B3 prop alignment

Ian · April 2020

Cool demo! Bookmarked!

YYZRC · April 2020

My 4.5 year old is mesmerized by your props!

aero3113 · April 2020

Awesome demo!
For 4 X 4 props it doesn’t matter, from Hill Marine.
See the bottom *
I’m still going to time mine.

LaRea · April 2020

It's so easy to align them ... I'd do it anyway.

Image: https://us.v-cdn.net/5020499/uploads/editor/6e/5xss91cksmfd.gif

TonyG13 · April 2020

Awesome!

rasbury · April 2020

Ok @LaRea, you for sure are a geek...JK! Awesome, but...so in your wrong set up, the props are aligning on the top as let's say 12:00. In the example of correct, they are aligning the same but at say a more 1:00 position...still don't get the problem! Now, when I put my props back on, I did align them correctly but still don't get why.

aero3113 · April 2020

@rasbury , the demo doesn’t have a cavitation plate in it. You don’t want the blades to align under it.

LaRea · April 2020

Thanks @aero3113, I updated the animations with the cavitation plate and the skeg.

OK, great, now we all understand the geometry of prop alignment. As @rasbury said -- so what? Why does it matter? What's the penalty if your props are misaligned? Is it vibration, loss of thrust, prop damage from cavitation? And is the effect large enough that you could actually notice it?

aero3113 · April 2020

Nice @LaRea

boatman37 · April 2020

Thanks! Pretty sure mine are ok but will double check to be sure

Ian · April 2020

For sure on the check list

davidbrooks · April 2020

ok so for those of us that have moved to the Hill 4 blade props...What are the recommendations on alignment?

aero3113 · April 2020

@davidbrooks , see my post above. That paperwork was from Hill Marine.

Spyderweb · April 2020

@LaRea Fantastic demonstration!

rasbury · April 2020

I checked mine this am and they are not aligned properly...

LaRea · April 2020

I made one more update, and now I swear I'm done. Every time two blades pass, it makes a mark where the pass happened.

With 3x3, it's straightforward ... blade passes every 60 degrees, and your alignment determines where they occur.

Image: https://us.v-cdn.net/5020499/uploads/editor/64/zbgcjo8ta66i.gif

Image: https://us.v-cdn.net/5020499/uploads/editor/ur/bzxnxq8zre14.gif

Like the 3x3, the 4x4 is easy to figure out. Blade passes every 45 degrees.

Image: https://us.v-cdn.net/5020499/uploads/editor/d9/kvvfys9a46bz.gif

Image: https://us.v-cdn.net/5020499/uploads/editor/b2/bgxe9lj84w7d.gif

What's really interesting is the 4x3. The blade passes happen every 15 degrees around the entire circle. Even with "perfect" alignment, you still get blade passes that are almost at 12 o'clock. That's why alignment doesn't matter with 4x3.

Image: https://us.v-cdn.net/5020499/uploads/editor/fk/0idij8hk7c4k.gif

Image: https://us.v-cdn.net/5020499/uploads/editor/6u/p5zbxoh5a2pn.gif

And so concludes my lunch-time brain exercise. Back to work.

Willhound · April 2020

That is freakin awesome @LaRea.

raybo3 · April 2020

Now I am not trying to start an argument but I would be curious if someone could in stall the props both ways on a twin. 1 aligned and 1"not" aligned and see what the difference is. My guess........... none. Although the drawing by @LaRea are nice but with the speed of the props and the turbulence of the water I am will to bet that there is no difference. Also if this is the case and its a big deal than this forum and any boating forum would be blowen up with the topic. Alot of these performance issues we talk about would go away because of this. Why are the splines and shafts keyed? Sorry I just don't buy it............ lol I love all the comments....... Go!

LaRea · April 2020

Raybo, here's the complete, unabridged list of reasons I know to align the props.

1) Mercruiser says to do it (but they don't explain why).

So I'm with you! We need data!

Let's find somebody who has:
* a Bravo 3 with 3x3 props
* A boat lift or trailer so they can change the prop easily
* Good nav electronics that show real-time fuel consumption

Remove the rear prop and install it wrong. At your normal cruise RPM and trim, measure speed and fuel consumption while listening/feeling for unusual vibration or noise. Then align the prop and repeat the test. Did it make a difference?

Who will volunteer? The boating world needs you.

raybo3 · April 2020

@LaRea I do not agree Merc says to do it. Like I showed everyone I contacted them and their service center said that there in NO timing on the props.

Cableguy Greg · April 2020

raybo3 said:

@LaRea I do not agree Merc says to do it. Like I showed everyone I contacted them and their service center said that there in NO timing on the props.

They might say that now. When that dialog from Merc changed, nobody on this forum knows that answer. All I know is that for all of the years that I helped out the mechanics at the marina where I dock at, they were told to time the props. As far as I am concerned, I am going with what my mechanic and Al have taught me, which is time the props.

LaRea · April 2020

@raybo3, RTFM. We have it in writing that Merc says to align 3x3 props. What they don't say is why they make that recommendation.

LaRea · April 2020

To quote one of the many forum threads I've read: "There are a lot of people who believe in astrology too."

reneechris14 · April 2020

Great demonstration. I do enjoy steering at the pics. @raybo3 just do it because we asked nicely that's a good reason.

LaRea · April 2020

BTW I've tried before to debunk unproven boating wisdom. Long-time readers might recall my debate with The World about outdrive coolers.

World: We all need drive coolers.
Me: Why? My drives don't overheat.
World: As anybody knows, cooler is better. It just is.
Me: But why? How does it make a difference?
World: ...<silence punctuated by cricket noises>

Somebody please volunteer to test the prop alignment theory!

Dream_Inn · April 2020

LaRea said:

BTW I've tried before to debunk unproven boating wisdom. Long-time readers might recall my debate with The World about outdrive coolers.

World: We all need drive coolers.
Me: Why? My drives don't overheat.
World: As anybody knows, cooler is better. It just is.
Me: But why? How does it make a difference?
World: ...<silence punctuated by cricket noises>

Somebody please volunteer to test the prop alignment theory!

I'm still in this belief too. Between the two of us, we do a lot of boating. I look at my drives after every weekend when I lift the boat back up. No chalky white. Lube looks good in the fall when I change it....sorry, back to topic.

I don't have any problems with alignment of my Big Cow Hill Marine props! Only need one on each of my Bravo drives!

raybo3 · April 2020

@Dream_Inn wise guy....lol

LaRea · April 2020

Prop burn on the aft props ... sounds like cavitation. So you combine the turbulence from the drive body, plus the prop wash from the front blade, plus being at the top of the stroke, and you get cavitation. Now that's something I can start to understand.

rasbury · April 2020

I'll have to fix mine but I swear that's how I installed them...because I figured there was a right and wrong way...

GMSLITHO · April 2020

This is my first boat with two props and I never even thought of alignment I have the 4x 3 when I bought the boat the drive was gone so I bought a new drive and props from the same company and no mention of the timing on the props . I’m going to take a look and see where there at .they've been on the drive now for three years so I should probably pull them and grease any way

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B3 prop alignment

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