Ventilated Props-School Me Please

[Iron Horse]

I have a 4 blade 23 pitch Trophy+ prop that has 4 ventilation holes on the leading edge of the hub. I know the holes are to vent exhaust.
Here is what I don’t know
1. What is the purpose of venting the prop?
2. In testing the prop should I begin testing the prop
fully ventilated or plugged?
3. A metered office can be installed to reduce venting. Under what conditions would I use them?
4. Can you run combinations of plugs or use only one or two plugs to tune the prop performance?

Any help would be greatly appreciated.

[Merc 2.5]

U can run a combo. Vents r fir hole shot ,more slip =more rpm which get u up faster ,

[PanRonnie]

https://www.mercuryracing.com/prop-school-part-1-introduction/

[big tom]

I would start with 2 in, full tank of gas and the amount of people you run around with in the boat. If you dont like the time it takes to get on plane then pull 1 more out ,again not happy pull the last one. I carry a zip lock bag in my tool kit to keep them in because they are usually cover with exhaust soot. A little spray bottle of your fav cleaner is also good to have on board for the hands too.

[flabum1017]

Expect some vibration if you run mixed.... aerating one or two blades at a time causes this.

Personally, I'd start out with all plugs in and carry a drill and a step drill bit..... (or four sets of vent plugs per motor drilled out incrementally)

Try with them all plugged, then drill all them 1/8", then try 1/4" then try 3/8" then 1/2"..... then all out. What ever gives the best overall performance.... Problem with using the drill, if you have great performance at 1/4" and lose it at 3/8".... you will need a new set to drill 1/4 "

[Gordon02]

Ventilating the prop does one thing - adds air (exhaust gases) to the blades and allows the engine to "rev-up" to a higher rpm where the production of torque and horsepower are greater. As long as the prop "bites" and has enough developed blade area to move the boat forward - acceleration is improved.

Your choice of plugged or open should depend on how your outboard reacts as soon as the throttle is pinned. If it struggles to gain rpm and is down on horsepower down low, then "venting/air" will cause slipping and allow the rpm to move up the band. If instead, you've got great response and your outboard does not struggle to jump up and move - then you don't need venting.

The ultimate ventilation prop - is an "overhub" where 100% of the exhaust is pushed through the blades (over the hub). This prop will ventilate like crazy for a few seconds and push rpm up to near peak torque maybe even near peak horsepower, then it would bite and let the full power be used for acceleration. Not all boats will benefit from venting. Some will spin wildly and not be able to move up and out of the hole due to high slippage, others feel like it's coming out of a slingshot - depends on the pitch, developed blade area, and the rigged weight.

I am a huge Trophy fan and run a 26 on mine. Decide if you need more air or less - the whole idea is that you want a great holeshot.

Gordon

[Iron Horse]

Gordon
That was an excellent post and I greatly appreciate you taking the time to explain. To all who contributed Thanks!! All provided some excellent info on how to tune and what to look for. I'm headed south shortly and have a good river to do some testing and tuning on.

[Motv18]

If running submerged some slower gear ratios will continue to vent until forward speed increases or the prop spins enough rpm. 2:1 + and such

I also find in heavier boats cruising occasionally they list if one side is heavy.