right prop
 

Hello All. We have a 20 cc Seacraft with a 150 Yamaha , 170 gal. tank, t top leaning post 4 batt. 2 are deep cyl. maby 100# gear. Total persons weight is about 700#. What pitch prop do I need? Thanks.

170 Gal tank on a 20cc, damn!!

tank
 

OK, I wrote that with only one cup of coffee & no Macallan chaser . Its 73 gal gas tank. Thanks .

My guess is to get 73 gallons in, you pushed your gas can forward helping to offset the hefty motor.
Presumably this is a repower or you'da offered previous performance numbers.
Probably need a 14-1/2 x 17p stern lifting prop.
Consider going to prop shop and asking to borrow a Merc black max/quicksilver black diamond in said dimensions. It is a simple prop, that is easy to turn and cheap to buy, but does what it's designed to do (lift a heavier stern) as well as any. If you can spin it up to top of desired yammie rpm range with full load you'll be in the zone. After that my guess is you'll want to go 4 blade and stainless to add aft lift and handling at lower speed, and likewise reducing minimum planing speed.

I think it's a bit of a crapshoot cuz of the stocky motor and added fuel.

you also didnt say if the Yamaha 150 was a 2 stroke or 4 stroke this matters due to the difference in the weight!

prop
 

Thanks , its a 2 stroke 2001 saltwater

What Mcgill said. I went Thur the prop thing about 1.5 years ago on the current ride. Had been running an old over propped 19" wheel for years and was lugging the motor/hard to kill an old looper/Rude.

Borrowed a 17" SS pitch prop and was pretty Happy with RPM and performance. Then went Burris prop shop in Cape Coral and bought a used 17" SS. Ran it but wanted more bow lift. Brought it back and had it re worked, re hub bed and polished.

Result: went from 2.2 mpg to 2.5+ and a better ride. Motor sounds happier too.