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· Premium Member
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Discussion Starter · #1 ·
What % is ideal for surface drive style setup. Just ran my numbers on Merc's website and got 9%.


Do you want to stay between a certain %, say 8-12, or is the lower the better?

Oh Ya, did you hear Micheal Jackson died!!!:D
 

· Lord of the Drinks
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cat...



Also, why do they not factor in (RAKE) when doing a prop slip test?
I believe rake is how far back the blades are swept, but does not matter when measuring inches of travel through the water.

For a cat, I think;
10 is OK
8 is good
6 is really good
 

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Discussion Starter · #6 ·
How do you determine what prop to go with on a new boat? Obviously you factor in RPM, Gear, and H.P., but is there a specific formula to see what prop would be a good starting point?
 

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How do you determine what prop to go with on a new boat? Obviously you factor in RPM, Gear, and H.P., but is there a specific formula to see what prop would be a good starting point?
I think that the manufacture will go through alot of testing initially to give their customers a good starting point prop because they have sold several of those models with XX engine's and XX drive's which means it needs a XX prop which is a good starting point. If in Southern CA, I would recommend taking your prop(s) to Hill Prop in Santa Ana and talking to them. They will ask what the RPM is currently on the boat, speed, and overall handling. They can then take your prop and modify the prop to better suit your needs.

P.S. Michael Who?
 

· Lord of the Drinks
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The thing most people don't realize is that props have a variable pitch on the blades. This means that a 34" prop blade will vary depending on where you measure it (the variable pitch helps reduce cavitation).

That means that almost any prop can be called a range of pitches.

So if someone takes a 34" prop, and labels it 32"...magically your slip drops...lol.
 

· 32 DW X-CAT
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2,266 Posts
The thing most people don't realize is that props have a variable pitch on the blades. This means that a 34" prop blade will vary depending on where you measure it (the variable pitch helps reduce cavitation).

That means that almost any prop can be called a range of pitches.

So if someone takes a 34" prop, and labels it 32"...magically your slip drops...lol.
Comment:

Hello Havasu Hangin:

I would like to add to the above statement you left some stuff out of the equation. I have spent a great deal of time and money learning propeller fundamentals thought I would add the following to your post:).

You have two types of pitch Constant and Progressive. The constant pitch prop has no changes when you measure the pitch from the leading edge to the trailing edge of the prop it is constant.

The Progressive pitch starts low from the leading edge to a higher pitch on the trailing edge. For clarification---- the leading edge is the edge that first makes contact going through the water and the trailing edge is the edge departing the cycle.

Pitch is like a gear set too low and you hit the rev limiter--- great down low but top end will suffer--- to high and the lower end will suffer and top end will improve. Way to high and both will suffer losses as the engine will not hit proper RPM and it will lug out of the hole.

You should also know the rake of your prop [the angle of the blade in relation to the hub] as DCB's like a lot of rake because they tend to run flat and more rake would give you the bow lift you need to run drier and hopefully faster.

BTW I think your prop slip numbers are very good and you should be happy with anything below 10% in a cleaver. I mean how much faster are you going to go altering props. [expensive ones to boot] with a single HP700wNXT2 drive without going to a stage two Whipple reprogram.

KAP
 

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Discussion Starter · #14 ·
Comment:

Hello Havasu Hangin:

I would like to add to the above statement you left some stuff out of the equation. I have spent a great deal of time and money learning propeller fundamentals thought I would add the following to your post:).

You have two types of pitch Constant and Progressive. The constant pitch prop has no changes when you measure the pitch from the leading edge to the trailing edge of the prop it is constant.

The Progressive pitch starts low from the leading edge to a higher pitch on the trailing edge. For clarification---- the leading edge is the edge that first makes contact going through the water and the trailing edge is the edge departing the cycle.

Pitch is like a gear set too low and you hit the rev limiter--- great down low but top end will suffer--- to high and the lower end will suffer and top end will improve. Way to high and both will suffer losses as the engine will not hit proper RPM and it will lug out of the hole.

You should also know the rake of your prop [the angle of the blade in relation to the hub] as DCB's like a lot of rake because they tend to run flat and more rake would give you the bow lift you need to run drier and hopefully faster.

BTW I think your prop slip numbers are very good and you should be happy with anything below 10% in a cleaver. I mean how much faster are you going to go altering props. [expensive ones to boot] with a single HP700wNXT2 drive without going to a stage two Whipple reprogram.

KAP
i am not looking to go any faster with my setup, my boat is setup great out of the box (hats off to dcb)... I was just wondering what is ideal for a setup such as mine, i know not many other boats are simliar.
 

· 32 DW X-CAT
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2,266 Posts
i am not looking to go any faster with my setup, my boat is setup great out of the box (hats off to dcb)... I was just wondering what is ideal for a setup such as mine, i know not many other boats are simliar.
Comment:

What prop were you running??? I do not recall you saying what your specs were on your prop?

Your right about DCB it would be an anomaly if they let something out of the shop which wasn't dialed in:D. I know of one other DCB a F-29 running a single engine surface drive but he is running monster HP.

As for single engine HP700NXT2 boats I think there is only a handful that I know about a couple v-bottoms and a few cats.

KAP
 

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Discussion Starter · #16 ·
Comment:

What prop were you running??? I do not recall you saying what your specs were on your prop?

Your right about DCB it would be an anomaly if they let something out of the shop which wasn't dialed in:D. I know of one other DCB a F-29 running a single engine surface drive but he is running monster HP.

As for single engine HP700NXT2 boats I think there is only a handful that I know about a couple v-bottoms and a few cats.

KAP
not 100% but i think i have a 30 pitch, 16.5 diameter with 18 rake. 5 blade merc prop. I would like to eventually try a hering and see what differences the two have to offer.
 

· Senior Member
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prop slip

The thing most people don't realize is that props have a variable pitch on the blades. This means that a 34" prop blade will vary depending on where you measure it (the variable pitch helps reduce cavitation).

That means that almost any prop can be called a range of pitches.

So if someone takes a 34" prop, and labels it 32"...magically your slip drops...lol.

Good point, I changed props from a 34 4 blade to a 39 5 blade and did not change that value in the speed-o so the numbers posted wont be correct.
 
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