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drilling prop vent holes, what size should i start with?

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drilling prop vent holes, what size should i start with?

Old 12-28-2019, 04:12 AM
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Default drilling prop vent holes, what size should i start with?

guys im running an etec 90 on my 17 ft boat, the boat is heavy and with 1 person the hole shot was okay but add more gears it really take a while to get up. im running 13.5 x13 SOLAS prop and i get 5300rpm with very light load and 4800 with 4-5 people. it's not so bad just when there is more than 1 person it take a while to get up, the engine will stuck under 2800 rpm for a long time before reving up. with 1 personal it will just instantly rev to 3200+ and im gone.... so im gonna be drilling some holes. i will be taking it to a propeller shop with proper tools and drill press to make the initial holes, and then will enlarge it myself which will become easy. putting the prop on my vice grip and hammer it with a punch will just damage it.

so what size hole should i start with, i am thinking maybe a 6mm, or 1/4" hole first and then if not enough enlarge it by 0.5mm at a time? what do u think is a good size as starting point ?
Old 12-28-2019, 04:23 AM
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Who told you to start drilling holes in your prop?
Old 12-28-2019, 05:03 AM
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You're better off dropping an inch in pitch. RPM's are on the low side even lightly loaded.
Old 12-28-2019, 05:18 AM
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Let this do by a professional prop shop, tha damage you may make is bigger than the cost of modifying the prop to your needs by a prop shop.
Chris
Old 12-28-2019, 05:19 AM
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Something doesn’t sound right.

What kind of boat and where is the motor mounted on the transom? Which hole?

Sounds like you are too deep.

Don’t drill holes. Setup the motor right first.
Old 12-28-2019, 05:38 AM
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He may be talking about aeration ports in the prop hub that allows the exhaust gases to escape 'more freely' and possibly spin faster. If you do a little searching u can find some of the 'prop gods' on THT that really know their stuff and can guide u bit prior to destroying a perfectly good prop. Just my 2 cents
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Old 12-28-2019, 05:42 AM
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Sounds normal to me, a 17' 90hp boat is going to have a tough time with 5 people on board. I wouldn't bother drilling holes in the prop
Old 12-28-2019, 05:46 AM
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Forget all the other posts and drill as many 1/2” holes in the prop you can get, and once you’ve finished hang it up in your mancave becauce that’s how useless it will be.
Old 12-28-2019, 05:50 AM
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Like others have said you are running low on the rpm scale. Drop down 1 inch in pitch. Also look at the height of the vent plate to the bottom of the boat. Assuming you have a aluminum prop? Vent plate should be flush to bottom of the boat. Holes in the hub are for higher performing boats. Don’t think you will get much for it.
Old 12-28-2019, 05:51 AM
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I'm going to edit this to say it sounds like you may have a too high of pitch prop too.
But , I had a prop with the holes , they were like 3/4 inch and you could buy inserts in different sizes to tune your holeshot ,
I loved it on my Ranger Z520 !
I think I used Rob at Delaware Props in Ohio .
Funny how the people above me have no clue but chime in anyway , LOL
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Old 12-28-2019, 06:28 AM
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Originally Posted by Smitty 45 View Post
I'm going to edit this to say it sounds like you may have a too high of pitch prop too.
But , I had a prop with the holes , they were like 3/4 inch and you could buy inserts in different sizes to tune your holeshot ,
I loved it on my Ranger Z520 !
I think I used Rob at Delaware Props in Ohio .
Funny how the people above me have no clue but chime in anyway , LOL
And reading comprehension seems to be an issue for others. RPMs overall, need to be addressed before tweaking, like, venting. It is obvious that he needs to go down in pitch.
Old 12-28-2019, 06:57 AM
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Originally Posted by vandlor View Post
And reading comprehension seems to be an issue for others. RPMs overall, need to be addressed before tweaking, like, venting. It is obvious that he needs to go down in pitch.
You sir , are correct !
On both counts , my bad , LOL
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Old 12-28-2019, 07:05 AM
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I’ve had great experience with vented propellers in the same situation as you. They make the boat way more versatile. Trim tabs also.
Old 12-28-2019, 07:19 AM
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A good prop shop can reduce the pitch on your existing prop and dial it in to a perfect RPM for your setup.

I have a ventilated prop and like it. Since your motor is a little undersized when the boat is carrying a big load, a ventilated prop will give a better hole shot without impacting high speed operation. For the benefit of the readers ventilated props increase RPM during hole shot so the motor achieves higher RPM and power. As RPM increases the speed of the prop prevents ventilation so operation is not affected as the boat goes on plane. Excessive ventilation can be reduced or blocked with plugs or filler. One ventilation hole is placed at the base of each blade.

I dont have my prop in front of me to measure the vent holes but guesstimate they are about 3/16”. I suspect placement of the ventilation holes is important so better to leave the drilling to a pro.
Old 12-28-2019, 07:26 AM
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Five people on a 17' boat with a 90....
Old 12-28-2019, 07:30 AM
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Originally Posted by gregb5220 View Post
Five people on a 17' boat with a 90....
I started with a family boat 17’ with a 25hp and it did fine with 5 people on board. I have been on a loaded 18’ and a 90hp with no problem.

I like bigger motors too, but mid sized works fine if propped correctly.
Old 12-28-2019, 07:33 AM
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Originally Posted by Inlander View Post
I started with a family boat 17’ with a 25hp and it did fine with 5 people on board. I have been on a loaded 18’ and a 90hp with no problem.

I like bigger motors too, but mid sized works fine if propped correctly.
I dont know..I had a 17' Mako in the 90's with a two stroke 90, propped right with the correct height and good compression and she was hard to get up with five high school seniors around 120 lbs each.
Old 12-28-2019, 07:37 AM
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Originally Posted by gregb5220 View Post
I dont know..I had a 17' Mako in the 90's with a two stroke 90, propped right with the correct height and good compression and she was hard to get up with five high school seniors around 120 lbs each.
Did you try a vented prop ?
LOL
Old 12-28-2019, 07:44 AM
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Originally Posted by Smitty 45 View Post
Did you try a vented prop ?
LOL
No thats a new one to me. I'm still not clear on what OP is referring too unless he means venting the hub. In that case just take it to a propeller shop. It's a real pain.

I would mess with the pitch first tho.
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Old 12-28-2019, 07:49 AM
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Stop drilling holes and get self levelling trim tabs... at app 120$, your problems will go away.

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