Is this ventalation?

gtownky

Seaman
Joined
Sep 14, 2008
Messages
68
I have a pontoon with a 85 hp evinrude. If i take off slow and build up speed everything works fine. If I start out about 1/4 throttle and go to half pretty quick. It seems the prop is not getting bite. Do I need a differant prop? If so what do I look for? Also what is happening to cause this? I sorry for so many question. Thanks
 

ezeke

Supreme Mariner
Joined
Sep 19, 2003
Messages
12,532
Re: Is this ventalation?

Check for a spun propeller first. Click the thumbnail.
 

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gtownky

Seaman
Joined
Sep 14, 2008
Messages
68
Re: Is this ventalation?

spun a hub? Sorry Im not sure I understand. You say "scribe a line". Then am I suppose to run the motor and see if the line is off? If so is this fixable? If so how? Thanks
 

1946Zephyr

Vice Admiral
Joined
Oct 21, 2008
Messages
5,556
Re: Is this ventalation?

That's exactly what it means my friend. If is infact spun, you'll either have to have it repaired or replaced.:(
 

ezeke

Supreme Mariner
Joined
Sep 19, 2003
Messages
12,532
Re: Is this ventalation?

The hub of an OMC prop consists of two parts with a rubber seal sandwiched between them. The seal would normally break down on impact with an underwater object to protect the drive train.

Over time age and the heat from the exhaust can degrade the seal so that it slips; once this begins it can only get worse.

Prop shops repair the damage by replacing the seal, using a press. It's a specialty rarely done by service departments but referred to the prop shops instead.

After marking the prop as shown, run the boat until you experience the slip, then check the mark for movement.
 

gtownky

Seaman
Joined
Sep 14, 2008
Messages
68
Re: Is this ventalation?

So is this hub built into the prop? If that is the case then I have two props that are doing this because i got another prop and am experiancing the same thing with it. I may be wrong and I will check for what you all have mentioned but it almost seams as if the prop is push water from the prop. Someone had told me that I may need a prop that is made for a pontoon. Im not sure I understand what the differance is. Thanks
 

surrender

Petty Officer 1st Class
Joined
Jan 25, 2009
Messages
393
Re: Is this ventalation?

two props doing the same thing, not spun hub. Motor may be mounted to high
 

emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Re: Is this ventalation?

If you have two props doing the same thing, you are probably experiencing ventilation. It is unlikely that the hubs are gone on both props. If an aluminum prop ventilates on a pontoon, it is probably due to the engine being mounted too high on the transom. When a tip of the prop blade cuts the surface of the water, it will suck in air, causing ventilation at higher speeds. You have some options: 1. lower the engine one hole on the transom. This is never my first preference, as it will increase drag on the boat with more of the engine in the water-slowing it down and affecting fuel economy. 2. you can see if you can locate a stainless steel prop of the same size and pitch. Stainless props typically have more cup and are made to run in slightly "ventilated" conditions and not slip. Not all prop companies make stainless props down to the pontoon pitch sizes, however. 3. You can try a special pontoon prop, which has the large blade area. My guess is that even this prop may ventilate, since it would probably be aluminum and have less cup.
 

ezeke

Supreme Mariner
Joined
Sep 19, 2003
Messages
12,532
Re: Is this ventalation?

If the propeller checks out OK, the next thing would be to watch for ventilation, a process by which air is introduced to the propeller, usually by objects ahead of the gearcase, or by having the motor mounted too high.

When the boat is moving at cruising speed, the A/V plate above the propeller should be just above the water and parallel with it.
 

junior1113

Senior Chief Petty Officer
Joined
Jan 29, 2009
Messages
763
Re: Is this ventalation?

how big is it i would say 13 maybee 15 on smaller one. propeller selection all has to do with being able to reach recomended wot rpm you want the wot rpms to be around 5500. what sizes are the ones you have?
 

gotmeaboat

Cadet
Joined
Feb 12, 2010
Messages
23
Re: Is this ventalation?

sorry, i don't want to steel this thread. junior1113 what kind of Hydra-Sropt in your sig?
tom
 
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