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-   -   Prop (http://www.maxumownersclub.com/forums/f8/prop-3754.html)

juggjiggler69 05-01-2012 01:15 PM

Prop
 
Hello new here,can anybody tell me what pitch prop would be good on a 2400scr with a 350 in it and a alpha 1i am running a 18 4blade now but top speed is only like 40mph,i had a 21 on it and was at like 55mph but the rpm were topping at 3500 only

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seapuppy 05-01-2012 02:09 PM

welcome to the zoo....first off..prop selection should be based on your WOT..wide open throttle....so...according to spec's of the boat...it should run wot at 4400-4800rpm...if your over or under..your not running the correct prop....

go out and run wot and tell us what you get...


SP

juggjiggler69 05-01-2012 02:38 PM

It will be a while till i get out but with the 21 on it i ran like 55mph at 3500rpm wot will that hurt anything

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pascavone 05-01-2012 02:38 PM

I'm not a memeber of the the first church of prop-ology but here are a few general guide line which i've picked up:

1. the main point is to get maxium horse power in the water.
2. most engine horse power curves, show horse power declining above 4600 rpm... by design of the engine. Meaning, if your turning more then 4600 your just buring gas for little effect.
3. The boat prop and your mechincal should WOT (wide open throttle) to match your boat loading condition and use for the maxium horse power curve of the engine... 4600rpm.
4. the stock props are for general use, like the new tires on your new car. (works for pulling a skier, works for 10 fat people, works for fuel eccomy, works for top speed)
5. there are 3 version of bravo III with 3 diffrent gear ratios, 1.81:1, 2:00:1 to 2.20:1 and i think a new 2.43:1, so that also effect the prob to HP ratio, so a higher ratio and a bigger prob could really cause problems.

So, 22 degree probs v.s 24 degree probs can give you more bite in the water, and push you further at 4600, but kill you on the low end getting up on plane, or pulling a skier.
Larger diameter probs sounds like a good idea, but your increasing the load on the engine throughout the power HP curve, and most time over load the engine at the wrong RPM as designed, and result in a blown head gasket. ( Like flooring your car at every green light, maxium load to the wheels, but on a boat maxium load to the prob.... same effect).

Bigger boat with more engine with a single prob, or one engine with a bravo III, still have equal performace becasue your hauling the ice maker around and full size frig.

So, end result is, if it works don't fix it, and like those out drive "whale tails", if it worked they would install it at the factory....

seapuppy 05-01-2012 03:19 PM

won't hurt much if you don't run it that way all the time.....running WOT a few times a yr or so is ok cuz the engine and drive are designed to handle max load ....but with the newer mpi engines there is a rev limiter that won't allow you to go past a certain rpm for fear of blowing the engine up..or drive....so...go out and load the boat with 2 people (if you can do it safely)...half fuel...and run it wot...after you trim up...see where your wot is....or have your pax watch the tach....when wot is achieved...back off and note what that number was...if you can't reach wot recommendations....your over propped...too much bite...if you hit the rev limiter or go way past wot recommendations of your manual....your under propped....to me it sounds like your way over propped....

SP


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