prop below transom

A general, non-powerplant specific, discussion on airboat technology, ie., hulls, rigging, polymer, etc..
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rcm243
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prop below transom

Post by rcm243 »

How far below the transom can the tip of the prop go before it looses thrust? RCM
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Hog Guts
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Re: prop below transom

Post by Hog Guts »

Technically if it's below at all it will lose thrust by virtue of the physics involved. But generally I believe I was told a beer can away from transom and 8 inches down max. I think mines down further and it's fine....


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pontoon outlaw
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Re: prop below transom

Post by pontoon outlaw »

:dontknow: mine is about 6 inches below and does just fine.....
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farmboy
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Re: prop below transom

Post by farmboy »

rcm243 wrote:How far below the transom can the tip of the prop go before it looses thrust? RCM
Probably depends on the kind of prop... I've always been told the swept tip props you can run up to 10inches in the boat. Mine I believe mine is 9 inches in the boat. I'm running a R series.
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Re: prop below transom

Post by SWAMPCRACKER85 »

I've always wondered that too.You would think their would be a loss on thrust :scratch:
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farmboy
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Re: prop below transom

Post by farmboy »

I'm sure at 7-10inches down its gotta lose something I would think...
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Quick Draw
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Re: prop below transom

Post by Quick Draw »

farmboy wrote:I'm sure at 7-10inches down its gotta lose something I would think...
The way you was showing off at the treehouse on Saturday with 6 or 7 people on the boat with a few others pushing grass rakes I can't tell if it's losing thrust :lol: :lol:
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Re: prop below transom

Post by jbtn »

Rcm243 where are you at in tn I am about 30 miles north of chattanooga we might ride together some time I got an old 350 dd I throwed together havent had in water yet just around in yard
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Re: prop below transom

Post by farmboy »

Quick Draw wrote:
farmboy wrote:I'm sure at 7-10inches down its gotta lose something I would think...
The way you was showing off at the treehouse on Saturday with 6 or 7 people on the boat with a few others pushing grass rakes I can't tell if it's losing thrust :lol: :lol:
I don't know what your talking about :scratch: :dontknow: :lol: :lol:
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plumcrazy
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Re: prop below transom

Post by plumcrazy »

a lower push point will gain you more than any so called loss of thrust.... and by the way thrust is a by product of what the prop really does, and that is screw through the air... its the same as a out board motor prop in the water .... all you young guys that have never ran a wood prop , heres how they used to gage a prop.
a 72 -32 wood prop in theory would move 32 inches forward every time it made 1 revolution, the best thing you can do to help your airboat is to have un obstructive air feeding your prop no matter what kind it is.... plus the lower the center of push of your boat the less down force you put on the nose , i have my 70 in prop 10 inchs below my transom 8)
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Re: prop below transom

Post by rick »

Plum wrote:a lower push point will gain you more than any so called loss of thrust....
My rigging was built on that theory and I've always been happy with it...12' Diamondback, F.I. 470 runout, 70" (3) blade - 5" below transom.

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Re: prop below transom

Post by larry7mm »

I've built and ran a lot of different airboats from ride to race boats, I can say that my best handling and performance boats all had between 10 to 12 inches inside the transom, handling and lower point of thrust far out ways any down side my boat right now has a 81 inch sensenich 12 inches inside and it works.
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Re: prop below transom

Post by harley »

I run a 14x8 DB , HULL WITH A 80'' 3 BLD R 268 gear , mine is 8'' below and does just fine... 8) :thumbleft: :rebel:
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junglecat
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Re: prop below transom

Post by junglecat »

Have mine 11 inches in , 82" R . The tips draw air in and middle of prop is where thrust generates. Thats the purpose of the winglets to cup air and force it toward middle and not escape off end.

Go to car wash , with motor running , spray front side toward end of prop and watch where the spray comes off, corkscrewing from the prop in the middle. It will do this even if you spray the tips in the lower half of prop in boat.
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Re: prop below transom

Post by swampdragster »

11'' deep on a 16x8 marsh master. Works great.
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Re: prop below transom

Post by rcm243 »

junglecat wrote:Have mine 11 inches in , 82" R . The tips draw air in and middle of prop is where thrust generates. Thats the purpose of the winglets to cup air and force it toward middle and not escape off end.

Go to car wash , with motor running , spray front side toward end of prop and watch where the spray comes off, corkscrewing from the prop in the middle. It will do this even if you spray the tips in the lower half of prop in boat.
You`re absolutely right, I watched the c 130, caribou and the c118 take off in viet nam nearly every day and on a damp humid morning you could see the vapor coming down the blades and going to about half way down and then trailing back. RCM
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cantrundry
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Re: prop below transom

Post by cantrundry »

plumcrazy wrote:a lower push point will gain you more than any so called loss of thrust.... and by the way thrust is a by product of what the prop really does, and that is screw through the air... its the same as a out board motor prop in the water .... all you young guys that have never ran a wood prop , heres how they used to gage a prop.
a 72 -32 wood prop in theory would move 32 inches forward every time it made 1 revolution, the best thing you can do to help your airboat is to have un obstructive air feeding your prop no matter what kind it is.... plus the lower the center of push of your boat the less down force you put on the nose , i have my 70 in prop 10 inchs below my transom 8)
Your boat is also on the north side of crazy where tq is concerned... been around that thing a time or 2. :thumbleft:
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calbrigsr
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Re: prop below transom

Post by calbrigsr »

Beer can both ways works fine!
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