Vented or Non-Vented
 

Whats the real difference between a vent hub and a non-vented hub???My 23 Mirage PLus is non-vented and spins at 4800, Will the vent provide better plane time?

Re: Vented or Non-Vented
 

What is the boat and motor set-up?
What happens when the boat gets up on plane, does the motor bog down or does it spin to a high rpm and feel like the prop is slipping?

Matt

Re: Vented or Non-Vented
 

Vented propellers will have holes of different sizes drilled in the leading edge of the prop just above the labirynth seal. Some ventig like Mercury's PVS system are adjustable with different size plugs to control the amount of exhaust gasses being released. Upon acceleration, the holes allow the exhaust to aireate the high pressure side of the blades so the rpm can come up fast. Once the boat is planing, the holes are really non-existant as the pressure differential inside the hub draws all the gasses through.

Answering Matt's questions will help to answer your second question.

Oh yeah, over hub exhaust propellers like choppers and Lightnong ET's are true vented propellers! They are also very fast on the top end with the right boat because ther is no drag from the outer hub.

Re: Vented or Non-Vented
 

I have a 26 Powerquest running a 454mag EFI 385hp spinning a standard Mirage Plus 23 at 4800 rpm at 60-62mph pending load and air temp. My thought was if the vented hub assisted in allowing the prop to slip could I spin a 25 Mirage Plus to increas top end?? More than likely not just a thought??

Re: Vented or Non-Vented
 

The vented hub is to help the boat get on plane. Typically for outboard applications. They will not help you to pick up rpm or speed at WOT.

After the boat is on plane it's almost as if the holes in the hub were not even there. The hydrostatic pressure of the water becomes greater than the exhaust pressure as the boat picks up speed and the water pressure keeps the exhaust gasses from coming out the holes. There are some down sides to the vented hub but for the average pleasure boater they do not pose a problem.

Matt

Re: Vented or Non-Vented
 

Hi!

I received your blueprinted Tempest 27 PVS this week, and it looks & perform just great. My stock A45 Tempest 25 came on plane instantly, but hit the rev limiter. The Tempest 27 is slower up in plane, expecially with 3-4 persons onboard.

As you said, the PVS system will help to get the engine rpms rise. The current plugs can be changed to bigger ones. I presume the local Merc dealer has larger plugs to help the engine rpms to rise faster. Does larger PVS holes have any downside re. cruise speed / wot speed?

Cheeeers!

Toffen G - Norway :rolleyes:

Re: Vented or Non-Vented
 

No, the PVS plugs will not affect your WOT rpm.
The part numbers and sizes for the PVS plugs are as follows;
19-889725028 .280"/7mm
19-889725035 .350"/9mm
19-889725047 .470"/12mm

You can mix and match these plugs until you find what works best for you. You may even find that you may want one hole plugged and the other two open, whatever works for you.

You can also drill holes in the solid plugs that are in the prop already, or remove one or all of the plugs completly.

Matt

Re: Vented or Non-Vented
 

I have a 30 foot shadow cat with twin 300 promax and I am spinning 28 bravo 4 blades that have been labbed.When I put the throttles up the engines need a little time to spool up and then the props cavitate and up I come on plane and off I go.It usually takes about 3 to 5 seconds.The props are non vented.Would I get a better response if I vent the props and would it be better if the engines spinup faster rather then bog down for a few seconds.When I have a larger load it takes even longer.And what would the cost be to make them vented if it would help.
Mark

Re: Vented or Non-Vented
 

You can vent the Bravo 1 props by drilling holes in them. Sounds like it would help your boat get on plane quicker without bogging down the motors when you try to get on plane. You can drill the holes yourself, keep in mind stainless is an abrasive material and can eat drill bits. It is best to have a drill press if you want to drill the holes yourself.

Start with 5/16" holes and work up from there. Sometimes with the Bravo 1 props we have to go as large as 1" with the vent holes.

The charge to drill the holes depends on the size of the hole, typically we charge about $3-5 per holes depending on the the size.

Matt

Re: Vented or Non-Vented
 

I have a press.Where are the holes drilled and how many on each prop.I have the 4 blade bravo.
Mark

Re: Vented or Non-Vented
 

If you had a picture it would help.

Re: Vented or Non-Vented
 

300 ProMax engine have a low rev limiter compared to the 300X. Because of that, large pitch propellers can be necessary to hold the upper rpm levels below the limiter. This is fine but can also affect the holeshot. This is your exact scenario.

We started this process of drilling vent holes in the Bravo 1's at Mercury Racing when the 300 ProMax first came out. I often suggested retooling the B! series to accomodate the PVS technology. We have found larger holes to be the best and most common remedy. Believe it or not we rarely cut holes under 1". We also go as high as 1.25".

The hole location is important although not critical. You will actually drill behind a blade so as to allow the aeration to cross the hub and attack the high pressure side of the oncoming blade. If you drill directly in front of the blade face, the venting is less effective as it will tumble off the trailing edge. Be careful as to not cut into the step on the front of the hub. Also known as the labyrinth seal.

We Will do a set of Bravo 1's for $75. Let us know if you have any other questions.

Re: Vented or Non-Vented
 

If I FEDEXED the props to you and you recieved them on a Tuesday Morning and gave you a return overnight airwaybill how long would it take to drill the props and would I have them back by the weeked.
Mark

Re: Vented or Non-Vented
 

fishead,

If you're asking us, this week is booked solid. We would try but I can't guarantee it. We can guarantee to have them back to you next week though.

Thanks

Re: Vented or Non-Vented
 

Talking about sending them out on the 15th so you get them on the 16th and I can have them back on the 19th.
Mark

Re: Vented or Non-Vented
 

Shouldn't be a problem, give us a call.