Hole shot blow out

JDMC807

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Joined
Jan 13, 2012
Messages
3
I thought I had my micro good to go but got a problem and need some experienced advice.
Im having a problem with blow out at about 1/3 to 1/2 throttle. Set up is 14'5 stumpknocker with 25 merc, Vance jackplate 5" setback, and aluminum solas 4 blade 12 pitch.
First I thought it was weight..I weigh about 280 and moved to the front to level it out...No good.
I started with the jackplate all the way down and motor pinned at the lowest setting and tested it at different settings with no improvement.
Im thinking motor is too high..Cavitation plate is about 2-3" above hull but originally I figured the setback would fix that...Then I read about prop blow out and blow out rings.I checked the prop and there is a small amount of exhaust that blows out behind it. I put my hand slightly over the prop/exhaust hub to simulate back pressure and a good amount of exhaust blows out from behind the prop.... I am absolutely baffled any input is greatly appreciated...Thanks.
 

alldodge

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Mar 8, 2009
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40,583
I thought I had my micro good to go but got a problem and need some experienced advice.
Im having a problem with blow out at about 1/3 to 1/2 throttle. Set up is 14'5 stumpknocker with 25 merc, Vance jackplate 5" setback, and aluminum solas 4 blade 12 pitch.
First I thought it was weight..I weigh about 280 and moved to the front to level it out...No good.
I started with the jackplate all the way down and motor pinned at the lowest setting and tested it at different settings with no improvement.
Im thinking motor is too high..Cavitation plate is about 2-3" above hull but originally I figured the setback would fix that...Then I read about prop blow out and blow out rings.I checked the prop and there is a small amount of exhaust that blows out behind it. I put my hand slightly over the prop/exhaust hub to simulate back pressure and a good amount of exhaust blows out from behind the prop.... I am absolutely baffled any input is greatly appreciated...Thanks.

:welcome: to iboats

Your cavitation plate is to high, it needs to be at the bottom of the keel
http://media.channelblade.com/boat_...s/dts/dealerlibraries/8441/copetipstricks.pdf
http://forums.iboats.com/forum/gene...estions-and-topics/399737-cavitation-problems
 

Bondo

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Apr 17, 2002
Messages
70,470
Ayuh,.... Yer motor is too short,....

Lower the jack plate All the way down, 'n try it,....
 

Texasmark

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Dec 20, 2005
Messages
14,544
.............and in doing so get it low enough to set the antivent plate (plate just above the prop) even with or +/- about 1" depending on which works best for you in an all around situation. Your prop blades are partially in the air when on plane and that's the reason for the blow out.
 

JDMC807

Recruit
Joined
Jan 13, 2012
Messages
3
That's what I'm thinking....The jackplate is all the way down and by everything i've read I thought the setback would compensate for the height..but apparently not. Well, back to the shop....Thank you all for the input and the literature on mounting an outboard.
 
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JDMC807

Recruit
Joined
Jan 13, 2012
Messages
3
Update: lowered it 2" and it will plane..takes a few but getting closer. Set at the lowest hole and cat plate is 1" above pad. That's the lowest I can set it due to tiller clearance. I'm definitely gonna have to reprop or look in cupping mine. Any input on self adjusting tabs? Thanks
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Smart tabs are relatively trouble free.Tabs need to be applied just enough to be effective.
While they can help hole shot and may stabilize handling too aggressive application will slow the boat from tab drag and too much wetted surface.
 

Bondo

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Apr 17, 2002
Messages
70,470
That's what I'm thinking....The jackplate is all the way down and by everything i've read I thought the setback would compensate for the height..but apparently not. Well, back to the shop....Thank you all for the input and the literature on mounting an outboard.

Ayuh,.... Try more set-back,.... space the plate out off the transom,.....

Tabs would probably have the opposite effect of what ya need,...
 

alldodge

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Mar 8, 2009
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40,583
Update: lowered it 2" and it will plane..takes a few but getting closer. Set at the lowest hole and cat plate is 1" above pad. That's the lowest I can set it due to tiller clearance. I'm definitely gonna have to reprop or look in cupping mine. Any input on self adjusting tabs? Thanks

IMO Smart tabs or self leveling tabs work but only to a degree, and all are going to allow you to burn more fuel. Think of putting something in the water which are causing drag which are non-adjustable or somewhat self adjusting. Either way there will always be more drag which you cannot stop without removing them. On your current issue you don't need anything which will pick your stern up, your ventilating your prop now.
 
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