,800 rpm.

And yes, you’re correct nothing has changed except I stopped trimming it so much, when I first had the engine I was ventilating but now I’ve realized the speed increase stops after about half trim. I haven’t made any other changes to the setup, just trying to pay more attention and look for different behaviors I didn’t notice before.

So.. if my rpm is fine, I still have the question of how to squeeze more top speed. Since it seems one way to get speed up is to lift the boat more, maybe a 4 blade is the correct move as people have suggested here.
View attachment 380258

remember...when your trying to get more bow lift....your pushing the stern down...against the plane....it can be tweaked, but it becomes a dance with speed, trim, and the end result.....

everyone uses different techniques for trimming for speed.....a neutral feel on the steering wheel....Or seeing an increase in rpm ( digital tach) for a set throttle while playing with the trim......but this fine tuning still doesn't result in a significant speed increase...at least for me...but I'm operating a pontoon..so there's that...
Ive used both.......

 

[jimmbo]

Blade design will certainly raise/lower the Bow, with no change of trim.

 

[jlh3rd]

Blade design will certainly raise/lower the Bow, with no change of trim.

or #of blades, etc....not denying that....
But it probably will affect his rpm to the point where he has to start all over again with the propping regimen.....
...tell him what enertia prop he needs, maybe it will be the holy grail and he won't have to return it and try another one....

 

[jimmbo]

I used the Enertia as a Example as to what is possible with a Blade Design. My Avatar pic, was shot when the Boat had an OMC RAKER, that used to be on my 150 FICHT(had to replace the Rubber Hub to a VP) I don't think the Enertia is made in a size that will fit on a 115hp engine.

 

[Texasmark]

Solace has a tutorial on their www explaining why you would use a 3 or 4 blade and the effects built into the blade design. As others have said, a 4 blade is to get a heavy ass up which reduces load on the engine and increases speed and a 3 blade is to get the nose up, reducing wetted surface area, reducing load on the engine, and as a result increase speed. Proper trim positioning with the 3 blade is very important. You don't have to wonder where is the proper trim position. The speed and RPMs will answer that question for you.

 

[jimmbo]

Solace has a tutorial on their www explaining why you would use a 3 or 4 blade and the effects built into the blade design. As others have said, a 4 blade is to get a heavy ass up which reduces load on the engine and increases speed and a 3 blade is to get the nose up, reducing wetted surface area, reducing load on the engine, and as a result increase speed. Proper trim positioning with the 3 blade is very important. You don't have to wonder where is the proper trim position. The speed and RPMs will answer that question for you.

I fail to see how an Extra Blade reduces the Load on the engine, unless there is a serious reduction in Pitch, which will kill any top speed

 

[Miked3]

I fail to see how an Extra Blade reduces the Load on the engine, unless there is a serious reduction in Pitch, which will kill any top speed

31.5mph@5650rpm with 3 blade 13.5"x14 alone, flat water.
30.5mph@5950rpm with 4 blade 13.25"x13 with wife and slight chop
Those are my latest numbers with the motor moved all the way up to last holes. No ventilation on turns with either prop. Ventilation plate is 1.5-2" above hull.

 

[Texasmark]

I fail to see how an Extra Blade reduces the Load on the engine, unless there is a serious reduction in Pitch, which will kill any top speed

Its not necessarly "the extra blade". Its a completely different design with a different desired outcome.....stern lifting with the 4 blade, getting the ass up and minimizing drag, or bow lifting raising the bow (at speed) to get the wetted area reduced.....in the Solace tutorial and when you look at the blades, rake and all that you can see the differences.

 

[jmok1978]

I have nothing to contribute other than saying you have a very pretty boat!

 

[jakec]

I was reading an old post about extending a boat, no don't worry I am not interested in doing that in the slightest... but I found an interesting passage that I think applies. Even tho the boat in the original post is a skagit, my make is pretty similar in form. I did the math and my length/beam ratio (226" length / 90.5" beam) is 2.497. Which I believe means it is even more beamy than the example boat).

I don't think it is possible to get the bow of this boat totally out of the water, while also being level (which is what you want, for speed correct)? I also attached a pic here of the boat showing how low the bow is compared to the transom when the boat is sitting on level ground.

Also, when I'm on plane at full speed and I look off the back of the boat (lay on the splashwell and look down) I see that the transom is maybe 6" deep in the water or more. You can see the wall of water go by as the boat is cutting through. So, that would make me think I want the 4 blade prop, to give lift? Does it lift the boat in a level fashion or just lift the stern, meaning bow goes down? In which case the benefits would cancel each other out?

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