Wedge

mattinri

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Saw this wedge positioned directly over the prop. Only about a foot or so long, not the full beam. Would it be to bring the bow down or some other purpose?

 

captainlarry84

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Boy never saw that before. On a guess I bet it has something to do with the wheel, blasting water on to the bottom. That is a rather larger wheel with plenty of pitch. Note the pattern of the missing paint on the rudder. There must be a lot going with that wheel spinning fast. Very nice push back on the wet tube install.
 

tunafishhkg

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Prop ventilator, Wedge is before the prop blades and mainly to help create low pressure area and spread out air. Those who have done this say its night and day difference in the prop noise. In his words "
Well, then I connected with Pete Lowell in Woods Hole. He came up with
the idea of creating an air cushion over the prop area to absorb the
prop noise. His system is very simple. He put a plastic strake about 2
feet long across the hull just forward of the prop. Its wedge shaped
behind the wedge he installed two 3/4" thruhulls that are plumbed
straight up to scuppers in the cockpit.

We went for a ride on my boat Friday in Woods Hole, and he said yup,
same noise I had. Went for a ride on his boat. Smooth. I stepped back
into the cockpit, and put my feet over the two scuppers and blocked the
airflow, and rumble, the noise came on. Stepped off the
scuppers, noise goes away entirely.
"

PropWash2.JPG
 
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captainlarry84

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Prop ventilator, Wedge is after the prop blades and mainly to help create low pressure area and spread out air. Those who have done this say its night and day difference in the prop noise. In his words "
Well, then I connected with Pete Lowell in Woods Hole. He came up with
the idea of creating an air cushion over the prop area to absorb the
prop noise. His system is very simple. He put a plastic strake about 2
feet long across the hull just forward of the prop. Its wedge shaped
behind the wedge he installed two 3/4" thruhulls that are plumbed
straight up to scuppers in the cockpit.

We went for a ride on my boat Friday in Woods Hole, and he said yup,
same noise I had. Went for a ride on his boat. Smooth. I stepped back
into the cockpit, and put my feet over the two scuppers and blocked the
airflow, and rumble, the noise came on. Stepped off the
scuppers, noise goes away entirely.
"

Amazing great info & new to me. I bet this boat has big power that wheel looks like a 26 X 26 wheel on what looks like a 36" boat but not sure.
 
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Toolate

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What is your boat/power/prop package Tunafishking?

How much tip clearance do you have and do you think that is the issue? Very cool.
 

WoundUpMarine

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captainlarry84

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I think that this system which I have very little knowledge on is for boats that really push the envelope with big power. I am only looking at the tail section of this boat & I bet she flies.

That wheel is pitched to the max along with max diameter. The shafting looks to be a full 2". This boat has very big HP. Note the lack of paint on the rudder and the pattern of loss....that's speed boys.

So I est this boat a 36 feet, 500 HP, 26 X 26 wheel, 2" shafting, 2:0 gearing. All just a guess but I would love to see how close I came from just looking at the tail shot.
 
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oldshell55

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I think that this system which I have very little knowledge on is for boats that really push the envelope with big power. I am only looking at the tail section of this boat & I bet she flies.

That wheel is pitched to the max along with max diameter. The shafting looks to be a full 2". This boat has very big HP. Note the lack of paint on the rudder and the pattern of loss....that's speed boys.

So I est this boat a 36 feet, 500 HP, 26 X 26 wheel, 2" shafting. All just a guess but I would love to see how close I came from just looking at the tail shot.

2.5:1 gear ?
 

tunafishhkg

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What is your boat/power/prop package Tunafishking?

How much tip clearance do you have and do you think that is the issue? Very cool.

In the efficiency thread in the engine section,, my boat and power is discussed and I believe I have 2 1/2" of clearance but not sure off hand. I know I am within spec. I do not have cavitation issue at the underside of my hull and only a little area of ablative paint off my rudder.

I know Eric S has a Yanmar 6CX 500hp on his 36 northern bay(HINDERANCE) and it was the rumble at the stern that he was concerned with. The excerpt was from him in an e-mail he sent me.
 

captainlarry84

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I bet the Eric S could smooth things out with a little wheel cupping. 500 HP in a 36 NB is not pushing the envelope. I assume it is a 4 bladed wheel also?
 

tunafishhkg

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Not sure on his wheel but he was on this site a while ago and maybe will comment. He put this syst on his boat and swears by it. At the time I spoke with him, it was a resonance type issue he concluded was the noise and knowing him, he would of explored and have any prop work done for optimum performance to resolve it before going this route.
 
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Old Mud

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Blitzen

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Prop ventilator, Wedge is before the prop blades and mainly to help create low pressure area and spread out air. Those who have done this say its night and day difference in the prop noise. In his words "
Well, then I connected with Pete Lowell in Woods Hole. He came up with
the idea of creating an air cushion over the prop area to absorb the
prop noise. His system is very simple. He put a plastic strake about 2
feet long across the hull just forward of the prop. Its wedge shaped
behind the wedge he installed two 3/4" thruhulls that are plumbed
straight up to scuppers in the cockpit.

We went for a ride on my boat Friday in Woods Hole, and he said yup,
same noise I had. Went for a ride on his boat. Smooth. I stepped back
into the cockpit, and put my feet over the two scuppers and blocked the
airflow, and rumble, the noise came on. Stepped off the
scuppers, noise goes away entirely.
"

Just switch to a DQX prop problem solved. I know of some one that want great lengths like this to solve the prop noise and all he had to do in the end is switch the prop.
 

Blitzen

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Couple more.

Don that is Eric's boat the "Endurance" a 36 NB. After he switched to a DQX the ventilators did next to nothing.
 
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