What pitch for a 21' 79 Century 250hp 351 Windsor with Stringer 800

[ggrace boater]

Hey, I have a 79 Century 21' boat with an OMC Sterndrive 351 Windsor 250hp and a stringer 800 that has the correct pinion teeth ratio. I have a 17 pitch prop, that won't plane with a load in the boat unless some people get up front, and planes slowly without a load. I'm thinking about drilling ventilation holes, but I am wondering If the pitch is off for the boat. I looked at a Sea Ray boat prop chart under 235hp OMC and it had a 13 pitch prop. The rpm guage isn't working and I haven't weighed the boat. I'm just wondering if there is anyone that can tell me if I have the correct pitch for the boat or not?

 

[jestor68]

Re: What pitch for a 21' 79 Century 250hp 351 Windsor with Stringer 800

It sounds like you need to reduce pitch with a 21:18 gear ratio.
You can't really prop a boat without knowing the engine rpm. Figure 150-200 rpm per inch of pitch when adjusting the pitch.
Get the tach working, or take wild guesses at prop sizes.

Or, you can pay a dealer to hook up their shop tach and go test props with the understanding that you're going to buy the correct prop from them.

 

[ggrace boater]

Re: What pitch for a 21' 79 Century 250hp 351 Windsor with Stringer 800

Ok, I'm wondering what rpm range the 351 should run WOT? The gear tooth count in the upper gear case is 21:16 on this one. I don't know what's inside the foot, because I have never taken it apart, but I do think it's the original foot. I have a 15 pitch prop I might try if the ventilation holes don't make a big difference in the 17. I do want to know what RPM it's running at WOT though, I don't want to be over-revving the engine. I'll try to fix the tach before I use it again. Thank You!