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