Rigging rules on repower?

[stevets]

I just re powered a 1991 Larson All American 17 footer from a johnson v4 90 to a 1987 Mariner in line 6 115 hp. Problem is I never saw either the hull or the motor at work (play?) in their previous set ups.
Prop issues aside ( !!) - should I be getting lots of water spraying up at the transom? I've read up on rigging a bit but am wondering if there are hard fast rules on prop hub to transom ratios or any such thing. I've examined some other boats of similar size and HP and feel like I'm close but want to get this right before moving to other issues.

Any simple rules or links to such info is appreciated.

 

[Dhadley]

Re: Rigging rules on repower?

If there's a lot of water spraying up the transom the motor is probably mounted too low. With the technology of todays props the AV palte (plate right above the prop) shoud be no lower than the hull at the very least. In most cases it'll end up at least an inch above.

 

[stevets]

Re: Rigging rules on repower?

Thanks for the reply. Since you opened the pandoras box that is prop performance, it is amazing that I can get none of my local marine shops to get me into the right neighborhood of prop size and pitch. I borrowed a 13"19 pitch from a friend and was short on rpms.

I plan to raise the motor on the transom and try to borrow a 13/17 prop. Does that sound like a reasonable plan?

 

[DJ]

Re: Rigging rules on repower?

I plan to raise the motor on the transom and try to borrow a 13/17 prop. Does that sound like a reasonable plan?

Yep. As a rule, each inch of pitch is worth about 200 RPM's, up or down.

As mentioned, excess water spray indicates an engine that is mounted too low.

 

[stevets]

Re: Rigging rules on repower?

Thanks for replies. I have moved the motor up and am anxious to run her out again except now the steering cable no longer hits the cavity in the splashwell. I had to flip the steering link upside down, and add a bushing on a longer bolt at the motor end in order to even come close to getting the angle between the drag link and the tilt tube paralell. I'm pretty confident my fix would hold up but, as I said, the bolt end of the drag link ( facing up) now is about 1/4 inch too high and hits the top of the splashwell cut out.



Any ideas?