Outboard Placement

royway7

Cadet
Joined
Sep 15, 2003
Messages
9
Can anyone give me a rule of thumb on optimal positioning of the outboard in relation to the transom? How far should the lower unit extend beneath the bottom of the boat? I've got a 25hp Johnson I'm putting on a 15' fiberglass skeeter hawk (like a fiberglass pirouge on steroids). Thanks for any insight.
 

B.autry4711A

Petty Officer 2nd Class
Joined
Feb 24, 2005
Messages
176
Re: Outboard Placement

Hello,<br /><br />I think the top of the anticavitation plate has to be even or no more than 1 and 1/2 inches above the bottom of the boat for the motor to operate correctly in the water.
 

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: Outboard Placement

Moving to Outboard Non-repair.
 

surlyjoe

Chief Petty Officer
Joined
Nov 21, 2005
Messages
486
Re: Outboard Placement

generally people will tell you the cav plate should not be above the water when planing but not be more than 2 1/2 inches underwater.
 

ob15

Chief Petty Officer
Joined
Jan 4, 2004
Messages
514
Re: Outboard Placement

Mount the motor with the AV plate even with or above the bottom of the boat. The only way to know exactly where to place the motor is trial and error. Some baots will like the AV plate even with the bottom and some will like it 2 inches above. It all depends but even with or slightly above (1/2" is a good place to start. Good luck and let us know how she runs when you get it all set up.
 

Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: Outboard Placement

The final X dimension (AV plate to keel) will depend largely on your prop and how it reacts with the water coming off the hull. The more technology built into the prop, the higher it likes to run.<br /><br />Set back also comes into play but with a 25 we're usually not dealing with any. <br /><br />I agree with Dave -- 1/2" up is a good starting point. If you get the AV plate below the keel you'll most likely get a spray of water up the transom and coming in the boat.
 

jtexas

Fleet Admiral
Joined
Oct 13, 2003
Messages
8,646
Re: Outboard Placement

Is that one of the original Skeeter boats? got a pic?
 

LORDY611

Petty Officer 2nd Class
Joined
Jan 17, 2006
Messages
189
Re: Outboard Placement

Originally posted by Dave F.:<br /> Mount the motor with the AV plate even with or above the bottom of the boat. The only way to know exactly where to place the motor is trial and error. Some baots will like the AV plate even with the bottom and some will like it 2 inches above. It all depends but even with or slightly above (1/2" is a good place to start. Good luck and let us know how she runs when you get it all set up.
To me this is like the problem of trying different props: you need to buy one to try, and if you want to try another, you have to buy another! Or is there a better way without knowing someone with a similar motor? So the placement quandry is similar: bolt your motor at a "good starting point" and try it. What then? Pull the motor off and drill some more holes and move it for trial no. 2? You could end up with a transom resembling Swiss cheese. This cant be the way it's done, is it?
 

ob15

Chief Petty Officer
Joined
Jan 4, 2004
Messages
514
Re: Outboard Placement

If you want to achieve the best setup for the boat, yes this is how it's done. <br /><br />Remember that there are multiple holes on a motor so you can move the motor easily to test setup. I've been there. I have a homebuilt boat and drilled my original mounting holes too low for the setup I finally figured out. I had to drill new holes to get where I am now. I now have 3 props now (1 prop all the time and 2 special purpose) and getting 2 more to test.
 

Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: Outboard Placement

Simple solution -- a jackplate. Allows an almost unlimited number of different X dimensions. Very easy to adjust with no special tools and no drilling the transom. <br /><br />Better yet -- a hydraulic jackplate. Just hit the button!
 

ob15

Chief Petty Officer
Joined
Jan 4, 2004
Messages
514
Re: Outboard Placement

I left that out so Dhadley could add it. I knew he would ;)
 
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