So I need some advice on starting point with completly new set up. Boat was set up with trs drives with prop shafts 7.5 inches below running surface. Was spinning 25 mirage plus's to 5600 rpm's which is my ideal rpm for the 600hp motors I am running. Running same motors, but now have number 5's, prop shaft 1 inch below running surface, and mounted on mercury extension boxes. Both the trs, and the number 5's are 1.5 ratio. Boat is a 86 formula 357 was running 71 gps before the conversion. Where do I start for new props?

Hey Rob, just sent you a pm before i saw this. Im glad to see you are running boxes with your setup. If you weren't, I think you'd have some trouble planing, with your hull and that x dimension.

For props, I'd try out a set of 17x26's or something like that. Get in touch with jeremy (carbiz) on here. He is from Grand Rapids area. He may have some ssm props for you to try in that size, just to get a ball park idea

I have 17x28 5 blade Hering's for testing.

I feel they will be too big but as you move forward, let us know if we can help.

Brett

Thanks Brett, I will keep that in mind. Just as an educated guess what do you feel would probably get me close? When running a surface style prop, do you usually go up in pitch from the fully submerged style? Or will I be twisting something in the 25 pitch range again?

Brett would be able to answer better, but my guess, your hull, twin 600hp, 5600rpm Target, your gonna be in the 24-26p range in a 5 blade. Speeds maybe upper 70s..

I'm sure raising the drive height will help, but as for swinging more pitch I doubt it. Lay that 25p mirage next to a 17" diameter 5 blade ssm prop, and you'll see why! It's ALOT more prop than a 25 mirage.

Agreed 17" diameter and 28" pitch will most likely not happen for the obvious size differences.

The higher drive height may require more diameter to get on plane but the V bottom will prefer smaller diameter once on plane for proper bow lift and attitude. The higher drive height will also require a touch more pitch. This will all be a balancing act.

Guess 16x26ish 4 blades. Tough to find.

Run anything you can and call me. I'll help you get there from that point. Might require custom props. No biggie, that's what we're here for.

Brett

Thanks for the advice guys, I am going to take it and keep an eye out for possible props to at least try, and narrow down to some close one's. And yes Brett I do expect to have you work your majic on the closest one's to make them just right.