R blades sweet spot

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Bob Burnside
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R blades sweet spot

Post by Bob Burnside »

Was wondering what the sweet spot for the R blades are and what best rpms to run them. What is the different in push from a 3 blades to 4 blades in a 83" length?

cntry141iq
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Re: R blades sweet spot

Post by cntry141iq »

sweetspot varies from setup to setup .. no appreciable difference in push unless 3 blade is over pitched or over spun .. then you need four blades. blades don't make push power makes push blades just convert power to thrust if 3 is gettin it done say on number 2.5 then four will be set at about 1.5 more or less give or take a little if they are the same length if they are longer they will need less pitch if shorter they will need more pitch .. hope it helped ya
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skinny99
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Re: R blades sweet spot

Post by skinny99 »

Waterthunder has posted on here that the "R" Series blade thrust curve starts to flatten out at around 2400 RPM's.
It does continue to gain thrust but much more slowly. Just passin on some info I read here. BTW I love my R blades on my boat.
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Re: R blades sweet spot

Post by cntry141iq »

I guess to further explain .. it depends on what you want to do with your boat .. do you want push down low or broadband or top end .. you talkin cruise rpms or topend rpms .. thunder turned his some insane numbers on his race boat so I was told anyways. that is why there is no such thing as a sweetspot that covers all situations
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Cowley
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Re: R blades sweet spot

Post by Cowley »

I spoke with Sensenich regarding my setup. I was told for all around performance, pitch the prop to achieve 2100-2200 rpm. With my 2.31 reduction that gives me a max engine rpm of 4900-5000 rpm which is conveniently right where my engine needs to be at wot.

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Re: R blades sweet spot

Post by greenhorn480 »

I have seen thunder post this a hundred times
I guess to further explain .. it depends on what you want to do with your boat .. do you want push down low or broadband or top end .. you talkin cruise rpms or topend rpms ..
I would call Sensenich and ask them

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airduds
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Re: R blades sweet spot

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cntry141iq wrote:sweetspot varies from setup to setup .. no appreciable difference in push unless 3 blade is over pitched or over spun .. then you need four blades. blades don't make push power makes push blades just convert power to thrust if 3 is gettin it done say on number 2.5 then four will be set at about 1.5 more or less give or take a little if they are the same length if they are longer they will need less pitch if shorter they will need more pitch .. hope it helped ya
I agree with everything you said here but think you stopped just short of the full answer. Less blades with more pitch should be a better setup for higher top end. More pitch means better angle of attack at higher relative speeds.
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Olf Art
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Re: R blades sweet spot

Post by Olf Art »

Over-pitching has it's own set of problems. The angle of attack (pitch) of a blade, when combined with relative wind (forward speed) can cause the prop blades to stall. When they begin to do that they lose thrust fast. With enough power the boat will run hard up to a certain point and then feel like it's 'hit a wall' ..... the push falls off fast. When that happens it's easy to misinterpret that as the engine losing power, when in fact the engine was just fine. That's where adding another blade and then pitching the fan a little less will start to pay off.

In-flow of air is a huge component in push. If you've got a lot of seats and rigging and such effectively hiding the prop, then the prop will be starved for something to get hold off as speed increases because relative airflow begins to deflect air away from the prop as speed increases. I've never built a race boat, but if I ever did I'd want to be sitting right in the bottom of the hull to keep my body from deflecting any air away from the prop.
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Re: R blades sweet spot

Post by cntry141iq »

sometimes ya gotta stop short cause ya don't know all the particulars LOL any statement made on here is always twisted an skewed an taken out of context and misquoted .. not by any means saying ya done that but it happens all too often .. so I chose safe ...
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Re: R blades sweet spot

Post by harley »

cntry141iq wrote:sometimes ya gotta stop short cause ya don't know all the particulars LOL any statement made on here is always twisted an skewed an taken out of context and misquoted .. not by any means saying ya done that but it happens all too often .. so I chose safe ...
not to get off topic.. but thats fact, very well put Cntry... 8)
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Re: R blades sweet spot

Post by Blackcoffee »

I have 4 80" R blades and sweet spot for my ride is blade mark set just over 3. I would guess most boats need around a 2.68 reduction and 580 HP @ 5400 rpm to have 4 blades.
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Re: R blades sweet spot

Post by marsh DooZer »

just got new r 80in have it set at 10 deg. with a 330hp./w.2.3 belt an turn 5100 its on a 14x7.6 db hull,my boy said runs grate an mabe a little faster,i will find out my self sat from 50 to 520

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Bob Burnside
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Re: R blades sweet spot

Post by Bob Burnside »

I'm turn 5000 rpm on a 2.3 belt with a 83.5 3 blade R just wonder if I added 4th blades what would happen.

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Re: R blades sweet spot

Post by cntry141iq »

you would spend money .. run less pitch .. if all else stayed the same but often other stuff gets changed then it is hard to actually make a comparison ..
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