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Author Topic:   Drilling prop vent holes

jgkmmoore posted 09-11-2006 08:36 PM ET (US)
I have a 13x19 SS Johnson prop on a 1982 John 140. Need to drill the vent holes to increase holeshot for water skiing.Somewhere, there exists a diagram with the hole size and location to drill. Anyone have it, or know where it is? May even have been an OMC Service Bulletin, but I can't find it.
Best Regards-Jeff Moore
The Judge posted 09-12-2006 12:08 PM ET (US)
I usually fill in the holes. It does not do that much and not worth ruining a prop. That is some thick azzes SS and will need a drill press, etc. Buy a 17" for skiing.
anthonylisske posted 09-13-2006 11:42 AM ET (US)
Won't the vent holes decrease the holeshot? you are adding cavitation in front of the blades rather than out the back.
I don't want to question your logic, but figured you may want the information.
John from IL posted 09-13-2006 12:02 PM ET (US)
It was OMC service bulletin 2092.
Here's an excerpt of the verbage:
Modify the propeller by drilling three 6mm (7/32") holes thru outer shell positioned as shown in the diagram. If there is a rib under any of the proposed hole locations, use another propeller.
Properly drilled, the holes will have no affect on top speed, maximum RPM or ventilation in turns. Incorrect hole size or location will result in no improvement or in excessive ventilation, particularly in turns.
Drilling the holes allows exhaust gasses to bleed onto the propeller blades causing controlled ventilation during acceleration. This allows the motor to turn higher RPM under acceleration providing more power to plane the boat.
I would try to obtain a copy of the bulletin from a local dealer so you can see the required diagram and measurement for locations.
-John
where2 posted 09-13-2006 09:59 PM ET (US)
Contrary to Nick's belief, you don't need a drill press. I think I actually used my 3/8" Black & Decker Firestorm 14.4v cordless drill, along with two sharp bits. Drill a pilot hole, then enlarge the hole to the final size, using some oil to lubricate the drill bit in both instances.
There's a service bulletin? With explicit instructions? I didn't have that when I drilled mine... Some day, I'll continue with my experimentation and enlarge my drill holes. I started at 8/32"...
The Judge posted 09-14-2006 11:38 AM ET (US)
Depends on how good your drill bits are and how good the SS is. I know it takes me about 15minutes to drill through a Whaler railing with a hand drill, can't imagine how long it would take at the base of a SS prop....3 times.
jgkmmoore posted 09-14-2006 06:31 PM ET (US)
Thanks John, you hit the nail on the head!
Years ago, I used the bulletin, and was careful to be exact in the measurements.I was working on a prop for a 70hp Johnson, and when finished, that mod transformed the holeshot to perfection for waterskiing.A friend of mine tried it without the directions, and failed miserably.Same boat/motor as mine.Interesting.Hmmmmm.
Best Regards-Jeff
where2 posted 09-14-2006 11:43 PM ET (US)
Ok, where can we come up with the diagram?
jgkmmoore posted 09-15-2006 02:16 PM ET (US)
I don't know yet. Have tried some local dlrs in Seattle area, but it's an older bulletin and no luck so far. I will post and make a copy if I find one.If anyone else finds one, please do the same? Thanks.
Jeff Moore
Bellevue, Wa
Tadpole posted 09-15-2006 03:25 PM ET (US)
Several years ago I successfully modified my prop this way, and I did it based on pictures of "factory" props with this feature - so I don't think the diagram is an absolute necessity.
An important note: First document where your rpms spike when you "nail it", and where they are as you "climb out of the hole".
Just behind the leading edge of each blade, and near the base where the prop meets the lower unit, I started with a 1/4" dia. hole per blade; I gradually increased my hole diameter until I saw a 500 rpm increase at the points previously noted. This was fine for my application - improved acceleration/planning time, and once on plane, performance was unchanged.
No drill press needed, but cobalt, or other high quality bits are required.
Good luck.
Boatplans posted 09-16-2006 08:29 PM ET (US)
Judge is right. Buy a lower pitch prop for water skiing. I have used the props with holes drilled. All they do is make the prop partially cavitate at slower speeds. This allows the prop to slip a bit. As boat speed increases, the inertia of the turning components in your engine apply torque to the propeller when it grabs. This transfers undue torque forces on the down shaft and gear case. Using a lower pitch propeller provides a much smoother application of torque to the engine components.
Eventually, your gear case will start showing stress cracks around the output bearings if you overstress it. Always use a propeller designed for your brand outboard motor. Though one is mightly tempted to use Mercury props on OMC engines and vice versa, it is a bad idea because the side loads are different and may exceed design loads.
towboater posted 09-17-2006 03:20 AM ET (US)
please excuse me, I have much to learn about outboard performance factors.
at one time I was a expert skier. Hole shots are nice but the bottom line was prefered speed/rpm's for the prevailing conditions to achieve the maximum performance factors of the ski itsef.
I dont understand why the boat hull/weight are not considered here?

jgkmmoore posted 02-09-2007 08:18 PM ET (US)
********Second effort**********SSTII vent hole drilling****
Pleeeeeze guys. I am really not looking for advice here.What I really need is help. I understand props, and I know what I want to do.Drill vent holes. I do not have, nor can I get from OMC dealers, even a copy of OMC Service Bulletin 2092 that diagrams the drilling location of vent holes in props. It can't be found locally.Thanks to all who have offered above advice (good job 'John from Il').
What I need to know are two dimensions: From the back edge of the prop (up) toward the exhaust edge, and from the base of the blade out to that line (with the prop on a horizontal surface). Just need to know exactly where to center the hole.That's all. I'd be most beholden to anyone that has a SSTII, or Michigan 'Rapture'prop that would measure theirs and send me the findings. I have 3 props to do, and the prop shops want $50 APIECE to drill them. I save two trips to the prop shop and a bill and a half? No brainer??
Thanks. Jeff
BTW- I've spent hours on the net looking for this answer already....to no avail. Google hasn't helped.

Binkie posted 02-10-2007 04:59 PM ET (US)
Judge if you want to drill through stainless, use cobalt drill bits.
jgkmmoore posted 02-11-2007 03:00 PM ET (US)
bump
where2 posted 02-13-2007 08:24 PM ET (US)
Good timing to bring this back up. I'll be at the boat show in Miami this weekend. How many manufacturers would you like this info from? I want to know the internal diameter on the Mercury PVS propeller holes.
cmarques posted 02-14-2007 06:12 PM ET (US)
Here are a few pic's of the vent hole locations on my Michigan Wheel Rapture 13x19 prop. It is hubbed for a 90hp Mercury. The holes are just under 5/16" diameter and slightly tapered inward and centered approx 1/2" from the back edge of the prop. The pictures may not be the clearest (flashlight and cellphone studio setting.) but if you need better or clearer I can take and measure better when I have the boat out of the garage this weekend. Hope these help.
http://s36.photobucket.com/albums/e43/cmarques1/prop%20vent%20holes/
Chris
jgkmmoore posted 02-14-2007 11:46 PM ET (US)
Where2- I have SSTII 13x19 props (2) and a Michigan Rapture in a 13 3/8 X17. I hope any older V4 OMC prop would have the same location. At any rate, would prefer something from OMC.cmarques sent some pics below that get it pretty much, but if you gain any info at the show I'd love to hear it.
cmarques- YEEEEEEEHAW !!!!!!!!! Thank you!!!!!!!!!! You got it, and you got it GOOD!!!A picture is worth a thousand words!! Many thanks. I am so relieved to have fished this up finally. I very much appreciate your effort!!
Perry posted 02-15-2007 12:02 AM ET (US)

Here is a vent hole diagram I found on the internet:
http://img.photobucket.com/albums/v235/perrycl/ventingprops.gif
Tom W Clark posted 02-15-2007 09:23 AM ET (US)
Vent holes can be sized to anything you like. 1/4" seems to be the smallest in common use.
I have a Yamaha Performance series three blade which uses 5/16" holes.
The original Mercury Laser II used 3/8" square holes.
The Mercury PVS plugs come in four sizes, Solid, 1/4", 3/8" and 1/2". If no plug is used the hole is about 3/4".
Note that with the PVS system you are free to mix and match any size and number of plugs if you want to really fool around with it.
In all cases, the vent holes need to be positioned as illustrated above.

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Author	Topic: Drilling prop vent holes
jgkmmoore	posted 09-11-2006 08:36 PM ET (US) I have a 13x19 SS Johnson prop on a 1982 John 140. Need to drill the vent holes to increase holeshot for water skiing.Somewhere, there exists a diagram with the hole size and location to drill. Anyone have it, or know where it is? May even have been an OMC Service Bulletin, but I can't find it. Best Regards-Jeff Moore
The Judge	posted 09-12-2006 12:08 PM ET (US) I usually fill in the holes. It does not do that much and not worth ruining a prop. That is some thick azzes SS and will need a drill press, etc. Buy a 17" for skiing.
anthonylisske	posted 09-13-2006 11:42 AM ET (US) Won't the vent holes decrease the holeshot? you are adding cavitation in front of the blades rather than out the back. I don't want to question your logic, but figured you may want the information.
John from IL	posted 09-13-2006 12:02 PM ET (US) It was OMC service bulletin 2092. Here's an excerpt of the verbage: Modify the propeller by drilling three 6mm (7/32") holes thru outer shell positioned as shown in the diagram. If there is a rib under any of the proposed hole locations, use another propeller. Properly drilled, the holes will have no affect on top speed, maximum RPM or ventilation in turns. Incorrect hole size or location will result in no improvement or in excessive ventilation, particularly in turns. Drilling the holes allows exhaust gasses to bleed onto the propeller blades causing controlled ventilation during acceleration. This allows the motor to turn higher RPM under acceleration providing more power to plane the boat. I would try to obtain a copy of the bulletin from a local dealer so you can see the required diagram and measurement for locations. -John
where2	posted 09-13-2006 09:59 PM ET (US) Contrary to Nick's belief, you don't need a drill press. I think I actually used my 3/8" Black & Decker Firestorm 14.4v cordless drill, along with two sharp bits. Drill a pilot hole, then enlarge the hole to the final size, using some oil to lubricate the drill bit in both instances. There's a service bulletin? With explicit instructions? I didn't have that when I drilled mine... Some day, I'll continue with my experimentation and enlarge my drill holes. I started at 8/32"...
The Judge	posted 09-14-2006 11:38 AM ET (US) Depends on how good your drill bits are and how good the SS is. I know it takes me about 15minutes to drill through a Whaler railing with a hand drill, can't imagine how long it would take at the base of a SS prop....3 times.
jgkmmoore	posted 09-14-2006 06:31 PM ET (US) Thanks John, you hit the nail on the head! Years ago, I used the bulletin, and was careful to be exact in the measurements.I was working on a prop for a 70hp Johnson, and when finished, that mod transformed the holeshot to perfection for waterskiing.A friend of mine tried it without the directions, and failed miserably.Same boat/motor as mine.Interesting.Hmmmmm. Best Regards-Jeff
where2	posted 09-14-2006 11:43 PM ET (US) Ok, where can we come up with the diagram?
jgkmmoore	posted 09-15-2006 02:16 PM ET (US) I don't know yet. Have tried some local dlrs in Seattle area, but it's an older bulletin and no luck so far. I will post and make a copy if I find one.If anyone else finds one, please do the same? Thanks. Jeff Moore Bellevue, Wa
Tadpole	posted 09-15-2006 03:25 PM ET (US) Several years ago I successfully modified my prop this way, and I did it based on pictures of "factory" props with this feature - so I don't think the diagram is an absolute necessity. An important note: First document where your rpms spike when you "nail it", and where they are as you "climb out of the hole". Just behind the leading edge of each blade, and near the base where the prop meets the lower unit, I started with a 1/4" dia. hole per blade; I gradually increased my hole diameter until I saw a 500 rpm increase at the points previously noted. This was fine for my application - improved acceleration/planning time, and once on plane, performance was unchanged. No drill press needed, but cobalt, or other high quality bits are required. Good luck.
Boatplans	posted 09-16-2006 08:29 PM ET (US) Judge is right. Buy a lower pitch prop for water skiing. I have used the props with holes drilled. All they do is make the prop partially cavitate at slower speeds. This allows the prop to slip a bit. As boat speed increases, the inertia of the turning components in your engine apply torque to the propeller when it grabs. This transfers undue torque forces on the down shaft and gear case. Using a lower pitch propeller provides a much smoother application of torque to the engine components. Eventually, your gear case will start showing stress cracks around the output bearings if you overstress it. Always use a propeller designed for your brand outboard motor. Though one is mightly tempted to use Mercury props on OMC engines and vice versa, it is a bad idea because the side loads are different and may exceed design loads.
towboater	posted 09-17-2006 03:20 AM ET (US) please excuse me, I have much to learn about outboard performance factors. at one time I was a expert skier. Hole shots are nice but the bottom line was prefered speed/rpm's for the prevailing conditions to achieve the maximum performance factors of the ski itsef. I dont understand why the boat hull/weight are not considered here?
jgkmmoore	posted 02-09-2007 08:18 PM ET (US) ******Second effort******SSTII vent hole drilling** Pleeeeeze guys. I am really not looking for advice here.What I really need is help. I understand props, and I know what I want to do.Drill vent holes. I do not have, nor can I get from OMC dealers, even a copy of OMC Service Bulletin 2092 that diagrams the drilling location of vent holes in props. It can't be found locally.Thanks to all who have offered above advice (good job 'John from Il'). What I need to know are two dimensions: From the back edge of the prop (up) toward the exhaust edge, and from the base of the blade out to that line (with the prop on a horizontal surface). Just need to know exactly where to center the hole.That's all. I'd be most beholden to anyone that has a SSTII, or Michigan 'Rapture'prop that would measure theirs and send me the findings. I have 3 props to do, and the prop shops want $50 APIECE to drill them. I save two trips to the prop shop and a bill and a half? No brainer?? Thanks. Jeff BTW- I've spent hours on the net looking for this answer already....to no avail. Google hasn't helped.
Binkie	posted 02-10-2007 04:59 PM ET (US) Judge if you want to drill through stainless, use cobalt drill bits.
jgkmmoore	posted 02-11-2007 03:00 PM ET (US) bump
where2	posted 02-13-2007 08:24 PM ET (US) Good timing to bring this back up. I'll be at the boat show in Miami this weekend. How many manufacturers would you like this info from? I want to know the internal diameter on the Mercury PVS propeller holes.
cmarques	posted 02-14-2007 06:12 PM ET (US) Here are a few pic's of the vent hole locations on my Michigan Wheel Rapture 13x19 prop. It is hubbed for a 90hp Mercury. The holes are just under 5/16" diameter and slightly tapered inward and centered approx 1/2" from the back edge of the prop. The pictures may not be the clearest (flashlight and cellphone studio setting.) but if you need better or clearer I can take and measure better when I have the boat out of the garage this weekend. Hope these help. http://s36.photobucket.com/albums/e43/cmarques1/prop%20vent%20holes/ Chris
jgkmmoore	posted 02-14-2007 11:46 PM ET (US) Where2- I have SSTII 13x19 props (2) and a Michigan Rapture in a 13 3/8 X17. I hope any older V4 OMC prop would have the same location. At any rate, would prefer something from OMC.cmarques sent some pics below that get it pretty much, but if you gain any info at the show I'd love to hear it. cmarques- YEEEEEEEHAW !!!!!!!!! Thank you!!!!!!!!!! You got it, and you got it GOOD!!!A picture is worth a thousand words!! Many thanks. I am so relieved to have fished this up finally. I very much appreciate your effort!!
Perry	posted 02-15-2007 12:02 AM ET (US) Here is a vent hole diagram I found on the internet: http://img.photobucket.com/albums/v235/perrycl/ventingprops.gif
Tom W Clark	posted 02-15-2007 09:23 AM ET (US) Vent holes can be sized to anything you like. 1/4" seems to be the smallest in common use. I have a Yamaha Performance series three blade which uses 5/16" holes. The original Mercury Laser II used 3/8" square holes. The Mercury PVS plugs come in four sizes, Solid, 1/4", 3/8" and 1/2". If no plug is used the hole is about 3/4". Note that with the PVS system you are free to mix and match any size and number of plugs if you want to really fool around with it. In all cases, the vent holes need to be positioned as illustrated above.