how far below the hull does the prop need to be

[superiormgmt]

This project is a 1980 30' velocity. I'm in the prosess of putting in twin 300 hp 350ci motors in conjunction w/ Alpha drives. "I know I should use bravos but this is a temporary"<br /><br />My question is: how far above the bottom of the hull can the prop be and still be ok.<br />I've mounted the transom and out drive. Looking from the front down the hull there is only ont blade you can see. Now, there is a step about 8 inches offset cutout from the back. <br /><br />Thank you for any help

 

[Don S]

Re: how far below the hull does the prop need to be

You have a problem already, the props have to be completly below the bottom of the hull. <br />Do you have a picture to help explain this 8" step you have?

 

[Reel Poor]

Re: how far below the hull does the prop need to be

On the starboard drive...the starboard most half of the cavitation plate (from the center of the drive to the outboard edge of plate) should be even with the bottom of the hull. This positioning will have the inboard half of the plate slightly above the bottom of the hull. <br /><br />On the port drive...the port most half of the cavitation plate (from the center of the drive to the outboard edge of the plate) should be even with the bottom of the hull. This positioning will have the inboard half of the plate slightly above the bottom of the hull.<br /><br />These drive positions will place both props below the hull.

 

[superiormgmt]

Re: how far below the hull does the prop need to be

Good News, the transom is cut out for tsr drives. I've had to make an adapter plate out of 3/8 inch aluminum. By using the bottom two holes from the old O/D insted of the top two I gain 3" and should put about 90% of the total prop below the bottom. If this does not work I'm having to use an adapter plate anyway which allow's me to adjust.

 

[superiormgmt]

Re: how far below the hull does the prop need to be

A pictre of what the step looks like is at www.superiormgmtco.com under trim tab and 8 inch cut out. If anyone knows where I can find a match to the transom plate for these trim taps that would be wonderful. The cut out is under the transom.

 

[Reel Poor]

Re: how far below the hull does the prop need to be

Not real sure here but I would tend to believe that for every 5 inches of setback/step they can be raised 1 inch. This is typical rule of thumb for outboards.<br /><br />With this in mind I would say that the cavitation plate could be approximately 1.5 inches above the bottom of the hull (plainning surface) not the step.