[difran25]

i have a merc 350, alpha 1 . right now my prop is a 14.5 x 19p. a lil banged up so getting new one. should i get the same size and pitch? or should i switch to something else? any advice would be great

[AirNavy]

My prop experience is very limited, but I have been reading up on it a lot lately. My boat came with two props, a stainless 3 blade 21P and an aluminum 4 blade 18P. The 21P is too high for me. The WOT rpm was only about 3900 and there was no such thing as a holeshot (slow out of the hole and excessive bow rise). The 18P is much better. WOT rpm right around 4500 and the holeshot is much improved (faster jump and a lot less bow rise). The only drawback is if I trim too close to the limit and hit a swell it can over-rev a bit. I want to try a stainless 4 blade 19P as I think it will give me the best of both. Another piece of this whole deal that I didn't mention is top speed. I didn't mention it because the only way I could compare top speed betwen the two is to do back to back runs with them since I boat in the intracoastal waterway and conditions vary everyday depending on wind and how rough the Gulf is (some days are smooth as glass and others 3-4 foot swells).

[Z 202]

I run a stainless 14 x 19p on my (202 Shabah 350ci/Alpha 1) It seems to offer the best all around performance; good hole shot and good top end. My only complaint would be that my lowest planing speed is a little too quick for novice watersports participants.

[difran25]

when im full open with the 14.5x19p im at about 5000-5200 rpm. someone said its too high and i should get a 21p to correct it. any thoughts.

[Z 202]

That's definately too high, the recommended WOT range is 4400 to 4800 rpm. I wondering what your drive gear ratio is. It's usually stamped on a small metal tag which is on one of the bolts securing the outdrive to the bellhousing.

Your tach may also be malfuctioning. There is a small switch on the back (to select 4, 6, or 8 cylinders), sometimes this can get corroded and provide inaccurate readings.

[mikeyt]

Notice the huge difference between difran's performance and AirNavy's??? There's no way that a 2" difference in prop pitch (both 3 blade props) should result in a 1100-1300rpm difference at WOT given both boats are nearly identical. A difference in gearing may account for some of that but not that much....

With difran's, his rpm numbers with the 19" seem high while Air Navy's (with the 21") seems low. hmmmm......

[difran25]

so what do you think i should do? go with a 21p? how about the radius? does that go bigger aswell or still 14.5. does anyone know what prop the boat came with oringinaly? or where i can find that out

[Z 202]

You can't go much bigger in diameter, or the prop won't clear the anti-cavitation plate. Besides, bigger isn't necessarily better, a larger diameter prop will have more drag.

[mikeyt]

Originally Posted by difran25

so what do you think i should do? go with a 21p? how about the radius? does that go bigger aswell or still 14.5. does anyone know what prop the boat came with oringinaly? or where i can find that out

If your rpms at WOT (5200) are accurate then i would suggest a 4 blade - 20" or a 3 blade - 21" prop. Both will drop your WOT rpms by about 300 - 400 which will get you into the recommended range. The 4 blade will have a bit more bite in the low / mid range area which is good for tubing/wakeboarding/skiing etc. The 21" may be more of a comfortable cruising prop & you might feel it to be a touch sluggish out of the hole but it should increase your top end speed and in theory give very slightly better fuel economy.
As for the radius anything between 14 & 14.5 should be fine. As Z202 says, increasing the radius isn't always a good thing.

[difran25]

thank you