Prop Rake angle

[Bduncan]

so how can one run a 17degree rake prop with same diameter with much lower strut (than say an 8 degree) and the hull rides the same at some point.

[dasboata]

so how can one run a 17degree rake prop with same diameter with much lower strut (than say an 8 degree) and the hull rides the same at some point.

Simply because the 17* is not causing the transom to lift,, there for raising your bow,, when you lower the strut it is putting the bow back in the water because the prop is lower in the water pushing the bow in !

[keithbradley]

Simply because the 17* is not causing the transom to lift,, there for raising your bow,, when you lower the strut it is putting the bow back in the water because the prop is lower in the water pushing the bow in !

^^^This^^^
The vector that causes the bow to "lift" is there either way. Running a lifting prop (which means lift at the transom as Jay said), counter-acts it by lifting at the transom.
Adding pitch always creates more lift, which sucks for us twin cat guys. The higher rake in the ABC props mentioned counter-acts the higher pitch.
Some boats (riggers, hydros) may need the extra lift. For others it will at least result in a drastic drive position or angle change.

[Bduncan]

My brother does set ups on some serious turbine boats. I wanted his take on this debate. He forwarded this to me.
from Mercury Racing. Keith it's time to go to prop school. http://www.mercuryracing.com/prop-sc...-3-blade-rake/

[keithbradley]

My brother does set ups on some serious turbine boats. I wanted his take on this debate. He forwarded this to me.
from Mercury Racing. Keith it's time to go to prop school. http://www.mercuryracing.com/prop-sc...-3-blade-rake/

Oh please do get him in this thread.

[Bduncan]

he also forwarded this to me from jeff johnston of herring propellers.

"Rake comes into play as Johnson helps his clients fine-tune their propeller choices to their specific boats. All hulls have different running characteristics. Generally speaking, higher rake angle translates to greater bow lift, which can be advantageous for V-bottoms and catamarans that need it. But in high-speed applications such as cats pushing 180 to 190 mph, too much bow lift can create problems. So in that case, Johnston would recommend a propeller with a lower rake angle, which would produce less bow lift than a prop with a higher rake angle.

[Bduncan]

well i guess mercury racing is wrong and one of the best guys in the prop business.
http://www.boats.com/reviews/boats/p...of-trade-offs/

[keithbradley]

I've already added more info to this thread than you know on the subject. I won't argue with someone who knows nothing about what they are talking about. Either learn and reach new highs, or stay where you are and you can continue to claim to have the fastest version of a boat that nobody is trying to go fast with.

For clarification on semantics, see post 9.

[kfxguy]

^^^This^^^
The vector that causes the bow to "lift" is there either way. Running a lifting prop (which means lift at the transom as Jay said), counter-acts it by lifting at the transom.
Adding pitch always creates more lift, which sucks for us twin cat guys. The higher rake in the ABC props mentioned counter-acts the higher pitch.
Some boats (riggers, hydros) may need the extra lift. For others it will at least result in a drastic drive position or angle change.

Look, I'm not concerned with what you think or think you know or what you want to call it. The fact of the matter is very simple.....if you change nothing but props to one(s) with a higher rake angle, the bow will be lifted. I could give two ***** why or how it's lifted or if the transom or stern is pushed down. If you feel compelled to try an over complicate things (as usual for some people) then so be it. I choose to try and explain things in a simple manner so the inexperienced guys can take something from this too. I feel no need to flex my internet muscles and try to make myself "seem" smart. What disappoints me here is there's some guys "in the know" here that are disagreeing with facts that's I've proved. Also how can you debate mercury racing and jeff johnston's identical take on the subject. millions of R&D are behind there claims. is it really up for debate or does God need to post his opinion

[Bduncan]

Keith,
Everytime someone puts it in your eye with supporting facts you respond with pot shots. can you kindly answer the following questions so we can put this bed.
1. do you disagree with Mercury Racing and Jeff Johnston's articles on rake angle and bow lift?
2 Keith all things remaining equal. Does higher rake angle result in bow being lifted or not?

[dasboata]

Look, I'm not concerned with what you think or think you know or what you want to call it. The fact of the matter is very simple.....if you change nothing but props to one(s) with a higher rake angle, the bow will be lifted. I could give two ***** why or how it's lifted or if the transom or stern is pushed down. If you feel compelled to try an over complicate things (as usual for some people) then so be it. I choose to try and explain things in a simple manner so the inexperienced guys can take something from this too. I feel no need to flex my internet muscles and try to make myself "seem" smart. What disappoints me here is there's some guys "in the know" here that are disagreeing with facts that's I've proved. Also how can you debate mercury racing and jeff johnston's identical take on the subject. millions of R&D are behind there claims. is it really up for debate or does God need to post his opinion

Pretty sure the article is saying the same thing we are,,, without mentioning why the bow is being lifted ( besides packing more air under the hull) we are only saying the bow is lifting because the transom is not being lifted by a lower raked prop whats the problem ?

[Bduncan]

well i would agree with you but with early testing with 1815 and M645 i had blow overs at lower speeds with 1815 verses M645 with strut in same position

[Darin Jordan]

Pretty sure the article is saying the same thing we are,,, without mentioning why the bow is being lifted ( besides packing more air under the hull) we are only saying the bow is lifting because the transom is not being lifted by a lower raked prop

Exactly. We are saying WHY the affects are happening, which is important to understand if you really want to make your boats perform.

[dasboata]

well i would agree with you but with early testing with 1815 and M645 i had blow overs at lower speeds with 1815 verses M645 with strut in same position

see post 33 I am beating a dead horse

[Bduncan]

Really? Neither kfguy or myself were asking why it was happening because we already knew. We were clearly debating the fact certain people were saying we were wrong. Jesus, the arrogance on this forum everytime the wolf pack gets together

[Darin Jordan]

Really? Neither kfguy or myself were asking why it was happening because we already knew. We were clearly debating the fact certain people were saying we were wrong. Jesus, the arrogance on this forum everytime the wolf pack gets together

So let me get this straight. Jay and I and Dasboata (and Brian, for a moment) chime in and state the actual PHYSICAL, actual, FACTUAL dynamic affects that are occurring, KFXGUY and you ARGUE against it, calling us wrong, not "giving a F*******" about the actual dynamics of what's happening (only the result), we further clarify our point, YOU call us "arrogant" and "know-it-all's" and WE'RE the ones being arrogant?

Tune your boat however you want. It's clear that what you know is "proven fact", so go with it. You have the video to prove it...

I'll choose to take advantage of the knowledge of those who have PROVEN TRACK RECORDS of performance to help guide my setups. You know, more than just ordering and bolting on the next best prop.

Have a great day.

[Bduncan]

Unless Dasboata is blowing smoke over email he didn't disagree with us. why dont we ask him?
Dasboata are we wrong?

[kfxguy]

So let me get this straight. Jay and I and Dasboata (and Brian, for a moment) chime in and state the actual PHYSICAL, actual, FACTUAL dynamic affects that are occurring, KFXGUY and you ARGUE against it, calling us wrong, not "giving a F*******" about the actual dynamics of what's happening (only the result), we further clarify our point, YOU call us "arrogant" and "know-it-all's" and WE'RE the ones being arrogant?

Tune your boat however you want. It's clear that what you know is "proven fact", so go with it. You have the video to prove it...

I'll choose to take advantage of the knowledge of those who have PROVEN TRACK RECORDS of performance to help guide my setups. You know, more than just ordering and bolting on the next best prop.

Have a great day.

And you'll stay at sub 50mph speeds with your twin cheetah and the rest of your "fast" boats. Maybe if you take the time to find the proper prop for a given boat instead of doing all this unnecessary modding to it, you'll go faster and you won't be heartbroken so much when you lose a prop. This is the reason we have a cheetah doing 90mph with just a s/b prop and also a rtr Genesis doing 95+ with a s/b prop. I've seen nothing special from you come out of your stable. You try to pick apart any answers I get and try to make me look bad. I get it. There's some guys here that feel threatened. Truth of the matter is I don't care about your records or anyone else's, besides some records held are just a first attempt and no one else cared enough to try and beat it. You have a great day too!

[Bduncan]

You have to be kidding me. a guy with a 50mph Cheetah is lecturing me. My god, you must be running plastic props to try and figure it out?

[Darin Jordan]

Really guys? Are you really THAT insecure? I don't think I need to quote my "qualifications" to you guys. You're the experts, you'll figure it out.

[Darin Jordan]

Darin do you have any boats that go over 80

What does this have to do with anything?? Would you like me to go home and throw some power into my Cheetah? KFXGUY tells me he can help me make is "fast"... Would that count?

In an "open" format, speed is relative, and frankly, doesn't really matter to me.

None of that has anything to do with my knowledge of how a prop works.

[kfxguy]

What does this have to do with anything?? Would you like me to go home and throw some power into my Cheetah? KFXGUY tells me he can help me make is "fast"... Would that count?

In an "open" format, speed is relative, and frankly, doesn't really matter to me.

None of that has anything to do with my knowledge of how a prop works.

Let's do this, cut the bs and stop arguing. Quite frankly it's getting old. Darin I'm not sure what your vendetta is against me, but you need to grow up and get over it. I pmed you in the past to try and figure it out and you ignored me. Real mature. You wanna sort this out privately I'll be glad to. It's getting old. I come here to enjoy myself and help people. I felt 100% confident in my answer to the original question and I still stick by it. I didn't know that any time you answer a question and it's a general question for that matter, than one is not allowed on here to give a general but accurate answer. I wasn't aware that I had to be so specific in every answer. If that's the case all we will do is confuse other people unnecessarily. Let's cut the crap. The short answer is this:

Lower rake is less bow lift
Higher rake is more bow lift.

More bow lift and you have more transom drop. And the opposite for less rake.

This depends on hull too but I'm not trying to over complicate things. Do you guys agree or not? Is this not a good enough answer?

[Fluid]

The biggest issue here is the use of the term "bow lift". It has never been a term used with FE boats, "prop lift" has always meant how the prop holds up the transom. OSE members are used to this term, it has been standard for a very long time, but now some guy comes along and decides that we have to use the term "bow lift".

Props are difficult for most boaters to understand as it is, especially newer boaters. This forum has become a great resource for the FE community. Suddenly changing the terminology does nothing positive and should be stopped.

But don't listen to me, I just wrote the book on FE boats.......



.

[Bduncan]

Fluid,
well said. I offered that as a solution early.

[raptor347]

I'll make a couple statements and pose a question here.

1. The articles that have been posted are in reference to submerged propellers generally found on heavy, full size mono-hulls with power trim. The error in applying the graphic with the thrust vector arrows to modern model boats (FSR-V being an exception) is that at least half of the hardware in that diagram is completely out of the water on our models. Several of those vector arrows simply don't exist in our application.

2. The only full size boat propeller tech that applies to models as we run them are the hydroplanes and to a lesser degree offshore cats (pesky power trim). All of them deal with drag loads that make prop dynamics different from what we deal with. You likely won't find the research the big money teams put into props published.

3. I know a few of the guys that do the big race props, bow lift is not a characteristic that comes into conversation. It is always the characteristic of the prop at the interface with the water. The terminology for model boat propellers is pretty well established and understood, why do we need to change it?

[Chrissharp]

I believe a lot of people have cluttered this thread with personal thoughts which is sad-but with that please realize I have never ran this prop nor this boat. A 10 degree to 17 degree rake will produce a different thrust cone coming off the prop. The 17 will be much narrower than the 10 by doing so it will reduce the amount of lift at the transom because it will be transferring more energy forward. This thrust cone is what allows the prop to be more efficient on some boats. Please remember that the changes positive and negative to the strut will be more pronounced causing the boat to fly. If it were me I would try the prop just to see if you liked it.

[rickwess]

I certainly hope that no one here thinks that any prop is designed to "dive" deeper into the water and push the transom deeper (therefore lifting the bow). That would be so inefficient if it was even possible. Of course it's to what degree the prop lifts and the effect that has the transom (and the opposite effect at the bow).

[dasboata]

[QUOTE=Bduncan;644699]Unless Dasboata is blowing smoke over email he didn't disagree with us. why dont we ask him?
Dasboata are we wrong?[/QUOT You Know what,,,, those words never came out of my mouth or fingers and keep me out of your BS post 33 was written by a idiot !!!

[Darin Jordan]

I certainly hope that no one here thinks that any prop is designed to "dive" deeper into the water and push the transom deeper (therefore lifting the bow). That would be so inefficient if it was even possible. Of course it's to what degree the prop lifts and the effect that has on transom (and the opposite effect at the bow).

I assure you that I certainly don't believe that.

[keithbradley]

Look, I'm not concerned with what you think or think you know or what you want to call it.

That's fine Travis, but this thread isn't about YOU, or what YOU are concerned with (well at least it wasn't, but you've clearly tried to make it that way).

I choose to try and explain things in a simple manner so the inexperienced guys can take something from this too.

Please. You "chose" to explain this to your full capacity, and when you realized you didn't understand it completely, you tried to argue to save face instead of just learn something. Nothing new here from you.
If you were just trying to make it easy for inexperienced guys, the last thing you would do is start this confusing dialogue about prop "lift" at the bow. What happens when someone reads this and then decides to order a "lifting" or "lifter" prop because they want to raise the bow of the boat? Would you consider your posts helpful to that person?

I feel no need to flex my internet muscles and try to make myself "seem" smart.

If that were true you wouldn't be arguing with people who actually do understand prop lift and did so BEFORE you and Brandon went on your Google searches. Sorry to be condescending, but if you did understand it you wouldn't have argued in the first place.

Also how can you debate mercury racing and jeff johnston's identical take on the subject. millions of R&D are behind there claims.

I'm not sure how to answer "How" I can debate, because I don't have to. I'm not going to read everything you guys find on a google search, but I'm 100% sure that there is no disagreement between myself and Mercury, or any other powerboat company for that matter. I have a number of customers who own and race real, world-class offshore boats Travis. When I build them boats, they don't tell me how to make them run well or what props to use, they ASK me. Likewise I would never tell them how to trim a 50ft cat, or what props they should run on their boats, because I wouldn't be qualified to do so.

This is getting pretty old. You and Brandon pretend that you know things you don't know to try and look knowledgeable, and then point the finger at anyone who disagrees with your nonsense. You play the victim quite a bit for someone who continually gets into arguments with people like Darin, Jay, and others who are much more knowledgeable in these subjects.