20' SC prop selection

mentalfloss · #1 01-11-2013, 08:23 PM

I am looking for some suggestions on prop size. I have a 1969 20' SC with a tower, jack plate and a 4 stroke 150 Suzuki. Can anyone be of any help?
I will have this boat in the water in about a week, after a 16 month long rebuild. I will post some pics after it is complete.

Thanks

McGillicuddy · #2 01-12-2013, 12:58 AM

What year is the Zuke. Late model is an odd choice for an old 20' cc. Very heavy at 480+ lbs w/oil and a jack plate further throwing CG aft. Your boat was designed for about 300 lbs.

If you don't yet have motor, I'd rethink it. Otherwise, make the dealer work with you. Your gear ratio is like 2.50:1 so get the biggest wheel you can spin. Key to prop is stern lifting shape. Low to moderate rake and cup. Try a Merc Black Max in 15 X 21 to see how close you are to the high end of the recommended rpm at WOT. That prop is everywhere, is cheap and is a great stern lifter. You may need to go to a 4 blade to keep your stern up and minimum planing speed down.

It's an odd combination but maybe someone else has a heavy motor and can chime in. I'd borrow as many used props as it takes to get it right. Trim tabs will be very helpful. Consider them if you haven't already mounted some. Good luck!

Fr. Frank · #3 01-12-2013, 04:05 PM

Gillie is absolutely right. You may have to go to a 19" depending on loaded weight and CG. If you can swing the Suzuki 16"D X 20"P four-blade stainless, that may be right where you need to be. Power Tech also makes a great 16"X20" 4B SS prop (called the LFS4) with a good stern-lifting rake progression.

mentalfloss · #4 01-13-2013, 09:51 PM

Thanks for the info guys. I will give it a try.
I do have trim tabs on the boat, so that should help. Jack plate is a 6 inch offset. Not to extreme.
I also raised the floor up 3 inches to help it bail. Moved the gas tank and batteries forward. I hope that this helps the cg...
I will post some boat porn in about a week......