Cobaltchat.com

Hi Everyone,

I have a DuoProp on my 220 and just saw a mention online about aligning or clocking the props. Had never given this any thought but I did notice last year that after painting the outdrive and changing the drive oil that my top speed was down about 5 MPH. Obviously new oil and fresh paint wouldnt cause the lower speeds and the only other "change" was the props were removed and replaced without any regard to orientation. After looking at some pictures when I purchased the boat, I noticed the props were set in an alignment that could create a water Flow or maybe better bite.

Below is a picture.

I did some searching here and other sources and there wasnt a consensus for either the DuoProp or Bravo to align in any manner for better performance. VP or Merc didnt have any recommendations per the other sources about aligning though some did mention several times about blades meeting at the cavitation plate.

My initial thought was relating this to aerodynamics on a race car and managing air flow, though in that case you are trying to move or direct air to create downforce while lowering drag. Hydrodynamics would need to work with similar principles to grab/direct the water while also limiting drag. The action of water shear, flow, drag and air bubbles entering the equation would need to be managed in some manner, so I figured would at least start a winter conversation.

I've heard of clocking so that the blades aren't at 12:00 at the same time, but I've never heard of anyone observing a difference with a Volvo Penta outdrive. I guess some older Mercury Bravo 3 outdrives could have more cavitation if they weren't clocked, but I've only heard anecdotal rumors of such things happening. I clocked mine anyway, despite not believing it really makes any difference.

I also have heard of this, but never any real world experience. I have had Bravo III's and now a VP Duoprop. My props get removed every year for service, sometimes by me, other times by the dealer. If they get "clocked" it's by accident and I have never noticed anything abnormal. But, there is no downside to doing it, so might as well align them if you think about it when installing.

I used to try to clock my props on my Volvo and then one time I forgot....there was no difference that I observed.

BTW, you try to clock them so that the props aren't at 12:00. What that really means is anyone's guess. Does it mean both blades at 12:00 or just the trailing edges at 12:00.

I would tell you mine look like this....on my old merc and current volvo, not 100% but this is what I pictured.

On my R5 with a Mercruiser, It has a rear 4 blade...pretty much impossible to clock that.

Maybe a silly question, but wouldn't they all look like the pic above if you rotate the counter rotating props and just stop when they line up??

Jimmy Buoy wrote: Fri Jan 05, 2024 6:15 pm Maybe a silly question, but wouldn't they all look like the pic above if you rotate the counter rotating props and just stop when they line up??

The theory is, you don't want them to line up at 12:00.

bruceb58 wrote: Sat Jan 06, 2024 12:53 am

Jimmy Buoy wrote: Fri Jan 05, 2024 6:15 pm Maybe a silly question, but wouldn't they all look like the pic above if you rotate the counter rotating props and just stop when they line up??

The theory is, you don't want them to line up at 12:00.

Ok. I think I get it. Will play with mine come spring and see at what hr they do line up!

Thanks for all of the feedback. I know most of us have already put away their Cobalt's in storage so no way to get real world data until things warm up quite a bit, especially here in the Northeast. A little boat talk, even if limited, is always a good thing to keep us engaged until the first spring startup video from BBP and the burbly Bib Block.

I will be conducting some back to back tests to give my results come spring.

I actually made a quick video on this subject at the end of last season.
In the end, I do not believe it is required or necessary for a VP drive. But see no reason not to do it when you put your props back on.
Just one more week till I fetch the boat from storage......

Late to the party here, but had to have a new prop installed and the guy who did it said nothing about this issue. He’s an old timer that changed my prop for $20. Sent the old one off to get rebuilt, it had a tear in the hub and I have no clue how it happened.

Looking at the skeg in your picture says that you hit something pretty hard to lose a chunk like that......and I'm sure the prop felt that as well.

Iowa Buckeye wrote: Sat Mar 23, 2024 9:40 pm I actually made a quick video on this subject at the end of last season.
In the end, I do not believe it is required or necessary for a VP drive. But see no reason not to do it when you put your props back on.
Just one more week till I fetch the boat from storage......

do you have a part number for that shop manual? Please email to kd4jaz@gmail.com