why don't big props work on Allisons?

[Lotus 50]

I was reading on another thread about someone running well over 100 with a 35" prop on a non Allison. What makes it hard to run big props on Ally's?

 

[Dave Hensley]

Tbuck needs to weigh in on this one as he understands props and Allisons. Beam width and weight are players.

 

[xb03fs]

My guess would be the lip creating so much stern lift, the depth of the v on allisons, our non flat pad, and the unforgiving nature of our boats when props blow out.

 

[whipper]

Paddle wheeling and enhanced parachute effect slowing down. It can be done just not as safe as smaller wheels at higher rpm ,they wouldnt be for the faint of heart or recommended buy anyone. Theres been a few guys run over 100 with a 32 on a GS with a 225 but they used cleavers with lots of rake. The old cleavers had more rake than the new ones. Less hairy slowing down from what I was told buy a guy who used to run 103 with a GS 225 combo.

 

[TBuck2003]

Great question and topic...Lotus the guys running the 35p QIV that I worked on that are getting the BIG numbers are drastically different than "US" Allisons. First off that is a modified top deck Stroker. They have changed the CG of the boat and made it way more efficient as far as air flow over deck. The Stroker is a wide body pad bottom with more beam and a MUCH wider pad than the Ally. Also as mentioned they do not have the lip we have and the pad is significantly different. This enables them especially with a 3.0 liter to run large diameter props with BIG pitch. Remember also that the Stroker guys run 2-3" ABOVE the bottom of the boat enabling them to turn said pitch and diameter without the same loading effect that we would get at lets say even with the pad. And without the lip they are getting most of their tail lift from prop and motor height, and NOT from lip on pad. Trust me there is still paddle wheeling going on, which is why set up and gear case are of most importance... Hope this helps !!!

 

[whipper]

Great question and topic...Lotus the guys running the 35p QIV that I worked on that are getting the BIG numbers are drastically different than "US" Allisons. First off that is a modified top deck Stroker. They have changed the CG of the boat and made it way more efficient as far as air flow over deck. The Stroker is a wide body pad bottom with more beam and a MUCH wider pad than the Ally. Also as mentioned they do not have the lip we have and the pad is significantly different. This enables them especially with a 3.0 liter to run large diameter props with BIG pitch. Remember also that the Stroker guys run 2-3" ABOVE the bottom of the boat enabling them to turn said pitch and diameter without the same loading effect that we would get at lets say even with the pad. And without the lip they are getting most of their tail lift from prop and motor height, and NOT from lip on pad. Trust me there is still paddle wheeling going on, which is why set up and gear case are of most importance... Hope this helps !!!

I like, great information Todd and very well explained. What kind of setback those guys run? Eli for instance to run 2-3 above?

 

[TBuck2003]

12-15" setback and yes Eli runs HIGH !!!!!!!!