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measurements for vents in the prop...

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Old 06-27-2002, 07:16 PM
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Default measurements for vents in the prop...

I am trying to get the measurements to find where I need to put vents in a prop.

how far from the back of the prop?

how far next to the blade?

I need to find out before i head up north in the morning, I lost my hydromotive paper work that had it....


anybody?

Thanks

Travis
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Old 06-27-2002, 09:30 PM
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Traviss,

I can give you the specs on a 25 Mirage Plus if you are interested. Have to wait till tommorow as it is raining cats and dogs at the moment. Are you still going to Cumberland next week? I can bring a prop or two if you want to try some. We will be there Monday night thru Saturday AM.

Tim T.
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Old 06-27-2002, 09:39 PM
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hey Tim... If you can get the specs that would be good.. I am around till about noon tommorrow then headed up to the cottage for the weekend.. We must have got our times messd up because we are gonna be at cumberland july 29th till august 5th.. not next week sorry man.. I just got a 25" mirage from mr. gadgets it should work perfect.. I am gonna do a few testing then put drill vents in it so I can spin my motor up into the torque band and get it on plane when I have a load of people..

I forgot what kinda boat you have? It would be nice to hook up when I am down there..
thanks tim

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Old 06-27-2002, 10:26 PM
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We should be down there for those dates as well. Force 235 with 502 and Lightnings, Grey/Light Grey and White. Did you get the plug kit from Merc? The Plugs go into a hole and come in various sizes, they just snap in. You would probably want to drill your holes to accept the plugs.

I will measure in the AM and post around 8:30. Let me know if you need the part # for the kit. I think my buddy with a dealership down at the ramp may have one in stock. I suppose you could start with small holes and if you go too large just go up to the size that accepts the plug kit. The kit comes with 3? Sizes, start with the smallest. Don't be afraid to drill a hole, if it does not work out duct tape will take care of it. I removed my plugs completely and could not come up on plane. Put some duct tape on the inner ID of the prop and it held for a few days until the kit arrived.

Tim T.
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Old 06-28-2002, 08:38 AM
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Traviss,

Here are how the vent holes in a 25 Mirage Plus are arranged.

Three holes, one between each blade. This prop is drilled/machined to accept the vent plug kit. On further inspection this is not a task you could easily undertake in the shop. The hole is a smaller ID with a relief around the small ID hole that is larger ID so that the plug will sit flush. Sort of a flat countersink around the small hole. You would need a drill bit that is not pointed. If you go the route of the vent kit you better look real close at one. It seems that if you tried to drill the countersink you would end up with an oval that was not flat. Merc must have machined these that way. You may be better off just drilling a hole and going in small steps.

The holes are .585 centerline back from the larger OD of the prop (there is a smaller OD lip that goes into the lower case such that the case and larger OD are flush). In other words moving from the leading edge of the prop towards the rear once the prop steps up to full OD the center of the holes would be .585 from the OD change. This would be at the leading edge of the blade on the backside.

From the backside of the blade at a 90-degree angle towards this line, the centerline of the hole is .75 inches. So your hole is .585 back from the lip and .75 perpendicular from the backside of the blade.

Hard to describe as I am not a machinist. You may be better off sitting tight for the weekend until you can find your Hydromotive documentation.

Here are a couple of links with pictures, the black spot is the plug showing location.

http://www.mercruiserparts.com/mirag..._propeller.htm

You can see the vent plug with a hole in it at this link under HighFive
http://www.marine-outboards.com/Prop...Propellers.htm

If I remember correctly the plug kit had three sizes of holes in the plug. From about 3/16 to 3/8? If you drill start small.

Tim T.

Last edited by BadDog; 06-28-2002 at 08:48 AM.
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Old 06-28-2002, 09:47 AM
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I was just wondering about this idea of yours . Do you think it realy works ? The last I herd about it ,about 2 years ago from 2 different prop places was the holes do nothing for you . What does it do for top end ? Does it just make it slip on the bottom or what ? Just curious . I was going to do it along time ago on some mirage props and they all told me not to . JOE
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Old 06-28-2002, 10:44 AM
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Thanks Tim thats what I needed to know... I should not need the plug kit.. gonna start small and stop at the size that works right.. gonna call hydromotive in a few mintues and chat with them..

Thanks again



boot- The vent holes introduce air to the propeller blades, so then the prop cavitates ( slips) and the rpms on the motor goes up into the torque band.. after 10 or so mph the water seals of the vents and the prop performs like normal.. i am gonna try it if it doesn;'t work I'll weld the holes up or plug them...


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