Prop and speed question for triple drives??????????
 

I can't post in the "prop talk" section so this question is here and thanks in advance for genuine information.

I was told that the center drive in a triple installation can be propped different from the outside drives for a speed benefit. When I think about that there seems to be a great deal of questions that need answered for my technical brain.

Is this idea only for outboards on a "V" hull and not stern drives?
With the center drive lower and dragging the prop harder would different pitches cause a push pull difference rather than speed benefit?
Is this some kind of a pricey test and tune splitting hair thing that barely shows up in competition levels of performance?
Is there enough difference in the water dynamics from the center drive to the outter drives to gain anything by different props?

I know my questions my not really be in a rational order to something but that is because I don't know if this is anything? My knowledge is hobby level and I have never heard of different pitches running on the same transom.

What can you speak to about this?

I have done trip outboards
and have found when trying to achieve the boats highest speeds
I run mixed props
for example my boat now I am running 2 matched props for outside motors
and center prop is +2 on pitch and -1/2" diameter
this keeps all 3 motors at same rpm
theory is boat runs the speed of the highest pitch
and rpms of the lower pitched
as with 3 they enhance each other
boat picked up 3-4mph with this set up
the center motor is the work horse motor on a vee
as it has more water on it than the outer 2 when boat is out running and rockin on slop
outside 2 will/does slip more while center is staying loaded more
so can play with center to find what the boat likes
again this is for best speed and motors are on the surface
also this is my ob and can move motors around with ease for best speed and handling
have bud with trips on 42 fountain and doing same thing,,,center propped worked differently but he did it to plane better
has a heavy rear coming on plane,,,,,

Thanks for the post. This is the kind of information I wanted to learn about.
So what about mono hull vs stepped? With the foam from steps is the center prop affected differently with steps? Is this some of where you say, "play with center to see what the boat likes"?

My stepped 419 Formula seems to run the center engine about 200 rpm lower than the outters. It this what the - 1/2 diam helps with?

Tricky question !!! I ll keep mine the same less headaches!!!

LOL, yea. But people talk and I notice these little details and my mind has to figure it all out. It is running nice now and we really enjoy the boat but my drag racing days really make me think of what I could do to it, lol. I may massage everything on the low end of power and money to keep it cheap or I may stroke these 502's and push it a little more. If there is something left on the table like 3-4mph then it might be worth it but if it is just 2-3 then the power would probably do more. We'll see in time.

a good prop man knows what to do
u can cut diameter down till rpms the same on center
as stated the center is the work drive as why rpms lower by 2,000
also can add cup to outside 2 to bring rpms down on them
u have options for fine tuning
I have a very small and light v with trips so it
really gains with fine tuning
the 419 is lots more boat so will be less advantage
this is mainly for last mph and trying to get to plane faster or less slip in turns working with trips

As the boat picks up speed, such as upper cruise speed and more, the rpm's seem to gradually even up. With weight like 13,000lbs is the prop tuning not quite as effective as it is with a smaller lighter craft? Is a boat like mine at 42 feet, 13,000lbs and a stepped hull not really a candidate for this type of prop tuning or the gains very minimal?

in ur case 13000 lbs and drives down below bottom
ur outside props are probably not slipping but very little from the center if not any more
if ur rpms even out in the upper rpms when hull gets lifted
as I stated for max speed with trips the center is messed with
surfacing the cases the ouside get more air in the slop
im runnin a little 27'er @ 2800lb hull with 3 2.5 offshores on at 8,000 rpm
cleaver props split shafted to water using the gearcases to lift the hull to where I want transom to ride at
so yes just a tad different in set ups to tweak props
as stated earlier bigger hull with less lift makes less difference

Mine trip set up was...
#4 drives port and starboard with 1.35 gears
#3 drive in the center with 1.5 gears

They geared and proped the center drive
Different to help get the boat on plane faster.

Also keep in mind the center drive will always
Work the hardest because it is buried so deep in
Clean water.

The port and starboard drives will slip
More hence part of the pitch difference.

As for #3 & #4 drives, different length drives
Set all X dementions and kept tie bar pretty level
Spanning all 3 drives.

Boat is now a #6 drive set up.

I'm running 31P on the outside, 32P on the center. At lower speeds, I do have to run a hair more throttle on the center engine to keep the revs even, but as speed increases things line up better. Getting on plane, it's almost impossible to keep the center motor in sync with the outsides. It gradually comes up to speed as the outside engines hook up.