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Low End Prop Push

Osceola Stumpy

Osceola Stumpy

Well-known member
Currently i am running a 72" Whirl Wind (older one)prop that is 10-1/2" wide. I have noticed that it takes longer for me to get on a plain than must of the boat i run with. I have a lot of top end. running dry is not so great. I am turning the prop at 2950 RPM.
Does the prop i have develop low end push or does it work better at higher RPM? I know that the prop manufactures all claim different things about their prop to try to get your money.
 
looks to me like youve got one sweet ride !!
from a pic its hard to tell esp. with hull in the water, but it looks like your engine is sitting quite a bit lower in the rear than front, maybe someone else can chime in or maybe you know if your engines level with the bottom of your hull. but it cant be hard to tweek it alittle to make it perfect, when your as close as you are already. :)
 
T IS ON THE BALL TODAY ! YOUR MOTOR DOES LOOK LIKE IT COULD BE RAISED UP SOME ! THAT WOULD CAUSE NOT TO PLANE OR RUN DRY ! JUST MY OPINION !
 
I am running a O435 190 hp. i think the motor is not producing all the hp that it can. i have raised the motor up. On dry ground the back of the boat was raising up about 2 1/2" so i raised the rear of the motor up. i am thinking of going to a "Q" series will this give me more low end push?
On plain the spray is breaking out in the middle of the rear seat.
 
Osceola,you would definitley like the Q series better than the whirlwind.Your limited on power,so its not going to be a real hillburner.If it was me I would cut the case and put 480 jugs on it and a Q series.
 
There easy to get.Pm me and I can probally hook you up pretty cheap.You would be putting out 260 horse then.
 
stumpy I have a o-435 with the 480 cylinders on a 12.5 x 7.5 diamondback ultralite and I love it I can hang with the 540/s pushing but maybe not top end we call them a poor man's 540 I have had mine about 5 yrs and I have had the oppurtunity to get acouple 54o /s but I can/t part with the motor it has never given me any problems.
 
Currently my set up is a 13x8 Alumitec hull 24" deep. i like the hull but want a little more hp. so i can relate to the poor man 540.
 
stumpy

that current set-up sure is loud! am i right?

i think you need to do some tweeking first before anything elese. i see that you have a mismatch there. just correct me if i am mistaken.

the way i see it, you'll be amaze at what you've been missing. YOU ARE OFF AT ENGINE TO PROP POWER MATCHING.... my guess!

first, ( if i got it right ), O-435 is 190 hp at 2550 rpm, is this your engine?. second, you have a good prop on it although you can upgrade if you want.

why dont you try this first: to get optimum static setting, reset your prop so that it will rev at 95% of your max. rated rpm which is 2550 static rpm.

so, 95% of 2550 is 2420 rpm.... you may set it at 2400 rpm. TEST IT!

now, if you like the result, fine tune it. you may reset it to 2300 rpm for a bit of a good economy at cruise (slightly lower rpm at cruise) or up to 2450 rpm for extra push on dry... just check how you like it or if any fine tuning gives good results.

please give us an update. btw, it will be much QUIET but it doesnt mean less power as you'll see. get used to it.... a much quieter boat!

happy boating.
 
It's an adjustable prop right? Back it off a notch and it develop more low end, you will lose top end though.

But if you can come up with some 480 cylinders and a Q...DO IT. You will like the Sensenich.

Sweet lookin ride.
 
dblj006

just an info, he already has a very high tip speed close to that of metal props.if ya back off a notch it will further overrev his engine BUT you gave me another point to ask stumpy... thanks.

stumpy, how accurate is your tach? coz if you really are at 2950 rpm with that prop, you're at about 930 feet per sec tip speed--- LOUD!
 
It is already loud. But if he increases pitch to run @ rated hp he will lose more low end than he has now. For the prop to push more at the low end he will have to decrease pitch and keep the throttle down below the max tip speed recommended by the manufacturer.

Really though if the prop is set and the motor turns 2950 that's about all he can ask for.
 
i dont think it would be that way. see, if you set a prop pitch which will load the engine less than the rated power then it only means that you are not making use of the full potential of the engine and as a result, it will overrev.

if an engine is rated 190 hp at 2550 rpm, then set the load to be 190 hp at that same rpm. either underpitch or overpitch will result to the engine producing less power. the prop is a device to convert engine power output into thrust. so, if you have 190 hp available, set your prop to absorb 190 hp.

if you're under pitched = you're engine is underloaded, produce less power and will overrev.

if you're overpitched = you're engine is held down and produce less power.

either of the two above, you produce less power, you produce less thrust. although on the second scenario, we can intentionally overpitch to a certain degree to get a certain advantage and a certain compromise on the other end.

with a prop load, there is a variable that comes into play--static rpm. this is set around the 90% to 95% of rated max rpm. this vary from prop to prop and operation parameters. this is a good ballpark figure in general. fine tuning for a particular set-up will be necessary.
 
Are u going to be a lake kissimmee tomorrow? I have a digital tach we can check to see if your tach is off.
 
I set the prop pitch 2450 RMP static. Ran the lake Sat at the jamboree this was positive improvement. But it still took a little time to get on plain. I raised the rear motor mount 1/4" and went on a run the boat now pops right up on plain so we all helped make the boat run better.

THANKS TO ALL FOR THE INFO!!!!!
 
When your on a plane how far from the bow does the water spray off the sides. You should at least have your motor level! From the pic and the angle it was at I bet it rides on the nose!
 
Thunder
you are correct. now that i have raised the motor and added pitch to the prop she runs better. Now i need to save the penny's to up grade the HP.

I had the pleasure to see a WATER THUNDER engine at the Jamboree on Sat.
that is very impressive engine and run. Great engines THUNDER.
 
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