craze1cars
Lieutenant Commander
- Joined
- Dec 26, 2004
- Messages
- 1,822
Re: Prop slip....4 blade ...the latest update - I'm out of ideas
Re: Prop slip....4 blade ...the latest update - I'm out of ideas
I'll take you all the way back to post #1 that you wrote. Your highest top speed reported to-date was when running 5,000 rpms. So it seems your motor probably makes a bit more power at higher RPMS.
And after all this time, finally your having 2 test results with identical props/different pitches helps. And may I quote myself before going any further?
With 2 identically designed props, you have now experienced:
42 mph at 3800 with 21 pitch
43 mph at 4100 with 19 pitch
You're going the right direction, and pretty much got the result I predicted with this 19...it is still too much pitch for your current motor's HP output, and therefore you are still under-revving.
So it seems I will speculate you'd get some RPMS up by going to a 17 pitch of the same design. I'll guess a 17 in this same prop would net you 4,500-ish. And would it get you more mph? Maybe 1 mph more, 2 if you're lucky, but doubtful. Holeshot will be better than it already is....and very noticable.
Bear in mind that 4 blade props are slower than 3 blade props....so if top speed is your only concern you need to get away from this 4 blade concept...no matter how great their marketing sounds on paper with this fantastic "high tech" prop. I'll guess you might gain 1 or 2 going back to a 3 blade. But you'll be starting your prop testing process over from scratch. And as always, I am only guessing.
I do not believe this statement of mine to be a guess: No matter which prop you finally decide is perfect for your boat, it will not exceed 45 mph without a substantial engine HP output increase.
I think Bondo said it best. You do not have enough HP to push larger pitch props. So if you want to go faster, you will need to add substantial hp. If other boats identical to your engine/hull combo can push bigger props, and/or can go 50 mph (I have no idea if either of these is a factual statement or not...but you seem convinced), while yours can only push 17 pitch prop and cannot get the boat past 45 mph, then it is a simple fact that your engine is making much less HP than, or your boat it is much much heavier than, those other "identical" boats. Why? Without personally spending hours...days...weeks....testing and playing with the state of tune of your engine, I have absolutely no idea.
A dyno test & tune session is the only way to quickly and quantitatively answer the question of how much HP your engine is making, and whether more can be found. Such sessions are worth their weight in gold, and are humbling experiences. Usually the motor needs to be pulled unless you can find someone with a propshaft dyno. In any event, I'll speculate a dyno session is probably out of your budget...but if properly done such a test session would answer questions with hard facts rather than guesses...
Re: Prop slip....4 blade ...the latest update - I'm out of ideas
I'll take you all the way back to post #1 that you wrote. Your highest top speed reported to-date was when running 5,000 rpms. So it seems your motor probably makes a bit more power at higher RPMS.
And after all this time, finally your having 2 test results with identical props/different pitches helps. And may I quote myself before going any further?
With 2 identically designed props, you have now experienced:
42 mph at 3800 with 21 pitch
43 mph at 4100 with 19 pitch
You're going the right direction, and pretty much got the result I predicted with this 19...it is still too much pitch for your current motor's HP output, and therefore you are still under-revving.
So it seems I will speculate you'd get some RPMS up by going to a 17 pitch of the same design. I'll guess a 17 in this same prop would net you 4,500-ish. And would it get you more mph? Maybe 1 mph more, 2 if you're lucky, but doubtful. Holeshot will be better than it already is....and very noticable.
Bear in mind that 4 blade props are slower than 3 blade props....so if top speed is your only concern you need to get away from this 4 blade concept...no matter how great their marketing sounds on paper with this fantastic "high tech" prop. I'll guess you might gain 1 or 2 going back to a 3 blade. But you'll be starting your prop testing process over from scratch. And as always, I am only guessing.
I do not believe this statement of mine to be a guess: No matter which prop you finally decide is perfect for your boat, it will not exceed 45 mph without a substantial engine HP output increase.
I think Bondo said it best. You do not have enough HP to push larger pitch props. So if you want to go faster, you will need to add substantial hp. If other boats identical to your engine/hull combo can push bigger props, and/or can go 50 mph (I have no idea if either of these is a factual statement or not...but you seem convinced), while yours can only push 17 pitch prop and cannot get the boat past 45 mph, then it is a simple fact that your engine is making much less HP than, or your boat it is much much heavier than, those other "identical" boats. Why? Without personally spending hours...days...weeks....testing and playing with the state of tune of your engine, I have absolutely no idea.
A dyno test & tune session is the only way to quickly and quantitatively answer the question of how much HP your engine is making, and whether more can be found. Such sessions are worth their weight in gold, and are humbling experiences. Usually the motor needs to be pulled unless you can find someone with a propshaft dyno. In any event, I'll speculate a dyno session is probably out of your budget...but if properly done such a test session would answer questions with hard facts rather than guesses...
