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Prop Recommendations 29' Profile Twins with Notched Transom

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Prop Recommendations 29' Profile Twins with Notched Transom

Old 01-30-2020, 08:32 AM
  #11  
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I currently have a 22, 24 and 26 Bravo One 4 blade RH while searching for a matching LH I'm finding that they all seem to have the ventilation holes Mine don't so I was curious about what effect would be if one was ventilated and one wasn't
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Old 01-30-2020, 02:35 PM
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Originally Posted by MooresWarlock View Post
I currently have a 22, 24 and 26 Bravo One 4 blade RH while searching for a matching LH I'm finding that they all seem to have the ventilation holes Mine don't so I was curious about what effect would be if one was ventilated and one wasn't

Good questions. So to answer the 1st question the PVS (Performance vent system) holes are indeed to potentially decrease planning time by ventilating the propeller for a second or two. Trapped ambient air in the out drive or exhaust gas (when present) is drawn through the exhaust tube on the propeller and finds its way out of the vent holes and disrupts the high pressure water on the faces of the blades. The prop loses grip and spins freely in the aerated water gaining rpm. As the boat moves forward, water around the lower unit crosses the prop exhaust tube/barrel and closes the the PVS holes stopping the flow of air to the prop blades. The propeller is now spinning at a high rate and as it loads the blades again with water at a high pressure, the thrust returns and launches the boat on plane.

That is the physics behind the system. Of course there are variable that play into the reality of it's effectiveness.

The PVS holes measure 5/8" in diameter when unplugged and fully open. There are various size plugs to vary the amount of air being bled to the blades to increase or decrease the amount of ventilation. Dialing in the venting can consist of lengthy testing to get just the right set up. Plugs can be mixed and matched in any order. Uniformity is not required.
BBLADES has there own version called CAPS. (Controlled Aeration Port System). It works the same way but we have a 7/8" hole for even more venting, as well as plugs made from hard rubber to aid in removal and installation. Here is a link to some propellers using the BBLADES CAP system. We can install BBLADES system or the Mercury PVS system or simple fixed size holes in most any non vented propellers
https://bblades.com/shop/propellers/...4-speed-ob-fx/
https://bblades.com/shop/propellers/...des/bravo-obf/
Through hull exhaust systems do not take full advantage of venting systems because they direct the exhaust gasses through the transom rather than through the out-drive and propeller. However, the out-drive are often not completely sealed or not sealed and air is pulled through the drive and offer some venting out of the vent holes. Also, there is some air trapped in sealed units from coming off plane that can offer a bit of vent during hole shot. So, outboards do take best advantage of the vents because exhaust always runs through the props.

The next question you are eluding to is a important one. You are asking if running a Bravo 1 with vent holes is ok to run together with a Bravo 1 without vent holes. It certainly can be done but the props will more than likely run at different rpm and personality. To many peoples surprise, no, it isn't the right thing to do. Unless, a performance prop shop like BBLADES modifies the prop without vent holes. In fact, even performance prop shops may not know the subtle changes these outboard version Bravo 1's have.
Many / most people do not realize that all of the vent holed new Bravo 1 propellers are actually made from the original Bravo 1 stern drive mold and castings. Seriously, they start as the same Bravo 1 we started building in 1996. The vent holed Bravo 1 series of XS, FS, OC, LT have tiny adjustments that allow them to often run at higher rpm than the non vented versions or have a few other modifications to them that change stern lift or trim response.

So, You can run different B1 props together but don't be alarmed if the Port and Starboard tachs are a bit off.
Sorry for such a long winded explanation but I hope I answered some questions without being even more confusing.
Please let me know if I can clear any of this up any more. As always, I can be reached at [email protected].


Brett

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Old 01-30-2020, 03:24 PM
  #13  
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Brett - EXCELLENT information and well presented! I'm only running stock 7.4L L29 310hp motors with 1:50 Bravo ones - I've got a few weeks to finish up my transom replacement and re-rigging - I'll contact you when we get closer to the 'water test' phase LOL!
Thanks again!!!
Larry
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Old 01-30-2020, 07:17 PM
  #14  
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Brett,
do the vented and non vented mirage plus props have the same / similar differences the bravo1 props have that you mentioned in post 12 ?
sorry for the temp hijack, thanks
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