Yamaha SHO prop question

[Beagleman]

I posted this in the bass boats forums but it was suggested I move it here. I know very little about props. I am looking for a prop for my sons 200HP Yamaha HPDI series 2. He was running a Powertech 4 blade and slung a blade.

I have a 2019 Yamaha SHO and run the Yamaha Vmax prop. When I look at this prop online, I saw a note that said “if you are going to run this prop on a HPDI or any other 2 stroke you will need to have vent holes machined into this prop.”

Can anyone help me understand why this is necessary? Thanks

[ThomasD]

2 strokes lack low end torque. Vent holes in the prop allow air around the blades it to help it slip when taking off letting the motors rpm's get up into the power band.

[21XDC]

[Beagleman]

Thanks for the responses.

[1ranger487vs]

Not always. I ran a non vented sho vmax prop on my 200 ox66 just fine. That was on a 487 vs ranger. Need to try it first

[21XDC]

Not always. I ran a non vented sho vmax prop on my 200 ox66 just fine. That was on a 487 vs ranger. Need to try it first

[Beagleman]

21XDC, I watched the video so I saw where they said the vent holes are required for the HPDI but is there a reason I’m missing other than rpm’s? I emailed Mark Croxton and he said he could vent the t2 prop for me. I take his and Yamaha’s word for it that they are needed, but would really like to learn something and understand why.

if the boat gets on plane quickly, (it’s an express so it’s light and it jumps out of the hole with the non vented prop) and turns the right rpm’s on top end, is there another reason that the holes are needed on the HPDI? I’ve spent quite a bit of time researching and getting the rpm’s up to get to the power band is the only reason anyone mentions. That doesn’t seem to be a problem on this boat but I don’t want my son to blow his motor up either. Edit to add: The powertech 4 blade prop that was on the boat when we bought it used does not have vent holes.

[21XDC]

Every combo is different.... The bulk of 2 stroke rigs benefit from venting..... Many of the 4 strokes benefit from venting. Lugging a motor is bad.

[Beagleman]

Gotcha. Thanks again.

[1ranger487vs]

It’s only for hole shot. My non vented 25 sho vmax prop had a great hole shot on a heavy 487 ranger with a 200 ox66. Was going to add vents but didn’t need them. Every setup is different that’s why it’s good to try them first. To much venting is worse

[21XDC]

When you vent with PVS holes, You can plug or adjust to maximize holeshot.

[mactlman]

21XDC, I watched the video so I saw where they said the vent holes are required for the HPDI but is there a reason I’m missing other than rpm’s? I emailed Mark Croxton and he said he could vent the t2 prop for me. I take his and Yamaha’s word for it that they are needed, but would really like to learn something and understand why.

if the boat gets on plane quickly, (it’s an express so it’s light and it jumps out of the hole with the non vented prop) and turns the right rpm’s on top end, is there another reason that the holes are needed on the HPDI? I’ve spent quite a bit of time researching and getting the rpm’s up to get to the power band is the only reason anyone mentions. That doesn’t seem to be a problem on this boat but I don’t want my son to blow his motor up either. Edit to add: The powertech 4 blade prop that was on the boat when we bought it used does not have vent holes.

needs venting to get about 3500-3800 rpms on take off for a 2 stroke, venting allows for you to dial that in-----venting doesn't affect prop any other time